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A different engine configuration ... constructive comments please!


cheekychimp Galant VR4.org Moderator
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Galant VR-4 org Post #: 922624 posted 08/13/10 10:39 PM     Remind Me!  Send Private Message   Edit Post      
I spoke with John and a few other members on here about my ideas for an engine build and it was suggested I open it up to the board to get your comments.

Don't lynch me straight out of the box (yes I'm talking to you Josh!)

I am aware that standard 2.0 litre engine builds are easier, well proven and far less complicated, but please, read the evidence, consider it and tell me if this idea has any merit whatsoever.

The background to this is a thread over on "Tooners" which actually I don't find to be as bad a place as some people make out. Just like here there are some very knowledgeable people on there and some good information can be found if you look around. Anyhow this is the thread that started it:-

Advantages of a 2.1 stroker

Cliff notes for those of you that aren't a member over there or don't want to read through 4 pages of a newbie thread. Newbie asks if there is any advantage to destroking his 2.4 to build a 2.1 litre engine with an 88mm stroke/crank, 162 mm rod length and an 87 mm bore. Somewhere along the line Slowboy jump in and state that a 2.0 litre long rod engine yields all of the benefits of the 2.1 litre engine (11,000 rpm redline) but is easier and cheaper to build using a 4G63 block, 4G63 cam belt, smaller diameter pistons. They then post up a dynograph of an engine they built:



Now that's pretty good on 23 psi. It's a damn good power/torque line all the way to redline with more rpms left over if you want to go there. Now I have heard all the arguments about high rpm motors being 'pointless' because the head can't flow properly at such high rpms. But as I stated in the above thread I am looking at this from the point of view of speed. There seems to be a great deal of concern about power falling off at higher rpms but once you are moving and have momentum, far less power is required to maintain speed than is required to overcome inertia and accelerate. Since your crankshaft spins at a rate proportionate to that of your axles, as long as you are not slipping at the clutch or spinning tyres, the faster your engine revs in any given gear the faster you go. As long as you maintain 11,000 rpms you will maintain that speed, how much horsepower you are producing is irrelevant.

I also see this type of engine as a failsafe. Irrespective of whether the engine is making more power at higher rpms it stands to reason that if an engine is built for 11,000 rpms and only sees 8000 rpms regularly, it should live a long time and quite possibly survive a missed shift at 8000 rpms that would cause an engine with an 8,500 rpm redline catastrophic failure.

Right. Onto my final point for those of you still with me. These are the configurations for various different engines pulled shamelessly from Magnus' site.



The 2.1 litre has the best stroke/rod ratio at 1.84:1 but the 2.0 litre long rod comes close at 1.77:1 but uses only an 85 mm bore instead of the 4G64 87 mm bore (lighter pistons)

So THIS is what I am thinking. Take a 4G64/G4CS block and SLEEVE IT. Yes, I know, I know ... stay with me here. Once sleeved I bore the 6mm taller deck to 85mm standard 2.0 litre specs. I then have two options. I can stay with 2.3 litre stroker pistons and go for a super long rod 2.0 litre engine with a 162 mm rod giving me that 1.84:1 stroke/rod ratio

OR (and this is the exciting bit!)

Could I not use the 156 mm custom rods retaining the still very good 1.77:1 stroke/rod ratio but keep standard 2G pistons? (extra deck height)

Pretty much entire OEM setup with a better than stock stroke/rod ratio. No forged pistons, just forged rods. 23 psi or under on something like a Evo III 16G or the HTA 16G equivalent to take advantage of the extra rpms flow and obviously you would need a built 4G63 head.

My questions/concerns:

1) How thick could you make the sleeves? Would .020 and .040 rebores at a later stage still be feasible?
2) Crank. Magnus doesn't mention the option of using an oem 4G63 88mm crank in the 4G64 block. Do I need a custom one?
3) Would a 2G or 1G head be better for this application?

