[Chris Peterson]

I am getting ready to go the 3.4L stroker route with my MKIV and wanted to get some feedback on other's experiences with them so far. My key question is what compression ratio people decided to go with and what their results were in terms of responsiveness on the street. I believe the "standard" BC kit that MVP stocks has an 8.5:1 CR, I don't know the CR details on the other stroker kits, but obviously custom CRs are available.

I would be mating the 3.4L to an Obiwan built/ported/polished head, going for a leftward heavy power curve by re-using my BL 67DBB (at least at first), running on pump (93) and meth at a low-ish boost (±20 psi), and tuned on the AEM. I am not too worried about the turbo running out of breath on this motor, my goal is not big dyno numbers.

I know that alpha6164 built his BC 3.4L with a 9:1 CR, but sadly I don't think he is going to be able to give any feedback for a while due to his motor problems. Anyone else built their stroker with a higher CR that can speak to the real world benefits/drawbacks they have experienced? Thanks in advance for any info!
Chris

 

[alpha6164]

I am sure you know that I went with the 9.0CR and during the few hundred miles of breaking the motor in, i can tell you the responsiveness with the 74mm turbo was great. I was never more than 2-3psi in boost during break in process. But the increase in displacement and CR definitely was noticable. On the dyno, before whatever the catastrophic event occured, it was making amazing power. 640whp/500tq and 700whp/550tq on 14psi and 17psi respectively is massive on a DynoDynamics even with a 10% correction factor. Those boost pressures were confirmed by the AEM logs which read the map sensor in the intake manifold, along with the dyno sensor and my incabin boost guage.

I can tell you though that I do not think that with my setup that my 74 turbo would have been able to go upto 30psi. That is just my guess, but no matter what that turbo is a 900horsepower turbo. You might make it at 11psi with a viper or 35psi on a stock supra. So if I was already making that much power at 17psi, i probably would have maxed the turbo out before most stock guys. I think this turbo would have probably run out of breath at 25psi. But we will not know for now, until i get the engine back up running.

 

[Chris Peterson]

alpha6164: Thanks for the reply, I certainly hope things go as best they can given your current engine situation. I followed your thread for a while in anticipation of the results as your build was similar to what I had in mind: pairing a mid-sized turbo with the 3.4L and not the GT47XXs you see on many of these builds. Good to hear you at least had some positive results in the short time you did have it up and running, good luck!

I am not sure if the info is out there for this car, but it would be interesting to know what the Do-Luck 3.4 TO4Z car has for a CR. Any one know by chance since it is a relatively comparable setup? Thanks in advance.
Chris

 

[breakemlose]

Go 8.2-8.5:1. Inside the cylinders you don't have intercooling affects.

If you want tons of power with out going crazy wtih the octane go lower compression.

 

[supradupaflyguy]

lowering compression will not allow you to make any more power, it will only allow you to run less octane, but in the end cylinder pressure is cylinder pressure whether you make it with boost or compression. i went with 9.5:1 because i dont ever plan on running pump gas and the extra compression will help with spool a little and squeeze those last few ponies out since i will be maxing my turbo(t88h) out. if you plan on using pump gas an running it primarily as a street car, stick with 8.5:1... you wont need the extra compression with the stroker and that small of a turbo

 

[KenHenderson]

I am not sure if the info is out there for this car, but it would be interesting to know what the Do-Luck 3.4 TO4Z car has for a CR. Any one know by chance since it is a relatively comparable setup? Thanks in advance.
Chris

Chris,

I'm almost 100% sure the Do-Luck car with the 3.4L HKS stroker had a static compression ratio of 8.5:1, the same as my car. The HKS pistons are slightly more dished than the OEM versions, in part to account for the larger bore. I suppose it's possible, but I don't believe HKS offers its stroker in anything other than an 8.5:1 SCR although, based upon HKS recommended head gasket thicknesses, I believe you can increase the static to as high as 8.8:1. Hope this helps.

Ken.

 

[Mark Conte]

Chris,

Really what it comes down to is - what are your goals with the car? You'll make more power on lower octane due to the fact that you can simply injest more air into your engine at a given 'boost pressure'. If you think you're going to be on pump gas primarily, then I'd say an 8.5:1 c/r would be fine for you. That turbo will come online nearly immediately with a 3.4L and built head.

If you're going to run race gas exclusively then sure, why not up the compression. It is more of a beating on the motor, but with a billet crank and a correct bearing/rod/piston/wrist pin package it should be able to take it for a good long while. It will shift your powerband to the left and it should yeild more horsepower at the same airflow as a lower SCR.

