Back from the track....did worse than last time!!

[82 GT]

Well...last time at the track I ran a 13.47@104mph with a 60' time in the 1.9 range.
Since then, I recurved my dizzy, installed an underdrive crank pulley and swaped my carter 600 for a holley 750 vac. secondary.
Tonight, I was running consistant 13.8's with trap speeds at barely over 100mph(100.81)!!
My 60' time were only in the 2.01-2.1 range.
My friend says my rpms sounded lazy for the first 60' and then picked up very well after that. I had no tire spin.
I experienced some detonation in 3rd gear and back the timing down a couple degrees....same results.
I think my secondaries are coming in too quick but I forgot to bring the different springs for the secondaries.
Since my mph was down, that means I lost hp somewhere.
What happened? I though the Holley would really make a huge difference but instead, I think it hurt my times.
What do you think is wrong? I have yet to install the stealth intake. Is it possible that the performer intake in even more of a bottle neck now that there is a bigger carb or is it in the adjustment of the Holley somewhere?
This thing should be running 12's by now and I'm high 13's now. I was sooo pissed I felt like putting a FOR SALE sign on the car tonight!!!!!!!!!!!!!!!!!!!

[mustangII460]

Honestly, I think the 750 is too big.

Go back and re-jet the 600, or barrow a 650 and do the same.

Im sure you went lean when the 4 barrels opened.

Run it that way and see what happens.

[Dark_5.0]

You lost about 30-40HP somewhere to drop 4mph.

When I got my car back together with the Canfield heads I went to the track and ran a best of 13.65 @98.6mph. I was really pissed the car ran great no missing or nothing.

I parked the car for two weeks. I had decided to remove and sell the crappy Canfield heads and put my ported stockers back on cause it was faster with them.

I removed my throttle body and guess what, the #4 injector was unplugged.

I went back to the track and ran high 12's @105-107mph.

Hopefully its something you are overlooking.

You need some dyno time. I sometimes use my G-tech as a tuning tool.

[82 GT]

Originally Posted by mustangII460

Honestly, I think the 750 is too big.

Go back and re-jet the 600, or barrow a 650 and do the same.

Im sure you went lean when the 4 barrels opened.

Run it that way and see what happens.

At first, I thought maybe the carb was too big but I checked the plugs and they had no indication of running too rich.
When I had the carter...I was running dangerously lean.
I'm getting a stealth intake soon and getting rid of this junk performer intake. I'm being told that the 750 is creating an even bigger bottle neck for the small intake.
I'm switching intakes first and going from there.
Besides, my friends mustang has a very similiar setup as mine with the exception of a solid lifer cam grind and 4800 stall converter and he ran low 12's with this same carb.

[~The Jester~]

750cfm should be fine bro. I'm thinking like you are, that the intake is getting flooded, and can't get rid of the air/fuel charge fast enough.

Like Dark said though, check all the stupid stuff again. Float levels, vacuum hoses, etc etc. One time we went from a single plane intake, back to a dual plane. Couldn't figure out why the car was OBSCENELY lean. Had the biggest jets we owned in it, still lean. Then we remembered to re-check the float level. Swithing intakes changed the angle of the carb, and the back float was waaaaaaay too low.

The Devil's in the details, bites my butt alot too!

[BLACK85GT]

I would think you need at least a Performer RPM to let that 750 breath. The plain performer is not much bigger than the stock one. My car was running 13.70 at 102 with the 302 non roller motor, ported stock heads, performer rpm, holley 600 vac. And this was with 3:08 gears.

[StockRustang]

WAYYY to big of a carb.

like someone said already, performer isnt much better then the stock intake, you'd be better off with an airgap and a 650, same setup i run on my new motor im building with a .512 comp cam.

[82 GT]

I don't understand why people think a 750 is too big for a 351w with several mods. If you read my setup, you will see that it's a 351 and not a little 302.
I agree that's it's probably too much for the performer intake but not for the entire setup.
Remember, you can go with a lager carb with a dual plane intake since the cylinders only ever see half the carb. at any one tiime as opposed to a single plane design where the engine will see the entire size of the carb.
When I install the steath intake this week, I'll know better what's going on.

