It seems that the common number amongst most s2k members concerning boost levels on a stock motor(meaning stock compression ratio) is about 8psi. Anything higher and things get a little on the worried side of things.

The most common cure for this is that people seem to use a head gasket. How much of a compression drop do you see using one?

I'm curious to know that if saw you are making around 350whp on stock compression with 8psi, then how much power would be lost if you are to say drop compression down to 9.5.1(this just seems like the best place for me) and run the same 8psi? How much more boost would you need to run the same whp numbers?

I guess my question is how much of a power loss will there be if you are running the same amount of boost on a motor with a lower comp ratio that you were running on a stock comp ratio? And how much more boost would need to be added to get you back to the same numbers before beginning to see higher ones?

I ask because ideally I wouldn't want to run anything higher then say 10-12psi, and am curious to see if it is even worth dropping to lower/safer comp ratios to run that amount of boost, or if it will just be a waste if it will only yield me the same numbers as me staying with stock comp ratio and running a safer 8psi.

 

come on guys help me out. Reading up on it a bit more and it seems that for every 1 poin comp drop we have to increase boost by 2psi to get the power back. I think this may be true going from 11.1 to 10.1, but the losses are greater if you kept dropping down from 10.1 to 9.1...which may result in a needed increase of a lot higher boost levels.

 

This has been discussed

ITS ALL IN THE TUNE

 

I know it has, and I agree the tune is what will determine the end result. However, of all the dicussions that I've found through the search there is just to much theary talk, and no hard evidence. It's just people stating there opinions on the matter. I'm curious to hear from someone who has gone through this process, and knows exactly how much boost he had to add to get back to his original numbers before seeing higher power levels.

 

I had a similar question awhile back in regards to RAISING compression and also RAISING boost! My question was how could I get away with running 12:1 compression with 12psi of boost! This is the answer I got....

I wouldn't even consider it unless you're an expert tuner, willing to tune the engine on a daily basis for changing weather conditions, and you'd also have to have access to at least 100+ octane fuel.The effects of all detonation (even detonation you can't hear) are cumulative. Little by little, detonation will loosen your top ring groove and eat away at the top ring land until it breaks away....So, a lot of "little" detonation adds up to being the same as a "lot" of detonation in the end, and raising the compression will make the tuning window grow smaller and smaller, so I wouldn't go there....unless of course, you have money to burn!

IMO, you would need to have the capability to go past 16psi in order to warrant any compression DROP!!! Im assuming droping from 11:1 to 10:1 even you would lose maybe 15hp! In order to compensate that 15hp, one would need 1-2 more psi just to bring you back up to even! Another 2 psi to make the compression drop even worth it... so now your at 12psi instead of 8psi with only 25 more hp???

you can run upwards of 14 psi on a stock motor, not sure where you got 8psi being max!! If I could spin my blower fast enough, I would run 14 psi all day!! (however thats not possible)


Ideally it makes sense to maximize whatever set up you have! I think the reason you are asking this is for nitrous.... which is another issue!

Everything is give and take... if you reduce the compression, then you can advance the timing! However you benefit from 100+ octanes with higher compression! So it really is all in the tune!!

 

juntuned thank you for your response. The reason I am asking these questions is because I am currently considering going with a SC. However, currently the highest pulley available is only at 10psi for this unit. Custom pulleys can be made, but anything higher and the blower will be spinning past its recommended levels.

I guess I'm trying to see if it's a good idea to risk 10psi on the stock motor, or slightly drop compression to make things a bit safer. The possibility of water/meth has also crossed my mind, but that's another issue. I'm also thinking of this because if I decide to go with the stroker set-up for this SC application then I want the motor to be built the right away the first time.

I'm thinking that the stock ratio should be ok considering my goals aren't set to high as far as hp gains, and I have no intention to shoot for to high of a boost level. I'll stick with the stock comp ratio, and hopefully my tune will be good enough to keep my motor strong t 10psi.

 

I boost to 12PSI, however I am running the AEM Methanol Injection Kit

Also PSI is not PSI, the Greddy Turbo is a very small turbo, not that same as 12PSI and a larger type of Turbo, CFM's I believe is what we need to look at moreso then PSI

 

My experience is the torque and horsepower difference is minimal.

Click on the photo a couple times and you should get high resolution.



Same top end with new 9.3:1 bottom end. The top blue line is the factory 11.0:1 bottom end. The red line is the new 9.3:1 bottom end. Both 2.0 liters. The new engine was not broken in so the difference should be less when broken in.

At peak torque the loss is 3.8 ft lbs. In some areas lower in the rpm range the difference is more than 10 ft lbs.

 

Sideways I cannot maximize the image...it seems my membership has run out :/

From the looks of it the difference is very minimal throughout the power band as far as hp. Looks like the biggest difference is seen in bottom end torque, which is to be expected. Were these dynos done on the same pulley?

From your experience would you recommend I go with a slightly lower compression ratio if I plan to boost 10psi, and not any higher? I think the 2.4L will more then make up for the slight drop in torque if I do, but then again if it's not really necessary then why bother.

 

I'm sure having the AEM Methanold set up helps a lot. How is your experience with it thus far? How often must you refill the tank? I know that does depend somewhat on how the car is driven.

My only fear with that system is if there is a malfunction and it stops working...then hope the engine doesn't go boom. Is there a fail safe in the system? say switching to a second tune if it fails.