 

[Chris Peterson]

Thanks for the replies, much appreciated.

breakemlose: I don't plan on going crazy with the octane, nor am I going for huge HP, on the other hand I am not planning on running crazy boost (30 psi+). My thoughts were to raise the compression somewhat from 8.5:1 to enhance the low-end improvements that come with the stroker.

SupraDupaFlyBoy: Are you talking about a 3.4L that you built to 9.5:1 or a 3.0L? It will primarily be a street car and see pump (93) with meth injection. I mainly wanted to see what people's results had been with the higher compression stroker and what issues they dealt with to make it work (boost, octane, timing, etc.). My initial instincts are to keep it safe and stick with the 8.5:1, but if I am going to spend the money on the stroker I might as well look into all the options

KenHenderson: Thanks for the info on the Do-Luck 3.4L TO4Z car. Not surprising it is in that range, I thought it might be relevant given that it is one of the few strokers I had heard of with a mid-sized turbo on it.

Mark Conte: I hear you, goals for the car are 550-600HP on pump (93) w/meth. The stroker will obviously help with the low-end and spool-up, I figured it was worth looking into raising the CR at the same time to enhance this effect. It may come back to keeping it somewhat safe and going with 8.5:1 to keep from pushing the motor too far given what I plan on doing with it. One other thing, you work for Titan, correct? Somewhere along the line I heard the Titan stroker's CR is 10:1, is that correct and do have any comments on how that has worked out? Thanks.

Thanks again for the replies. I also saw that JamesN1830 was building a 3.4 at 9.5:1, I will PM him to see if he has any input.
Chris

 

[Mark Conte]

Chris,

I personally don't like supplimentary methanol injection. It is almost never tuned correctly and it is absolutely imperative to have equal cyl-to-cyl distribution considering it is a fuel itself. However, do what you will in that regard, I wish you luck.

As for the Titan kit, if there was a 'shelf' titan kit, it would be in the 8.7-8.8 c/r range...depends on the chamber work on your head and thickness of your headgasket of course, but it's about there.

The Titan kit can be ordered with virtually any compression ratio you want, I've personally ordered custom 2JZ pistons at up to 11.5:1 compression ratio if memory serves. I'm sure I could go higher if necessary.

 

[SupraSpeedMKIV]

Somewhere along the line I heard the Titan stroker's CR is 10:1, is that correct and do have any comments on how that has worked out? Thanks.

From what I've read, you can get the Titan stroker in any compression ratio you want.

edit: beat me to it.

 

[JamesN1830]

My BC kit is 9.5:1... still waiting on the machine shop though, so no results. I'm only c16 though.

 

[Chris Peterson]

Mark Conte: Understood on the meth injection, for me it will be more of an adder to stay safe if I spike above the ±20 PSI I plan on running. The person who will be doing the tuning swears by it and gets good results from everyone I have spoken to, but I do not plan to use it as a crutch for high boost by any means

SupraSpeedMKIV: I imagined Titan could do a range of CRs with their stroker, just heard from somewhere that 10:1 was the number they used or recommended. Obviously second hand info, but it would be interesting to know if they had found a particular CR that worked better with this setup or if they had any insight.

JamesN1830: Thanks for chiming in, good luck with the build. Since you're running C16 you are going in a different direction than I, but is there any particular info you had or advice you got that made you settle on the 9.5:1?

Thanks again.
Chris

 

[JamesN1830]

JamesN1830: Thanks for chiming in, good luck with the build. Since you're running C16 you are going in a different direction than I, but is there any particular info you had or advice you got that made you settle on the 9.5:1?

Thanks again.
Chris

spool and responsiveness.... more compression = more off boost power (basically).

 

[Mark Conte]

Chris,

What I'd recommend would be based on what you use the car for. I generally will not recommend a high compression ratio to anyone looking to run pump gas, nor do I recommend a large turbo in the first place. Your setup should be awesome and you'll get a ton out of that 67 on pump gas with 8.5:1, just keep that exhaust side large.

James is an example of someone who I'd probably say should run higher compression (like he is) because he's exclusively going to run C16.

 

[Chris Peterson]

JamesN1830: Thanks for the reply. I imagine you have a different purpose for your build, hence the issues you might run into with the higher CR aren't a big factor for you since you will be running C16. Hope it works out well for you, you having someone local do the stroker work or one of the known machine shops/builders on here?

Mark Conte: Thanks for the comments. I think my default position would be to go with the 8.5:1 since it will allow some leeway with tuning and the fuel I will be running. More than anything I was curious if anyone had pushed the CR up a bit in this situation and what the results had been. I have no problem going the safer route, thought I might as well check into it

Thanks again.
Chris