I've been doing research about the turbo and have decided to go turbo, but everyone is saying the pistons are only rated at 300 hp but people that are already turbo haven't changed there pistons and have been ok because the turbo doesn"t create as mush heat as the supercharger. so heres my question i have found two different pistons the first set is the diamond racing pistons i have not found how much power they can hold but was wondering if they were a good buy? the other set was jbp and they are capable of holding 850 i just wasn.t sure what our bore is on the ss. jbp has three different pistons two diferent 86mm and a 86.5 mm they have different compression ratio's. what is our compression ratio does anyone know. what would be a better buy jbp or the diamond?

 

Drop compression to 8:1 and turn the boost up to 18-20 psi with a turbo kit.

 

so i should go with the jbp the 86 mm with the compression at 8.0:1 will i need a bore for that size and i know some will give me **** about this but how do i change compression do i need hp tunners for that.

 

Any major modification you need to do tuning. The compression of the engine is based upon the design of the piston, you get lower compression pistons, and wow, you have got lower compression.

 

I have a set of 8:1 SRP's on order as we speak. Please god don't buy from JBP. Complete ripoffs.

 

As this quote from Garrett's website states, there are many factors in choosing compression ratio and that there is no one right answer for every application. Instead of giving you some made up BS numbers, just read this and take it into consideration. You want to run as high of a compression ratio as you can while still being able to compensate for the max load your engine will encounter. In other words, you only need to drop compression all the way to 8:1 if you plan on running higher boost levels:

"What compression ratio should I run with my turbo engine?
Allowable compression ratio depends on many factors, and there is no one right answer for every application. Generally, compression ratio should be set as high as feasible without encountering detonation at the maximum load condition. Setting the compression ratio too low will result in an engine that is a bit sluggish in off-boost operation. Setting it too high however, can lead to serious engine problems due to knock.
Factors that influence the compression ratio can include: fuel anti-knock properties (octane rating), boost pressure, intake air temperature, combustion chamber design, ignition timing, and exhaust backpressure. Many modern engines have well designed combustion chambers that will allow modest boost levels with no change to compression ratio, assuming appropriate tuning. For higher power targets with more boost, compression ratios should be adjusted to compensate."

You would need to do the math to figure out exactly what to use; I highly doubt you are going to be running boost levels which will require you to drop all the way to 8:1. If guys are hitting 300WHP on the stock internals at moderate boost, you'll be able to run even higher boost and maintain a higher power level with forged internals and a slightly dropped compression ratio (9:1 or so).

 

Just remember that people who are putting down 300 with a small pulley, ported blower, etc are making *much* more at the crank. It's not just drivetrain loss - that blower is taking probably north of 75hp to spin and produce that much boost at redline. In other words, the pistons are likely doing well over 400hp of work to make 300 whp with the stock blower.

 

Take a page out of the SRT4 guys book. They have 8.1:1 compression and run 20psi daily and safely. I wouldn't even consider doing 20psi on 9:1 compression.

As for power potential. Every full point of compression is about 10 horsepower at the crank.

 

dude just buy a nuclear reactor engine

 

I know what you're saying. SOME (Keep in mind I said some) SRT-4 owners actually buy aftermarket pistons which raise their compression AND they run higher than stock boost. To me that seems like if you take a page from them, it will say if your engine can already handle X amount of power don't handicap yourself unless it would have a benefit. In other words, why drop all the way down to 8:1 when there are already people running over 15psi on 9.5:1 hypereuteptic pistons? Sure it won't be a HUGE difference, but every little bit counts.

Edit: Also, the you aren't to expect alot of HP gains from a higher compression, that isn't the point. It provides more torque/turbo pickup at lower rpms by making the most of the air which IS available to compress that is being drawn in by the engine. I'm not saying you want a high compression ratio, you just don't want to undercut yourself, if you don't have to; and like I said it depends on how much boost you run, fuel used, tuning, timing, cooling solutions etc. etc.

