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These kinds of questions and the responses are what I enjoy the most about this site(ls1tech.com).
When I first visited this site, I had an LT1 and was running cams, heads and nitrous. Then in 2008, I started delving into turbo's for it. The most common notation I saw everyone using was the 76mm this, the 76mm that. So I looked for a 76mm turbo that has the smallest footprint for my engine bay and that appeared to be the ForceInductions TC76. I had no idea that the turbine housing size (65mm?) had any role in the equation. Naïve.... I looked at the way people were talking about A/R and I came away with the impression, the smaller the A/R, the quicker the spool and anything over .96 (that's what the TC76 had) was bad because it would be 'laggy'. The TC76 on my 355 LT1 was a winner for me. I annihilated every car I raced on the street with the setup(6 speed, SPEC stage 4 clutch, 4.10 gears in a Ford 8.8 and drag radials).
But then one day, I read a post here from SpeedInc talking about turbine housings and his (INTIMID8 ?) statement on watching turbo guys at the strip hitting 5K RPM and their cars nosing over as they hit backpressure thresholds because the turbines were too small. I contacted him privately and asked for further information. Before the conversation was over, I ordered a new PT7675 from him. still with the .96 A/R.
I'd been pretty happy with that turbo for both the LT1 and the 5.3 I was to subsequently employ. Then, the statement, "I've got twin turbos" began to loom large in my mind. A friend of mine in Houston, Tiago, was running TWO TC76's at the time in his 4xx 4th Gen T/A and had dyno'd at 1,3xx wheel hp. I was astonished by that. I decided to try twins but in a less ambitious manner and so bought two of the On3 GT35's with .80 A/R turbine housings. I ran those last year and other than some hiccups unrelated to the turbos, I was very happy with them.
But at the same time.... All thru my turbo experiences, I'd been reading here and there, within LS1tech, about the big Borg Warners and their 1.32 A/R. I always envisioned it would take a week to spool up something so large in A/R. Initially, I would see the BW 475 and 480 notation and then skip anything else because I just figured that's a terrible turbo for the street. About 10 months ago, I started seeing guys that had experience with these turbos (ForceFed for one) that said the BW475/480 with the 1.32 A/R spooled quickly enough on their 4.8's and 5.3's. This really piqued my interest. I started researching more and more, asking questions to the guys that had them. Before long , I was convinced and ended up ordering my current VSRacing S480 but with the larger turbine of 102/92. I welded up my hot/cold sides with twin Tial 38mmm wastgates, switched back to E85 and got it all done about a week ago.
After a breakin for the freshly rebuilt 5.3, I've started testing/tweaking the tune with very mild timing and have gone up as high as 27psi in one test(boost comes on so fast, I didn't moderate with my foot quickly enough). That wasn't even 100% throttle nor above 6,200 rpm. I have my AEM Tru-Boost setting on a more moderate value now but it still gets to 19psi at less that 100% throttle and by mid 5000 rpm as I continue to test. Needless to say, I'm very impressed by these turbos and their 1.32 A/R.
Last edited by mightyquickz28; 04-16-2021 at 02:33 PM.
Funny that this topic pops up...
I am pretty sure the 78/75 and .96 is about tapped out on my 6.0 liter, so I actually contacted Viren on Monday.
Gave him my current ET/MPH/Weight/etc...which was 9.76@142 on transbrake (15#), and 9.88@147 footbraking (22#), at 4060# race weight... and his reply was:
I would hold off and do a proper t6 would be a better option however you can run the 1.25 housing and gain some power output about 6-7mph but that all she wrote
Since my hotside is fresh, with dual 44mm wastegates, and setup for a T-4, going to a T-6 is not an option until the end of the season.
So...placed an order...
I plan to swap it out when I get caught up at work/sidework.
I obviously do not need this change to run 3# of boost bracket racing, so there's no rush.
Just want to have it swapped out before next N/T Test & Tune.
That's pretty much my gripe. Everyone loves the huge AR's, but their data is with stalled autos or switching from a stick to an auto.
Originally Posted by ddnspider
Super interested in your data, especially street driving and rolling into the throttle not launching.
Well, you know I try to share everything I can. This will be no different.
There won't be any other changes made, except the required 4" to 3" exhaust adapter.
I have a mild 3200 stall, but have just added a BMR Xtreme drag bar, so the car "should" 60 foot next time out, but we shall see...probably still a turd, haha
If I decide NOT to ever go to the T-6, the end goal will be to either eliminate the entire exhaust and run an open 4" downpipe, OR...retain my quiet factory style 3" exhaust, front to back, but instead of a 3" cutout, just past the starter, it'll be a 4" cutout just beyond the 3"/4" "Y" as it comes out of the turbo...so closed cutout will force exhaust through the whole system, and open cutout will be an open 4" DP, if that makes sense?
See awesome Sharpie picture below, lol.
Originally Posted by Shownomercy
I have a 80e car just debating if the negatives of a smaller AR outweighs the benefits of getting a new turbo.
Think backpressure was in the 1.6:1 area, so not terrible, not great, but also have not gone past 15psi of boost.
FWIW, on my car, at 15-16psi, it shows no signs whatsoever, of being "held back"...RPM and MPH are steady climbing, usually (and consistently) 5-6mph beyond my trap speed, before I physically let off the gas pedal.
