Okay, so the first time I went to the strip, I had a pretty much stock 1991 Z28 350ci Camaro w/ a 3.23 posi rear end. SLP 1 3/4" headers, an aluminum driveshaft, 'Vette servo, and a couple of free mods were all I had done. I best was a 14.2 ET at I think 99 mph with a .8 R/T (I can't find the timeslips).

Tonight was the first night I had a chance to get my car to the track after I had changed a few things...:

ZZ4 cam
Ported stock iron heads
Ported intake
1.6:1 roller rockers
Dual chambered mufflers
New plugs and wires
AFPR

That's all I can think of now. Anyway, I really sucked it up tonight. My best time was
15.161 @ 92.84, and the other 3 runs were in the mid 16's (all at less than 90 mph).

I'm kinda rambling now, but I'll try and get to the point. 2nd, 3rd, 4th gear all seemed to be fine. But 1st gear was like I had no torque at all. It would take forever to wind up, but then when it finally would I'd take off. But by then it was long over. My 60' times tonight were all over 2.7XX, and my reaction times were all in the .6 range. I don't know why 1st gear is acting like it is. It's like I've got the torque of a Yugo or something. So, what I'm looking for is for anybody to let me know what they think might be the cause of this. I'm still pretty PO'd, but I'll probably fiddle around under the hood a little tomorrow, and see if I find anything unusual.

Any input is appreciated, thanks.

P.S. Sorry for such a long post

 

You need to go to the DIY PROM board and read up on what you
need to do to burn a new prom.

The computer still thinks you have a stock engine.

 

not only that but you need a TC. the engines powerband has been moved up. that's you reason 1st sucked. i assume it doesn't have the same low end as before. as previously stated you need to make some changes in your PROM.

 

Yeah, that's what I kept thinking last night, was I needed to get my PROM modified and a new torque converter. I've been planning on starting making my own PROM's anyway, I just really don't have the money...

Would you say 500 above stock for the torque converter, or is that not enough? And, is there anywhere you know of that has good prices I can check out?

 

Something else is wrong. You lost 6 ... 6 ... 6mph! PROM changes won't get you 6mph. A Torque Converter won't get you 6mph. Now, lets put this in perspective. You should be around 100 mph which means you are losing 7mph from something. To me that means that something is wrong with the car. Maybe the cam isn't installed properly, or something else. Start with the both a compression check and a leakdown test of the cylinders to make sure the bottom end is in good condition. Then move on to the more complex stuff.

Tim

 

Yeah, I second what Traxion said. Also check for vacuum leaks, timing, burned plug wires, stuff like that. Check your fuel pressure too, maybe the fuel pump is going out. You lost a ton of HP. Later

 

Well fella I'm right there with ya!

read about my exciting dilema here:

http://forums.corvetteforum.com/zerothread?id=283240

I am assuming that you have an Automatic.

I just ordered my 3200 vigilante. Should be here by mid enxt week. I am going to try to get to the track friday.

If you find something please let me know via email! I will do the same and let you know how the converter works out.

Good luck and let keep each other posted. We are experiencing the same thing. Perhaps we can get together and race our Yugos! My 5 yrs old boy, Hunter, looked at me after hearing my dad and I laughing at the videos of my car taking out and said, "Dad I could beat you on my new mountain bike!" That was it. Five minutes later I ordered the 3200 Vigilante.

 

1991_Z28

What were your 60' times before the mods. I believe your loosing A LOT of time with a 2.7 60'.

With bad 60' times, the car being so lazy at the start (1st gear), and finally going great in the higher RPM's, I'd start to wonder aobut the stator in your converter.

A stator is applied at low RPMs for a torque increase. As the engine speeds up, the stator is used less and less.

And the only way to be sure that it is a bad stator is to open the converter or replace it....

 

I agree. 7mph is like 70hp. If it was just 1st gear that was bad then that would explain your 60', but not the drop in mph. And that cam isn't that bad for an auto. It start to make power at 1500rpm.

Who ported your heads? Did the grind the combustion chamber? This would change your c/r. (I think. someone will know for sure) if it did lower your c/r then that would cause a BIG power lose.

 

A rule of thumb, if you gain a tenth at the 60', your pick up 3 tenths at the end of the track.

Example of one that works with my car.

2000 season

1.7 60'
11.59 at 117 MPH


2002 season - replaced an "unstalling" 10" TCI converter with a Dynamic 8" 4500 RPM stall, change to roller rockers, and replaced the steel rear wheels with aluminum.

1.5 60'
11.01 at 122 MPH.

I do wish that I did one change at a time, but it wasn't really possible.

 

Actually, the rule of thumb is that you gain 0.15 in ET for every 0.1 drop in the first 60ft. His current problem has nothing to do with needing a higher stall torque converter. He lost mph ... A LOT of mph. Granted, a higher stall converter more suited to the current engine combo is always a good thing. But, there is something else going on here. He lost way too much mph. A converter is not going to make that up.

Since you threw out an example let me do the same. I went 13.0 at 107mph on a 1.99 60ft. After installing a vig I went 12.5's @ 107.9mph on a 1.71 60ft.

Tim

 

I agree, something is definitely wrong. It's not like he's trying to run Tim's cam on stock gear and TC, the ZZ4 would have no problem running good 60's and mph.

