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N/A 2.4 with 1.6 (4g61) crank


thedsmguy
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Galant VR-4 org Post #: 1045863 posted 01/16/12 03:20 PM     Remind Me!  Send Private Message   Edit Post      
What chance do you think there would be to build a competitive n/a car (drag racing) from a 2.4 with 1.6 crank, high compression, high revs. I read a thread on tuners that said this would basically be a 1.7 liter or 1.8 liter depending on bore size. Put it in a super light car, maybe a mirage hatchback completely gutted, appropriate sized slick and skinnies etc..
The thread was old, so I'm wondering would things such as Kiggly springs, 288 cams etc work at a 10k rev N/A?

This isn't a project I'm going to be trying anytime real soon, just something I "could" do since I do have the car, and motor parts available.

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Jesus_Negros
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Galant VR-4 org Post #: 1045865 posted 01/16/12 03:27 PM     Remind Me!  Send Private Message   Edit Post      
How many mm is the 1.6 crank? you destroking it.



Quoting coyotes:

Just because you WANT your rare turd to be valuable doesn't mean it's gonna be.




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thedsmguy
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Galant VR-4 org Post #: 1045867 posted 01/16/12 03:37 PM     Remind Me!  Send Private Message   Edit Post      
75mm

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Jesus_Negros
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Galant VR-4 org Post #: 1045869 posted 01/16/12 03:43 PM     Remind Me!  Send Private Message   Edit Post      
you would be destroking it to less than a 2.0 but could use long ass rods that would have to be custom made and would give you an high rod ratio. + side super high revving like 12k+ but downside no lowend torque, you'll need a turbo to flow very very well to make power in those extra rpm's also a valvetrain and tranny to support the high revs. IMO waste of money...build a 2.1 if you want to destroke something and still spool a turbo at the same time.

Remember the 4g64 deck is 6mm higher so if you destroke it with a 88mm 4g63 crank u can run up to 162mm rod with -compression height pistons.



Quoting coyotes:

Just because you WANT your rare turd to be valuable doesn't mean it's gonna be.





Edited by Turbro_Negro (01/16/12 03:47 PM)

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thedsmguy
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Galant VR-4 org Post #: 1045870 posted 01/16/12 03:54 PM     Remind Me!  Send Private Message   Edit Post      
Did you even read my post?
Just curious cause I never mentioned trying to spool a turbo or anything about boost.



Edited by thedsmguy (01/16/12 03:56 PM)

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Jesus_Negros
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Galant VR-4 org Post #: 1045875 posted 01/16/12 04:16 PM     Remind Me!  Send Private Message   Edit Post      
Didnt see the "N/A"
Still would be a dog with no lowend and tons of topend.


Edited by Turbro_Negro (01/16/12 04:17 PM)

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gramkrakr89
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Galant VR-4 org Post #: 1045893 posted 01/16/12 07:09 PM     Remind Me!  Send Private Message   Edit Post      
As long as opinions are being offered, I think it would be a neat project. With the right rods and some decent balancing, it could be done rather easily.

Though it sounds a little like we're diving into Honda territory

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Justin
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Galant VR-4 org Post #: 1045906 posted 01/16/12 08:31 PM     Remind Me!  Send Private Message   Edit Post      
It is possible yes, but it is going to take some serious research and probably a decent amount of trial and error. I'm working on what is turning out to be a fairly long post, and I'm speaking mostly in general terms.

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Justin
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Galant VR-4 org Post #: 1045912 posted 01/16/12 08:49 PM     Remind Me!  Send Private Message   Edit Post      
Well, lets look at a few numbers.

(The below info in bold is incorrect because stock rods are 150mm. I wanted to leave it here though because the math is correct for the 75mm crank with 156mm rods.)


In a stock 2.4, stroke is 100mm and rod length is 156 mm. Rod ratio is 1.56.

So at TDC, the total distance between the main journal centerline and the piston wrist pin centerline is 206 mm. (rod length plus half of the stroke).

The minimun distance (BDC) is 106 mm.

Assuming no other changes, to match that 206 mm TDC distance with a 75 mm stroke, you would need a rod that is 168.5 mm.

This combination would result in a rod ratio of 2.2467.

Now you could also have custom pistons made to utilize the stock 156mm rods, by lowering the wrist pin in the piston body by 12.5mm. This method would bring the rod ratio to 2.08.


All of this is important to your question because of piston velocity.

Piston velocity is going to be the biggest factor in determining the reasonable RPM expectations of any particular engine.

The value that we are interested in here is the peak velocity. An engine of the same displacement of another, but having a lower peak piston velocity at the same RPM, will always rev higher than the other.

