408ci T76 Setup Question PLEASE HELP!!
09-19-2011, 10:02 PM
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408ci T76 Setup Question PLEASE HELP!! To start things off you can read my signature, that has most of my build as far as parts. Three main questions about this setup. THANKS IN ADVANCE!
First Question
Backpressure. I am adding pictures to this post to show what the exhaust looks like. I was told that this turbo is too small for my setup, which I can agree with but there has to be a happy medium. I have tried several things. Still trying to figure this setup out.
Shifting at 5000rpms which I am thinking, is extremely low. With 9# boost, I managed to pull off the time in the signature. Thinking all this is caused by reversion. I am in 1st gear just under a second. In second gear for a little over a second. Then high gear until almost 1000FT then I hit reverb (over 5k).
Second Question
Exhaust, which relates to the first question. As seen in the picture, will I be better off to run full 3" exhaust in place of where it splits off into two. I have never seen this before on any setup but I am sure the person who built this had some clue of what they were doing.
Also, I am about to put an electric cutout somewhere close to the downpipe but I am needing to know how long the downpipe needs to be, I'd like it as short (free flowing) as possible to help with backpressure. I put a picture down there where I would like it to go. What are your thoughts about this location.
Third Question
I have done a ton of reading under this FI thread. Seems that most people have ran much faster times with less.
Is there any small changes or something that I am missing to help this setup reach its full potential? Will a higher gear help? Something in the range of a 3.08-3.31?
I appreciate any and all help provided. I see a bigger turbo in my future but I want to reach full potential with what I have while I am saving up!
First Question
Backpressure. I am adding pictures to this post to show what the exhaust looks like. I was told that this turbo is too small for my setup, which I can agree with but there has to be a happy medium. I have tried several things. Still trying to figure this setup out.
Shifting at 5000rpms which I am thinking, is extremely low. With 9# boost, I managed to pull off the time in the signature. Thinking all this is caused by reversion. I am in 1st gear just under a second. In second gear for a little over a second. Then high gear until almost 1000FT then I hit reverb (over 5k).
Second Question
Exhaust, which relates to the first question. As seen in the picture, will I be better off to run full 3" exhaust in place of where it splits off into two. I have never seen this before on any setup but I am sure the person who built this had some clue of what they were doing.
Also, I am about to put an electric cutout somewhere close to the downpipe but I am needing to know how long the downpipe needs to be, I'd like it as short (free flowing) as possible to help with backpressure. I put a picture down there where I would like it to go. What are your thoughts about this location.
Third Question
I have done a ton of reading under this FI thread. Seems that most people have ran much faster times with less.
Is there any small changes or something that I am missing to help this setup reach its full potential? Will a higher gear help? Something in the range of a 3.08-3.31?I appreciate any and all help provided. I see a bigger turbo in my future but I want to reach full potential with what I have while I am saving up!
09-19-2011, 10:28 PM
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Not sure about the Springs, the motor was built by someone else. He said the motor was fresh and is good for 1000HP. I am assuming he left the springs in it that came from Patriot. On there site it says Patriot Gold Dual .650 list springs. The cam is .550 lift that is in it now. Outside Diameter of the spring is 1.45 in.
Hope this helps!
Hope this helps!
09-20-2011, 06:03 AM
#5
68mm turbine wheel will not support a 408 past 5000 rpm as you have found out. It's 100% a back pressure issue, which can cause the exhaust valves to float while they are supposed to be seated. Here is a guy with a 40x cube engine who went from a turbo with a 68mm turbine wheel to a 75mm turbine wheel. Although a 75mm is still way too small you can see how it allowed him to pull past 5000 rpm.
https://ls1tech.com/forums/forced-in...04ci-76mm.html
https://ls1tech.com/forums/forced-in...04ci-76mm.html
09-20-2011, 07:01 AM
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This was the conclusion that I came to before posting after working with the car and adjusting the shift point/boost level, along with reading countless hours on this forum. This is where I was asking about the exhaust, I have the cutout to help with a "free flowing" exhaust but want to make sure I have a long enough downpipe. I know this should help some anyway.
Also, was asking about rear gears. From what I have seen, a 3.73 is not very common in turbo setups. Do I need to run a higher gear?
Also, was asking about rear gears. From what I have seen, a 3.73 is not very common in turbo setups. Do I need to run a higher gear?
Last edited by bcablig; 09-20-2011 at 07:09 AM.
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09-20-2011, 09:54 PM
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Here is a picture of the exhaust off the car, would this exhaust flow better if it were one 3" pipe all the way through? Not sure about splitting into two smaller pipes.
Last edited by bcablig; 09-20-2011 at 10:01 PM.
09-20-2011, 09:59 PM
#10
The exhaust gasses have to pass through that turbine wheel no matter what.
It is the bottleneck, and unless you open the bottleneck up your other 'fixes' will be useless. Sorry for being the bearer of bad news.
But that exhaust going into two and back into one could be improved upon greatly by stepping it up to 4" single where it goes from one to two and run it 4" out the back.
It is the bottleneck, and unless you open the bottleneck up your other 'fixes' will be useless. Sorry for being the bearer of bad news.
But that exhaust going into two and back into one could be improved upon greatly by stepping it up to 4" single where it goes from one to two and run it 4" out the back.
09-21-2011, 04:52 AM
#11
Try running just an open down pipe that will be the least restriction. Not sure who did the exhaust like that or why but it doesn't look like it was cheap. The back pressure issue like stated is a pre turbine issue not so much a post turbine issue. Ditching the exhaust certainly will not hurt performance.
09-21-2011, 06:34 AM
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