Compression Ratios

[cheekychimp]

I'd be interested to hear what compression ratios most of you are using and specifically if you are using a higher than standard compression ratio together with a little info on your setup (i.e. displacement, type of fuel, type of turbocharger, amount of boost pressure you run etc).

I understand the basic principles involved here and I realize that guys running large snails at very high boost pressures are going to want lower compression pistons, I'm just wondering how far people have actually gone 9.5:1, 10:1, 10.5:1 or higher and specifically what the driving characteristics were like and if it was worth the effort to do it and tune it.

FWIW I'm really trying to pep up the driving characteristics of the daily driver after a lot of consideration and short of going to a twin scroll setup or a six speed transmission, I think I'm getting there. I'm just wondering if going higher than 8.8:1 (or whatever it is the EVO pistons are rated at) is a viable option, or if it is going to create more problems that it solves. I'm really looking at improving the idle to 3,000 rpm area and short of going stroker or adding compression I'm not sure what else I can do here. Any tuning tricks with timing or fueling that I could utilize if I installed DSMLink or ECMLink on this car?

 

[broxma]

I'm running evo pistons on E-85. I'd say for anything higher than 9.0-1 I'd want to run E-85 honestly. My next engine build will be 9.5-1 on the same fuel but I'll probably switch over to a AEM computer.

I know there are some evos running as high as 10.5-1 on E-90 and they had skirted the notion of running 11.0-1 but apparently there was no gain over the lower compression once timing was taken into account.

/brox

 

[cheekychimp]

I thought someone ran 10:1 on here, it might have been Tom Noonen back in the day. I thought that since I didn't really intend running much over 1 bar and most people run 22-23 psi on the 16G turbos I might get away with bumping up compression to 9.5:1 or 10:1. You think it would prove difficult to tune on pump gas even with say water/meth injection?

 

[boostx]

Yea Tom Noonen was running 10:1.
The engine i am building now i am going to be running 10:1 with pump gas and e85. The off idle acceleration is great in a 10:1 car. The biggest thing is with he tuner if he knows what he is doing you will have a beast.
Tom's car

 

[Jason G.]

Haven't heard that name in a long time.

 

[Lukefraizer]

Quoting cheekychimp:
I thought someone ran 10:1 on here, it might have been Tom Noonen back in the day. I thought that since I didn't really intend running much over 1 bar and most people run 22-23 psi on the 16G turbos I might get away with bumping up compression to 9.5:1 or 10:1. You think it would prove difficult to tune on pump gas even with say water/meth injection?



I'm running 9.0-1 and only running about 20 psi boost on a evoIII turbo AEM stand alone 91 octane and water meth and we are still getting knock. I can't really see it being that advantageous to put in higher compression pistons unless you are going to run E85 or race fuel. If you are going to run E85 than I would say go for it but until you switch to just that I wouldn't do it. Just my opinion though.

 

[cheekychimp]

Thanks, Luke. I appreciate your honesty, real world experience like this is what I am looking for. I was hoping to bump up compression but there doesn't seem a lot to be gained by going from 8.8:1 (EVO 6 pistons) to 9.0:1 (EVO III pistons or forged). This car feels soggy just off idle and nowhere else. If I could just pep up the 750-3000 rpm range I'd be there.

 

[SouthCaliVR4]

I'm also 9 to 1. I had no problems in Washington on an evo3 16g at 17 psi & 93 octane however, Since moving to Cali & running into 91 I have been fighting knock big time. in fact I'm ready to build another lower end, maybe go 2.3 stroker.

I loved the low end grunt of the higher compression when I had access to better fuel but I'll go 8.5 or eight with the new build & make up the difference with higher boost. I did like that I could drive around without ever hitting boost & keep up with the flow of traffic just fine & I'm hoping the bigger expense of a 2.3 will be justified by retaining this characteristic.

I'm going to try a link set up & see if better tuning can solve my issue first but I'm not too hopeful based on my own research.

 

[cheekychimp]

Mmmm that's interesting though because it assumes at that sort of boost that a minimal increase in octane could negate the knock. I wonder if I used meth/water injection I could bump past 9.0:1. I only run regular fuel on the 8.8:1 compression so I could step up to premium as well but it would be nice to manage on the cheaper fuel.

 

[thecman02]

Quoting Lukefraizer:
Quoting cheekychimp:
I thought someone ran 10:1 on here, it might have been Tom Noonen back in the day. I thought that since I didn't really intend running much over 1 bar and most people run 22-23 psi on the 16G turbos I might get away with bumping up compression to 9.5:1 or 10:1. You think it would prove difficult to tune on pump gas even with say water/meth injection?



I'm running 9.0-1 and only running about 20 psi boost on a evoIII turbo AEM stand alone 91 octane and water meth and we are still getting knock. I can't really see it being that advantageous to put in higher compression pistons unless you are going to run E85 or race fuel. If you are going to run E85 than I would say go for it but until you switch to just that I wouldn't do it. Just my opinion though.



That's pretty disappointing. What kind of intercooler and intake temps are you rocking?