To recap here. We are talking about a lot of work just to avoid using a forged piston. What it means however is that with just a set of rods you could essentially build from stock OEM parts an 11,000 rpm capable engine. As an essentially stock engine it would drive like stock and be as durable as stock (possibly more so given the better stroke/rod ratio) but with a built head it would be capable of ridiculously high rpms at the track.

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ktmrider
Cool Guy Crowd


Galant VR-4 org Post #: 922647 posted 08/14/10 12:36 AM     Remind Me!  Send Private Message   Edit Post      
Read the Tooners info a few years back, you recap it quite well.

Nearly all the sub-10 second drag 4G63 vehicles run 2.1L motors. The extra rpm's really compliment bigger turbos.

Next, nearly all the track/time attack 4G63 lumps are 2.3L strokers. Better torque and comes on much earlier.

Head wise, I would say it depends on your use. I have not read your build info, sorry, but the logical answer would be 1g for dragstrip and 2g or EVO1-3 for track.

So the final question but already asked, what are ya doing with it?



Mike O.
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cheekychimp Galant VR4.org Moderator
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Galant VR-4 org Post #: 922658 posted 08/14/10 02:25 AM     Remind Me!  Send Private Message   Edit Post      
I have another car, and I started a thread a while ago asking what sort of options I had if I wanted to do a rebuild using entirely OEM parts this time around. The brief was that I wanted as good as factory serviceability but that it had to be fun. It is a street car, so I figured a standard 2.0 litre build would do just fine and I wanted all OEM internals for a long service life.

I have nothing against 2.3 setups but I already have a stroker on the other car and every stroker setup I've seen requires non-OEM stroker pistons. Even a 2.0 litre long rod setup requires non-OEM 2.3 stroker pistons on 6mm longer rods.

It just struck me that if you are using a 6mm shorter piston on a 6mm longer rod, you could retain the stock piston and retain the longer road by simply using the taller 2.4 litre block.

It's a lot of effort at the end of the day for 6mm extra stroke, but if it produces as good a power/torque curve as shown, retains stock serviceability and means at 8,000 rpm it is only just getting into it's stride, it seems worth doing. Other than the extra work, is there any downside to this?



Getting old sucks ... but it sure beats the alternative !!!


Edited by cheekychimp (08/14/10 02:31 AM)

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ktmrider
Cool Guy Crowd


Galant VR-4 org Post #: 922669 posted 08/14/10 07:29 AM     Remind Me!  Send Private Message   Edit Post      
I'd say no real downside unless you are running a small snail that wouldn't take advantage of the extra spins.

Funny you post this, I may well end up with a non-running GVR4 that has a seized engine. One of the local DSM peeps has a 92mm crank with low miles ( cracked main pulley and chucked the timing belt at speed ). He wants $325 for it, likely could get it at or below $300. The 2.1L or 2.2L option with 2g pistons is looking mighty fine right now....



Mike O.
#464/1000 - Sold
05 Legacy GT - slush box
#86/2000 - Sold ( again )

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Justin
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Galant VR-4 org Post #: 922687 posted 08/14/10 10:24 AM     Remind Me!  Send Private Message   Edit Post      
As for your question regarding whether .020" or .040" overbores would be possible on a sleeved block, yes, absolutely. Many times when a block is sleeved, its only to save one hole, the other holes are already bored larger, and the one that gets sleeved simply wouldn't clean up, so they sleeve it, and the bore the sleeved hole to match the others. The other advantage you'll have is that a standard repair sleeve (dry sleeve) is too tall for the bore. Therefore, using a 4G63 sleeve in a 4G64 block should still net the proper sleeve length when installed. The machinist will have to deck the block, to insure that everything gets cut down equally. But the decking shouldn't have to be any more severe than .005".

I don't see why the 88mm crank wouldn't work just fine in that block. People put the 100mm cranks into 4G63 blocks with no crankshaft mods, why wouldn't you be able to reverse it?


