high compression with turbo

[dp]

what is the highest compression that can be safely run with turbo and at what boost levels. How reliable is it and what cars do you know of that run high compression with turbo and resist detonation?

[91TSiAWD_Mark]

2G DSM's run 8.5:1 at about 12psi

New 911T run 9.4:1 with something like 26psi

I run 7.8:1 with 14psi.

[Mystik]

7.8? did you lower the compression with a thicker head gasket or something? or new pistons? becuase the 1g 6 bolts are 8.0 stock right?

[91TSiAWD_Mark]

According to the Service Manual 90-91's had 7.8 (Page 9-8 or Page 292)

[Mystik]

hmm im gonna take a look at that

[lordyosh]

Originally posted by 91TSiAWD_Mark
New 911T run 9.4:1 with something like 26psi

Wow, is this stock? I never knew 911s ran so much boost.

[RS/377]

boost levels are a real funny thing that have a ton of factors.

First you have to realize that engine damage from high boost and compresion is because of the heat created by compressing the air causing the fuel to detonate in the combustion nchamber. If you caould keep the combustion chamber cool, you could run 10,000 to one compresion and a million pounds of boost.

As far as compresion ratio goes I would run 8.5 -9 to one. This gives you snappy throttle response and a sort of low compresion, this will also spool your turbo faster.

The boost is were it gets weird- you have to take efficency into acount, both of your intercooler and turbo. Right now I have the stock 1g DSm turbo and intercooler. Everyone says that about 18 is the max for that set up on pump gas. After that it starts blowing hotter and hotter air through it.

At that point your choices are improve your intercooler set up of get a more effiecent turbo. I chose to imrove my intercooling to run more boost.

Depending on what you want you can finf turbos that will run 29lbs+ efficently. However that is from a bigger turbo, which will have more lag because of the bigger wheel that is needed to move that much boost. Thats why people go TT, becuse it is way better to turn two small turbos that one big one.

My advice is to go get a book on turbocharging so you don't cost yourself a motor. I don't know how much a motor for your car would cost, but I can gaurentee that a twenty dolar book and some knowledge is way cheaper

[Joshhasa99dsm]

Hey, I was talking to a guy at Jotech here in Garland, and he said that if i wanted to put a turbo in my car (which i'm going to) that i could only run about 6-7 lbs of boost. Which he said is still pretty could that i'd have to lower my compression due to because my car isn't a turbo charged car so it was made with a higher compression. And my question is, how do you lower the compression??? And about how much would i cost???

[Niño]

Originally posted by Joshhasa99dsm
Hey, I was talking to a guy at Jotech here in Garland, and he said that if i wanted to put a turbo in my car (which i'm going to) that i could only run about 6-7 lbs of boost. Which he said is still pretty could that i'd have to lower my compression due to because my car isn't a turbo charged car so it was made with a higher compression. And my question is, how do you lower the compression??? And about how much would i cost???

You get pistons. If one isn't already available, most piston manufacturers can make them for you per spec. There is also the option of a thicker copper headgasket to increase deck height.

[NaMeLeSsEcLiPSe]

I don't have turbo yet either but will be running it within the next couple of months. I've found out that the diamond star stage 2 is a great fit for the NT's and could run up to 12-15 psi. The compression on our car is kinda low I think 7.8 if i remember currectly and they recommened that I run the JE pistons that are 9.5 compression so ill get more power out of the turbo. I don't really know myself but the higher the compression the better the power. It can also hold up to nos if you have a high compression HEHEHEHE Are u sure that isnt a 2 liter coke? LOL j/k

[Joshhasa99dsm]

Well i guess we have a debate then. Is it the lower the compression the more psi you can run on turbo, or is it the higher the compression the more psi you can run???

And personally i think turbo is better. You can't run out of turbo, it's on all the time so it's ready when you are. It might be more expensive than NOS, but you don't have to keep refilling the stupid bottle.

Hey Nameless, where do you live?

[SE-Rage]

Originally posted by Joshhasa99dsm
Well i guess we have a debate then. Is it the lower the compression the more psi you can run on turbo, or is it the higher the compression the more psi you can run???

And personally i think turbo is better. You can't run out of turbo, it's on all the time so it's ready when you are. It might be more expensive than NOS, but you don't have to keep refilling the stupid bottle.


I don't think there's a debate. The compression is just that; compressing the fuel/air mixture to make the explosion inside the combustion chamber. Increasing the compression ratio would thus add power, unless it is compressed so much that the compression forces the air/fuel mixture to spontaneously explode before the spark plug ignites the mixture. This applies to any engine, including engines with forced induction, but the compression ratios of engines that have forced induction are much lower because turbochargers compress the air entering the engine, allowing more air and fuel to enter the combustion chamber. Higher compression in the combustion chamber with the addition of the compressed air entering the engine increases the chances of the mixture spontaneously exploding before the spark plug ignites, ie knock, auto-ignition, etc. So you want to run as a high a compression as you can if you want to maximize power, but if you get high compression, you run the risk of knock. Running higher compression than "normal" and also increasing the pressure of the air from the turbine/comressor (I guess increasing the "boost" is what people say) increases the chances of knock even more so than doing each by themselves. That's why turbocharged engines have a lower compression ratio than NA engines.

[Edited by SE-Rage on 04-26-2001 at 07:12 PM]

[Joshhasa99dsm]

Exactly SE! You should run lower compression in turbo engines, so therefore you can run higher pounds of boost.

