I have an 88mm billet wheel Borg mid-frame from Forced Inductions with a custom t4 1.25 AR turbine side and 4" outlet.

This is on a 363 solid roller with 225 high ports. The engine made ~600 on a superflow dyno with an old 850 carb, so it is a good engine.

The turbo flattens out at 26.5 psi at 6800 RPM and rolls off about 1 psi as RPM goes up toward 7800 maximum.

My ET and MPH is the same as with a 363 that had lesser head flow. The very same turbo would make 30 psi on that engine but get about the same ET. The power calculates to be about 1400 HP.

I'm space restricted under the hood. I can only fit a 4" pipe down past my frame and I have to keep exhaust under the car. I could get a 5" at the turbo but would have to taper it to 4" within a foot distance.

Would a Gen II Pro Mod 85 or 88 and a T6 be a good upgrade? I can't go large frame, but I could go T6. I have an inch or more room around the turbo. What is the smallest turbo that will give me another 15%?

 

Just my thought is that the efficiency of your turbo at that much boost vs your actual power goal and then consider space so let’s say you want 1400hp (crank) lets see what turbo options you will have with your space lol I have a s488 t6 1.32 ar and it’s huge 88/118 -96/88 and space is a bitch and I have the same issue with down pipe so I go from a 5” to 4 to 3.5” for only a few feet. Post a pic of your turbo and also what is your power goal to the crank?

 

I want about 5000 at the tire but I'll take what I can get.

My options are:

1.) Leave the billet wheel 88 compressor on and change to a bigger T6 housing. This will cost $1000 total. I can get a T6 with a 4" outlet.

2.) Get a Gen II pro mod 85 or 88. That will cost an arm and leg, probably $6000 to swap in.

3.) Get a T5 V band turbine and also tep up the compressor size. This will cost about $3000

Two people that play with turbos tell me it is mostly my turbine. My one buddy says I should just get a Gen II pro mod.

My engine is good into the low 30 psi range, at which point it should be in the 1600-1700 crank range if something doesn't choke up. With the present engine at 26.5 boost Wallace racing says I'm 1400 HP. My fuel use and AFR say 1500. But I'm 20% below what the engine should safely handle for boost.

It's just tough fitting things and keeping the radiator area clear.

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Well do you know how much air your current can move? But if you can step up to a large frame (I know limited space) that’s where the power will be! I think you will be fine and no choose anyway to do a 5” to 4” and let it ride

 

The problem with all these custom piece together turbos is no data. I know a lot about the engines based on dyno test of the base engines, but I have no idea what the turbo is other than an 88mm forged wheel compressor and 1.25 AR turbine housing that has been opened up a good bit.

I probably need to flow around 170 lbs/minute

 

Can you tak the turbo compressor cover off and use a caliper of the inducer and exducer and then do the same with the turbine and we can figure a lot out from there it’s easy to do just depending on your room and time but worth it

 

Seems like you have money to spend to get what you need.
I would talk to Bill at Bullseye. He should be able to supply you with what you need. No internet guessing. It will just work.

 

I'm talking to Bullseye now. Are they top line turbos?

 

Nothing wrong with bullseye, but I would be going back to Jose at forced inductions if it were me. Nothing but good things to say about them. You don't know what turbine you have?

 

My notes say turbine is a 91/100 mm wheel in a 1.25 A/R.

 

Id be checking pressure drop across that intercooler too.

 

Less than 1.2 psi from the turbo housing to the intake elbow.

 

That surprising looking at the crossection of the core.....must be some more there that isnt shown in the pictures.....glad you checked.

 

That intercooler works surprisingly well for the size. I could clean up the outlet box where it makes a 90 into the throttle body and help flow. I've been looking at adding a curved baffle, but the drop actually isn't too bad just as it sits.

Most of the issue with it is getting enough water flow. I don't think that will ever happen. My IAT goes up around 50-60F by the end of a pass, so if I start at 80F I'm up to 130-140F. I know it is a water flow issue, but the water volume I need is unobtainable.

