I have a decently build 302 with an HP performance single turbo kit.
At 12 psi the car dynoed at 590 horse and like 540 ft/lb. fuel boosted reached by like 3400.
The hp kit has 1 3/4 primaries 3 inch cross over and a 3.5 inch downpipe. I am using a single comp turbo 6265 turbo with .81 housing
CTR3693S-6265
COMPRESSOR
Exducer Inducer
62mm 93mm
Turbine
74 od 65 exducer

I was considering changing the turbo to something larger. I feel that I have to much back pressure. However the turbo fits pretty tight so I may need something in the same case. That leads me to
CTR3993S-6871
COMPRESSOR
Exducer Inducer
68mm 93mm
Turbine
76 OD 71 exducer.

Is the size difference that much in reality?id like something that would help the exhaust breath a little better but not move spool time up 1000 RPM.

I’ve also looked at the next size case up. The 7675 might be alight also.

any tips or suggestions would be great

 

How much BP are you seeing at full boogy?

 

I have not done that. I know, I know. It just has some symptoms of a plugged exhaust.

 

I think its making really good power at 12psi.

What leads you to believe your statement. Details.

 

I'm curious about what you're seeing. Frankly, i'm surprised it's making as much as it is right now so saying it has some BP issue doesn't make sense to me.

 

Well until I measure back pressure I won’t know for sure. However, I expected to motor to rev out until 6200 or so. Just looking around at what everyone else is uses for turbo makes me think this one is tiny. I’ve seen people post about using 2 of these on v8. . It’s hard to compare because it seems everyone users their own things for Naming them.

I honestly expected more of a math answer. Based on cubic inches moving so much exhaust will require this much wheel.

I just haven’t tapped into my system to check the pressure. I need to just haven’t figured out where I want to.
Attached is the dyno sheet.

 

#ad

 

My last one I had a 78mm turbo on it and I don't think it would break 400whp. So you're almost 200hp better with a smaller turbo. I'm guessing you have a pretty hot motor to start with though. Can you give some specs on that? size, heads, cam, etc.?? If your motor makes 500na, then yes it would seem the turbo is holding you back. If your engine makes 250hp NA and you now made 590, you're about to sell a shit load of Comp turbos.

 

Sure its no secret:
stock bottom end 302 from fox body. no machine work. I did put studs in mains/heads and moved a piston and rod from another 302 into this one. I also replaced rod bearings. this shortbock had a rod that was slightly bend, (is that even a thing, "slightly bend rod"?, lol)
TW 190 11R heads with 56cc chambers
TW TFS Box R intake
Custom Roller cam (less that 230 duration each side and almost 600 lift)
all prepped by Flow Tech induction.

Engine management is a Pro M EFI system with the individual coils. This was not dyno tuned.

Sure max power is fine. I guess i am a little concerned that the turbine being so small that is spinning the crap out of it. Comp lists this turbo as suporting 850 horse.

relooking at my data log from dyno run it looks like max boost came in after 4000 RPM. i wonder if the thing can't move enough air untill later on, where as if I had a bigger unit it would improve things.

attached is a screen shot. The boost is not on the same scale as rpm. M1 is rom peak (info on right side of graph). the information in the graph is the boost peak (its only a couple psi different) boost controller may have over shot. thats a different discussion. This is to show boost coming in. #ad

 

There's no way that turbo should be making that hp on that combination at that rpm. Modern wheel design kinda skews the old size to flow comparison, but most would have a 70-80 mm compressor with a matching turbine. That thing should have block killing torque down low, but the dyno doesn't show that. More info would definitely be helpful. Any track times?

 

That dyno graph looks great... you might be able to flatten it slightly with an electric boost controller but that seems to be doing everything a turbo engine is supposed to. It looks as if boost in right after the NA torque peak, its climbing and producing a really nice flat torque curve at the top.

What are you trying to get this engine to do?

 

by the time the track finally opened (thanks covid) it was hott (90s and 100s). So no track times. i beleive the track will open again in about 2 months.

i guess my question should be, how much more turbo can i run before things become a major trade off. I look at this as one of those dyno tests that puts small heads on a big motor, yea they produce more than you would think, but going a size or two up gains everywhere.

 

What are your goals? You're at a power level now where you're on borrowed time with the stock block. Any more tq/hp and you're going to want to shift the boost and rpm curves up to save the block, but this will cost you low speed torque.

 

The combo and dyno numbers don't really jive. For example I had a stock 1990 5.0 with a T6 1.10 S465 65mm compressor and a 80/73 turbine wheel that was making full boost well before 4k.

 

well I don’t know either. All I do know is the turbo that came with the used kit I purchased was about the same size and responded the same way. However I don’t hAve the logs anymore.
This was a test to see where Max power was to help figure shifting spot.
It was less than 60 degrees that morning in Oklahoma City. I’ve seen video where some dynos are easier than others but At what percentage starts to make since for the numbers? 30,20% something running that high seems weird.

I wish there was a dealer around here that I could do testing with. This is my first turbo build. I usually use data to spawn ideas. When the bearing went out of the original turbo I called comp. told them what I had and what I wanted. The idea was about the same as it was but spool sooner. That’s why I got the .81 housing.

I had to get a different v band welded on the down pipe to use their 3 5/8 outlet size.

if my engine makes 330 to the tires ( not uncommon with my parts) then maybe the 590 at 12 is realistic. Throw in a 5-10 percent high dyno and maybe we are close.

 

I can tell you for certain that i'd hook up a boost gauge to the hot side to measure BP before I changed anything. Your combo seems to be working great and unless you just want more I don't see a good reason to touch it.