 

Because running a turbo is a lot different then our airflow starved eaton. You wanna run 9:1 that's all good. Just make sure it's tuned right.

 

Edit: Oh, I was saying that there are already members who run more than 15psi with a turbo on the stock pistons at power levels of around 300WHP, not the eaton.

Yeah it would definatley need to be tuned right. And, you're right that our Eaton doesn't flow near the volume that the turbo can, but the turbo also creates much less heat which is another factor.

All I was saying was to evaluate his situation, and just giving 9:1 as an example. You can get anywhere from 9.5:1 down to 8:1 in increments, and if you really want to fine tune your engine, consider your circumstance and in the end he may find that he does need to run 8:1.

 

dropping it to 8:1 is pointless, unless you really can't tune
people on jbo drop compression to 9:1 on the 2.2's and run anywhere from 8-25psi of boost
the key is keeping the intake charge cool, really cool.. meaning effeceint intercooler (not the biggest you can find) and keeping in the range of effiecency of the turbo.

when i was designing my 2.2 turbo build (that i decided to give up on because it was to much money to put into a cavalier) i had everything needed to make 450whp using 8.9:1 cr pistons and a 60-1.. i did my research and those numbers are very achevable on 92 oct that we have here, or even e85

 

smartest thing you've said j/p
um, see below
right on, screw JBP.... I'll buy a set of 8.0:1 or 8.8:1 pistons soon. I'm gonna keep the eaton too

 

heres a thought...

if you have to make a thread to get answers you have no business spec'ing out a turbo kit.
it'll get way over you head.....sorry to be a dick but its the truth, it took me over 3 weeks to spec the houseings for mine and i do this and i do these types of things for a living.

 

I'm going with a custom 1.6L whipple kit and want to run 16-18psi on a daily basis so 8:1 is only logical for me. Could i make more power with 9:1? Sure but i'd rather play it safe.

 

20 PSI, sure...but on what compressor?

You're just suggesting he runs a high amount of air pressure and you're not mentioning and he doesn't know either what turbo he's going to run either.

Why wouldn't you do 20 PSI on 9:1 compression? That makes 0 sense in my head even if you knew what compressor you had. It's not about the air pressure. When compression is involved in picking out for performance, the whole point in lowering compression is to keep combustion temperatures lower when introducing boost air pressure along with natural heat created inside the combustion chamber from static compression of the engine's pistons.

It's easier to tune for the fact of not having to have such a heat battle of tuning and you may even be able to run more of a aggressive timing advance and not nearly as rich fuel mixtures compared to a engine with a much higher compression ratio (example: 10.5:1 +)

8:1, 9:1 and even 9.5:1 is completely fine. The lower you go, the more air pressure you'll need to make up from the natural engine power loss.

 

Yeah, I looked at the math and 8:1 will be good and safe for your application. You could run a little higher, but I guess you're right, it's not really worth it when you do the numbers.

 

I agree with Adam here. You really need to decide on what turbo and everything else your getting first, then see what would be safe to run with that setup.

 

That's what I was getting at; you need to make the decision based on what you know about your engine.

 

Exactly.

and even still, with a efficient aftermarket turbocharger, compression ratio is not going to be that much of the concern.

No it wasn't...

Just playing LOL

 

I'm sticking with the 9.5:1 with my setup, and plan on starting around 15psi.

 

What turbo you using?

 

Another thing to keep in mind is whether you want to be able to run your car on pump gas or not and how much boost your are planning on running. If you leave the piston compression too high you will need to run higher octane to prevent knock at higher boost levels.

 

Not necessarily

This is where playing with ignition timing is key. There are many ways to fight knocking besides going with higher octane that can be successful but retarding timing is usually a great way of doing so.

The big advantage to running a higher octane and gaining power is that you can run a more aggressive timing advance with higher octane because it allows a higher resistance to detonation.