There are two ways to modify the peak piston velocity. You can change the stroke or you can change the rod ratio.

To lower the peak velocity, you can decrease the stroke, or increase the rod ratio.

To increase the peak velocity, you can increase the stroke or decrease the rod ratio.





Okay, so now that we have that cleared up, , looking at this engine again shows that decreasing the stroke will automatically increase the rod ratio. Both changes will allow you to increase the peak RPM of the motor. This is good for drag racing.

The one thing that you'll need to remember is that by decreasing the peak piston velocity, you are also decreasing the speed at which air moves past the valves at any given RPM. The decrease in air velocity is the underlying reason why shorter strokes yield less torque. And this also means that increased rod ratios will also lead to decreased torque.

Bigger cams will also affect where the torque is made. More importantly, bigger cams reduce air velocity even further at a given RPM, as compared to smaller cams.



With a super light mirage shell, lower torque will be less of a concern once you're moving. However, regardless of the platform, if the air velocity is too low, the engine may never idle.

You'll have to find a balance between being able to idle and chasing the high revving beast that you're looking at creating.


Edited by galant1517 (01/16/12 10:17 PM)

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Jesus_Negros
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Galant VR-4 org Post #: 1045917 posted 01/16/12 09:13 PM     Remind Me!  Send Private Message   Edit Post      
The 2.4 rods arent 150mm stock? I'm pretty sure the 156mm rods are longrods made by magnus.
I think you can go up as high as 175mm rods(?) unsure though.

Nice post galant1517

I'm currently using 159mm rods with -6 compression height Wiseco 1400HD in my 2.4
Had to get R&R to make the rods and Wiseco custom make the pistons for my desired cr. Destrokers arent exactly cheap, the cheapest part was the actual 94mm crank.


Edited by Turbro_Negro (01/16/12 09:21 PM)

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Justin
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Galant VR-4 org Post #: 1045921 posted 01/16/12 09:28 PM     Remind Me!  Send Private Message   Edit Post      
You might be right on the rod length.

Yes, you are right. The stock rods are 150mm, not 156mm. I will edit the above post to reflect the correct info.


Edited by galant1517 (01/16/12 09:39 PM)

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Justin
Unregistered


Galant VR-4 org Post #: 1045928 posted 01/16/12 09:57 PM     Remind Me!  Send Private Message   Edit Post      
Quoting galant1517:

Well, lets look at a few numbers.

In a stock 2.4, stroke is 100mm and rod length is 150 mm. Rod ratio is 1.50.

So at TDC, the total distance between the main journal centerline and the piston wrist pin centerline is 200mm. (rod length plus half of the stroke).

The minimun distance (BDC) is 100 mm.

Assuming no other changes, to match that 200mm TDC distance with a 75 mm stroke, you would need a rod that is 162.5 mm.

This combination would result in a rod ratio of 2.1667.

Now you could also have custom pistons made to utilize the stock 150mm rods, by lowering the wrist pin in the piston body by 12.5mm. This method would bring the rod ratio to 2.00.

All of this is important to your question because of piston velocity.

Piston velocity is going to be the biggest factor in determining the reasonable RPM expectations of any particular engine.

The value that we are interested in here is the peak velocity. An engine of the same displacement of another, but having a lower peak piston velocity at the same RPM, will always rev higher than the other.

There are two ways to modify the peak piston velocity. You can change the stroke or you can change the rod ratio.

To lower the peak velocity, you can decrease the stroke, or increase the rod ratio.

To increase the peak velocity, you can increase the stroke or decrease the rod ratio.





Okay, so now that we have that cleared up, , looking at this engine again shows that decreasing the stroke will automatically increase the rod ratio. Both changes will allow you to increase the peak RPM of the motor. This is good for drag racing.

The one thing that you'll need to remember is that by decreasing the peak piston velocity, you are also decreasing the speed at which air moves past the valves at any given RPM. The decrease in air velocity is the underlying reason why shorter strokes yield less torque. And this also means that increased rod ratios will also lead to decreased torque.

Bigger cams will also affect where the torque is made. More importantly, bigger cams reduce air velocity even further at a given RPM, as compared to smaller cams.



With a super light mirage shell, lower torque will be less of a concern once you're moving. However, regardless of the platform, if the air velocity is too low, the engine may never idle.

You'll have to find a balance between being able to idle and chasing the high revving beast that you're looking at creating.




Edited by galant1517 (01/16/12 10:27 PM)

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Jesus_Negros
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Galant VR-4 org Post #: 1045932 posted 01/16/12 10:29 PM     Remind Me!  Send Private Message   Edit Post      
Moving the piston beyond -6mm would probably be frowned upon buy the piston maker and your machinist. 162mm rods are a bitch to fit btw.

