Oh, I believe it. The last time I tuned an old SBC was around 2002, a twin 17c Syclone turbo'd 5.7L with edelbrock performer RPM heads and a holley C950 on a stealth ram. I was def pushing 22-24* of timing around 15psi of boost through some jank intercoolers. Back then we didn't have cheap widebands yet so it was plug-color and dyno tune only.

He did the whole plug thing so I wasn't so worried. Only trying to say, simply I guess, that you can be over timed, and not even realize it, with such great fuel. Remember hes not using 93. And if the fuel quality wavers even for an instant; its insta-kill when you are over timed or over heated.

Normally I would be sitting on the dyno with 93 octane, pulling timing until I saw a spike of EGT coupled to a significant drop of torque. Then push a couple degrees back to get within 5 to 7% of mean best torque and there is a typical reliable street tune as long as you have 4 to 5* of headroom. But you can't do that with a racing fuel because the whole point of such great fuel is to run a little more advance and gain a bit of torque/pressure earlier (rod length = dwell is a factor). But unlike Alcohol fuels there is no significant cooling taking place over the valve, no carbon cleaning to keep the compression/hot spots in check over time. So I wouldn't be so greedy unless I had an nearby chamber EGT probe and some kind of water injection in that case for the long term, some kind of warning.
Its tougher to tune for variety of situations because you assume the racing fuel is going to 'make it safe' no matter what, but those non-alcohol racing fuels can still overheat the chamber/piston and so forth easily in the wrong gear going uphill on a hot day or whatever.

 

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I'm seeing 110° iat on the dyno at 14 psi, outside air temp 83°

 

Well, after going through everything on the engine, leakdown/compression normal (165 psi), ohmed all the plug wires, pressure tested the exhaust from the turbos to the heads(including the wastegates), pressure tested the whole air side(from the turbos to the intake manifold)(I pulled all the rockers and pressurized everything), checked valve spring pressure, checked the degreeing of the cam, verified ignition timing at 3k rpm, i ran it last night on the transbrake. I even put more timing in, currently running on 112, have 36° in it, at not pulling any timing until 4 psi. Anyway, it managed to see 3.5 psi, at 4400 on the brake. It's definitely got to be that the turbos are too big, I'm out of things to check. Here's a pic of the datalog from the holley. It also runs open 3" downpipes. #ad

 

Can you get smaller a/r turbine housings? Squirrel tuning made 1300ish wheel with basic Borg S366s on a 4.8l LS.

 

Actmo, I cant see anything wrong with the way you have tuned it. You watched plugs, watched power output, gave it what it wants, went over things well.

All I can say is Ive experience the same thing on a single turbo setup when I used a ching chong turbo. Also seen guys that struggled with the same.
It just seems that CC turbos lack wheel tech. Most are pretty much using old tech. Even the ones that have billet wheels are very new.
Ive heard nothing but good things about some of the various performance turbo companies.
My experience has been great from Bullseye.

I needed to go to a better turbo, called a company that supplies ching chang turbos. They sold me what they said should work great for the combo.
Spooled horribly. When it finally reached boost target it was very obvious it was down on power when compared to the undersized unit that it replaced.
Bullseye spec'd one of theirs but at near 3 times the cost. Swapped it on , instant night and day spool and bunches more power at the same boost, timing , afr.

So I guess what i suggest is to step away from the junk and spend the money to get professional support on the turbos. You got a good combo and you seem like you are knowledgable enough to reach your goals.

 

Thing is, the China turbo is still far from what a true Borg is.

 

This is true.

 

he only makes an .84 a/r housing, he originally had told me it would only make a 200 rpm difference. As far as the ls stuff, compared to sbc. I talked to my machinist, who also builds engines and dynos them, and my buddies machinist, who does the same, and forced induction solutions, and tony at tuners inc. all said the same thing, that you can't compare an ls to a sbc. Cylinder head flow is totally different, which I don't understand either, seeing as I have a 383(6.2 l), but also I only have 9.2:1 compression also, which effects it. So they basically said because it works on a 6 l ls doesn't mean it will work on a sbc

 

I actually talked to Jose from induction solutions this morning, and he is looking into the new gtx35 for this. I originally ran a set of gt 35's, 61/62, .63 ar, and it made 850 rwhp at 16 psi, and went into boost immediately. He said he can do a larger a/r, and slightly bigger wheels to get me to my 1300 crankshaft hp goal, and still get into boost quickly, with roughly a 63 wheel. Turbonetics has some good pricing as well (within 50$ of the vs racing turbos on the car now.

 

I wonder if it just crappy built turbos? Maybe too much wheel to cover gap?

 

as far as the housings for s366. Bullseye has their own foundry and makes various sizes turbine housing for for their borg stuff.
So anything can be spec'd for a combo.

 

The comparison from sbc to lsx. There is something different there. Its something Ive thought about. Now consider that a stock 799 ls head only flow 240 stock.
Also consider the chamber efficiency. On average in the teens under 15 or more psi of boost.

Now consider that your a set of afr aluminum heads with a 215 port away from the same head flow as a 799.
But the chamber efficiency is still lower.

Now most good running , good spooling LSx will have like 30-35 deg up to 5 psi ish and then drop down quick.
What if there is a differential there where a sbc wants 30 under boost so it needs 50 deg to come up quick.
I will add that Ive seen a few guys at 40 deg on sbc before 5 psi that spool great on a big turbo.

There are sbc with real good heads doing the same as lsx. Just seen one the other day that made 2000hp at 28psi.

 

I just talked to viren, and he finally agreed that the turbos are too big. He is going to take an unmachined exhaust housing, and make a pair of .68 housings for it, hopefully that will be enough

 

But I am not referring to a 6.0 LS. This is a 9:1 294" engine.

Why did you go with the knockoff turbo? A pair of genuine borg S366 cast units can't be that much more $$.

 

I had good luck with the knockoffs on my last combination, cx racing gt35's, back then they were 200/each, made 850 rwhp and ran 9.50's with them, @ 3950 lbs, and 16 psi, so I had no complaints at that point

 

Well, I did them same thing, practically no difference.

Hope it works out for ya.

 

Great, lol. I just want to be done working on this thing already

 

After all this, I still have a hard time believing that the turbos are too large, unless it's a machining, or quality issue. I've personally seen twin T70 Masterpowers, spool a couple thousand rpm quicker than these, on a similar 383 sbc. I really hope you find the issue, it'll be helpful to everyone involved. Have any pics of the wheel to housing fit?

 

No, I haven't taken it apart yet. How much of a difference will it be going from a .96 to a .68 ar?