3.1cutlass Posted September 22, 2008 Report Share Posted September 22, 2008 I took my car to the track and ran a miserable 17.7 three times. This is aweful so i changed the plugs and wires and went back to the track this week and ran a 17.7 again. The probnlem here is that last year i ran a 17.1 before the echaust and moror mounts. I checked the fuel pressure at the rail and it is 2psi low. What eles could be the culprit? This is a 91 3.1 cutlass btw. Quote Link to comment Share on other sites More sharing options...
Crazy K Posted September 22, 2008 Report Share Posted September 22, 2008 well... have you seafoamed the engine recently? could you exhaust be at fault with the large Y pipe you have? people say the exhaust slows too much with the oversized exhaust????!!????!!?!? Quote Link to comment Share on other sites More sharing options...
pontiacmaniac94 Posted September 22, 2008 Report Share Posted September 22, 2008 i was under the impression that the 3.1 of that era was pretty much a slug....not that mine is much beter, but, it seems like it will happen that you would be running 17s.... Quote Link to comment Share on other sites More sharing options...
3.1cutlass Posted September 22, 2008 Author Report Share Posted September 22, 2008 well... have you seafoamed the engine recently? could you exhaust be at fault with the large Y pipe you have? people say the exhaust slows too much with the oversized exhaust????!!????!!?!? never but i will before the track this week. Where do you reccomend adding it? It os only 2.5 back to the Y and 2.75 after that. I doubt it is the case here. i was under the impression that the 3.1 of that era was pretty much a slug....not that mine is much beter, but, it seems like it will happen that you would be running 17s.... I am fine running 17's but i am running stock times on a not stock car. Quote Link to comment Share on other sites More sharing options...
Crazy K Posted September 22, 2008 Report Share Posted September 22, 2008 well... have you seafoamed the engine recently? could you exhaust be at fault with the large Y pipe you have? people say the exhaust slows too much with the oversized exhaust????!!????!!?!? never but i will before the track this week. Where do you reccomend adding it? It os only 2.5 back to the Y and 2.75 after that. I doubt it is the case here. I think it has been said that after the Y pipe it is important for the size of the pipes to reduce, not increase! otherwise the pressure drops off and the flow really slows down. Quote Link to comment Share on other sites More sharing options...
BXX Posted September 22, 2008 Report Share Posted September 22, 2008 2.5" is too big for a 3.1L... Your exhaust is cooling too quick and stalling out in the pipe before it can exit. That causes turbulance and more backpressure. Get a 2.25" all the way on there with some mufflers. Quote Link to comment Share on other sites More sharing options...
3.1cutlass Posted September 22, 2008 Author Report Share Posted September 22, 2008 well... have you seafoamed the engine recently? could you exhaust be at fault with the large Y pipe you have? people say the exhaust slows too much with the oversized exhaust????!!????!!?!? never but i will before the track this week. Where do you reccomend adding it? It os only 2.5 back to the Y and 2.75 after that. I doubt it is the case here. I think it has been said that after the Y pipe it is important for the size of the pipes to reduce, not increase! otherwise the pressure drops off and the flow really slows down. Wrote that wrong lol it goes down to 2 1/4. 2.5" is too big for a 3.1L... Your exhaust is cooling too quick and stalling out in the pipe before it can exit. That causes turbulance and more backpressure. Get a 2.25" all the way on there with some mufflers. I am not changing it now. It will be 3'' when the turbo goes on. I find it very hard to believe that it is dropping my times 7 tenths of a second anyways. Quote Link to comment Share on other sites More sharing options...
BXX Posted September 22, 2008 Report Share Posted September 22, 2008 Yeah, oversized exhaust causes the gases to quickly stall out which in effect adds quite a bit of backpressure... NA engine need a couple PSI of backpressure to boot to run efficiently. Too little or too much and power suffers, especially at the higher RPMs where the 2.8L/3.1L have trouble making power as it is.. sooo, 7 tenths does actually sound about right. Feel luck you havent lost a full second or more due to it.. Quote Link to comment Share on other sites More sharing options...
3.1cutlass Posted September 22, 2008 Author Report Share Posted September 22, 2008 Yeah, oversized exhaust causes the gases to quickly stall out which in effect adds quite a bit of backpressure... NA engine need a couple PSI of backpressure to boot to run efficiently. Too little or too much and power suffers, especially at the higher RPMs where the 2.8L/3.1L have trouble making power as it is.. sooo, 7 tenths does actually sound about right. Feel luck you havent lost a full second or more due to it.. Well it's not like i have srtaight pipes either. There is a muffler and resnonator on the car. hmmm Quote Link to comment Share on other sites More sharing options...
3.1cutlass Posted September 23, 2008 Author Report Share Posted September 23, 2008 I seafoamed it today. Quite a bit of smoke. I poured it into the crankcase and through the brake booster line. Quote Link to comment Share on other sites More sharing options...
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