I'm looking at forged pistons for my 97 ITR motor for boost and considering either 9.8:1 flat top pistons, or going lower to around 9:1. Reason being tuning advances have changed a lot in recent years and enabled higher compression ratios on pump gas and I'm finding a lot of very old data, so I'm trying to get some opinions on what makes the most sense now for a street car on pump gas driven hard in terms of reliability, the cluster of E85 and pump gas info has gotten a bit mixed up in the same pile. I'm planning to run somewhere around 12-16 pounds on a T3/T4 .57 Trim with a power goal of around 350whp, not more than 400.

I ran 9.0:1 pistons between between 12 and 15 pounds on my previous turbo cars and never had reliability issues. Lag was also not an issue.

A sacrifice of reliability for a slight gain in power from compression does not seem worth it to me when I can just turn up the boost another pound, but I don't want to go lower than necessary either. I'd like to hear from some people running higher compression on pump gas and any pros/cons. The reason I'm asking is because it has been safer to make power through boost rather than compression because of the heat under high compression and boost (Even at the same hp level), but apparently the threshold been pushed up to a higher compression, so I'm trying to figure out how reasonable it is from a reliability standpoint.

Thanks,

 

9.8 will be just fine with everything you mentioned.

 

yep I would shoot for 10.5:1 give or take .5.

basically 10 or higher, this will give you best all around response and still easily make the power you are looking for on pump gas


my b18c1 with flat top pistons and type R head come out to about 9.5:1 with the handfull of resurfacing done on my head and block. I built the block a few years back. performs rather well but next time i build a block im going to use a slightly more aggressive piston.

 

Do you know how much boost you could push safely though? (it will be some variation of T3/T4 probably .57 trim)

The 9.8:1 pistons are actually flat top in the Type R, they make 10:1 in the GSR because of the combustion chamber difference in the head.

I'm not worried so much about the max power I can make, more getting a good power curve while still being in the efficiency range of the turbo and staying reliable.

I guess the question is more weighing out the pro's and cons of making power though more boost or compression of any compression between 9:1 or 10:1.

 

Well see, there is no "perfect" or "Best" compression to use when it comes to any of the B18C series engines, just a matter of what's overall not good for a turbocharged application. Going with 9.5:1-10.5:1 is actually one of the best compression ranges to go with on 93 octane. Using this as a street/circuit application is perfectly fine. Once you've taken the entire Block apart for this build, over 70% of what gives the engine it's "Type R-ness"is actually gone anyway.

Now, considering that you have a 97 ITR, and didn't change the camshafts from 1997, the advantages of having "Type R Camshafts" is a little lost compared to if you had the camshafts from the 00-01 model, as they were a bit more aggressively suited with a turbocharged application. It's perfectly fine to keep what you have for the 57 trim model you're using, but again, the answer is more of a "not really an advantage", than a "yes" or a "no".

 

your thinking about this the wrong way you need to be asking "how much HP" not "how much boost"

PSI is irellevent, could be 5 PSI could be 30 PSI its all the same for the most part

This is not much of a factor any differences will be negligible, the difference is higher CR will give you more responsiveness when not in boost

 

not sure why your so stuck on 9:1. you have already been recommended 10:1 by multiple users .....maybe thats not what you wanted to hear??

for your power goals there is no reason to go 9:1. heck 11:1 would be would be completely safe with a proper tune. so 10:1 is somewhat conservative already. In the end its up to you but theres no benefit to going 9:1

 

You're looking at using the compression need in a way that it wasn't intended to be configured. The point of increased compression is not only to help with efficiency range of the turbocharger that you plan to use, but so that off-boost response is much better than with a lower compression engine.

 

Well, I was hoping to get some data or experience with the setup to support the opinions, building motors isn't cheap. Running 11:1 would not be smart for turbo unless you plan on only running very low boost, or running e85. I have no idea why people try to make setups work like that. I hear the same story every time, they detonate and get frustrated. I know 10:1 is manageable with a good tune but I would not call it conservative, I consider that the line. I've got it down to somewhere between 9:1 and 10:1 but I'm trying to refine my understanding a bit before I build my motor. I'm trying to get and idea of what kind of trade off we're looking at.

Also, when you match your turbo correctly with your target power level and engine size you don't deal with a lot of lag even with a low compression engine, it sounds like a lot of people are using a turbo that is way to big for the power level they are aiming at and running it way out of the efficiency range, so they spend a lot of time in off boost rpms and are trying to use high compression to eliminate lag, which is much less effective and more dangerous then using the right turbo in it's efficiency range.

Anyways, all I'm really trying to figure out here is if all these turbo setups with 10:1 compression are only popular because of e85, and still need to run lower boost levels on pump OR if the changes in tuning are significant enough that on pump gas and high boost that actually makes sense now and there is no longer a need to go lower. If there is a trade off with reliability or if it just does not matter. There are other things to consider... boost spikes, bad gas, tuning error, who knows, but if I'm flying too close to the sun I'd rather be safe than sorry.

