[steve25]

I agree that like you posted , you shot yourself in the foot either way those 3.7 gears and only that size cam.

The motor is reving thru the motors torque cradle too fast.

[ebartone]

Originally Posted by Stan Weiss

Can you post the dyno sheet? A WAG would be, you should be shifting at a min of 5600 RPM and crossing the finish at 5600 RPM or higher.

Stan

PS Can you also post a before and after time slips? Also how much different was the weather between these runs?

Hopefully that worked. This was the first (engine dyno) run. Did a little better in the next few runs, HP topped at 5,200

[ebartone]

Originally Posted by PONTIAC LARRY

small block mentality with a big Pontiac , my old 68 GTO automatic TH400 on column and the original 2.93 Safe Track on 26x9.5x14 Hoosier QT Pro DOT on 14x7 Rally 2's with my also 10.5:1 iron head 462 cid with just mild flat tappet hyd cam .465 v.488 lift 224/234 @050 LS 112 , iron 68 intake , 800 Qjet , iron HO exhaust stock 1972-1978 style Carter mechanical fuel pump..... sticking the car on the launch with a stock 13" converter and shifting at 4900 RPM went 12.6@109 even got into the 1.8 60 ft .. Ya got too much gear for a mild Combo and flying past your torque curve therefore your not "riding the torque train" as I like to refer it. Think like ya got a diesel and dont over speed the rpm of the engine that can't really breath and let it stay in the torque curve thru the run in the midrange , no reason it cant run a little quicker than the 3.36 did but since its already changed to 3.70 the other way is a tall as tire change from what ya got or stick some big ass KRE heads on it and a bigger cam

This is great, thanks! Turns out the smallest I can get on there (per Strange) is 3.54 - But seems an improvement. Great post, thanks!

[ebartone]

Originally Posted by GOAT8U2

Steve C
What tire and pressure?
What launch rpm, 4200?

See above
MT Street Radial Pro 275/60/15
Trying to Launch just off idle, say 1,200

[GOAT8U2]

Gotcha E but......

My question was for details on Steve's 1.5s 60ft.
If he's running a 4200 stall converter he's most likely not doing an idle stomp and flash and he was on slicks so that gives him an edge over Radial Pros but some comparison.

Since you're 485hp and 590tq you got a nice 12 sitting in there for sure even at say 4000lbs.

[Formulas]

Could it be possible he should re'visit jetting ? I am not implying gearing effects jetting but more RPM'S means more air pumping and if fuel delivery or A/F ratio is marginal to start with then it would be aggravated with more gear?

Secondary air flaps fully opening ? = top end extension

Qjet dashpot functioning properly not leaking?

The 60" loss seems to me shouldn't be happening with full traction and .4 gear change

[Half-Inch Stud]

The DYNO power says 10's. Go back to 3.31:1 posi. See signature. There must be a fuel problem (maybe the timing backed-off?).

Get a fuel psi gauge. I missed top end mph?

[ebartone]

My top MPH went from about 108 last year to about 104 this year. This carburetor was rebuilt by cliff, and I’ve had zero problems with it, I’m pretty sure everything is opening properly, and I have verified the full plates open when foot on the floor. again, I know there are thousand things that could be wrong with an engine, but I think my case is simple because I’m only comparing where I was last year, to where I am now with the gearing change. At least that’s what I think. I have the Rob Mick 550 hp fuel pump.

[ebartone]

Originally Posted by Half-Inch Stud

The DYNO power says 10's. Go back to 3.31:1 posi. See signature. There must be a fuel problem (maybe the timing backed-off?).

Get a fuel psi gauge. I missed top end mph?

