Twin Rear Mount Setup
Thread Starter
Staging Lane
Joined: Mar 2009
Posts: 94
Likes: 0
From: Perth Australia
Twin Rear Mount Setup Hi All, Looking for any Rear mount turbo people,
Toying with the idea of going twin rear mount turbo on my set up and after a bit of feedback. Car is set up to make the power just changing the method from single front mount to twin rear mount for something different.
Combo 408 ally block Ls
4l80e with 3500 stall.
9" with detroit locker and 3.25 ratio.
I'm trying to achieve 800rwhp with twin rear mounts and have good spool, Street combo with rev limit of 6500. Have a pair of T3 GT3037 (57mm) journal bearing turbos sitting around with 0.84 turbine A/R
How I was looking at doing it was stock wrapped manifolds, y into a single 2.5" wrapped Intermediate pipe to rear, then split again into 2x2" to the turbos placed under the rear seat where the original mufflers were, Twin 2" boost pipes into a single 2.5" all the way back through the intercooler and 3" from cooler to engine.
My main concerns are:
1: Size of motor feeding through a single 2.5" to the turbos being a bottle neck. I know keeping the velocity up is good but is this a bottle neck on the 408 cubes?
2: Size of motor feeding the twin T3 GT30 Turbines being a limiting factor and not reaching my goal.
I understand the whole front vs rear mount debate, that doesn't matter to me. This is an experiment to have the 800rwhp with a stockish looking engine bay.
I believe the GT30 twin 57mm top out on a 408 in front mount configuration. Hoping in a rear mount configuration they are ok. Thought about twin gt3582s but I have these 30s already.
Thanks for any input.
Toying with the idea of going twin rear mount turbo on my set up and after a bit of feedback. Car is set up to make the power just changing the method from single front mount to twin rear mount for something different.
Combo 408 ally block Ls
4l80e with 3500 stall.
9" with detroit locker and 3.25 ratio.
I'm trying to achieve 800rwhp with twin rear mounts and have good spool, Street combo with rev limit of 6500. Have a pair of T3 GT3037 (57mm) journal bearing turbos sitting around with 0.84 turbine A/R
How I was looking at doing it was stock wrapped manifolds, y into a single 2.5" wrapped Intermediate pipe to rear, then split again into 2x2" to the turbos placed under the rear seat where the original mufflers were, Twin 2" boost pipes into a single 2.5" all the way back through the intercooler and 3" from cooler to engine.
My main concerns are:
1: Size of motor feeding through a single 2.5" to the turbos being a bottle neck. I know keeping the velocity up is good but is this a bottle neck on the 408 cubes?
2: Size of motor feeding the twin T3 GT30 Turbines being a limiting factor and not reaching my goal.
I understand the whole front vs rear mount debate, that doesn't matter to me. This is an experiment to have the 800rwhp with a stockish looking engine bay.
I believe the GT30 twin 57mm top out on a 408 in front mount configuration. Hoping in a rear mount configuration they are ok. Thought about twin gt3582s but I have these 30s already.
Thanks for any input.
I'm running a rear mount. Get the oiling right and pay attention to heat retention and its alot of fun. I'm running a single billet 7875 at 15 psi. Keep stock manifolds (yes I know its a 408) and wrap/coat as much of the hot side as possible. Keep the hot side piping diameter reasonable to the turbos as well as the cold side and you'll hit your target. Are you planning on keeping both banks independent from the manifolds to the turbo or are you going to join and then split again?
Thread Starter
Staging Lane
Joined: Mar 2009
Posts: 94
Likes: 0
From: Perth Australia
Its in a Holden Caprice, luxo barge style car.
Ok Plan was:
Stock manifolds wrapped
2" off each manifold and merge into a single 2.5" to the back of the car
Split back into 2x 2" pipes to go into the t3 Flanges of the turbos.
Twin 2" cold pipes merge into single 2.5" cold pipe to run to the front of car.
Intercooler at front with 3" piping to the engine.
Thought process being less surface area to lose heat, less space taken up with pipework, velocity stays high and have it all wrapped as mentioned to keep it all hot.
Concern being if the single 2.5" pipe will be a bottle neck for the 408 cubes and cut me short of my goal.