 

as far as 10:1 requiring E85 absolutely not I still stand behind 11:1 being safe on pump gas at the power levels you are looking at. once again going with a lower CR does not equal a more reliable motor either.

there will be some spool up time with just about any turbo you go with at these power levels so yes of course get something that will work effectively.no one has stated higher compression = faster spool (see quoted text above)

 

Agreed. My older 70k mile motor was at 10.2:1 on about 17psi 93 octane TR3030R.

Will still be at about 10.5:1 on the rebuild (by choice to continue my boost habits) at 2.0 litre for the same reason. Better response off-boost with well-matched turbo. (Ask me how I know , hehe) and still on 93 octane fuel until time attack season.

Not sure what evidence you're looking for on paper. The testimonies given from those like myself are from experience of comparing to racing teams and companies from their data, utilizing a technological trickle down effect.. And, well, it works.

 

What whp with the TR3030R at 17 psi?

 

A bit over 400whp-420whp or so. I'm always rather on the conservative side...

I know of another who made much more on the same 93 octane fuel at over 20psi with that same turbocharger

https://honda-tech.com/forums/forced...12whp-2991155/

 

Appreciate the feedback, after more research it's looking like I will probably keep my original decision and go with flat top 9.8:1 pistons.

I still have some time before I ordering so any more opinions are welcome.

Also I want to make sure it will still be reliable on 91 octane because there is a chance I could end up relocating West. I'd love to hear some street setups with turbo size, boost level, octane fuel, compression ratio, and how long it's been running. Thanks.

 

it will be just fine on 91 with a good tune. im at 407HP on 92 octane

 

Not exactly sure what kind of data you are looking for? You're only going to get anecdotal responses here. Your basing your opinion on other people failing but you really dont know why they failed. People have been boosting stock R's and GSRs for a long time now and they are both over 10:1. I would say its safe practice with a built motor to be in the 10:1-11:1 range. As long as the tune is good I dont see why it wouldnt hold up.

Thats true that people go way over sized on the turbo for modest goals (6262 for 400whp IE). Those of us who dont, however, can clearly see the difference higher compression and properly sizing the turbo can do.

My opinion again is no. If you are pushing a ton of power, or trying to squeeze all you can out of a turbo, your going to need a better fuel regardless.

 

I take everything with a grain of salt on any forum, but it's still good to hear what people are saying, it's one of many thing I consider. I've asked some tuners and piston manufacturers as well to see how broad the consensus is before starting the build. In the old days, when I got into turbo imports, 10:1 on high boost was almost a guaranteed meltdown. At that time, you could only tune out so much, so I'm trying to understand what exactly has changed to make higher compression and boost possible. I like to understand why, and the concept behind things. When people say 10:1 will be fine for example, I don't know if that means fine for a while, fine for a few passes, fine for years, fine but not as long as 9:1, fine if you have a perfect tune but no margin for error, fine until you get a bad tank or gas or a boost spike, or fine like no issues at all. I have melted a 10:1 piston before under low boost, but tuning was in the stone age back then, and it was not a forged piston either. I also drove it pretty hard. A lot of the new cars like the Nissan GTR and EVO X are still made with 9:1, it makes me think there must be some reason the manufacture does this. So far though, I am getting that nowadays a 10:1 forged piston will be fine under good tuning, although I'm not sure under what boost/hp threshold.

 

The bridge that you may be looking for is the change in tuning technology, and it's exponential hyperbole'd increase in the utility of both software & hardware that really assists in increasing the tuner's ability to keep the car in good shape for years. Although some aftermarket ECU platfoms still use circuit boards as an interface with the OEM ECU, it's these on-board interfaces that make the tuning easier to work with, so that you don't have to depend upon a lower compression ratio in order perform the results needed.

(That is to say, however, that this increase in technology with the ease of availability of high-knock resistant fuel has also created a sub-group of people who think they can tune and properly calibrate these cars when they still don't have the underlying knowledge to make the car's drivability as good as stock. That's still for the professionals from my experience. Some of these new "self-proclaimed" tuners say they're tuning professionals when they really aren't yet. Give them something outside of their normal comfort zone, and they fold like paper compared to the experienced professional).

You also can't compare the stock compression of utility of Factory-based performance cars with what we do, because their purpose is to have thousands of units sold, using various levels of fuels in various climate conditions. There are variables that the OEM has to account for that custom tuning doesn't account for. We've taken many of those same lowered-compressioned applications are now commonly mass-customed to be at that same 10.0:1 and higher that you're so "fond" of .

I mean, do as you will, of course. No one will slight you for it. Some of us are giving you the recommendations that we've used , for years..

(I was at 10.2:1 for about 12 years on the same tune w/ 93 octane. over 70,000 miles on my older build. I'm now changing builds because I want larger displacement)

My B18C1 (2002-2014)Not bad for 12 years and over 20 events

 

Nice.