I'm running 9.0 with about 14* and 30 psi out of bw259 with no knock at all. That's on 93 octane.
My only problem is I did both the stroker and compression raise at the same time. The car feels great off boost though.

As far as off boost acceleration you won't really pick up too much from tuning. Making sure your fueling is spot on, clean airfilter. Cyclone intake with working butterfly will help. How much hp do you want out of this daily? You could always downsize your turbo housing to reduce spool up time. I think I remember reading posts saying you struggled with hills and what not. If you resist shifting to get into boost you will be disappointed with these cars. Torque = boost.

 

[GSX_TC]

im running 8; 5 to 1 with an Evo III big 16g on 15 pounds

 

[beaner]

Awesome.

 

[cheekychimp]

Quoting thecman02:

As far as off boost acceleration you won't really pick up too much from tuning. Making sure your fueling is spot on, clean airfilter. Cyclone intake with working butterfly will help. How much hp do you want out of this daily? You could always downsize your turbo housing to reduce spool up time. I think I remember reading posts saying you struggled with hills and what not. If you resist shifting to get into boost you will be disappointed with these cars. Torque = boost.



I think my problem is I'm a perfectionist, always wanting better and looking for the holy grail. I already have a 4.3 final ratio transmission, 2G head, cyclone manifold with working butterflies. My fuel pressure regulator was losing pressure. I have a new one so when that is fitted it might possibly help with off idle response.

I don't think the car could be set up much better for low end and midrange. Would my larger throttle body affect off idle response? I thought it would actually help. I think the biggest problem I have had is being spoiled by the Type R. Everyone says NA Honduhs have no torque. That might be true once you are comparing them to a turbocharged car planted firmly in the midrange at 18lbs but off idle the Type R just rips and is so smooth in every gear. Creeping up a 1 in 4 (might not be that bad but it feels like it) at 2000 rpms stuck behind a dumper truck or a bus just sucks but when it comes to the point where you can overtake the Type R just pulls instantaneously in 2nd whereas the VR4 still feels really sluggish until you hit about 3000 rpms.

I am not looking to make a huge amount of power. I picked up a small 16G because it is supposed to spool marginally faster than the EVOIII although since everyone has told me I won't notice the difference in spool between the two I thought I might step up to the EVOIII later. So I guess I'm expecting maybe 300-350. I'm not chasing figures on this one though. I don't want a knife edge tune, I'd just like it to be running as efficiently as possible and getting the best mpg it is capable of doing. I just thought that perhaps since trying to squeeze 400 hp out of an EVOIII wasn't the aim and since I wasn't looking to run more than about 1bar (14 pounds) that I might get away with running a 10:1 CR which I think is my best bet for picking up power off boost. I'd trade maximum power for the off idle response and I feel sure, knock issues aside that an EVOIII at 14 lbs on a 10:1 CR would still make over 300 hp fairly easily.

The other possible thing that might help is cams but that seems like a crap shoot because it stands to reason that I want an NA type profile (at least on the intake side) to help with off boost power but that more than likely is going to limit the midrange as well as the top end once I get into boost.

 

[thecman02]

"I'm running 9.0 with about 14* and 30 psi out of bw259 with no knock at all. That's on 93 octane.
My only problem is I did both the stroker and compression raise at the same time. The car feels great off boost though. " I meant to say that doing the stroker and high compression is awesome, but I did it at the same time so I don't know which part made off boost feel better.

I know what you mean about the TypeR being really responsive though. I think part of it has to do with the 10.6 compression or 11:1 uk/jdm engine, and the nice tight gear ratios in the Type R tranny's.

I think you could get away with 10:1 on the 97ron = 93oct especially if you stay under 20psi. It will definitely take some time to tune though. Some adjustable cam gears can help. You could add overlap. It will really help non boost situations, but will kill boost power haha.

 

[cheekychimp]

I think you are right about the gear ratios, 6th gear in the Civic is still shorter than 5th in the Galant. It isn't a problem over here, in fact I think the ratios are close to perfect for Hong Kong but I guarantee you it would annoy the hell out of me in the UK. I can't imagine travelling everywhere at 70-80 mph if I had to spend the whole time at 4000-5000 rpms. The close ratio VR4 rally box is nice because only 1st to 4th are close ratio. 5th is identical to the 3.545 ratio box so I am still only at 3000 rpms if doing 100 km/h (62 mph).

I think getting closer to the Civic CR would close the gap considerably and obviously once into boost the VR4 wins hands down. I forgot to mention earlier, that if you travel 5 up in the Civic the balance quickly gets restored. You really notice a drop in power especially up those steep hills. In contrast with the VR4 once you hit boost at around 3K it doesn't care if you are 1 up, 2 up or fully loaded!

I have a MAFT Pro I bought from Curtis and the idea originally was to eventually set the car up on SD and add Meth/Water injection and let the MAFT Pro control it. Unfortunately I can't control timing on the JDM code and until I sort out whatever issue I am having on my other 90 JDM car, I'm reluctant to swap over to a USDM ECU. If the MAFT Pro can keep knock under control, I'd be happy to just let the stock ECU handle timing, but do you think that would be enough? Curtis said as long as your injection system can spray enough, you essentially just set a target AFR in MAFT Pro and it controls the injection to maintain that AFR. On the stock ECU I'm limited to 550 injectors at present although Yiuwa might be able to burn me a chip with identical code for larger injectors.

