The motor:

396 w/ AFR210 heads, 236/236 cam

Naturally aspirated (but still spinning the blower) it made 305 rwhp (about 380hp at the crank). No real tuning done in this mode, I was just curious.

With the blower producing 8psi it made 490 rwhp (about 612hp at the crank).

The boost drifts down smoothly from 5000-6000 from 8psi to about 6psi, and I'm not sure if its belt slip or just the S-Trim is maxed and the motor breathes well.

 

What transmission do you have? What kind of dyno?

I think your belt is slipping. Even an undersized blower will build boost with rpm. What pulley set-up are you using? With a 6.66/2.75 combo, I think it will do 12 psi. Running an intercooler?

Mike

 

I am running an intercooller, and I think that's the problem, to be honest.

I'm running the ATI air-to-air LT1 intercooler, and my rwhp is 490 at 4000rpm, and at 5000rpm, and at 6000rpm.

I really think the intercooler is like a big restrictor plate. I'm really tempted to yank it and go to alcohol injection if needed to get the timing back.

It could be belt slip as well, but the MAP curve is pretty smooth, just decreasing smoothly with RPM from 156kpa to 140kpa. Usually with belt slip doesn't it jump around?

 

(FYI, this is an LT1 Vette, which is why its the ati air-to-air)

This is an auto trans with a 2800rpm converter (which flashes to 5000 as soon as it sees the 700 ft/lb at the crank). It was a Dynojet, and a hot day (88F).

 

I made 425 hp at 4000, but 550 rwhp peak using a 2800 stall converter that also goes to 5000 when you stomp it.

Move your boost gauge tap to upstream of the intercooler. If it's doing 14 psi there, you found the problem.

I'm curious about your camshaft. That cam goes along with Vizard's logic, but no one has tried anything like that yet. I'll be interested in your results once you get the bugs worked out.

Is the converter a lock-up?

Mike

 

The converter is lockup, but the stock PCM unlocks it at WOT of course. I do plan to swap in my GMPP transmission controller at some point and I can force it to keep lockup even at WOT.

You're right, I do need to find out what the boost is like pre-intercooler... that should be interesting.

- Dave

 

Well, I drilled and tapped a boost pickup point before the intercooler, and there's obvious and audible belt slip... it flashes to 10psi when you nail it and falls back to 5 right away, accompanied by a loud squealing.

For whatever reason, its much more obivous on the highway in 1st than it was in the dyno cell in 3rd. Maybe the slower engine acceleration in 3rd is easier for the belt to grip?

Anyhoo, I'm a poor 6-rib Vette guy, so I definately need to upgrade to an 8. Sadly ASP takes many, many months.

Last time I had the bracket off I added my own little tensioner assist (a big bolt threaded through the bracket that I can use to force the tensioner beyond what its spring will do). I'm nervous about the blower bearings if I use it, but I guess now is the time!

 

Try some VHT traction compound on the belt.

Mike

 

How long does VHT last (ie: is it for testing only, or a workable solution?)

I tightened down my tensioner assist and took it out, and before the aftercooler I saw a steady 15psi, flashing to 17psi.

I pulled over and moved the pickup back to the intake, and couldn't get more than 7, but I think it was slipping again. So all I really learned is that if it doesn't slip, it makes a lot of boost with the 2.62 pulley!

 

VHT is for testing only.

7.00/2.65 is pretty steep and should make for 15 psi. I'm at 6.66/2.75 and seeing 13 psi.

Mike

 

Mike,

What size belt do you use with the 2.75/6.66? Brand and part number please. What RPM do you spin to?
Thanks

 

Coincidentally, the 6.66/2.75 belt length is the same as the Vortech kit-supplied 6.00/3.33 belt (one pulley bigger, one smaller).

Mike