Edited by galant1517 (08/14/10 10:41 AM)

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cheekychimp Galant VR4.org Moderator
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Galant VR-4 org Post #: 922691 posted 08/14/10 11:27 AM     Remind Me!  Send Private Message   Edit Post      
So it sounds like it's something worthwhile considering then! That's good. Now I just need a 2.4 block. I presume there is nothing different in doing this with a G4CS block which is I believe the 6-bolt equivalent of the 4G63.



Getting old sucks ... but it sure beats the alternative !!!

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Justin
Unregistered


Galant VR-4 org Post #: 922824 posted 08/15/10 03:51 AM     Remind Me!  Send Private Message   Edit Post      
I believe you can pull a "true" 4G64 6-Bolt from an early expo wagon or colt vista wagon. Most of them came with 1.8's, but if you can find one it'll be with the SOHC head. I think you already know this though, I think I've seen you on the 4G61t forums. Either way though, a G4CS is the same.

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cheekychimp Galant VR4.org Moderator
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Galant VR-4 org Post #: 922832 posted 08/15/10 07:46 AM     Remind Me!  Send Private Message   Edit Post      
Thanks, I appreciate your help in this thread, you and ktmrider. I'll be sure to let you know how this pans out eventually.

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Muskrat
Senior Member
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Galant VR-4 org Post #: 922834 posted 08/15/10 08:18 AM     Remind Me!  Send Private Message   Edit Post      
Quote:

far less power is required to maintain speed than is required to overcome inertia and accelerate. Since your crankshaft spins at a rate proportionate to that of your axles, as long as you are not slipping at the clutch or spinning tyres, the faster your engine revs in any given gear the faster you go. As long as you maintain 11,000 rpms you will maintain that speed, how much horsepower you are producing is irrelevant.




There's a fundamental flaw in your thinking here: AERODYNAMIC drag is your biggest hurdle at speed. This is where power drop off will hurt you. If you don't have enough power to spin up to 10,000 rpm, you'll never see it.



Brian L.
91 Galant VR-4 #665/2000

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cheekychimp Galant VR4.org Moderator
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Galant VR-4 org Post #: 922836 posted 08/15/10 09:10 AM     Remind Me!  Send Private Message   Edit Post      
^^^ Yes agreed, I think when I posted this elsewhere I did state that this was true as long as the car didn't start to bog. I think the analogy I used there was if you were going uphill. What I was trying to get at here was that as long as the engine is making 11,000 rpms you will see that speed regardless of how much power the dyno says you are making. It goes back to the idea that within reason if you have enough road and enough gear ratio you can get any car up to high speed.

What you say is absolutely correct, but I think you would have had a field day if you had read the thread I did. I have no doubt that there is plenty of truth in the idea that our heads are basically unable to cope with about 8,500 to 9,000 rpms due to the turbulence caused when the air tries to flow faster. But they were discussing a car happily making 11,000 rpms not being able to go any faster than one only making 9,000 rpms because it would make no more power. I stick by my argument that if drag isn't STOPPING it making to 11,000 rpms then if there is no clutch slip or wheel spin all other things being equal it has to be going faster than the 9,000 rpm car.

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toybreaker Galant VR4.org Moderator
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Galant VR-4 org Post #: 922844 posted 08/15/10 10:50 AM     Remind Me!  Send Private Message   Edit Post      
subscribed



It sure is nice having you back on the board, Paul!

That's an interesting combination you're thinking thru, and I can see many advantages.

The sleeving aspect is no big deal, just costs some money. In fact, a much better cylinder wall material can be selected when you sleeve a motor, so that's all win there.

The other parts all sound like they can be sourced from the yards, so that's more win.

I'm not so sure about the 2g pistons in this application, though...

