08 TBSS, STS intercooled rear mount system with 67/76 turbo, 5#s of boost, stock everything else including convertor, ran 13.50 at 104.66 at 5100 #'s w/driver in 85-90 degree weather at 2600 ft altitude. Stock LS2, 364ci stock heads intake came etc but for long tube headers, hi flow cats and the STS system. Replaced engine after some other issues, 415ci, cathedral port heads, new springs retainers etc, LS6 camshaft. Changed coverter 2500+ and built 4l70E for the power difference. (Not a cheap convertor) retained same everything else, turbo did not change but was rebuilt (w/o need), boost raised to 7#s at WOT. Running 12.8 A:F ratio all the way through when testing. Same vehicle weight, Track temp outside was 45 degrees, vehicle ran 12.96 at 103. What gives?? Bigger cam, Bigger CI, same turbo, same intercooler, new engine and better 60 ft but overall makes less MPH with only .6 second gain which is solely attributable to the converter change. Previously left with absolutlely no boost. Now had 2-3#s and tires spun but MPH indicates let HP/CI by a significant factor. Any ideas would be helpful from the Turboforums wealth of knowledge.

 

This post makes my head hurt!!


I suggest you back away from the #ad


And, post something that's at least a bit coherent....

 

Turbo was small before you added na hp, and cid which only makes it worse. Put a proper turbo on it.

 

thanks. I've
been considering that.

 

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Okay, here's the map of a T66. Lets do some analysis of what you're trying to do. A TBSS engine is lets say about 42lb/min flow. Going up to 1.3 pressure ratio and multiplying that 42lb/min by the same we end up with 56 lb/min. Even with it stock you're way to the right of the map. ANYTHING you do that adds HP is going to make this worse. So lets say you've got a 52lb/min flow engine and we multiply that by 1.3. That's 67.6lb/min at a 1.3 pressure ratio! You're right in the last "0" of 56,200 on the compressor map. You may gain a little bit if you're running a billet wheel or a fancy cover or something but it's not going to make that up.

Now then, lets look at another map:

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If you went to where 67 and 1.3 crossed, you'd be in the low 70% range. Very acceptable.

You're in way over your head on the turbo capacity wise. I'm not going to say that you'd be better off pulling it off at this point, but it's certainly plausible. I'd give big consideration to another turbocharger to stick on the back. Bare minimum a 70mm and preferably a 76+mm. That T88 doesn't look as if it'd be a horrible fit though.

 

Probably lost power due to drive pressure and the turbo being flat out of air.

 

You're running way too lean. Watch after the 4:30 mark.

 

That A/F ratio is far too lean for a turbo setup. You want to shoot for 11.0-11.5, assuming 93 octane. For race gas, you can get leaner, based on which brand and octane.

12.8 is good for an N/A setup.

Al