It has been a while since I have posted and updated everyone here on my progress with my '79. Over the past wo weeks we removed the original Torque Converter and replaced it with a Precision Industries 2800 Stall Vigilante Torque Converter with new aluminum pan, gaskets and filter. We also replaced the rear 6'' tailshaft which had new bearing and seal. The disassemble and reassmeble of the components went fine. No problems which in itself I find unusual as there is always something else along the way that is either broke or needs replacing. Now, the vette started fine and we added fluid accordingly. The first two test runs were disappointing. Yes, I do feel a difference by being in the powerband quicker but the lack of initial torque and not spinning the wheels from a stop position is something we were expecting. The only other work we did was removing the AC compressor, new spark plugs, and header gaskets. All relatively simple. So, what should be our expectations with this converter upgrade and/or maybe we installed it incorrectly, which I think is difficult to do. The engine is a SB 355 with 180cc AFR Heads, TH350 Auto, and original rearend. Headers, dual exhaust, 1.6 full roller rockers. I'm running a XE 218\224 CompCam. Some technical experience and insight would be appreciated.

 

What cam did you install. If you have the stock '79 cam in place, that would be your 'deal breaker'. If the new heads have a weak cam that won't let them 'breathe', well....

Also, potential issues are the tune of the carburetor and distributor timing curve.

 

With a looser converter you can advance the timing and if you want to break the wheels loose lowering the idle can help by making the converter hit harder from a dead stop. BUT I think you're running into a too much cam or not enough compression that is killing low end torque.

 

Good question. I'm running a XE 218\224 CompCam. It's an upgrade but probably could have gone bigger earlier during top-end build but at the time this was the highest I could really go without really compromising initial torque with original stall.

 

What rear end gears are you running?

 

I was in your same boat. comp xe268h w/ 60cc heads, the change made good power but in all the wrong places... I had 3.08 gears.

installed a 2800 stall in with the th400 and it would take off quick but no loss of traction.

next, I replaced the differential with a 3.55 unit. that did it. I can burn now with no problem if i want. follow the above advice but consider 3.08 is pretty hard to get moving if that is the case.

 

You should be able to burn rubber easily with your setup, even with 3.08 gears. How is your timing and advance set up?

 

i completely agree. if You were to rev the engine in neutral to 2800 and drop it in gear it would destroy your tires, and alot of other stuff! something is amiss for sure, is the trans fresh?

 

Yep, trans is fresh and I have 3.55 rearend. PI recommended this stall and we installed it correctly. I'm not sure what else to do. The Holley seems to be installed and configured properly. I can look at timing again. What do you think it should be set at?

 

The short version is roughly 36° btdc total (initial + mechanical) with full advance coming in by 3000 rpm. Initial timing should be at least 12° and probably more if your engine likes it.
If you just set the total, you may find that your initial just happens to be at a good setting.

Now for the long detailed version, read here- http://www.digitalcorvettes.com/foru...ad.php?t=75830
That same information is somewhere on this site too, but its no longer easy to find.

 

Cool. Also, when I installed the holley 9895 I replaced the secondary spring with the lightest spring they offered. I'm wondering now if I need to go with a stiffer spring? Secondaries opening too soon.

 

If you went with the lightest spring there is a good chance that they are coming in too soon. You might go back to the original spring until you get the timing sorted out.
Then once the timing is good, go back and change springs until you start to feel the secondaries when they open.
They say if you can feel them they are probably opening too soon, but I'm not happy unless I can feel it.

 

I'm wondering if changing the secondary spring is even going to make a difference as the secondaries are opening around 3500rpm's now, well, at least before the new stall anyway.

 

From a standing start, in drive, at idle, when you floor the gas pedal, the engine should rev, secondaries should open and the tires should break loose - simultaneously. I have the same cam, with 1.5 rockers, you have better heads, I have a few more cubic inches (383), and a 3,000 stall converter. Timing advance is critical to this. Are you getting full advance (35 - 36*) by about 2,500 rpm?

 

I'll be checking this soon. I noticed the vacuum advance was connected to the wrong port on the Holley 9895. For some reason it was on the EGR port. It's now connected to the lower right port for vacuum advance.

 

Just want to keep you all informed. Made some real progress today. Did a compression check on all cylinders. They all were between 201 and 205. 12* BTDC base timing and 36* BTDC at WOT at 2500 RPM. WOT vacuum is almost at 0 and we are at 11.1 - 11.5 at WOT Air Fuel Ratio so we are running rich at WOT a bit. We had an air flow problem which was solved by installing a 3'' air cleaner element and removing the 2''. So, overall we made some changes with timing and airflow and we do have some wheel spin from a stop position. We did use an Innovative wide band oxygen sensor for air/fuel ratio numbers.

 

Sounds like you're making progress. Have you changed the spring controlling the secondary opening rate? You might try a couple different ones.

 

It's one thing to say it's a 2800 stall converter, and quite another to know where it actually stalls...
Try this: On an open parking or road, apply full brake pedal HARD and hold it, and then, apply full throttle smoothly and quickly, at about a 1 second rate (still holding the brake applied), and watch the tach to see what the stall rpm is. Caution - Don't hold WOT for more than ~ 2 seconds because the trans fluid will be heating rapidly. This is YOUR brake stall rpm. Another caution - strong engines can overpower the brakes and result in rapid forward movement, so make sure nothing is in front of your car!

As you might guess, the rpm reached is a function of how much torque your engine can produce at that rpm, as well as the coupling tightness of the converter. This rpm is rarely within 100 rpm of the quoted "stall speed", so it can have a big effect on how your car launches.

 

I've tried several now. The lightest one (white) is not the best for my configuration. I'm currently using the yellow long spring which is the third one from the white. Third spring in order from white. Like I said she runs and pulls really well but we can get more out of it once we work on jetting the Holley. Think we should go down a size since we are rich at WOT.