 

My car seems not to follow typical rules. I also switched two other items. The example was also of a jacked up converter.

Ya'll heard of for each hundred pounds lost, you lost a tenth with your ET. Best time (YEARS AGO) was a 14.2 in a 3400 # car/driver. I added an 8-point roll bar and lighten up the car 600 #. No other changes yielded a 12.9. That is like 2 tenths for every 100 #. At least the rule breaking is in my favor....


Back to the original question -- 1991_Z28 is describing a failed stator in the torque converter. It not like he put in a 320°, 0.750" cam in there. And 1991_Z28 never noted the poor running of the engine (backfires or "coughs"), just that power is fine at the higher RPMs.

I didn't say to get a higher stall converter, but I believe that he convert is suspect.

 

No, you may very well be right a73. It was an earlier response in this thread that said that he 'needed' a TC after the cam swap, which is flat out wrong. As we both know, he's not losing all his MPH to improper stall, he is dealing with a real malfunction/failure.

I could see a dead TC sucking some MPH out as well as sacking his 60' like that. Of course it could also be something else dumb sucking out all his power from the under 3500 RPM area (like excessive knock retard). At this point i wouldn't rule anything out myself, thats when you end up chasing your tail...

 

Guys,

I have the same exact problem he is describing. Loss of low end toque after my mods. My car takes out like my freakin lawn tractor. Never stumbles/coughs just steady then at 3000RPM it rockets forward like you hit the nitrous. Compression is all within specs. Everything else is new. No knock retard.

The car has never been able to spin the tires. Converter locks at 1100 RPM! When powerbraking the car spins the tires and RPMs will NOT exceed 2000RPM. Just goes bwaaaaaaaaaaaaaaaaaaa! Never misses nothing. Car pulls like no tomorrow all the way to 6000RPM.

Scanner hooked up indicated good air flow, etc. No codes set.

Seems to me like we both share the same problem.

Went as far as checking all the gaskets to make sure that none were blocking the exhaust ports, etc.

My thought it that I am loosing the first good 75' of the track. I bet I'm only going about 25-30 MPH then off it goes after 3500 RPM.

I suspect something is seriously screwed up in the converter or some dumb *** put the wrong one in it.

At times the car will stall after you start it and you know how they tend to rev up to ~1000-1100 RPm then calm back down to idle 750ROM. If I start it and pull it into gear right away, it'll stall every time. If I wait till it calms back down, no problem at all. It feels just like when you pull a standard into gear at idle without using the clutch. Minus the grinding.

I should have the vigilante installed by the end of the week and be at the track hopefully Friday.

Good luck to the other fella and I will keep you posted on the results of my TC install.

Also refering to the comments that the TC shouldn't improve your MPH I have to say this. True if you converter was working before and you just upgrade to a higher stall. Nevertheless, in my situation its like cutting the track 70-100' shorter than usually because the car is SOOoooooooooo bad off the line. I can literally see the tires turns (slight exageration). But you can't say that you would run the same MPH at the strip if one time you ran the full length and another time they cut it 70' shorter. Unless your car isn't still pulling at the end and has leveled off.

I realize that the lengths above are just gestimates from watching the videos etc, but I bet I'm pretty close. During the videos there was consistantly ~2.8 sec before you heard the car come alive and take off. Surely that will be decreased significantly with the New TC. Granted this example is only if you are experiencing the lul that we have been. If your coming off the line strong to begin with then no you will not realize as much as I expect to gain.

Just my .02

 

Thanks for all the input guys, but I think I solved my problem (it's at least a hell of a lot better than it was). My distributor hold down must have been loose, because the timing was retarded by about 8°. I then checked the IAC and TPS, and my TPS was at .38V, when it should be at .71 ±.05V for SD (if memory serves me right). Fixed that, too. Did some other small things, too, but I'm sure the timing was mostly to blame. Now it's like I've got a new car! I was sure my car was quicker right after I installed the mods; I guess I was right. I'll go back to the drags either this Friday or the Friday after, and I'll let you guys know how I do. There might be some other small things, but it's definately better than it was. I'm pretty sure it's launching harder than when it was stock; I'm leaving rubber longer than I used to.

Oh, and ski_dwn_it, I read about your troubles on the Corvette Forum. That sounds just like my predicament! Luckily my problem was fixed pretty easily (and cheaply). I hope your new torque converter works for you. Let me know how it goes.

 

Hey glad to hear you got it!

Its the little things that get you every time. Except in my case!

I'll spend another 2000 dollars before I find mine probably. Thats just my luck though.

For instance. I ordered my SR through Lingenfelter. He sends it and I install it. Try to mount the provided cable mounting bracket for all the cables that go to the TB and bolt holes are all misaligned. I looked at it and made the assumption they had to have sent me the wrong bracket. Called them the next day and the guy said look buddy we sell thousands of these things and no one has ever complained about the wrong bracket. Are you sure you have it right? I told him look buddy. I am a mechanical engineer that oversees hundereds of design projects for one of the worlds largest companies (GE). I think I can recognize if the item is mismatched or not. He agreed reluctantly to send another. It came and lined up perfectly.

That is just a typical day for me though. Items that should take about 15 minutes take 3 days. It would have surprised me adn I would probably be afraid if everything went 100% with this project.

Good to hear you got it going again. Good luck at the races!