 

Can you explain why do you think its a water issue? There's very little core there, and I would suspect it can't pull enough heat quick enough with the little surface area compared to what you typically see on a 1000+ hp a2w cooler. Any more info on the cooler? If it works that well on yours, I have a home for one.

 

I calculated the BTU/hr water flow required to dissipate the heat at a certain rise and it was right about on the expected rise based on my pump size. The curve also looks like a water issue, because right after the throttle closes the IAT crests and then slopes down at about the same rate it went up. That tells me the IC core is getting hot, and the gradual slopes are caused by thermal lag.

Of course I could be wrong, but it seems to me if the cooler was too small the up slope would be real fast and the down slope almost immediate. I calculate 25 GPM to have a 50 degree rise with a perfect intercooler and I have about half that flow. I think what is happening is the thermal latency in the cooler, which is mostly from the water, is doing most of the heat dissipating. I'm flowing about 10-12 gpm water and it needs way more than twice that to be stable.

A bigger cooler would, of course, have more water and hold temperature better.

It's been a while since I measured all this and I have changed things, so I probably need to recheck it, but everything was pretty much as expected. I don't have a jpg showing the cool down but it is a similar slope. If the cooler was just not cooling the air I expect the IAT cool down would be pretty abrupt when the throttle closes. If the IC core is hot I'd expect it to be a gradual pull down with water exchange.

I guess I could measure the IC core temp.

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Is it a problem of pushing enough coolant through the IC or just a lack of pump capacity? Pumps with the requisite volume are available. Davies-Craig comes to mind: https://daviescraig.com.au/electric-water-pumps

Getting back to the turbo, have you checked backpressure in the DP or plotted turbine drive pressure against boost? It seems to me that if the hot housing was a choke point, exhaust pressure would be quite high compared to boost and boost pressure could sag on the top end like you're seeing.

 

The problem with any system that does not go turbulent is always pressure delta across the restriction. I did my best to keep hoses as large as possible and angle fitting minimized, but I have a room issue. I can's reduce restriction much more, but I can always increase pressure with a bigger pump or a booster pump. It just isn't worth the worry because the air isn't that hot even at the end. If I wanted it cooler I could use more ice and get the IC tank down to maybe 50F, then the start air is 60F or so and goes to maybe 110 or 120F. It just isn't even worth doing that.

Everything about the intercooler and water system behaves like expected.

We have to remember I'm using a 1.25 AR T4 housing. While it has been cleaned out as much as reasonably safe, I'm flowing a lot of exhaust through that small housing. The 91/100 turbine isn't spectacular either. I'm running about the best of anyone with the turbo and weight.

While old engine was just about as fast, I had to run 30 psi boost to do that. The new engine is the same or faster at 26 psi or less, I just can't make more any boost than that. If something was choking it seems to me it would not be the same or faster at less boost. You can see the drive pressure and boost and RPM in the graph above. The dashed lines are the new engine. The MPH (and RPM of course) on the new engine was up at the end, the boost way down, the drive pressure down a bit. It just won't go any faster, but if I jam enough air in the old engine it is about the same.

I think I will get a little more data before I do anything, but to me it looks like it needs a bigger or better turbo. It's laid up now waiting on replacement axles, then I can get more data.

 

What your seeing is normal - it's making the same power at a lower boost level with the ported heads. Positive boost pressure is caused by restriction. You removed some of the restriction by porting the heads.

Since you can't turn up the boost, it is out of turbo.

Al

 

That's what I'm thinking and what two turbo builders told me.

If I get this thing back at 30-32 psi without pushing drive pressure higher than it was, or hopefully even lowering drive pressure, I will be way beyond the power I can use at most tracks.

My real decision is buying a Bullseye Power T5 V band light weight ball bearing or buying a T5 V band from Jose. Bullseye Power tells me their turbo will outrun anything of comparable physical size and spool faster, Jose has a good reputation. Both recommended a much larger compressor and the T5 V band turbine housing. Neither was too concerned about my ~4" downpipe.