Tech / General EngineIs your car making a strange sound or won't start? Thinking of adding power with a new combination? Need other technical information or engine specific advice? Don't see another board for your problem? Post it here!
Welcome to ThirdGen.org!
Welcome to ThirdGen.org.
You are currently viewing our forum as a guest, which gives you limited access to view most discussions and access our other features. By joining our community, at no cost, you will have access to post topics, communicate privately with other members (PM), respond to polls, upload content and access many other special features. Registration is free, fast and simple, join the ThirdGen.org community today!
Okay, A month ago I went 12.95 in the quarter with a junk edelbrock carb and the stock 9 bolt with 3.27's on 89 octane cheap gas. That night on the way home the rear end went out so I opted for a 9" with a locker and 4.11's. I also bought a 750 demon with mechanical secondaries from a buddy who raced it for years and reworked it for me when I bought it.
This weekend I took it out expecting an easy 12.50, possibly a 12.30 with some extensive tuning. Not even close, I went 13.70 on the first pass on 91 octane and added a boat load of timing and only ended up with a best of 13.40 for the weekend. I have all tubular rear suspension pieces and the car is hooking really well. I expected alot more for a $2200 rear end and large step up in carburation. I'm running a 10 to 1 pump gas 383, solid flat tappet cam, vic jr. intake, summit HEI with digital box, 110 gph mechanical fuel pump, turbo 400 manual valve body with a 3500 TCI stall converter. The car weighs 3600# with me in it and half a tank of gas. Thanks
Any other 1/4 mile numbers?
60'.
Trap speed.
1/8 mile et and mph.
Your previous combo is similar to my current ride in weight and gearing and I would expect better times with a rear gear upgrade and better carburation too.
__________________ 1986 Sport Coupe, underside & engine bay sandblasted/painted, 353 Gen 1 SBC, Vortec heads, XR276HR Comp cam, 1.6 Comp Pro Mag rockers, Full MSD Ignition, 700R4 w/ usual upgrades, 10" TCI convertor,3" driveshaft w/ 1350 u-joints, Dana 44 w/3.73 posi. All new suspension, LS1 front brakes, 1LE rear brakes, Del-A-Lum bushings, UMI adjustable torque arm, Intrax 2" drop springs. Best time on old chassis(86IROC,3700lbs)12.77@105/8.09@84(1/8th)w/1.70 60'. New chassis...12.74 @ 108. (Same weight)
86 TA 502. Work in progress. 86 IROC-Z. Winter beater.
Any other 1/4 mile numbers?
60'.
Trap speed.
1/8 mile et and mph.
Your previous combo is similar to my current ride in weight and gearing and I would expect better times with a rear gear upgrade and better carburation too.
It could be in the carb tuning. Takes a while to dial in but it really is worth it. I dunno if you've been messing with it or not though.
The carb when I got it had an "off idle stumble" so I checked the accelerater pump sqirters they were 31's I put 35's in it. That cleared it right up. The car does feel a little weak from just before the 1000' mark all the way to the traps. Bigger jets maybe? I am in no way a carb guru.
talk to five7 he's pretty good with carbs. Yeah, I know it usually takes a lot of trial and error to get em' running the best they can for any particular motor.
Other than tuning for the highest trap speed your best carburator friend is a wide band O2 sensor. It can eliminate a lot of trial and error WOT tuning.
Other than tuning for the highest rap speed your best carburator friend is a wide band O2 sensor. It can eliminate all lot of trial and error WOT tuning.
That's not much of a 60' time either. ( Even I call pull off a 1.7x with a 3.27 gear )Did I read somewhere that you have a 28" tire?
Yes, I'm running a 28 BFG Drag radial, I'm about done with these, thinking about quick time pro's. Any suggestions? I would like to stay with a radial street tire.
check your jets. make sure everything in your carb is up to factory specs. my 11 sec motor was running 13's after i bolted on a 750 mighty demon. took some research to get it to 11's.. btw what cam are you running?
__________________
1984 Trans Am
385sbc(RIP)/t-5/4.30-9"
1.69-7.44-11.65 @ 116
next up-->383 with mild upgrades
check your jets. make sure everything in your carb is up to factory specs. my 11 sec motor was running 13's after i bolted on a 750 mighty demon. took some research to get it to 11's.. btw what cam are you running?
I am running a Comp Cams solid flat tappet cam. @ .050 it's 236/240 and
.501"/.510", 2400-7200 Rpm, I believe the comp number is 12-677-4. Sounds awesome and is very streetable. The carb I bought from a friend who raced it for a few years. I'm not sure of what he had it set up as, but this I believe is what I am going to do: Order a jet kit and put it back to stock and also figure out the power valve. I'm sure he was running alot more over lap and would be a considerable difference in vacuum. He also said he had it pretty rich for his SBF.