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Justin
Unregistered


Galant VR-4 org Post #: 1045939 posted 01/16/12 10:51 PM     Remind Me!  Send Private Message   Edit Post      
With this 75mm crank, my boosted brother, the stock style piston can be retained. There is no need to modify the wrist pin location. I think that the confusion we have here is the difference between our terminolgy.

I'm talking about using a custom piston with a +12.5mm compression height, when trying to also use the stock length rods.

I think that you think I'm talking about a -12.5 piston.


Edited by galant1517 (01/16/12 10:57 PM)

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fuel
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Galant VR-4 org Post #: 1045949 posted 01/16/12 11:22 PM     Remind Me!  Send Private Message   Edit Post      
even so, I don't think a +12.5mm piston crown is a good idea - you don't want the crown to be too much higher than the wrist pin. If you're going to use the 75mm crank you may as well just stick with the 4G63 block.



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Justin
Unregistered


Galant VR-4 org Post #: 1045952 posted 01/16/12 11:52 PM     Remind Me!  Send Private Message   Edit Post      
I'm simply throwing out some numbers. I am not endorsing or condemning the idea. The reality is that the pistons are going to have to be custom made anyway. To get enough CR out of that block, with that crank, the easiest way would be to use 162mm rods ('cause they sound like they are already available) and have a piston made where the manufacturer can use the piston dome to compensate for the subsequent .5mm drop in piston height at TDC. But this guy isn't talking about building something that has been done a hundred thousand times either. I'm sure that he knows that he will need some custom made parts.

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Jesus_Negros
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Galant VR-4 org Post #: 1045954 posted 01/17/12 12:02 AM     Remind Me!  Send Private Message   Edit Post      
Quoting galant1517:

With this 75mm crank, my boosted brother, the stock style piston can be retained. There is no need to modify the wrist pin location. I think that the confusion we have here is the difference between our terminolgy.

I'm talking about using a custom piston with a +12.5mm compression height, when trying to also use the stock length rods.

I think that you think I'm talking about a -12.5 piston.




Got ya 100% now! hence why i use "-6"
You'll need some high compression pistons for this kind of N/A build.

162mm rods arent off the shelf as far as I know but R&R made mine for just under $900.
That much rod though you'll need to use aluminum because it'll just add weight with that much more metal.

The idea is creative but not worth it in any instance. Except to say "I have money to blow and and the balls to build a useless motor".


Edited by Turbro_Negro (01/17/12 12:09 AM)

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beaner
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Galant VR-4 org Post #: 1045975 posted 01/17/12 02:02 AM     Remind Me!  Send Private Message   Edit Post      
So what dsm trans are you using to shift at that rpm? $$

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raptorWagon
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Galant VR-4 org Post #: 1045992 posted 01/17/12 07:48 AM     Remind Me!  Send Private Message   Edit Post      
go RWD and use a RX-7 turbo II trans!



92 Galant VR-4 362/1000
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thedsmguy
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Galant VR-4 org Post #: 1046023 posted 01/17/12 01:38 PM     Remind Me!  Send Private Message   Edit Post      
Ok, It all just a question. Not probably ever going to happen unless I stumbled upon some really good idea etc. I think a N/A 2.4 with a 1.8 dohc is way more likely to be built in my garage and put in a light car (possibly a rwd setup even). Believe me, I have my hands full and pockets empty by my current vr4, but its nice to think ahead to the next car sometimes.

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beaner
Blew1 Guy Today


Galant VR-4 org Post #: 1046081 posted 01/17/12 06:48 PM     Remind Me!  Send Private Message   Edit Post      
Quoting raptorreed:

go RWD and use a RX-7 turbo II trans!



Yeah if you can find the rare 2.4 wide block and even more rare b2600 bellhousing.

It think its a lot of money and effort to end up with a N/A 4cyl drag car. Just get a dumped busa and swap that in instead. It'll at least sound cooler.

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DR1665
Kill him in the face with Wilson Phillips


Galant VR-4 org Post #: 1046128 posted 01/17/12 09:16 PM     Remind Me!  Send Private Message   Edit Post   
There's something very cool about building an all-motor Mitsubishi. I don't know too much about rod ratios and the original question of swapping crankshafts, but if you're on Tuners, you might look up 'bullettdsm.' He's a wiseman and plays on both sides of the fence. His 2L 420A Eclipse puts down north of 200whp and runs mid-13s all motor and he also has a couple 4G63s. Guy knows his way around a Mitsubishi drag car. He would know for sure. (Not saying anyone here doesn't. Just offering another resource.)



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