Other option is to run twin 2" all the way to the back and keep each bank separate. All wrapped of course.
I think the oiling side is all good for me. Just looking at this pipework detail.
Ok Plan was:
Stock manifolds wrapped
2" off each manifold and merge into a single 2.5" to the back of the car
Split back into 2x 2" pipes to go into the t3 Flanges of the turbos.
Twin 2" cold pipes merge into single 2.5" cold pipe to run to the front of car.
Intercooler at front with 3" piping to the engine.
Thought process being less surface area to lose heat, less space taken up with pipework, velocity stays high and have it all wrapped as mentioned to keep it all hot.
Concern being if the single 2.5" pipe will be a bottle neck for the 408 cubes and cut me short of my goal.
Other option is to run twin 2" all the way to the back and keep each bank separate. All wrapped of course.
I think the oiling side is all good for me. Just looking at this pipework detail.
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Those turbos seem awful small. The hot side may be ok, but they will run out of compressor quick on a 408. I don't think they'll make 800whp. The gt3582's struggled to make 800whp on a buds LS1 and it was manual trans setup. Pushed to the ragged edge and barely making any power per pound he squealed out 855... But the gt35's were done by 18lbs or so... Pushed to 24lbs , but were literally making like 7-8hp per pound after that. At minimum I'd upgrade to the GT35's. They are $109 shipped... not a huge investment. personally I'd run the 64mm compressor gt35 upgrades.
As far at the hot side goes, I think 2" OD piping is too restrictive for a 408. Actual ID is 1.8". I'd keep it simple and run 2.25" (2.13 ID). all the way back on each manifold.
As far at the hot side goes, I think 2" OD piping is too restrictive for a 408. Actual ID is 1.8". I'd keep it simple and run 2.25" (2.13 ID). all the way back on each manifold.
Last edited by Forcefed86; Jan 26, 2021 at 08:54 AM.
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Thread Starter
Staging Lane
Joined: Mar 2009
Posts: 94
Likes: 0
From: Perth Australia
Ok I thought the 3582s were a bit more capable than what you are saying you had.achieved.
the 30s will definitely be too small then.
So in summary for my 408:
This at least gives me a ballpark to play. Might need to offload my gt30s.
Oh and the car is a WB Caprice not WM. An old girl.
the 30s will definitely be too small then.
So in summary for my 408:
- Run twin 2.25 pipe to the 2x turbos off my stock wrapped manifolds as anything smaller will choke the 408. Wrap the pipes all the way to retain heat.
- Need more compressor than my gt3037s have to make the power goal i have. So bare minimum gt3582 and they may still be borderline.
- Option with the bigger 64mm compressors to support the 408.
This at least gives me a ballpark to play. Might need to offload my gt30s.
Oh and the car is a WB Caprice not WM. An old girl.
These were the ones I ordered, but in a .63 T3. They took a $250 offer,
https://www.ebay.com/itm/Universal-P...YAAOSwAYZbkxdg
https://www.ebay.com/itm/Universal-P...YAAOSwAYZbkxdg
Thread Starter
Staging Lane
Joined: Mar 2009
Posts: 94
Likes: 0
From: Perth Australia
These were the ones I ordered, but in a .63 T3. They took a $250 offer,
https://www.ebay.com/itm/Universal-P...YAAOSwAYZbkxdg
https://www.ebay.com/itm/Universal-P...YAAOSwAYZbkxdg
Yes. Twin setup on a low compression baby cam (gm hot cam) 5.3. non-intercooled. Made 560/600 on 11-12lbs. I run them on 19 now. Guessing around 700 hp. They feel great for a really mild setup.
Thread Starter
Staging Lane
Joined: Mar 2009
Posts: 94
Likes: 0
From: Perth Australia
I understand its a guess but I would have thought 19lbs would yield bigger numbers than 700 with twin 64mm turbos?
It might... I'm going off what other gt35 combos I've seen have made at 19-20. They are generally 61mm. Also factor in no intercooler and low compression and I'm at a bit of a handicap. I also dyno'd in 2nd gear since I run a 2.73 and didn't want to spin the rollers too fast. So my whp numbers would be skewed slightly lower that was as well.