 

[Lukefraizer]

I'm running a 3 in intercooler. And I'm not sure what the temp is... Ill have to look as some data.

Quoting thecman02:
Quoting Lukefraizer:
Quoting cheekychimp:
I thought someone ran 10:1 on here, it might have been Tom Noonen back in the day. I thought that since I didn't really intend running much over 1 bar and most people run 22-23 psi on the 16G turbos I might get away with bumping up compression to 9.5:1 or 10:1. You think it would prove difficult to tune on pump gas even with say water/meth injection?



I'm running 9.0-1 and only running about 20 psi boost on a evoIII turbo AEM stand alone 91 octane and water meth and we are still getting knock. I can't really see it being that advantageous to put in higher compression pistons unless you are going to run E85 or race fuel. If you are going to run E85 than I would say go for it but until you switch to just that I wouldn't do it. Just my opinion though.



That's pretty disappointing. What kind of intercooler and intake temps are you rocking?

I'm running 9.0 with about 14* and 30 psi out of bw259 with no knock at all. That's on 93 octane.
My only problem is I did both the stroker and compression raise at the same time. The car feels great off boost though.

As far as off boost acceleration you won't really pick up too much from tuning. Making sure your fueling is spot on, clean airfilter. Cyclone intake with working butterfly will help. How much hp do you want out of this daily? You could always downsize your turbo housing to reduce spool up time. I think I remember reading posts saying you struggled with hills and what not. If you resist shifting to get into boost you will be disappointed with these cars. Torque = boost.

 

[Eaglesfly]

I'm running 9.5:1 compression custom CP pistons with an AGP T3 67mm turbo. I regularly run 33psi of boost on pump gas (93 octane) with methanol (100%)injection with NO knock. The added compression definitely gives it more power down low and I would never run any lower compression. Without methanol injection on straight 93 octane I'm able to run 20psi of boost with no knock and the max timing set at 15 degrees.

 

[thecman02]

Not to threadjack, but definitely need to see the intake temps to get a good idea what's going on causing the knock. Are you running a 1g or 2g knock sensor with your aem? I've only just started helping my friend tune on AEM, but the good news is I believe you can pick up quite a bit more power with some more time experimenting and diagnosing issues.

On topic, if you get the meth injection setup then not having a way to tune timing becomes less of an issue. Its too bad we lost our asset keydiver. He could probably get you a nice chip setup for whatever injectors, timing and whatever and still be able to have the code to actuate your cyclone butterfly. I used to have a chip burner and could mess with code but it is a royal pain in the ass.

 

[cheekychimp]

Quoting Eaglesfly:
I'm running 9.5:1 compression custom CP pistons with an AGP T3 67mm turbo. I regularly run 33psi of boost on pump gas (93 octane) with methanol (100%)injection with NO knock. The added compression definitely gives it more power down low and I would never run any lower compression. Without methanol injection on straight 93 octane I'm able to run 20psi of boost with no knock and the max timing set at 15 degrees.



Would you mind sharing anymore information on your setup. Judging from your 1/4 mile time you seem to have some idea of what you are doing. What are you tuning with? This is very promising.

Quoting thecman02:
On topic, if you get the meth injection setup then not having a way to tune timing becomes less of an issue. Its too bad we lost our asset keydiver. He could probably get you a nice chip setup for whatever injectors, timing and whatever and still be able to have the code to actuate your cyclone butterfly. I used to have a chip burner and could mess with code but it is a royal pain in the ass.



Well according to Jeff's site he can still do re-flashing of existing chips so I could send him a chip back, I just feel a bit uncomfortable doing that since the chips I do have he burned for me free. That would be the best option. He already told me he can do me a JDM code chip. He also did a MAFT Pro specific chip but from what I gather, the only additional feature that gives was some timing control which he told me he can't include on JDM code. I basically only need an exact copy of the code I have setup for larger injectors. The MAFT Pro does everything else. I actually have a 2.3 chip setup for a 3G MAS, 850 cc injectors and 9.0 compression on 93 octane. I actually bet that would work with some injection because timing is already pulled slightly for the stroker it just has no Cyclone function.

 

[Eaglesfly]

I started out tuning my meth injection setup with a custom Jestr chip, SAFC and a MAFT. I went 10.56@137mph on this setup before going to DSMLink over 6 years ago. That time was on pump gas/Meth with a HUGE meth jet and a Ross/Eagle 8.5:1 setup. 37psi of boost and a BETE PJ40 jet. Jestr had to lock my timing tables back then, otherwise the SAFC would trick the ECU into WAY too much timing so we locked it down to 18*.

Now on the newest motor (my first 9.5:1 motor with a stock head blew up at 40psi on 110 and Meth; bent an H beam Manley rod) I'm using less Meth and less boost to make more power on the 9.5:1 motor and a ported head. I now have V3 for tuning with the 3.5" GM maf; boost is set at 33psi with a PJ26 jet for Meth duties with max timing set at 13*.