I like the signature, actually that’s pretty helpful. It gives me hope! 😁

[Benziii]

Originally Posted by PONTIAC LARRY

small block mentality with a big Pontiac , my old 68 GTO automatic TH400 on column and the original 2.93 Safe Track on 26x9.5x14 Hoosier QT Pro DOT on 14x7 Rally 2's with my also 10.5:1 iron head 462 cid with just mild flat tappet hyd cam .465 v.488 lift 224/234 @050 LS 112 , iron 68 intake , 800 Qjet , iron HO exhaust stock 1972-1978 style Carter mechanical fuel pump..... sticking the car on the launch with a stock 13" converter and shifting at 4900 RPM went 12.6@109 even got into the 1.8 60 ft .. Ya got too much gear for a mild Combo and flying past your torque curve therefore your not "riding the torque train" as I like to refer it. Think like ya got a diesel and dont over speed the rpm of the engine that can't really breath and let it stay in the torque curve thru the run in the midrange , no reason it cant run a little quicker than the 3.36 did but since its already changed to 3.70 the other way is a tall as tire change from what ya got or stick some big ass KRE heads on it and a bigger cam

This is great, thanks for the info.

[OCMDGTO]

You need to video rear tires at the track to see if you're spinning. When I was setting my car up my 60 went from 1.70s to 1.90s. New converter and trans and it went down in the 1.60s.

[indymanjoe]

I talked to ebartone earlier today and does anyone think this air filter could be an issue?

https://www.summitracing.com/parts/edl-43662

[Steve C.]

For interest only....

Your 1/4 ET is 11.59 seconds and 117.61 MPH
Using vehicle weight of 3900 pounds and HP of 495

http://www.wallaceracing.com/et-hp-mph.php


.

[65 Lamnas]

I didn't see in any of your posts where you mentioned your fuel system or your fuel pressure. You HAVE TO have an adequate volume of fuel to a Q-jet.

[ebartone]

Originally Posted by 65 Lamnas

I didn't see in any of your posts where you mentioned your fuel system or your fuel pressure. You HAVE TO have an adequate volume of fuel to a Q-jet.

Thanks, yes Rob Mc pump at 7 psi.

[ebartone]

Originally Posted by indymanjoe

I talked to ebartone earlier today and does anyone think this air filter could be an issue?

https://www.summitracing.com/parts/edl-43662

Thanks Joe, I’m picking up a 14x3” Wix element tomorrow to try next time out, that’s a great idea. Again, though, pre gear change I was seeing hig 12s, so I know it’s capable. But I do notice that the top end of the track I seem to be gasping for air, so I think this is definitely worth trying. Thank you!

[65 Lamnas]

Originally Posted by ebartone

Thanks, yes Rob Mc pump at 7 psi.

I guess I should have worded it differently….

What is your fuel pressure during a pass?

[ebartone]

Originally Posted by 65 Lamnas

I guess I should have worded it differently….

What is your fuel pressure during a pass?

I don’t have a way to know that, however, I can tell you that there is no feeling of starving for fuel, no stumbling, etc. but I do not have a fuel pressure gauge that I can monitor while I’m making a pass.

[scott70]

To lose 2/10s in 60ft. and lose 4 mph in the 1/4 mile is a lot . You’ve lost it on both ends. Hard to believe only going from a 3.36 gear to a 3.70 would affect 60 ft so much and to blame it all on the gear change. And you went with a taller tire which would have cancelled out some of that gear change. Something else has to be going on here. Is that new rear end robbing horsepower compared to the other rear?

Also you might not feel a complete loss of power at the other end but still be running out of fuel. For the heck of it you can hook up a temporary fuel pressure gauge to see if you’re dipping below 4 psi or so at the other end. Not saying that’s your problem, but it’s always nice to know that information.

They say going from a c4 trans to a c6 robs about 20-30 hp just because of the internals.

[ebartone]

Thank you, Scott, and everyone else for the ideas. I do agree with your post, though, it does seem to be a lot just to blame on a gear change. I’m gonna work through a few things for the rest of the summer such as finding a way to measure fuel pressure, and changing out this Air filter as Joe suggested. A few other things as well, thank you everyone for the tips! I really appreciate it.