I can't help but think there's going to be some special requirements there. The side loading is probably going to be fairly high with this combination, and the pin location will be mission critical to making this combination work. A 2g piston will probably not be the best choice, and this build may require a cu$tom piston.

Be interesting to hear what Curtis and the other smart guys have to say about this...



One other aspect about this build is the headwork required to make the package work over such a large rpm range.

Setting things up to breathe well at high rpm's may make it pretty soft/soggy off the line. It'll wake up at a fairly low rpm, but right off idle, this thing is going to be soft. A Curtis-spec cyclone manifold could minimise many of the effects, but anyway you slice it a motor that works well up top will be soggy on the bottom. May make rush hour Hong Kong traffic quite the chore...

In addition the valve springs will have to be fairly stiff to follow the lobes at high rpm, so they'll be some acceleration to the wear in the valvetrain. The rocker tip/valve stem area will be where the problems *may** manifest themselves first, but the whole system will be somewhat high strung, and will require spot on machine work and the fine$t part$ ever put in a 4g head...

A well prepped head is the key to making this project work.

... It would be very interesting to see what Mr. Beran could do with the head for this build ...




There will also be some money to spend on the clutch/driveline.

Shifting at 8k and up takes some pretty heroic clutch part$, and a tranny that's cu$tom spec'd for the abuse the synchro's will see at that rpm.


It is an intriguing package, that's for sure!



Probably a good thing Mr. O'Malia (ktmrider) didn't score another vr4, as he'd be following you into the poorhouse.

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cheekychimp Galant VR4.org Moderator
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Galant VR-4 org Post #: 923008 posted 08/16/10 09:40 AM     Remind Me!  Send Private Message   Edit Post      
Well it's great to get all this input, but I need to say that I was not intending to build this as an 11,000 rpm drag strip powerplant. IF I build it, then yes I would do it properly and spend a bit of money to make it worth the effort but one of my MAIN reasons for doing this was so that I could use STOCK OEM pistons rather than custom ones which are usually forged.

Now I appreciate the importance of the wrist pin location but I don't really see why it gets so critical here. The wrist pin location is usually moved up on the stroker pistons to allow them to be used in the shorter 4G63 block. The whole idea of using the taller 4G64 block was that no such 'custom' piston would be necessary and I could retain a stock cast piston that would supposedly wear better. I'm not criticizing input here, I want to know from you guys that have far more experience here if I have got the concept or the maths wrong.

Same goes for side loading. I have no doubt whatsoever if I rev this to it's upper limits that both side loading and loading on the rods will get severe. However I was under the impression that when run to around 8,000 rpms, side loadings would actually be less than on a stock block because of the better rod/stroke ratio. Again, if I am wrong, can you please tell me why, because this would be a major factor in deciding if this is worthwhile.

Again, finally the issue of low end response. I was under the impression that the long rod engines produced slightly more torque and should therefore be no less responsive than a standard 2.0 litre. Is the soggy low end response mentioned associated with the head specifically? I assume the issue here is that porting the head to flow ridiculously well at high rpms would mean low velocity and sluggish response off boost/idle.

To put this in perspective. This would still be a street motor with a relatively small turbo (EVO III 16G or FP 68 HTA). Boost would be limited to the 17-23 psi range and power is therefore unlikely to be more than 300-350 whp. The idea is to use as many stock OEM parts as possible. This would include an AMG Head and AMG Cyclone Intake Manifold. As it stands that head is only good for 7500 rpms so possibly different cams and an upgraded valve train could be swapped in, OR the AMG Cyclone would need to be JB welded and reported to match a 2G/EVO III head either with or without camshaft/valve train mods.

I'm not really looking to take advantage of the 9,000-11,000 rpm rev range. I would rather retain low end torque even if it means choking airflow in the upper rpm range. I simply want the motor to be comfortable at 8,000 rpms rather than at it's absolute limit by that point. I can probably do EXACTLY the same with a stock 2.0 litre build in a 4G63 block but I was simply hoping for a little more torque and to use the better rod/stroke ratio to reduce piston/bore wear.

