Rear mount turbo efficiency
Thread Starter
Staging Lane
Joined: Jun 2019
Posts: 73
Likes: 0
Rear mount turbo efficiency Just droped a forged 346ci in my C5 vet. (6 speed / T56)
I'm running the new revised STS kit with the rear mounted twins.
Im wondering how far I can safely push the base turbos that came with the system.
Specs on the twins are T3/T40b hybrids.
48.4mm compressor side and .36ar exhaust housings.
I made 580whp / 641wtq with the stock engine on 10psi with these tiny turbos and a healthy amount of 50 /50 water meth. (Mustang dyno) Since then I've went forged rods, pistons, custom ground TT cam, ect. Compression on the new engine is set at 10.3
What I'm wondering is would spining these little guys any higher be risking a turbo failure? Say another 5lbs? (15lbs total) If so then I do have a set of .48 ar housings I can throw on.
I like the quick spool and sound of the .36 housings.
I have tried the .48s before and they do make more power at the same boost levels but the spool is just a little slower than I'd like for a street car / Daily driver.
I also didn't just forge the bottom end to stay at 580whp though so if I have to switch to the .48s for It to be safe I will.
Ideally 700whp is the max goal for right now. If I can get by with the little .36s and make near 650 that would be fine too.
Thoughts?
I'm running the new revised STS kit with the rear mounted twins.
Im wondering how far I can safely push the base turbos that came with the system.
Specs on the twins are T3/T40b hybrids.
48.4mm compressor side and .36ar exhaust housings.
I made 580whp / 641wtq with the stock engine on 10psi with these tiny turbos and a healthy amount of 50 /50 water meth. (Mustang dyno) Since then I've went forged rods, pistons, custom ground TT cam, ect. Compression on the new engine is set at 10.3
What I'm wondering is would spining these little guys any higher be risking a turbo failure? Say another 5lbs? (15lbs total) If so then I do have a set of .48 ar housings I can throw on.
I like the quick spool and sound of the .36 housings.
I have tried the .48s before and they do make more power at the same boost levels but the spool is just a little slower than I'd like for a street car / Daily driver.
I also didn't just forge the bottom end to stay at 580whp though so if I have to switch to the .48s for It to be safe I will.
Ideally 700whp is the max goal for right now. If I can get by with the little .36s and make near 650 that would be fine too.
Thoughts?
Power per psi is a good indication unless you want to measure backpressure. Do a pull at 10 psi and then increase the boost and see the gains. Less than 20whp per psi is diminishing returns.
Thread Starter
Staging Lane
Joined: Jun 2019
Posts: 73
Likes: 0
what about shaft speeds? at a higher psi with the tiny housing I would think that would be an issue before back pressure. I'm no expert though which is why I'm asking.
I'll give upping the boost 1 psi at a time and watching the power output a shot though. Thanks for the advice.
Ive got dual 38mm external wastegates so I cant imagine back pressure being that bad once the gates are both open.
what about shaft speeds? at a higher psi with the tiny housing I would think that would be an issue before back pressure. I'm no expert though which is why I'm asking.
I'll give upping the boost 1 psi at a time and watching the power output a shot though. Thanks for the advice.
what about shaft speeds? at a higher psi with the tiny housing I would think that would be an issue before back pressure. I'm no expert though which is why I'm asking.
I'll give upping the boost 1 psi at a time and watching the power output a shot though. Thanks for the advice.
Thread Starter
Staging Lane
Joined: Jun 2019
Posts: 73
Likes: 0
I feel like I'll probably end up going to the .48 housings at the end of the day. The .36s just look way too restrictive. I'm actually surprised I made the power I did with them.
A bit off topic but do you have any insight on tuning for faster spool with a manual?
(Ive tuned the car myself so far and it runs pretty good)
I've heard people arguing both points. (tune spark table like its N/A until your in boost for max off boost power. And I've also heard of dropping timing some and run it a bit richer before your in boost to put more heat / fuel burning in the exhaust to spool the rear mounted turbos quicker)
Thread Starter
Staging Lane
Joined: Jun 2019
Posts: 73
Likes: 0
and yeah, that's about the size of them.
the bigger set I have laying around is the .48 housings.
and the compressor side is a 48.4mm according to the holley website.
I was told that the small housings are to help it spool up since its a rear mount setup. (Twins not a single)
It runs and drives great, spool up is stupid fast. It definitely dies off above 5,500 rpm though at 10psi.
Trending Topics
Yeah they are .36.....tiny little guys lol. As far as tuning, for spool up great like NA until right in boost then drop AFR and timing quick. The talk of regarding timing works better for launching with a 2 step to get the turbos lit.
