highest street compression?

[AMS97EclipseGSX]

Yes, becuase the more you mill the head, the lower your compression gets. I am definitley all for getting tuning advice from AMS!

Actually I mistakenly stated that. The head being milled would make the compression higher. My fault for the bad info there. So really I would guess my compression to be up around 9:1, but still besides the point, 8.5:1 compression is fine, You can and will make good power on those parts. That is the least of your worries. Stick with what you got, get it tuned and see what happens.

 

[1fast97gsx]

just took the car out for a drive and stepped on it ... looks like it's shooting white smoke out the exhaust. I checked my coolant reservior and my dipstick and there's no signs of oil / coolant mix. Maybe I just got a bad set of rings and they didn't seat properly and that's causing all my problems? Ideas?

 

[autronicDSM]

Audi S4 has 9.3:1 or 9.5:1 so there you have it, you could make lot more low end torque with higher compression but you will have to be extra careful with your timing. I'd say stand alone would be a huge help.

As far as white smoke. Who built that motor for you? Did you measure your bores afterwards to make sure piston to wall clearence is with in spec?

 

[1fast97gsx]

some friends and I did the engine .. just the machine work was done at a shop. The clearances were supposed to be measured by them as well as the ring gaps ... and they said it was all good to go when I picked it up so I'm assuming they did it right. I did swap on a 1g head that had a few miles on it so I'm thinking the valves may just be leaking. A leakdown test will tell me for sure right?

 

[autronicDSM]

Never assume. I had a motor built by a shop everybody I talked to recommended. Unfortunately it didn't last at 5 psi. It got blow by. After I pulled the pistons out one side looked like it was grinded by D. Leary in that oil commercial. Rings are melted with the piston and you can't see it. I've learned my expensive lesson. I don't care if God himself built it, always check what you can.

 

[AMS97EclipseGSX]

some friends and I did the engine .. just the machine work was done at a shop. The clearances were supposed to be measured by them as well as the ring gaps ... and they said it was all good to go when I picked it up so I'm assuming they did it right. I did swap on a 1g head that had a few miles on it so I'm thinking the valves may just be leaking. A leakdown test will tell me for sure right?

You should do a compression test and a leakdown test. That will tell you if anything is wrong with the motor. I had a spun rod bearing and it caused my car to be down on power a lot! I fixed it and now it runs fine. If the car feels like it is down on power then it is usually something to do with the motor. Do you smell coolant when the white smoke comes out?? Does the car push any coolant at all?? These are signs of a blown hg. What hg is on the car??

 

[autronicDSM]

Leak down should tell you what the problem might be.

By the way, I didn't blow a head gasket but I did get a lot of white smoke out the breather. I didn't check the exhaust but I didn't really care, motor was a dud by that time.

 

[AMS stampy]

sounds like your rings might not of set totally. do a leakdown to check where its losing compression. was it blowing smoke durring acceleration or between shifts?

As far as the street tune goes I highly recomend it. I always street tune my car and when I actually did throw it on a dyno it was making 580whp.

Eric

 

[1fast97gsx]

sounds like your rings might not of set totally. do a leakdown to check where its losing compression. was it blowing smoke durring acceleration or between shifts?

As far as the street tune goes I highly recomend it. I always street tune my car and when I actually did throw it on a dyno it was making 580whp.

Eric

it blows smoke sometimes during acceleration ... doesn't seem to be loosing coolant at all. Its leaking oil through the return line and the middle stud for the exhaust manifold, but I highly doubt the headgasket is leaking. I don't smell anything abnormal and the car hits 24 psi. Headgasket is an MLS gasket. ( block and head were both decked ) Could it just be from not having a cat? I wouldn't think so but I didn't really notice any smoke until after I ditched that. Also my back bumper turns black after like 100 miles :thumbdown

AMSstampy: Can you guys do a leakdown test and for how much? How much for the street tune ( $135 still? ) and who drives the car and in what gear does that get done? Does that include messing with the high and low throttle settings assuming an safc? I have the eprom installed and running but don't feel like messing with the cams or dsmlink just yet since I've never used dsmlink and I don't feel like taking the timing belt off again for the cams.

 

[AMS stampy]

ok well the smoke could be the turbo. I know it sucks but I have seen stragner things. as far as a street tune goes if you have a bung for the wideband O2 sensor its $125 for the tune. we only mess with high throttle and martin and tim go out to tune the car. if we are tuning on DSM link the cost would most likely go up 20-40 because its a little more involved to tune on link over an AFC.

oh and a leakdown test goes for $60

Eric

 

[leakyfaucet]

Not to mention that you will suffer from lower gas milage cause of the more work the engine has to do (due to the high CR) to bring the pistons to TDC.