Now, at 22.5psi, it only went 3mph faster than the timeslip, and the poor 78/75 Billet NextGen was SMOKING when I got back to pits...Not OIL smoke, or any leak, but externally smoking, like overheated, and it was on the verge of implosion...lol.
That 22.5psi was the absolute most boost my car could make. I say that because that was when my wastegate was not opening, so basically "pinned shut", as they say. If it's still running strong at the end of the season, as soon as "boost weather" comes back, it'll be "pinned shut" on purpose this time, but with the bigger turbine housing, shooting for 150+
If going to a 1.25 is only worth a few more mph trap wise, that to me is not worth it. I'd have to buy a new turbo with that 1.25 housing, so not looking like its a valid choice.
None the less, still looking forward to seeing your data.
If going to a 1.25 is only worth a few more mph trap wise, that to me is not worth it. I'd have to buy a new turbo with that 1.25 housing, so not looking like its a valid choice.
None the less, still looking forward to seeing your data.
Well, if his guesstimate of 6 to 7 mph is even close, that should be a conservative 50 or so hp, shouldn't it? I'll take that for a $169 mod all day.
In perspective, on my car,
15# with my cast 78/75 went 9.92@138...
15# with the billet 78/75 went 9.76@142
So 4 mph got me .16
If the trend continues, it should go 9.50-9.60, which I'll be pretty happy with on a turbo thatis probably too small for what I'm asking of it.
The 1.25 housing showed up today and I am surprised with how much just this part of the turbo weighs.
Yes, that cast portion of the turbo is really a boat anchor. When I had the On3 GT35's , they came with the usual T3 cast iron turbine housings (.63 A/R). A couple of years later, they offered a stainless turbine housing which was enhanced with V-Band flanges and a .80 A/R. I ordered those and was really happy with the weight reduction , plus the prospect of avoiding the rust coating that always seems to be part of the cast versions life. The VSRacing 480 clones turbine housing is so massive compared to the PT7675 it's replacing and the weight was really noticed by my back as I went about various location explorations in the engine bay over this past winter. Even after deciding to put it front and center, leaning over the nose of the car trying to mock up the best compromise of height, downpipe room, wastegate, discharge orientation , etc really challenged my back muscles. I'll have to see if theres a stainless turbine housing for this turbo
Does your turbo have any supporting bracketry?
I'm really impressed with your MPH's. While I would love to get that kind of MPH performance, I don't think I have the brakes(stock LS1 Fbody brakes) to scrub off enough speed before I'd be in trouble at the end of the track if I ran the full quarter mile. This season(track opens soon) I'll see what the 1/8th mile will show to know if it's improved from my prior best of 6.4 @ 112mph.
Yes, that cast portion of the turbo is really a boat anchor.
Does your turbo have any supporting bracketry?
I'm really impressed with your MPH's. While I would love to get that kind of MPH performance, I don't think I have the brakes(stock LS1 Fbody brakes) to scrub off enough speed before I'd be in trouble at the end of the track if I ran the full quarter mile. This season(track opens soon) I'll see what the 1/8th mile will show to know if it's improved from my prior best of 6.4 @ 112mph.
No doubt about its boat anchor status, lol. When my son brought it in off the porch, I thought VSR screwed up and sent me a whole new turbo, LOL.
Mine is only supported by the modified On3 crossover. I thought about adding some sort of brace, but no idea where it'd go.
I never expected my boat anchor of a car to run the way it does. I leave a lot of ET on the table too since my 60 foots are about as lame as can be. Best ever was a 1.52 I think it was, and most are only in the low 1.6 range. I "hope" the subpar launches are soon to change. I recently swapped on an anti rollbar, and the new Hoosier Drag Bracket Radials seem to hook better than all the different Mickeys I've used. Time will tell on that.
P.S. As much as I have fought it, I do have an 8 point rollbar in the works. At least itll be "legal" to 10.00 instead of the current 11.50 and up. It sucks having a proven 9 second ride and being forced to turn it down so far, that they dont even make weaker wastegate springs for it, lol.
BTW, i have stock brakes (WS6 but dont think that matters?) I do have PowerStop drilled and slotted rotors, and "Track Day" ceramic pads at all 4 corners. It has easily stopped from 150, but I still pucker everytime I let off the gas at that speed.
Rel3rd, interested in your results , does your next gen have the 10 blade or 9 blade turbine ? That should make a difference also
Originally Posted by GMCGreg
Forgot whether you are on pump gas or e85 ?
The turbine is 10 blades. I'm only changing the housing itself though.
I run mostly ethanol. I try for 70%, but it runs the same from 60% to 87%, lol.
I run 5-6 degrees more timing with ethanol in the tank regardless of boost psi..
WOT, @15psi, my total flex fuel timing is 19 degrees at 2500, tapered down to 15 @ 4400, then tapers back up to 20 @ 6000 and up.
At 3-5 psi, I run as high as 24 degrees, total timing.
If it's just got 93 in the tank, itll be anywhere from 10 - 18 degrees depending on boost.
Zero knock retard no matter what's in the tank.
I took a nice drive today, trying to get a handle on my cruise fueling and think I may have a bad injector. Bank 1 will show -.1% and Bank 2 will be adding 10%, so newd to figure out wtf is going on there. I chased the idle and cruise AFR around until my laptop died and just kept chasing my tail.
04-09-2021, 07:37 PM
