lcvette

iTrader: (3)

Hey guys,

I know I really wanted to see a comparison on this since so many people get caught trying to decide between the two turbos I tried out so at my expense here is an apples to apples comparison of two turbo on the same exact motor with nothing else changed. note the PT88 on the same exact boost settings made 24psi and the 78GTS made only 22psi. my guess is the lowered back pressure of the larger turbine wheel afforded some new flow. and didn't forced the wastegate open as it appeared to be doing on the 78GTS.

Here you go I put them in comparison on speed, engine speed, and time so you can see the different spool characterists in more of a dimensional comparison.

Enjoy!

Grr

iTrader: (2)

wow that is very helpful, thanks! BTW what happened to the 88 that it broke?

lcvette

iTrader: (3)

the nut came off. I have arrived at this conclusion because the nut and the broken portion of the shaft were no longer together but laying by themselves in the air filter. The shaft piece will not allow the nut to thread on from either side, the base where it broke has aluminum melted to it, another sign that the nut cam off first and the compressor spun on the shaft before the shaft broke. and the other end that the nut would normally thread onto is so beaten up by the compressor wheel it will in no way shape or form thread more then 1/4 turn before completely binding.. no way it came off in the shape it is in so the nut must have come off first and when it hit the compressor wheel blades this must have been what snapped the snout of the shaft off.

Chris

ModularTurbo

iTrader: (14)

I am curious as to which turbo would produce the better ET. From the graphs it seems that the smaller turbo has better average horsepower, that may make it faster at the track.... any thoughts.

Got Me SOM

iTrader: (2)

i'd go with the original turbo, that bigger one is sleepy and looks like supra dyno

B18CYA

iTrader: (17)

very nice. how about some info on the motor

cjg454ss

iTrader: (27)

what size motor was used??

lcvette

iTrader: (3)

Hey guys, here is the motor run down:

- 355CID, Eagle crank 4340, Eagle H-Beam rods 5.7 w/ L19 bolts, Ross Custom designed pistons.

- Trickflow 195cc heads ported by myself ( I used to Port Heads Don't try this at home kids)

- LT4 Edelbrock Manifold (unported currently)

- 58mm THrottle body

- 7 quart oil pan custom by me

- Ebay 12x24x4" thick A2A Intercooler

- Custom 3" Intercooler plumbing

- Custom manifolds/crossover by me

- 4" Downpipe to 4" single exhaust split at the end to twin 3" pipes with Megan Racing Mufflers

- PT88mm turbo or PT78mm Turbo

- 44mm TIal Gate

- 50mm Tial Q BOV

- DFI Gen 7 w/ Dual Synch Distributor (opti Delete), WB02

-160lb injectors

- Fuelab 42401 Pump with -10 feed lines, -8 return A1000 Regulator

- 224 224 .570 .570 115 LSA Comp Cams

- 1.6 comp rockers

- AFR Hydra Rev kit

- Caddy Racing Lifters

think that is about it, nothing really crazy pretty basic build up sure I forget a few details but for the most part that looks like the important stuff.

lcvette

iTrader: (3)

from the feel on the street I would bank on the larger turbo, I have a two step and no lift to shift electronics so once that big boy is online it stays there and there is more power under the curve across 4 gears on the larger turbo with less then 2psi boost drop between shifts and it pulls further into the rev range so hands down on an all business run at the track coming off the two step, once she grabbed and went from there on it is all under the big end of the graph pushing the car to the end.

Now on the street the PT78HPS hit hard as hell down low buit it fizzled on the big end as you can see in the graph. I would have liked to try a PT80 with a turbine wheel in between the GTS and the PT88's rear wheel, I think it would have been the absolute perfect size for my goals, it would have come on a bit later then the 78 but pulled strong to redline without fizzling out and back pressure would have been reduced as well making it much more efficient.

the PT88 felt insane when it came online and didn't quit, with the 335 hoosiers out back in second gear with Veee8 int he car I have never felt the nose so high as that one hit.. unfortunately the next hit was when the nut for the compressor came off. I just took some pictures and will post them up in a bit.

Chris

HUNTER02SS

iTrader: (24)

If it was a side by side track comparison, I would say that the smaller turbo would get out of the whole by maybe half a car, but after that the larger turbo is going to pull right by the smaller turbo. If that was a footbrake comparison. Both on trans breaks, the bigger turbo for the win!

ModularTurbo

iTrader: (14)

Yes you are right in a perfert situation where all available power can be had at all times more power wins. But for most this is not the case, I was just thinking out loud.

DrTurbo

iTrader: (3)

All depends on the setup. With both on a 2 step and all things being equal, the 88 will mop the floor....period.

As for something in between.....their is the GT45F-78. Non-BB GT45, 88mm turbine wheel so its right in the middle of the PT88 and 78GTS. Price is only around 1400 or so for it as well.

qqwqeqwrqwqtq

Nice #'s!

killerinparadise

iTrader: (2)

Wow that 78 really falls on it's face in the upper RPM, you've got me second guessing my turbo choice now. Thanks for posting up the comparison.

Shearer

LCVette,
Are you John Wigger's buddy?

Is it just me finding it odd that the 78 nosed over so hard like that though.I would expect power to fall off up top but that curve took a jump off of a cliff. Did you find any other issues with the turbo or have a problem holding boost to redline?

NicD

iTrader: (7)

Yea, very odd. I would not think the turbo is out of steam at that power/boost level to drop off in that fashion. It almost looks like valve float from higher hot side back pressure? For comparison my 76GTS holds just fine at that power level on my 346ci motor.

Zombie

iTrader: (2)

I'd love to see this comparison done on a Mustang or other eddy current dyno. Dynojets without a load cell will not produce a realistic comparison to spool and power band. They do not load the car realistically.

I can't see how a TC78 would drop off so hard in the upper RPMs on a 355 ci motor. Even my t76 *** turbo held power to 6000 rpms on a 370 LS1.

lcvette

iTrader: (3)

Shearer,

yes, that would be me. nothing else changed from turbo to turbo and the PT88 as you can see had no issues holding boost or making power to redline at a higher RPM so I don't think it is valve float, plus I am running a very good set of springs with 155lbs on the seat closed as well as an AFR Hydra rev kit which should eliminate any valve float.... my best guess is that the higher back pressure was forcing the wastegate open due to the smaller turbine wheel. John and I noticed great boost that started tapering quickly after peak and that was when we were using a large blue and small blue spring int he Tial 44mm Gate with no boost controller. I installed an Eboost2 to see if I could add in some duty cycle at the point at which it began falling and that helped a little bit but even with many many runs on the dyno we were unable to get rid of all of the drop and the hard fall off was evident on the dyno as the nose would drop as soon as boost started falling.

I thought it may be the twin disk slipping but we didn't change it for the PT88 so I imagined if it was going to slip with the 78, the 88 would have done the same thing.

from the 78mm to the 88mm the Eboost did not change settings at all and I gained 2-3psi just from changing the turbo so this leads me to believe it was excessive turbine inlet pressure.. I will hopefully have some twin 62mm be it PT or Turbonetics units to compare to these graphs as well.. I am hoping for spool more like the 78 and staying power like the 88.. we shall see!

Chris

lcvette

iTrader: (3)

also, I had a T76MPS on there first and it did it worse then the 78, the 78 would hold boost perfectly to redline when it was down in the 16-17psi range.. it just didn't like trying to hold higher boost? the 88 cured the issue so it may be in the design of the manifolds whihc are space restricted to a log on one side.. maybe the turbine wheel and larger housing on the PT88 offered a better platform?

Chris

Frost

iTrader: (45)

thanks for taking the time to share your work.