[mustangII460]

Rarely have ever used a carb bigger than a 700cfm on any smallblock no matter what the mods were.

My favorite carb as of now is the speed demon 650. We've gone well over 400 Hp with them. 302's 351's .

A simple guess doesn't work. There is too many factors is choosing a carb. Heads, cam, intake, compression, ignition curve, etc.

Adding a too big a carb is the single biggest mistake most hot rodders make. Ive seen this over the last 20 years Ive been building these airpumps.

Simply having camX or intakeX, headsX does'nt mean you need carbX. Your motor will only pump so much air. Adding a bigger CFM carb won't make it pump anymore. Re-jetting a carb is king.

This topic always starts a debate. "NEVER take my word on anything, search google instead." [quote of the year]

Put the carter back on and run it. Change the carb to the 750 and run it. Better yet get a 600-650 and put a bigger jet in it, I bet your time will improve. That being said, all other things must be equal.

[rwhite65]

I think you can make the 750 work good for your set-up. I do not really think it is too big, but I do agree that jetting a 650 could be very benifitial also.
Ryan

[82 GT]

Hey guys, this might be a dumb question but where does the vacuum port on the back of the Holley go?
Right now, I just have it plugged. Does it NEED to go somewhere?

[HotRoddin]

I totally disagree with the 750 being to big, back in my time you could buy two 4 barrel setups straight from Ford for use on a 289 ... The most potent per cubic inch car I ever owned was a 406 with a Ford Factory 3 2bbl setup (950cfm), and I was personally involved with a 427 cammer that ran right at the NHRA national record with 2 dominators, thats 2300 cfm. So if a 750 is waaaay to big for a modified 351, then none of the three motors I just mentioned should have even run.

I'm not saying the 600 won't work, but i still think if you get that thing running like its capable of, then way out on the top end you're going to be approaching the edge of the envelope for a 600, you aren't going to get the top end push from a 600 that you would from a 750, with your combo.

Bottom line IMHO the size of that carburetor isn't what is keeping you out of the 12's, you should be able to get there with either of your carbs.

Keep tuning man, you'll get there
Rod
PS: as to that vac port, if you don't need it, plug it.

[Dark_5.0]

My brothers heavily modded 327 punched 60 over runs way better with a 750 than with a 650.

The jetting of a carb is crucial. I have seen cars drop 5 tenths when they get the carb jetted right.

[82 GT]

Yeah, I'll ge there but it won't be until I get that stealth intake on.
Hopefully, I'll have the stealth on soon. There isn't much I can do, as far as tuning, that I can do until I get that on there.

[~The Jester~]

I had a STOCK 302 shortblock (other than a Lunati cam) from a truck in my car. Vic Jr. intake, iron heads, and a 750 cfm Holley with the Proform main body. And the car wanted MORE fuel! Borrowed my buddies 850 and the car picked up. IMHO The intake is the problem here, not the carb.

No, the vacuum port on the back doesn't HAVE to go anywhere. You're just fine with it plugged.

[82 GT]

Indications so far suggest I may need to jet up the 750

[Dark_5.0]

Originally Posted by 82 GT

Indications so far suggest I may need to jet up the 750

More than likely you need to jet it down IMO.

[tarmon8r]

Have you thought about the recurved distributor? Personally speaking, I have made that mistake on my MSD distributor. Had to much timing, after i first installed it. Time slowed up big time. Scratching my head, my buddy forced me to retard my timing, cause that was the only thing i changed. Times went back to what it should of been, it was over a .7 sec difference in 1/8 mile if i remember correctly, maybe more. Sounds like too much timing to me.

[82 GT]

There is no sense in making any adjustments until I get the stealth on there.
DARK 50, Actually, I might need a different shooter size.
If my car stumbled off the line, like my friends says it did, it would indicate it need a larger shooter or the secondaries are coming in too soon.
One the highway, at 3000rpms, it pulls hard.
I can't test a standing start on street tires or it results in instant tire smoke. I have to wait until I'm back at the track with the slicks on again.