ok I have a 66 that the G-tech pro says turns 14.5 best. I heard someone on here say the g-tech is way off without traction is that true? ok heres my combo so far, suggestion are greatly apreciatied
motor:
1977 truck 454, stock long block.
edelbrock performer intake with a 750vac. sec
HEI ignition with a MSD 6a box and super coil
full length headers with 1 7/8 primaries.
2.5inch pipes with flowmasters.

driveline:
th350, 13in corvette converter ,2300stall
light shift kit
10 bolt rear with 3.08 posi gears.

any suggestions are greatly aperciated. I dont want to go to a really low rear gear. cause the car is somewhat of a comuter. I need topend speed.
thanx
Justin Mciver

Nitrous plate system.
Harley

Justin, the way I see it, whether you hook up or smoke the tires, your 1/4 mile ET is your ET. If you cant gain traction, then plain and simple youre car cant run faster than what you're clocked at.

If you mean, the GTech doesnt know when to start timing your ET; then the answer is that all it takes is a small forward jolt to start it. Unless you are purposely doing a standstill burnout, the GTech will be doing its thing right.. and if in doubt, then do your burnout before the run.. also you must average together 3 or more runs to really get an accurate reading.

Since its such a relatively late model stock/smog engine Id say your heads are probably holding you back a bit.. are they peanut (small oval) port? I bet they are.... Most people think the large oval port heads are the best for all around street use...

im not sure on this one but your exhaust system sounds a little small at 2.5"..(for a 454)

other than that Id say get some Mid 3.XX gears in there and that would help quite a bit..

Mike Reeh

Justin, I haven't played around with the Gtech yet, soon, but my friend tried it on his Camaro and I beleive it's way off. Maybe he did something wrong, I don't know. He did have allot of wheelspin.

Justin, it's simple the 3.08's gotts to go to get you into the 13's.

how much top end speed will I loose going to a 3.55 or 3.73? right now the car cruzes at 3k RPM doing about 80. I make 400mi road trips frequently. I would like to keep up my speed. lower gears and a TH400 would that keep the MPH up

t400 wouldnt make a difference. its still a 3 speed like the t350 with a final drive ratio of 1:1.... if you want over drive you'd need a 700r4 or 200-4r (or 5+ speed manual)..

id say build up the motor first because with a 454 you should have the power for a decent holeshot and be able to keep the high rear gears... thats my opinion though

Mike

I think the motor needs work. Maybe a cam, or some head work. That should bump things up a bit. Considering you have a stock motor that is. I would say use a Comp Cams 280H, that would help a bunch. Your car already has a good foundation.

You don't necessarily need lower than 3.08s to get into the 13s but for that heavy truck you just might have to.
My 64 EC runs very consistant 13.5s at 103-105 on my G-tech with 3.08s.

Your biggest problem is big block weight in a heavy truck with a light rearend. Unless you get traction, a lower gear will cost you even more time. I was running 3.55s in mine but my et's were slower due to no traction in 1st gear.

------------------
Long time Chevelle fan and an owner since 1973 :)

Justin, I've got a '70SS with a 454 from a '77 pickup, like you. As Mike said, the heads are peanut-ported. These bigblocks were designed to haul big loads (i.e., torque). The head need to be replaced if you're serious about racing.

Regarding your rear gears, I changed my 3.31 open-differential to a 3.73 posi and cut one second off my ET (now mid-13's). Yes, it adversely affected drivability on the interstate, though not to a great degree. Since I only race and cruise, and my Chevelle is not my daily driver, I was fine with the change. But if I was on the road alot, I'd stay with the 3.08's and to hell with worrying about ET's. Sounds like you've got yourself a very nice car, even if it doesn't beat everything at the track.

With 3.73's ( yes it's comfirmed ) I run 2500 rpm at 55mph and 3000 at 65. But torquey BBC's don't mind a high gear as much as SBC.

Stock long block. There in lies the 1.5 seconds I believe you'll gain if you switch to non peanut port heads ( stick with ovals though for your rpm range) and replace the stock cam with a mild hydraulic. That's allot of stuff but it should power you into the 13's.