If I'm wrong here someone correct me then. From what I've read on forced induction and what I know building small block chevys over the years is what I've stated.

Well, you asked for it. You're wrong. You'll get better gas mileage with higher compression pistons. More power for the same RPM.

 

[1fast97gsx]

ok well the smoke could be the turbo. I know it sucks but I have seen stragner things. as far as a street tune goes if you have a bung for the wideband O2 sensor its $125 for the tune. we only mess with high throttle and martin and tim go out to tune the car. if we are tuning on DSM link the cost would most likely go up 20-40 because its a little more involved to tune on link over an AFC.

oh and a leakdown test goes for $60

Eric

Can't it just go in the O2 housing where the stock O2 sensor is and that just gets unplugged for the tune?

 

[AMS stampy]

on a 2g so long as you have a rear o2 sensor bung we can use that and save you $30.

Eric

 

[talonted_one]

FWIW I am running 9.3:1 on 93 octane. the car isnt tuned yet so I am only running 11psi of boost. My turbo is a lil bigger than normal tho.

 

[AMS stampy]

holy christ that is rich

 

[Mirage2LTurbo]

In response to some I read above...

Your C/R does not change whether you run 7 or 35psi of boost.

You can run up to about 11:1 on 93 pump gas.. you CAN run higher, but you risk getting a bad tank and detonating. This is n/a.

You can run any c/r you want in a turbo car, you just won't be able to run as much boost on x octane. You'll make a lot more hp per lb of boost though..

If you are building an engine for turbo use, most people go with an 8:1-9:1 c/r motor, just because it's a good mix. You can look at the pros and cons from a ton of different angles, it really comes down to whatever you want.

 

[1fast97gsx]

well I'm thinking of raising the compression because it 1) makes more power per pund of boost as stated ... and 2) better spool up. I'm still not sure though if I were to be able to run 24 psi safely with 8.0:1 cr does that mean I will only be able to run 20 psi at 9.0:1 or is the boost difference minimal such that I could still run around 23 then?

 

[Mirage2LTurbo]

well I'm thinking of raising the compression because it 1) makes more power per pund of boost as stated ... and 2) better spool up. I'm still not sure though if I were to be able to run 24 psi safely with 8.0:1 cr does that mean I will only be able to run 20 psi at 9.0:1 or is the boost difference minimal such that I could still run around 23 then?

You need to put your car on the dyno and find that out. Our motors will peak their powerband just before detonating. Watch your EGT's, keep the a/f's safe, and turn up the boost 1lb at a time.

Also, I don't think that a higher c/r motor offers better spoolup. Rather, with the high c/r, you make more power offboost, and it helps you get through those rpm's faster. I could be wrong, but I don't recall seeing any evidence as to this.

 

[1fast97gsx]

You need to put your car on the dyno and find that out. Our motors will peak their powerband just before detonating. Watch your EGT's, keep the a/f's safe, and turn up the boost 1lb at a time.

Also, I don't think that a higher c/r motor offers better spoolup. Rather, with the high c/r, you make more power offboost, and it helps you get through those rpm's faster. I could be wrong, but I don't recall seeing any evidence as to this.

yea thats true .. in my mind I was just tihnking if the engine will rip through the rpms faster it would still be flowing the same amount of air just faster ... so faster spool up. I could be wrong though as well.

 

[00 Agent]

Well just to throw in my .02 I had JE 9:1's in my last engine and HATED it.

 

[Mirage2LTurbo]

I've heard a lot of people complain about the JE's piston slapping, esp. on cold start. What were your complaints with them?

 

[Black94TSI]

You need to put your car on the dyno and find that out. Our motors will peak their powerband just before detonating. Watch your EGT's, keep the a/f's safe, and turn up the boost 1lb at a time.

Also, I don't think that a higher c/r motor offers better spoolup. Rather, with the high c/r, you make more power offboost, and it helps you get through those rpm's faster. I could be wrong, but I don't recall seeing any evidence as to this.

The higher compression motor produces more power before boost hits, so there is more exhaust gas to push the turbine wheel. Same reason why spraying nitrous spools up a turbo, although it is much less dramatic.

 

[1fast97gsx]

Well just to throw in my .02 I had JE 9:1's in my last engine and HATED it.

why?

 

[talonted_one]

If I had to do it all over again I would go with 8.5:1. Tuning a high compression DSM can be a confusing pain in teh @$$.

 

[Mirage2LTurbo]

The higher compression motor produces more power before boost hits, so there is more exhaust gas to push the turbine wheel. Same reason why spraying nitrous spools up a turbo, although it is much less dramatic.

How does more compression produce more exhaust gas?

talonted_one: How is tuning a high c/r engine different than a low c/r engine, other than the fact you can't run as much boost?