I could not find a definate answer to this question. I am building a rearmount GT88 set up on my 02 WS6 with 408. I have the hot side complete except for the 5" down piping coming out of the turbine section. I am ready to run the Piping from the compressor side to the intercooler. The compressor outlet OD is 3.5" but it looks like the ID of the outlet is 3". I want to reduce this down to 2.5" piping to run up front to the intercooler for clearance reasons. My question is what would be the optimal sized piping and will 2.5" work (when I say work will it be alright or is it just too small)? Also since I am asking, for the exhaust piping I used my stock manifolds, I built cat delete's out of 2.5", I used a new 2.5" SLP Y pipe, opend up the outlet of the y pipe to 3" and ran mandrel bent 3" all the way to the turbine inlet. I plan on wraping the exhaust up too. Is 3" large enough for the hot parts? I will post pics latter this weekend when I get back to work on it.

Thanks guys.

 

I would be concerned with any reduction of the cold side piping diameter. Whether or not it will hurt "enough" to be a problem for you, I don't know. I'm sure this will be a controversial issue, but I don't see a problem with your hot side plans.

 

I have started running the 2.5 cold side, I have not gone far and could start over again with 3". The way I am routing it is I bought the upper panhard bar that alows you to run dual exhaust. I placed the turbine side to the drivers side. I ran the cold side to the drivers side of the exhaust piping all the way to the drivers side of the engine. I relocated the alternator so that I can go over the engine craddle instead of under it. Even with the new panhard bar, I bearly had enough room for the 3" exhaust and the 2.5" cold piping to go threw. The next big clearence issue spot is the cross bar I have for my BMR Torque arm. It would be close to get two 3" inch pipes threw there and still have enough room for the drive shaft to move up and down. Not to mention the ground clearence under the drivers side running the cold piping outside the Y pipe. I want to run 2.5" but I am worried it will be too small for the turbo I have.

 

With everything else you have done, do a truck manifold front mount. In the long run you will be much happier. Take this advice from a rear-mount user.

 

No room up front for such. It is a rear mount. I do not mind up sizing the cold air piping but I am too far into this thing (Money and completion of install) to just scrap it and go front mount. I will finish this and prove it. If I do not like it then I will sell it and start over but I am finishing this one.

 

just do a front mount you cheap bastard,lol.....



whats another $5-6,000 gonna hurt

 

Go 3" on your cold side piping. I have a pretty strong feeling that my 2.5"/2.25" piping is really hurting me due to my air speed being around 450 ft/s. I'm pushing somewhere around 900 HP at the engine and it's a struggle. Mine will be getting changed out later this year.

Your exhaust setup sounds good as well. I'm probably going to do have the same thing done later this year. 2.5" y to 3" i-pipe to turbo.

 

True, true, want to buy some kids? They look like you anyways.

 

I will post the pics of it so far this weekend. I built a turbo mount "T" bar that goes from the trunk to the upper panhard bar. It has rubber mounts on all three corners and bolts to the turbo. The turbo hangs there with no piping holding it up. I am going to also mount my return oil pump to this bar. Like I said before I have the turbine outlet pointed to the driverside. I plan on running a 5" mandrel bent 90 out of it aimed at the drivers side exhuast outlet under the bumper. Once it makes the 90 I plan to build a collector type part that will reduce the downpipe to 2-3" pipes, routing one to the drivers side and the other over to the passenger side. That way it will have factory looking dual outlets. The waistgate I mounted directly in line with the exhaust flow right were it 90's into the turbine inlet. It will dump directly into the 5". The exhaust is only close the fuel tank were it goes over the rear end. I have the factory heat shiled still in place there and across the top of the turbo. Once the exhaust clears the upper panhard bar it comes down and 90's over to the turbo. The cold air piping leaves the turbo and runs next to the heat shield all the way over the rear end and is on the drivers side of the exhaust pipe all the way to the drivers side of the engine craddle. It is 2.5" mandrel bent all the way, utilizing V-band clamps/flanges on every conection point for bothe the 3" and 2.5" hot/cold piping.

900hp will make me very happy. How much boost are you running? Do you know what the boost pressure is at the compressor outlet as compaired to the throttle body inlet? I would think the delta p would tell us if the piping was big enough. Do you know what your pressure is in the exhaust piping? Just trying to get a good idea of all the delto p's.

Thanks for the help everyone.

 

ssshhh be quiet,i been waiting for you to put 2 and 2 together

 

Has Dave decided on a car or is Cathy not going to let him get one?

 

My car is in storage for the summer so no testing being done. Once it cools off testing will continue. I've been wanting to measure the compressor outlet vs manifold pressure but haven't gotten around to it yet. My IATs go sky high on a pass. I gain around 60 degrees (from 100 iat to 160) when ambient is 90. Now it's 110+ every day so it's probably a 70 degree gain in temp.

 

That is wicked temps, sounds like the intercooler is lacking, what size is it. Time for a meth kit. I have a pretty good idea on an inexpesive DIY meth kit. When I get home I will post what I am going to do. Driving down a desert road right now.

 

What cam are you running? I am debating changing from my 230/240 114 600 lift to a reverse split 240/230 on 115 or 116 with about 600 lift. Running the 10.25:1 408 with ported L92 heads and a GMPP intake as pictured in my sign. I noticed your gears, is there an advantage to the higher gear you are running? Whats your 60' ets?

 

Du, I see the 60' et now, sorry.

 

Here are those pictures I promised.

https://ls1tech.com/forums/forced-in...you-think.html