Can someone explain this to me
09-17-2006, 10:30 AM
#1
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Can someone explain this to me How is it that with dual cutouts open I gain not ONE horsepower over the cutouts being closed?? I am running Pacesetter longtubes and and y-pipe with a Borla. The car is an 11 psi P1-SC 383. I went to get a dynotune and Jeff finished tuning and uncapped the cutouts and didnt make one horse on the next pull. I wouldnt have thought my exhaust would have flowed that well with 1 3/4" LTs. The car still put down 585 so I'm not disappointed but I would have liked to the hit the 600 mark. Even Jeff thought it would go over 600
09-17-2006, 02:50 PM
#2
Whats your Pulley combination and max RPM. We need to figure in how hard your a spinning the blower. You still have them pimp LT4 heads from LE??
Whats your Blower intake tract?? Are having any best slippage problems?
I don't understand why you aren't making any more HP with the cutouts open, the better the exhaust on a Blower car always the better. I have been researching camshafts a lot here lately and a Wide LSA is not always needed on a Blower car, something to think about.
Whats your Blower intake tract?? Are having any best slippage problems?
I don't understand why you aren't making any more HP with the cutouts open, the better the exhaust on a Blower car always the better. I have been researching camshafts a lot here lately and a Wide LSA is not always needed on a Blower car, something to think about.
09-17-2006, 03:27 PM
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Yes I am still using the LE worked LT4 heads. They are still holding up great. Im using the stock crank pulley which is 7.65" I think ( it measures 7 3/4" across the outside of the pulley) and a 3.4 blower pulley. I did the math and I think I'm still a few thousand rpms under the 60k max for the P1-SC. I upgraded to an SDCE setup and I have checked it several times and havent seen any belt dust on the blower. The intake for the blower is a 4 inch to a 3 1/2 inch 90 degree silicone elbow with a 3 1/2" mandrel bent exhaust pipe to a rather large K&N filter. I am starting to wonder if I have surpassed the abilites of the LT4 heads and need to start looking aftermarket
Last edited by wicked_95z; 09-17-2006 at 04:44 PM.
09-17-2006, 05:38 PM
#5
Do you know what your boost level was at before and after you opened your cut-out? You may of lost some boost with the exhaust open, which would explain why the car didn't make anymore power. Bob
09-17-2006, 05:42 PM
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I dont think they even checked it that last pull. But, shouldnt I expect a boost loss if the exhaust was a restriction because of the lack of back pressure allowing more cfms to move through the motor. I wouldnt think my exhaust sys was that efficient
09-18-2006, 06:04 PM
#7
I've run across this a few times with blower cars. Mine, for example, picked up <5 hp when I dropped my whole 3" cat-back and Aerochamber. I believe that 1 of 2 things is going on:
1. When you drop the exhaust, you lose more boost through the chamber during overlap, but gain power because of pumping losses - breaking even in the end.
2. The cylinder depressures too fast toward the end of the power stroke. Opening up the exhaust makes it blow down too quick, thus losing some power, but getting it back because of reduced pumping losses.
Either case would be fixed (or, um. . ., broken?) with less exhaust duration on the cam. I'm not totally convinced that blower cams need alot more exhaust duration than intake.
Mike
1. When you drop the exhaust, you lose more boost through the chamber during overlap, but gain power because of pumping losses - breaking even in the end.
2. The cylinder depressures too fast toward the end of the power stroke. Opening up the exhaust makes it blow down too quick, thus losing some power, but getting it back because of reduced pumping losses.
Either case would be fixed (or, um. . ., broken?) with less exhaust duration on the cam. I'm not totally convinced that blower cams need alot more exhaust duration than intake.
Mike
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09-19-2006, 05:10 AM
#8
Originally Posted by wicked_95z
I dont think they even checked it that last pull. But, shouldnt I expect a boost loss if the exhaust was a restriction because of the lack of back pressure allowing more cfms to move through the motor. I wouldnt think my exhaust sys was that efficient
09-19-2006, 07:54 AM
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It was the same. Right at 11:1 across the board until about 5500 and it starts going lean. I was told that this wouldn't be a prolem because you are only at that rpm for a second or two. It was just like I hadn't changed anything from the previous pull
Last edited by wicked_95z; 09-19-2006 at 08:26 AM.