[TurboRs]

Go to 2gnt.com you'll find every answer under the sun about your car. I have a 97 Rs that i've turbocharged. Right now i'm boosting 5lbs cuz the wastegate but, as soon as i install my boost controller i'm going to turn up the boost to 7-9 lbs. The 420A engine on stock internals can handle that much boost pretty well...10psi and up is when i'll look into start building the bottom end. I am on that site(dsm1) is my post name. Check it out!

[PreludeBoy]

something else you should take into consideration is that if you lower compression, and add boost, the difference in the power from boosting to non boosting will be more dramatic. So if your car has a lot of turbo lag, it might suck more for things like autocross cause all your power is more dependent on the boosting. Mine is running at stock compression (10.6) with low boost (although my fuel curve is messed up) so that i still get some nice low end power for normal driving. It's ALL about tuning!!!!!!!!

[NaMeLeSsEcLiPSe]

When I do put turbo in my car should I put less compression or more compression cause now Im totally confussed. LOL sorry im out of it today.

[Joshhasa99dsm]

Yea, the guy that i was talking to said that if i plainly just put on a turbo with out messing with my compression, that i could run about 6-7 pounds of boost safely. Which is still pretty good but i eventually wanna run about 15-18 pounds of boost.

To do this, what would i need to do???

[SE-Rage]

High compression and high boost do not go well together. Factory turbo cars are more reliable in my opinion than aftermarket turbocharged cars (probably because people don't take the necessary steps to use a turbo safely). The factory turbocharged cars come with the necessary parts to use a turbocharger. For example, the SR20DET, although maintaining the same basic block design, has a few subtle differences. The DET has a lower compression ratio (9.5:1 to 8.3:1), bigger oil pump, bigger injectors, and a few other differences and additions. These subtle differences do make an impact. If I had the money to add a turbocharger to my SR20DE, I'd rather just buy the DET (in a world with no smog) simply to avoid the hassles of setting up the engine to handle a turbocharger.

If you want to run high amounts of pressure from the turbine, you're going to have to use higher octane fuel to prevent knock, and probably lower your compression ratio. An intercooler will also help in providing more power and preventing damage. I'm not a turbo expert, so I don't know if the stock block of a NA Eclipse could handle that much power and pressure, but I'd also "strengthen the internals", or make the block stronger. You'll also probably want to upgrade you're fuel delivery; you don't want to be delivering all that air into your engine and not have enough fuel to mix with it.

Like PreludeBoy said, it depends what you want. Also, a bigger turbo will take more time to spool but will provide more pressure/boost overall while a smaller turbo will provide more power quicker but less overall pressure than what a larger turbine/compressor can provide. It all depends on what you want.

[TurboRs]

I'm going to be getting a whole new engine to work on from a friend so that i will not be pedaling a bike for months that most engine shops take with peoples cars. Plus i'll be doing all the work myself. Plans are as follows:
stock internals will be replaced with je pistons to provide lower compression. Crower or eagle rods to provide strength. the block has to bored .20 for the new pistons which are custom for the 420A engine. New total seal piston rings. knife the crank and reduce weight. 5 angle valve job. Most important is upgrading the fuel system...right now i have a walbro 255lph intank pump with a vortech 12:1 fmu, i'll upgrade to a s-fmu(adj) RC eng. 440cc injectors and to trim them down with a Apexi s-afc. msd-ignition system to help with the timing. My FMIC is a spearco unit. The turbo i'm using is a turbonetics T3/04e and will be good enough to take me to the hp range i'll be boosting with the engine i'm building, no turbo musical chairs for me. At 5psi I dynoed at 173hp to the wheels...thats equavalent to a stock gs-t i believe. At 10psi i can expact 230+- hp at the wheels. So you can see the potential of our cars under boost with some engine work.
For more imfo check out 2gnt.com or turbosystems.com

[RS/377]

Don't forget that turbo size also affects the amount of boost you can run. A little 14b will blow hot air around 20-22 I think- but a frank can move that amount of air with very little heat. then you get into lag.....

[Wolf]

You want a low compression engine if you're going to run a turbo. If the compression ratio is too high, or you run high boost levels, you'll get detonation (pinging), which will kill your engine quick. To solve this, use an intercooler, and high octane gas.

(I'm running 8:1 CR, 10-15lbs boost(adjustable), air-to-air intercooler, and 92 octane with no problems)

[MatT3T4]

Sorry if someone already said it, but I don't feel like reading the whole damn thread.

You are going to make more power with a high compression, high boost motor. But, that is when perfect tuning comes into play. An 8.5-9.0:1 motor will give a little more leeway as far as tuning is concerned on 20psi, than say, a 11.0:1 motor. If you are running a track only car, tuning it with Motec, and you are a great tuner, an 11.0:1 turbo motor properly setup and tuned is going to kick the crap out of an 8.5:1 motor with the same boost and setup.

[RS/377]

Well, I can say that ot those two motors the high compresion one will of course make more power.

However, the low compresion motor (assuming identisal intercooler and turbos) will be able to run more boost.

The idea of compaing these tow motors does not show any useful information. You are handicapping one unfairly.

Tuning does play into the amount of bost you can run. However a motor that has low compresion and high boost will have more peak power, while the high compresion low boost motor will have excelent throttle response.

The tuning end of it is in the timing, the higher the timing the better. A lot of the people who are running outrageous amounts of boost on DSM can find the computer has pulled timing to handle the added boost without detonation. When they reset their ECU's and lower the boost, they usually find they are quicker even with the lower levels of boost