Again, I might be proved wrong but I feel very strongly that if I do build this engine to be responsive, it will still rev to 11,000 rpm if pushed that hard and will still push the car that much faster even if it doesn't make significantly more power by revving it that hard. This theory would probably fall flat in circuit racing because efficiency at high revs would be compromised. But in a 1/4 mile scenario or low gear high rpm cornering I don't think it is going to be an issue. A 2G head might well turn out to be a better choice in this application.

So am I completely mad, or could this be an alternative approach to a bulletproof street build that packs a bit of a punch?

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slugsgomoo
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Galant VR-4 org Post #: 923116 posted 08/16/10 07:19 PM     Remind Me!  Send Private Message   Edit Post      
I doubt that the 2g pistons would survive very well having excursions to 10k+ and contrary to what's been stated in this thread, the majority of sub 10 second cars out there are running 2.0 not 2.1-- If you want to know why go dig through tuners, but it comes down to issues with the 2.4 block, incredible oil pressure problems (basically you need a dry sump ($$$) to fix it), and ridiculous cost, among other things.

Honestly for your goals I'd skip the exotic and build a very sensible 2.0 with something like wiseco 1400HD at like 9:1 and some decent rods.

Keep in mind that Kiggly has gone mid 8's on a 2.3L stroker with wisecos in it (and the motor has lived a long time, surprisingly).



-andrew
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DR1665
Kill him in the face with Wilson Phillips


Galant VR-4 org Post #: 923119 posted 08/16/10 07:50 PM     Remind Me!  Send Private Message   Edit Post      
The engine in my old Talon was set up for about a 9000rpm redline. She was still pulling (barely) at an un-tuned, hard limit of 8300rpm.

Much like John suggested, she was way soft down low. In fact, before about 3000rpm, she was a turd. 10.5:1CR, forged everything, headwork and cams for days, she was a real screamer 3500rpm on. It was almost like VTACK, yo. 2L of naturally aspirated, Mopar World Engine was an absolute riot, though. I'd hit the open road at 90mph+ with the AC running across the desert to LA and get 38mpg all day long.

There's no escaping that trade-off, though. If you want the flow up top, you're gonna lose the velocity down low and, if you can't make regular use of that shifted powerband, you're going to be frustrated. Conversely, if you build for a peak around 8000rpm, you might be able to firm things up down low with the right headwork and manifold selection, but now you're increasing your costs to get that additional 3000rpm leeway. There's always a trade-off.

Why not forgo the sleeves and all that and just build a long rod, 2L six bolt? If the car isn't going to be tuned, or even driven, much beyond 8000rpm, why invest so much energy into accommodating another 3000rpm into the equation? Not to suggest you're in this camp, but it seems like there's far too many 4G63 owners these days who think they need a fully forged bottom end, GT99RS terbo, 10000CC injectors and EMS to have fun in a daily driver.

If it were me, I'd go long rod 2.0. Bump the CR a hair to firm up the low end, and get it all balanced out to 9000-9500rpm and see how well she plays with others. Select a turbo that wakes up around 2500rpm and gets righteously pissed off around 4000rpm, then holds its ground until 7000rpm, thus realizing 2000-2500rpm "safety" net, without giving up precious bottom end.

Damn. I miss talking about this sort of thing.


Edited by DR1665 (08/16/10 07:52 PM)

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cheekychimp Galant VR4.org Moderator
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Galant VR-4 org Post #: 923168 posted 08/16/10 10:40 PM     Remind Me!  Send Private Message   Edit Post      
^^^ Then talk some more. I have absolutely no problem whatsoever in being told to do A rather than B, I'm just at that point having fumbled along in the dark for years relying on other peoples recommendations that I now just want to understand WHY I am doing something.