I am running a Comp Cams solid flat tappet cam. @ .050 it's 236/240 and
.501"/.510", 2400-7200 Rpm, I believe the comp number is 12-677-4. Sounds awesome and is very streetable. The carb I bought from a friend who raced it for a few years. I'm not sure of what he had it set up as, but this I believe is what I am going to do: Order a jet kit and put it back to stock and also figure out the power valve. I'm sure he was running alot more over lap and would be a considerable difference in vacuum. He also said he had it pretty rich for his SBF.
cute cam. just kidding. but if his car was running rich, you are probably running rich too unless you have a beast motor compared to his. your jetting should be 75 primary and 83 secondary for a 750 demon with a 6.5 powervalve up front. rear valve should be blocked. just get those set and work from there. a wideband air/fuel ratio meter is a great tool if you have the money. takes the guess work out of tuning.
btw, check out the link for all the factory specs. use the scroll bar to find your carb series.
cute cam. just kidding. but if his car was running rich, you are probably running rich too unless you have a beast motor compared to his. your jetting should be 75 primary and 83 secondary for a 750 demon with a 6.5 powervalve up front. rear valve should be blocked. just get those set and work from there. a wideband air/fuel ratio meter is a great tool if you have the money. takes the guess work out of tuning.
btw, check out the link for all the factory specs. use the scroll bar to find your carb series.
cool. so you are definitely running richer than him since you are not cycling as much air. i'm guessing he was not running powervalves. or at most the smallest one. good luck with the tuning.
3rd gear, I figured it wouldn't turn many RPM until it is running right.
Just getting back to the gearing for a second. Are you saying that you're turning 5800 rpm in third gear at 95 mph? With 4.11 gears, a 28" tire and 3rd gear ( 1:1 turbo 400 ) you should be more like 117 mph.
Or are you just shifting at 5800?
Just getting back to the gearing for a second. Are you saying that you're turning 5800 rpm in third gear at 95 mph? With 4.11 gears, a 28" tire and 3rd gear ( 1:1 turbo 400 ) you should be more like 117 mph.
Or are you just shifting at 5800?
I'm turning 5800 RPM at the finish line in third gear at 95 MPH. Could I have a trans problem or not shifting high enough? I'm shifting at 5500RPM. Should I go to 6000 at shifts?
I'm turning 5800 RPM at the finish line in third gear at 95 MPH. Could I have a trans problem or not shifting high enough? I'm shifting at 5500RPM. Should I go to 6000 at shifts?
A couple of observations:
5800 rpm at 95 mph amounts to nearly 20% convertor slippage. I'm no expert however I find that to be excessive especially at high rpms. There could be other factors giving you the 5800 rpm indicated engine speed. Factory tachs are notoriously innaccurate. Have you checked your tachs accuracy against another? Or perhaps your convertor is on the way out. That could explain your weak 60' times.
Others that have replyed to your thread believe your combo should be making plenty of horsepower. That to me says that 5500 rpm is not taking full advantage of the engine's capability.
Of course there's the learning curve with the new carb. Undoubtedly there's more power available with tuning. Have you considered installing the old carb for the next trip to the track?
A couple of observations:
5800 rpm at 95 mph amounts to nearly 20% convertor slippage. I'm no expert however I find that to be excessive especially at high rpms. There could be other factors giving you the 5800 rpm indicated engine speed. Factory tachs are notoriously innaccurate. Have you checked your tachs accuracy against another? Or perhaps your convertor is on the way out. That could explain your weak 60' times.
Others that have replyed to your thread believe your combo should be making plenty of horsepower. That to me says that 5500 rpm is not taking full advantage of the engine's capability.
Of course there's the learning curve with the new carb. Undoubtedly there's more power available with tuning. Have you considered installing the old carb for the next trip to the track?
I really hope it's not my convertor, it's a TCI super streetfighter that I bought it new in april and had the good 12.95 pass with it with the stock gears and edelbrock carb. I am going to keep messing with the timing and check out the carb first. Seems like an easy place to start, and cheaper.
I can always go deeper later. Thanks guys.
I still find the 5800 rpm at 95 mph unususal. Have you tried bringing it up to 95 mph without being at WOT? The Street Fighter is the same convertor that I use and it works great except the lock up clutch (I run a 700R4) went out of it a few weeks ago. If you were running a 700 I'd say it sounds like the 3/4 clutch pack is on the way out. With a turbo 400, I can't say.
You're right on track with the timing curve. What heads do you use? I find most small blocks like quite a bit of initial timing. General consensus in these forums is to start at 10 or 12 degrees. You may have to limit the mechanical advance so as not to have too much overall. My Vortec heads seem to run best with 34* total. I've limited the mechanical advance built into the distributor to 18* with the initial set at 16*.
Keep working on the fuel curve too. If you could afford the wide band O2 sensor, you'll find that it's a carb tuners best friend. I found my AFR's were getting quite lean at the top end (13-13.5:1). My trap speeds are off by 2 mph compared to last years carb so I'm sure there's more to be gained too.
