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

mustangII460 · 05-08-2005, 07:25 PM

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 · 05-09-2005, 12:12 AM

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 · 05-09-2005, 08:01 AM

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 · 05-12-2005, 03:07 AM

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 · 05-12-2005, 09:41 AM

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 · 05-12-2005, 02:12 PM

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~ · 05-12-2005, 02:38 PM

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.

05-08-2005, 07:25 PM	#1
mustangII460 Factoy Five Roadster Join Date: May 2000 Location: Sevier Co,Tennessee Posts: 1,681	Re: Back from the track....did worse than last time!! 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. __________________ Frank

05-09-2005, 12:12 AM	#2
rwhite65 Ride Hard Join Date: Oct 2000 Location: Wyoming IL Posts: 1,094	Re: Back from the track....did worse than last time!! 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 __________________ 65 Fastback 91 roller 306, H/C/I AOD-Bauman, PI Stallion, 4.10's and traction loc 04 Grand Cherokee Freedom Edition 79 Ford F-250 4x4 - Restored

05-09-2005, 08:01 AM	#3
82 GT Import Slayer Join Date: May 1999 Posts: 2,241	Re: Back from the track....did worse than last time!! 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? __________________ '82 GT 351W (.060)Comp Cams 274* Extreme Energy cam, ported & polished heads w/ 1.94/1.60 valves 10.3:1 flat top pistons,stealth intake, Mallory dizzy,Holley 750dp carb, BBK shorties,Flowmaster exhaust,C-4 with 3700 stall converter, B&M pro shifter,8.8 rear, 4:10's, subframes, electric fan, powermaster alternator, 4 core radiator.

05-12-2005, 03:07 AM	#4
HotRoddin cranky old man Join Date: Sep 2001 Location: Longview Texas Posts: 683	Re: Back from the track....did worse than last time!! 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. __________________ Under Construction: 64 Falcon 372 cu in. stroker 1:72 rod ratio 6.250" rods (long rod), Comp Cams XE274 230/236 520/526 @ .050, Scorpion Rollers, Roush 200 irons, 10:1 Keith Blacks, Hedman long tubes, 750 Holley DP, Edelbrock Victor Jr., C4 3500 stall, gears and tires to be anounced.

05-12-2005, 09:41 AM	#5
Dark_5.0 Registered Member Join Date: Apr 2001 Location: Staging lane Posts: 4,337	Re: Back from the track....did worse than last time!! 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. __________________ 92' LX-Big brakes, Lots and lots of suspension, GT40X heads, Ported cobra intake, stock cam, Vortech SC trim. 00' Lightning-Stock 88'CRX-13 second ego killer

05-12-2005, 02:12 PM	#6
82 GT Import Slayer Join Date: May 1999 Posts: 2,241	Re: Back from the track....did worse than last time!! 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. __________________ '82 GT 351W (.060)Comp Cams 274* Extreme Energy cam, ported & polished heads w/ 1.94/1.60 valves 10.3:1 flat top pistons,stealth intake, Mallory dizzy,Holley 750dp carb, BBK shorties,Flowmaster exhaust,C-4 with 3700 stall converter, B&M pro shifter,8.8 rear, 4:10's, subframes, electric fan, powermaster alternator, 4 core radiator.

05-12-2005, 02:38 PM	#7
~The Jester~ Rat Killer Join Date: Aug 2002 Location: Cold ass Ohio Posts: 1,143	Re: Back from the track....did worse than last time!! 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. __________________ d-Con Racing "Nothing fancy, just 347 inches of RAT POISON!" MICE need not apply.....

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