You mentioned before that the whole world thinks they need an entire forged bottom end. This time around at least I am NOT in that camp. If anything I was leaning the other way towards completely eradicating forged parts which although stronger I was told caused increased wear characteristics and required far more 'warm up' than stock parts. For reference this was a post in one of my other threads: -


Quoting CutlassJim:


My current set-up
2G pistons
1G rods
6 bolt crank
4G61 Oil pump
2G head
Evo 3 intake manifold
1G throttle body
Evo 8/9 springs/retainers
Evo 8 intake cam HKS 264 exhaust cam
FP exhaust manifold
EVO 3 turbo and O2
880's
ETS front mount
2G MAF

Car runs 22 psi on 93 pump and I have know idea how much power it makes but it is the fastest car I have ever owned. Including my [email protected] 91 Talon. I would like to think it would be a solid high 11 second car and seriously think it could do low 12's on pump. It walks on my friends 12.7 LS1 Camaro.

I can't really comment on if the 2G head was a huge factor in the power my motor is making as I did everything at once but I can certainly tell you its not "choking" the motor in the slightest. The car makes GREAT power the second it comes on boost all the way to it's 7500rpm redline. Oh I also have my 22psi at 3k flat.

EDIT: Oh yeah since it seems to be coming up in the thread. Car runs on a stock head gasket and stock timing belt. I'm too busy beating the crap outta my car and actually enjoying it then "collecting parts" like most people I see.




I could happily just do something like this ... it is a lot less trouble after all. I only suggested what I suggested because I thought that there would be benefits. So can someone please tell me if I go the long rod route, WHY would the bottom end be soggy.

(1) Does the extra stroke affect the compression ratio making it less responsive without the extra displacement of the 2.1 litre confguration; OR
(2) Is it the additional head work required to liberate the flow needed at 10,000+ rpms, what causes that issue down low.

It may seem pointless to many, but if I put a bog standard 2G head on a long rod motor would I get the same low end response without the flow at higher rpms or would it still be a turd off idle?

You see what you said here: -

Quoting 1665:

Why not forgo the sleeves and all that and just build a long rod, 2L six bolt? If the car isn't going to be tuned, or even driven, much beyond 8000rpm, why invest so much energy into accommodating another 3000rpm into the equation? Not to suggest you're in this camp, but it seems like there's far too many 4G63 owners these days who think they need a fully forged bottom end, GT99RS terbo, 10000CC injectors and EMS to have fun in a daily driver.




I am struggling to understand if it is the stroke of the long rod that creates the soggy lower end why this would be better. My configuration and the one you suggested would have an identical stroke. All that I am doing is creating an additional 6mm of deck height by using the taller block to enable me to fit the 2G pistons in the bore so that at TDC they are flush and don't smash into the valves as they would in the 4G63 block. The only way to get around this issue in the 4G63 block is to use 6mm shorter stroker pistons. The standard 2.0 litre long rod that you suggest also has a theoretical 11,000 rpm redline and was revved to around 9,000 rpms without issue (see the dynograph in my first post).

I was just trying to do that with stock pistons. Am I wasting my time?

Again I don't want or need to rev to 11,000. I want to rev to something far more conservative but retain a better rod/stroke ratio using stock OEM parts. THAT IS ALL.

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belize1334
well bread and nobly conceived
1334/2000


Galant VR-4 org Post #: 923177 posted 08/16/10 11:08 PM     Remind Me!  Send Private Message   Edit Post      
You may recall that I had a thread going about possible ways to build stroked and destroked 4g setups using all Mitsu parts. The SINGLE BIGGEST hurdle is that you CANNOT get OE replacement pistons with a big enough bore for the 64 block. 86.5mm is 0.060 over for 4g63 pistons and NPR doesn't make them more than 0.030 over. The local machinist said that sleeving the block and then boring it to 63 bore specs is POSSIBLE but it adds basically $600 over the rest of the machine bill.