I still find the 5800 rpm at 95 mph unususal. Have you tried bringing it up to 95 mph without being at WOT? The Street Fighter is the same convertor that I use and it works great except the lock up clutch (I run a 700R4) went out of it a few weeks ago. If you were running a 700 I'd say it sounds like the 3/4 clutch pack is on the way out. With a turbo 400, I can't say.
You're right on track with the timing curve. What heads do you use? I find most small blocks like quite a bit of initial timing. General consensus in these forums is to start at 10 or 12 degrees. You may have to limit the mechanical advance so as not to have too much overall. My Vortec heads seem to run best with 34* total. I've limited the mechanical advance built into the distributor to 18* with the initial set at 16*.
Keep working on the fuel curve too. If you could afford the wide band O2 sensor, you'll find that it's a carb tuners best friend. I found my AFR's were getting quite lean at the top end (13-13.5:1). My trap speeds are off by 2 mph compared to last years carb so I'm sure there's more to be gained too.
I'm running Dart iron eagles with 215cc 2.05/1.64, initial timing at about 12* and total right now at 30*. I've only made 2 passes messing with timing so I think I can pick up a tenth or two just messing with timing hopefully another half second setting the carb.
30 degrees total timing isn't much. There's certainly more to be used. I find that the more initial timing I can use, the better the throttle response is. You may find the same.
By what you've just posted, I read that you get only 18* mechanical advance out of your distributor. HEI's and most aftermarket ( with adjustable total mechanical ) have between 20 -22 degrees. Could you be missing the last couple of degrees of advance when you use the timing light? Keep in mind too that you should have all the advance in by 3000rpm.
hey i just got a 1986 camaro with a 92 v8 5.7 liter engine in it . the car was running really crappy so i had to change firing order on the car it was running alot better.. but still wasnt right about a week later i discovred the smog silinoid was disconnected from the terminal where it goes into the top of the engine also the electric was not pluged into the conponent. i did some research and found out the correct way to hook it up .. i started and drove the car about 5 blocks car seamed to be running better then ever smooth and more power . after i turned the car off and tryed to start it up the next day .. car does not start .. as u hold the exnition and pump the gas the engine gets slowly to full running speed as if its running and when i let go of the exnition it turnes off as quick as i let go ?? i also tryed removing the smog silinoid back to how i org found it still same story any suggestions ?? thanks
30 degrees total timing isn't much. There's certainly more to be used. I find that the more initial timing I can use, the better the throttle response is. You may find the same.
By what you've just posted, I read that you get only 18* mechanical advance out of your distributor. HEI's and most aftermarket ( with adjustable total mechanical ) have between 20 -22 degrees. Could you be missing the last couple of degrees of advance when you use the timing light? Keep in mind too that you should have all the advance in by 3000rpm.
I believe I found it! I was checking my timing in the garage yesterday and found that with my vacuum advance hooked up my total timing was all in by 3000 rpm and was 63*. I am doing away with the vacuum advance and putting lighter springs in my mechanical advance. I am anticipating it all in by 2800 rpm. I will be starting my tuning at 32* and start tuning from there. I think my timing way out of wack was atributing to the low rpms at the stripe and the nosing over at 1000 feet. Am I on the right track now?
A lot of racers do away with vacuum advance. Although it's not a factor at WOT (because there should be no vacuum) it will come into play when you're moving the throttle by hand and checking the timing vs rpm. You could just disconnect it while checking the mechanical advance. Personally I like the vacuum advance because it helps with fuel economy when I'm cruising on the highway.
As for being on the right track, a poor timing curve can give you all kinds of trouble. Once you've established that you have it figured out, you'll know if that was the problem.
At this point it's difficult to say if that's the only issue. The nosing over a 1000 feet could be too much advance and the engine is into detonation. It could also be the fuel related.
Keep testing and keep posting.
A lot of racers do away with vacuum advance. Although it's not a factor at WOT (because there should be no vacuum) it will come into play when you're moving the throttle by hand and checking the timing vs rpm. You could just disconnect it while checking the mechanical advance. Personally I like the vacuum advance because it helps with fuel economy when I'm cruising on the highway.
As for being on the right track, a poor timing curve can give you all kinds of trouble. Once you've established that you have it figured out, you'll know if that was the problem.
At this point it's difficult to say if that's the only issue. The nosing over a 1000 feet could be too much advance and the engine is into detonation. It could also be the fuel related.
Keep testing and keep posting.
Found a broken stud in the HEI last night. There was nothing holding the advance weight on one side except the spring. Put a light spring and medium spring in fixed the stud and seemed like a new car. Ran hard to 6500 RPM. Still leaving the vacuum advance un hooked for now. At an idle I set it at 12* at 1000 it is 20* and all in at 2500 rpm at 35*. Will be starting at 35* when I go to the track Saturday night. Thanks for all your input!
just kidding. but if his car was running rich, you are probably running rich too unless you have a beast motor compared to his. your jetting should be 75 primary and 83 secondary for a 750 demon with a 6.5 powervalve up front. rear valve should be blocked. just get those set and work from there. a wideband air/fuel ratio meter is a great tool if you have the money. takes the guess work out of tuning. 