Well I got to play with my "shared" Gtech last night. My 67 ran a 13.60 with stock 325/396 ( well almost), 3.73's, drag radials and a Muncie. Not bad if it's right. The 427 should bring me into the 12's. That was only one run, so I'll have to play somemore. Mike's right, one datapoint won't run. You need an average. I don't know what my friend did wrong, but with the BFG's at 30 psi, I don't have much wheelspin. Right know the Gtech says my stock 396 Chevelle is faster than his 509 Camaro with T400 and 3.73. Not likely.

OK this is my edit. I read your other post in performance. I agree with Mr. Bill. Well I always do he's a professional and 100 times more knowledgable than I. I run those BFG Drags on my '67 and I spin very, very little on launch ( with a little throttle finesse), so maybe that is the key. Do you break them loose when you launch?

I mean my litlle 396 only puts out 400, maybe 425, but I'd easily take a "greater" combo becasue I can get it down to the "tarmac". And my front springs are too stiff and my shocks suck for weight transfer.



[This message has been edited by Gene Chas (edited 08-03-99).]

I have a set of really stiff front springs too. wouldnt give em up for hte world. makes a huge difrence in corners. I guess Im just wanting too much huh? I dont have the money to get the best out of all the performance areas. thanx for all of your replies. .

Gene Chas
big blocks dont mind a higner gear? isnt 3.31 lower than a 3.08?
thans again
Justin

Justin, I have the same dilemna with my front springs. The old girl does surprisingly well in corners. ( new bushings all the way around too).

I meant to say that BBC are more "forgiving" with high ratios ( low numerical ) than the less torquey SBC. I wouldn't go any more than the '73s I'm running.( my dream is a Richmond with 3.31s!) Oh, and this is quite relevant, my rear tires stand 27.5" tall. That's pretty tall, which cuts things down. You could always put some really squat 235/50's on and effectively lower your gear ratio.

But what about the spin question? Are you melting 'em on launch ? This seems to make a big dif with that Gtech.

BTW, who said 14.5's are bad?? I mean if you didn't have 13's to look forward to and to work towards what would be the fun of it!
Eventually, you'll want fresh heads and you can do the heads/cam then. No big shakes. Until then, enjoy your ride!




[This message has been edited by Gene Chas (edited 08-04-99).]

thanx for all of your guys help.
right now im running a very tall tire. its a 295 50 15...so when I buy slicks I should try and get the smallest diameter possible?

Yeah. It may look funny, but what you're doing is effectively reducing your rear ratio. The BFG 295/50 ( nice size tire BTW)are 28" tall. That's pretty big. So your 3.08 are really working like a 2.73 ( or less!) would with a normal size tire. It's like my 3.73's behaving like 3.31's or 3.55 because of my 27.5" tire.

With that size tire your final drive ratio is very, very tall. Great for cruising. El sucko for rippin'. You've got a 13 sec engine. I now know it doesn't take a "rat"ical BBC to do 13's. But your final drive is hurting you pretty bad. Dont believe me.Use Wes's equations in tech reference and check it out yourself.

[This message has been edited by Gene Chas (edited 08-04-99).]

ok I think this is all making sense to me now. I can get a 3.55 and they would run like 2.23? sounds good to me. then I can have some small slicks and rip at the track. thanx for your help.
Justin

Justin, if you did the math it means a 10% reduction in your final drive ratio. Your 3.08's become 2.73's and so on. 55's become 3.20, etc.

I used my G-Tech to test the times in my '71 GMC Sprint (original LS5). It is completely stock appearing, except for stock-size radial tires. It ran a 13.7 @ 107 at 5000 feet altitiude. Corrected for altitude that would be a 12.95 @ 113 at sea level.

I recently took a different car ('68 Buick) to a real track. I ran the G-Tech and compared its times to the track time slips. The G-Tech was very consistent. It reported two tenths quicker and two mph faster than the track in *every* run. This was in a slower car with little or no wheelspin.

This shows that the G-Tech would be a good tool for checking the relative perfomance increases/decreases after modifications.