So, if you want to run OEM mitsu pistons on a 4g64/G4CS block it will cost you ~$600 more in machine work to have the block sleeved and then rebored. I LIKE the idea of all OEM components but IMHO that's too much money so unless you have a hookup at the machine shop you may as well get forged pistons.



Roger B. Scott
'91 Belize Green

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cheekychimp Galant VR4.org Moderator
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Galant VR-4 org Post #: 923196 posted 08/17/10 12:28 AM     Remind Me!  Send Private Message   Edit Post      
Yes I remember us discussing this before. I think cost is an important factor but in deciding whether this is worth it financially I need to clear up the issues above re whether my idea is going to result in an engine which is any less usable as a daily driver power plant than the stock 2.0 litre long rod configuration. What is your take on that seeing as you and I seem to be on a similar page?



Getting old sucks ... but it sure beats the alternative !!!

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belize1334
well bread and nobly conceived
1334/2000


Galant VR-4 org Post #: 923222 posted 08/17/10 02:53 AM     Remind Me!  Send Private Message   Edit Post      
I'm no engine designer, but I honestly don't see how a higher rod/stroke ratio could possibly have a negative effect on torque response. Taking it the other way, the 3sgte has a rod/stroke of 1.6 compared to our 1.7 for the same 2.0L displacement. Power wise they're VERY similar motors with similar torque curves when paired to the same turbo. What do we gain for our extra 0.1 in that ratio? Reliability and peak power potential. IMHO a destroked G4CS is win-win as far as performance goes. I don't think there is a downside... It just comes down to whether it's worth the investment.

But remember that for it to be a 2.1L you'd need the increased bore of the G4cs which means no OEM pistons. If you ring-sleave it then you're back in 2.0L territory. On the other hand, a 92mm crank puts you almost at 2.1L on standard size pistons. If you were running OEM pistons in a sleeved block you'd need a 152mm rods which gives you a rod/stroke of 1.65... better than standard stroker but not as good as stock. And again, now we're using OEM pistons but aftermarket rods and crank which defeats the purpose a bit.



Roger B. Scott
'91 Belize Green


Edited by belize1334 (08/17/10 02:55 AM)

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Galant VR-4 org Post #: 923230 posted 08/17/10 03:57 AM     Remind Me!  Send Private Message   Edit Post      
Excellent! That was what I was hoping to hear. I know to many, maybe even yourself it may seem stupid to go to all this effort and not make use of the additional rpms but this configuration makes a lot of sense to me as long as I don't try to squeeze more out of it than it is capable of giving.


Edited by cheekychimp (08/17/10 04:20 AM)

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Galant VR-4 org Post #: 923570 posted 08/18/10 01:14 AM     Remind Me!  Send Private Message   Edit Post      
I've been waiting for a thread like this...

I do recall reading somewhere that using a 2L head on otherwise stock 2.4L blocks results in an 11.5:1 compression ratio and is quite undersqaure. A few months ago I got it in my head that you can utilize the 162mm rods and and the 88mm crank, along with the stock 87mm pistons and 2L head, to bring the combination much closer to square while retaining the same 11.5:1cr. What I'm getting at is that you perhaps you can use the 156mm rods and 87mm stock pistons for your setup to yield a more turbo-friendly CR and still achieve your goals. I'm not sure of the durability on those pistons, but I believe you might be more knowledgeable on that than myself.

The reason for the idea was that I wanted to build a high-comp NA engine for my Colt, and wished to reduce average piston speed - I feel I might be satisfied with the reduced displacement.

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belize1334
well bread and nobly conceived
1334/2000


Galant VR-4 org Post #: 923604 posted 08/18/10 02:49 AM     Remind Me!  Send Private Message   Edit Post      
If you reduce displacement while keeping the dome volume the same then the comp ratio will drop. Comp ratio is found by dividing the dome volume by the displacement + dome volume. With 2.4L and 11:1 comp the dome volume is 0.24L. If you then drop the displacement to 2.1L the new comp ratio will be (2.1+0.24)/2.1 = 9.75:1. Of course that's a guestimate since most engines aren't actually 2.4L but rather 2.375L or whatever. Still, you get the idea.