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
6 Common C5 Corvette Failures and What's Involved In Repairing Them
Pouria Savadkouei
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph
Verdad Gallardo
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Pouria Savadkouei
Top 10 Most Powerful Chevy Trucks Ever Made!
Hennessey's New Supercharged Silverado ZR2 Has 700 HP
Verdad Gallardo
Coachbuilt N2A Anteros Is an LS2-Powered C6 Corvette In Italian Clothes
Verdad Gallardo
Awesome K5 Blazer Restomod Comes With C7 Corvette Power
Verdad Gallardo
10 Camaros You Should Never Buy
10 LS Engine Myths That Refuse to Die
Verdad Gallardo
Restricted User
Joined: Mar 2014
Posts: 7,192
Likes: 109
From: Ohio
I dunno, they claim .36 but then they also claim its a 36mm turbine housing. I'm thinking something got mixed up somewhere.
Either way, those turbos are tiny, but rear mount turbos handle things completely differently.
Smaller turbines can be pushed a lot farther because the exhaust cools before it hits the turbo so it takes up less volume. Backpressure ratios are usually very favorable with rear mount setups.
Either way, those turbos are tiny, but rear mount turbos handle things completely differently.
Smaller turbines can be pushed a lot farther because the exhaust cools before it hits the turbo so it takes up less volume. Backpressure ratios are usually very favorable with rear mount setups.
9 Second Club
Joined: Nov 2003
Posts: 13,616
Likes: 185
From: Norn Iron
Seems rather inappropriate for a V8, even with 2.
Thread Starter
Staging Lane
Joined: Jun 2019
Posts: 73
Likes: 0
Well I swapped back over to the .48 housings, I think I'll stick with the bigger housings. Last time I tried them it was before I built the motor and compression was at 10.0. Spool up was pretty bad then. Now the new engine is in and at 10.3 compression with a custom ground cam for rear mounted turbos. The Spool is definitely more manageable now but still slower, as expected.
With the .48s on it and just light throttle crusing off boost it just feels like it can breathe better, I dont have to downshift to 5th or 4th as much when going up a hill or bridge on the highway.
Over all power is definitely up with the .48s both on and off boost. Thanks for the responses. Now if I could just get UUP's secondary fuel system to work right I'll be all set.
With the .48s on it and just light throttle crusing off boost it just feels like it can breathe better, I dont have to downshift to 5th or 4th as much when going up a hill or bridge on the highway.
Over all power is definitely up with the .48s both on and off boost. Thanks for the responses. Now if I could just get UUP's secondary fuel system to work right I'll be all set.
Thread Starter
Staging Lane
Joined: Jun 2019
Posts: 73
Likes: 0
That's the plan. Working on sorting out these fuel pressure issues now. The UPP Secondary pump kicks on and everything is rock solid, 59psi till 6,500 at 8 lbs of boost.
Soon as I bump it up to 10lbs though I'm dropping to like 45psi at 4,400 rpms and going super lean..
The plan is to run 15 psi and shoot for 700whp but i cant even get a decent pull in at 10 lbs right now.
Any ideas? I run dual nozzle 50/50 water meth, a UPP secondary fuel system, and a racetronics single intake pump with a hot wire kit. I should not be loosing fuel psi at 10lbs and 600ish whp.
Soon as I bump it up to 10lbs though I'm dropping to like 45psi at 4,400 rpms and going super lean..
The plan is to run 15 psi and shoot for 700whp but i cant even get a decent pull in at 10 lbs right now.
Any ideas? I run dual nozzle 50/50 water meth, a UPP secondary fuel system, and a racetronics single intake pump with a hot wire kit. I should not be loosing fuel psi at 10lbs and 600ish whp.
Thread Starter
Staging Lane
Joined: Jun 2019
Posts: 73
Likes: 0
No but I'm real close to having one, lol.
I may use the regulator I have from upp and add a Y fitting to the fuel in side so both pumps feed into the same port. Then have the other side go to the rail. Then I can run a boost reference line and on the bottom of the regulator I'll just make the return line a little bigger.
Tuning is supposed to be way eaiser with it referenced as long as you adjust your kpa vs flow rate and your volts vs kpa vs flow rate tables. Both tables should just have whatever your 0 kpa value is across the board for that table since the pressure regulates your flow rate now. It's just one less thing for the ecm to calculate.
I may use the regulator I have from upp and add a Y fitting to the fuel in side so both pumps feed into the same port. Then have the other side go to the rail. Then I can run a boost reference line and on the bottom of the regulator I'll just make the return line a little bigger.
Tuning is supposed to be way eaiser with it referenced as long as you adjust your kpa vs flow rate and your volts vs kpa vs flow rate tables. Both tables should just have whatever your 0 kpa value is across the board for that table since the pressure regulates your flow rate now. It's just one less thing for the ecm to calculate.