Took the Barracuda to the track today for first time

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v8fish

v8fish

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OK Guys and Gals, took my total street barracuda to the track today and need some suggestions.

67 Barracuda, 360/904 3.55 rear 3000 convertor .509 cam, headers 3" exhaust dumped at rear axle 3" dynomax mufflers. Stock bottom end running 93 octane pump gas. 750 double pumper Holley, 3/8 fuel pick up and line to carb running Holley blue pump set at 7 psi. Drag radials hooked with no tire spin.

90 degrees 70% humidity.

During entire run there is no missing, noise or surging, no electrical cut in or out. Heres the thing. during burn out engine revs to 6400 very quickly in 1st and 2nd gear. lanched at idle pulled 5500 in first was not making any power past that shifted 2nd and it would barely pull 5000 RPMs it went flat shifted to high for 13.5 @ 100mph.

2nd pass left off idle short shifted at 5000 again it strugled to pull 5000 in 2nd gear and ran 13.46 @ 101mph.

60 ft is 1.89 on both runs I know it needs more gear and convertor but that is the trade off for the street. I am thinking it is not getting the fuel later in the run although it never acts like it is running out of fuel. It pulls smoothly the whole way just struggles to RPM in the middle of the track. ANy suggestions appreciated.
 
What static compression? .509 is a somewhat big cam if you're on the low end I would think. Is it the MP .509?

During burnout you have no load, so naturally it will rev freely. But under acceleration in higher gears the load is pretty high, so that's when it will fall on it's face if cranking compression is inadequate.

Other than that I'd say check your timing curve?
 
You could be anywhere....

Jetting, fuel pressure, clogged fuel/air filter, valve spring pressure, check fuel pressure regulator, use a nice high end regulator. I would tend to not use those holley units that come with those blue pumps. Can you try a 650, I'm sure it would have better throttle responce. Wheres the timing at?

Does the engine combonation match? Intake, heads, cam, compression, cylinder head flow, converter and gears, car weight?

Do you have any dyno information? What were you expecting?

In the water box just about any engine can pull higher rpm. Theres really no load compared to being in high gear at the top end of the track.

Don't foreget about corrected altitude, 90 degrees and 70% humidity I'm sure put its pretty high. If your running tall drag radials with 3:55's your 360 might not have enough torque to pull the higher rpm with bad air. Where does the rpm drop to after each shift, maybe your falling to much and the converter is slipping. You want that converter to multiply the torque.

What shape or how nice is the converter? could the sprag in the converter broken/cracked - not letting it pull the higher rpm. There is a big difference between a $400 converter and a $1200 converter even if there a low stall unit. I'm not saying you need a $1200 converter, just there is a performance difference.

Just in general, do the brakes have alot of drag..

Maybe get on http://www.wallaceracing.com/Calculators.htm punch in your numbers and see where your at. I'm not sure how much faith I would put into those calculators but...

This one has been pretty good too. The equation I use is 1320 / MPH = optimum ET
 
Isn't a 750 DP carb kinda big? I run a 650 DP on my 340 with .505 cam, M1 MP intake, 4-speed, 4.10 rear, my engine loves to rev with this carb and I have a stock fuel pump, no fuel issues and great throttle response.
 
i have no idea what is the problem except maybe you hurt the valve springs (what kind are they and are they matched to the .509"?) going to 6500rpm during the burn out but you need to stay out of 1st gear doing a burn out or you can hurt your tran's sprag.
 
Maybe you need jet extensions on the secondary's, might be uncovering the rear jets.
 
70aarcuda said:
check jetting in carb....valve springs???
Click to expand...

I agree and will add, fuel delivery issues or possible ignition problems.

If it's dieing under load, sounds like fuel to me.

That should be a solid 12 second ride with a 101 MPH not pulling above 5K. It's likely missing 3-5 mph. 60' is pretty darn good for first time out.
 
From what it sounds like it just didn't have the stones to keep accelerating in high gear, which tells me cranking compression is really low.

If it was fuel delivery, it would stutter and miss in high gear, which he says it didn't. Hurt valve springs would show itself in the burnout box as well as high gear.

If it was mine, I would do a cranking compression check. If they all show low, drop down to a .484 cam or one of the 340 grinds, and possibly swap to a thin gasket or even get the heads cut .050. Even a low compression 360 can be deep in the 12s with the right pieces...
 
Sounds about right for the parts you listed.
 
It may be pig fat too.

If it won't pull up top, roll out of the throttle a little and see if it picks up. Not chop the throttle just a little. If it picks back up, it may be REALLY fat. Make sure it's not sloshing fuel, blowing any black smoke. Make sure all the setting are correct, float, idle mix, initial timing/total timing. Is the jetting stock or changed from holley factory settings?

I've had 9:1 360 with 484/509 cams run a lot better than 5K with a similar set up and it wasn't any 13 second car. There's a reason it shuts off at 5K and won't pull.
 
If he actually has 9:1, yeah I'd agree it should be ok.

Mistakes are made all the time, especially with cheap import engine parts and budget builds. Even original parts can be pretty far out of spec.

I recently helped a friend in a similar situation...his 440 was supposed to be 8.2:1 (with NOS cast pistons for '76 440) and after a lot of head scratching we measured and it turned out to actually be 7.1:1. Was a stock rebuild for a New Yorker except for a hp cam, and that thing barely got out of it's own way and struggled to reach 75 mph.
 
Thanks for the ideas I will start looking into it and see what I can find. I will try the cheap/easy stuff first. Jets, timing and comp check.
 
We have never had any problems using the Holley blue pump on motors up to 700 HP with the pressure set at 6-6 1/2 PSI. I kinda scrolled thru fast and didnt catch what intake, the rpms sound like a dual plane intake.
 
Our fuel bowls on our barracuda with a 750 were very sensitive. I had to run them a touch to high. Everyone who looked at them said something but thats what worked. Just a touch not alot. Esp. in the rear!!! With or w/out the ext...
 
That's not bad quicker than most 50k vettes
I see at the track
A little tweaking and a different intake
You'll be in the 12.50/60's
I would agree sounds like a fuel issue.
Nice car
 
SOrry it has been a while. Cracked back wins the prize "Pig Fat" it is. The carb had been modified by previous owner seems it is a modified 850 DP. After pulling several plugs they are severly fuel fouled. Bought a 650 DP today at a swapmeet to rebuild and try. Hope for lower ETs soon.
 
What cracked said. Running out of fuel, or as the load increases in 2nd, ignition not up to it.
 
Maybe take the bowls off your 850 and see where it is jetted. Look on the holley site for stock jetting.

Make sure you have a good timing curve in the distributor. Try 20-22 initial and whatever total you need all in by 2200-2500. The idle may be REALLY rich too with that cam.
 
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