Roger B. Scott
'91 Belize Green

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Galant VR-4 org Post #: 923617 posted 08/18/10 04:03 AM     Remind Me!  Send Private Message   Edit Post      
So assuming I am crazy enough to sleeve this block down to a 2.0 litre displacement what compression could I expect if I used 2G pistons or even Evo spec 9.0:1 CR pistons?



Getting old sucks ... but it sure beats the alternative !!!

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belize1334
well bread and nobly conceived
1334/2000


Galant VR-4 org Post #: 923690 posted 08/18/10 11:41 AM     Remind Me!  Send Private Message   Edit Post      
If you sleeved it to run OE pistons and did a FULL destroked long rod 2.0L with 88mm crank then you'd get the same CR as before. You've changed the geometry but the displacement is the same so the CR is the same. On the other hand if you used a 92mm crank then you'd be bumping the displacement and that will change the CR.

You can always figure out the new comp ratio if you know the old comp ratio and the displacement for which it was intended. You have to assume that the rod length will be correct so that the piston rises to the same final height. Then the dome volume is the same in both setups. We start there.

CR = (disp + dv)/dv = disp/dv + 1 --> dv = disp /(CR - 1).

Then we calculate the new CR...

CR2 = (disp2 + dv)/dv = disp2/dv + 1 = (disp2/disp)(CR - 1) + 1.

So, if we assume that the old displacement was 2.02L (first overbore pistons, 88m stroke) and the new displacement is 2.113L (same pistons with 92mm stroke). Then we can get the CRs.

Starting with 8.5 we get CR2=(2.113/2.02)*7.5 + 1 = 8.85. Starting with 9.0 we get CR2=(2.113/2.02)*8.0 + 1 = 9.37. This of course assumes that you use the appropriate HG to achieve the intended CR. If you use a thinner HG you'll bump that value just like you would with a normal build.



Roger B. Scott
'91 Belize Green


Edited by belize1334 (08/18/10 11:43 AM)

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Galant VR-4 org Post #: 923695 posted 08/18/10 11:58 AM     Remind Me!  Send Private Message   Edit Post      
I wish I had paid more attention at school

Thanks. So essentially I can be sure in this case that apart from the head gasket whatever CR the pistons are rated for in a 2.0 litre 85mm bore and 88 mm stroke is what I'll get in the new build. That makes things simpler.

I think I'm going to do this. I don't think it will be amazing but I think it will work and work well and live a long time and for a stock car that's what it is all about.



Getting old sucks ... but it sure beats the alternative !!!

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belize1334
well bread and nobly conceived
1334/2000


Galant VR-4 org Post #: 923701 posted 08/18/10 12:07 PM     Remind Me!  Send Private Message   Edit Post   
So you're talking about using Mitsu pistons and an 88mm 4g63 crank in a G4CS block with 156mm rods to make a long-rod 2.0L? Basically not worrying about displacement gains but just banking on the longevity of the long-rod?

If it were me, and considering that you have to use custom rods anyway, I'd drop the OEM pistons and sleeving and use stroker pistons and 162mm rods. Basically you get 6mm from the destroke ((100-88)/2=6) and another 6mm from the lifted wrist pins in the stroker pistons. Then you'd be uber long-rod at 162/88 = 1.84 AND you'd have 2.1L to boot from keeping the larger bore of the G4CS. I know that you want to use OEM pistons, but once you're using custom rods it's not an all-oem build anyway and you could do the above for CHEAPER than the machine work for sleeving the block.



Roger B. Scott
'91 Belize Green


Edited by belize1334 (08/18/10 12:12 PM)

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