1000cfm of carb on a mild 302?

zookeeper · Aug 26, 2005

Since you've got some experience with 2x4's, I've got a question: most of the 2x4's I've seen use the rear carb as the primary carb and remove the choke assembly from the front. Does it matter which carb is the primary on a dual-plane manifold? The only experience I have with 2x4's is on a blower and it ran straight linkage and two 600 cfm, vacuum secondary carbs and it ran fine. It actually got 14mpg, believe it or not! Did the center-squirt carbs have a bog or flat-spot off idle?

brianj5600 · Aug 26, 2005

I see no reason for multiple carbs on the street other than appearance, period. The plenum and runners must be comprimized to accomodate A/F coming from different places at idle and WOT. Once upon a time there where no such thing as performance carbs capable of flowing enough air, so the flat head boys used multiple carbs. The 2x4s pictured earlier are alot nicer looking than my lonely dp, but... If you wanna go fast, get an up to date intake with an up to date carb. If you want wow factor and don't mind giving up some performance and drivability, get 2 or 3 carbs. Two 500 cfm carbs is not too much as long as they are vacuum secondaries. Vacuum secondaries only open up to the point that intake vacuum can opens them, and those look cool!

1320stang · Aug 26, 2005

The only experience I have with a street driven 2x4 setup was on a '68 Chevy Impala with a Tunnel Ram and a pair of 1850 600's. The carbs had the equalization tubes removed and the holes plugged. Everything else has been dual race carbs, 660's, 850 DP's, 1050's, 1150's, split Dom's.

My 660's are stock with no modifications and had no bog or flat-spot, it was like turning on a light switch, BAMMM!!!!

I agree with Brian's first couple of sentences, as far as the going fast part, if we're talking street driving, with occasional jaunt's down the 1/4 and decent milage when your off the throttle, I've got no problem with that. If you don't care about mileage or tickets and know how to make radials stick, the performance of a proper multi carb package can't be beat. The thing is, I don't condone street racing or testing on the street, but if you drive your car to the track, kick some GM tail, then drive home, that's great.

My race 289 with '69 351w heads ran 11.0s with the 660's. With ported Canfields, a Funnel Web and a Pro Systems carb it's run 11.90's. Now the first was a Jerico and the second, an $1800 PA C4, but I don't think a race C4 is worth 9/10s.

10secgoal · Aug 27, 2005

1320stang said:
Now the first was a Jerico and the second, an $1800 PA C4, but I don't think a race C4 is worth 9/10s.

Wrong size stall ? Hell, if I thought for a sec I could get .9's out of a stick....sorry :OT:

Ronstang · Aug 27, 2005

brianj5600 said:
I see no reason for multiple carbs on the street other than appearance, period. The plenum and runners must be comprimized to accomodate A/F coming from different places at idle and WOT. Once upon a time there where no such thing as performance carbs capable of flowing enough air, so the flat head boys used multiple carbs. The 2x4s pictured earlier are alot nicer looking than my lonely dp, but... If you wanna go fast, get an up to date intake with an up to date carb. If you want wow factor and don't mind giving up some performance and drivability, get 2 or 3 carbs. Two 500 cfm carbs is not too much as long as they are vacuum secondaries. Vacuum secondaries only open up to the point that intake vacuum can opens them, and those look cool!

Blah....multiple carbs can be great. Want to put a single 4bbl on an engine of equal specs except the 48IDA Webbers on mine? I would blow you away....and with ~1700 cfm.

zookeeper · Aug 27, 2005

I agree that multi-carbs can be both neat to look at and functional. I've had too many streetbikes with one carb per cylinder to be told otherwise. If I were to believe everything I read here, I'd think that weekly carb adjustments were the only way to get ANY Holley to run at all, nevermind trying to get two of them to work! I will admit that it's probably not the easiest route to a streetable motor, but like I've said before, if I wanted easy, I'd buy a Toyota. Yes, multi-carbs big appeal is the visual aspect, but can't the same be said about vintage Mustangs in general? Think about it, they aren't nearly as functional or as practical or as economical as a Hyundai, so why bother? Why not just act like a zombie, buy what everyone else has and live our whole lives without having to get dirty or think about ways to make our cars work better? I say screw that, do what YOU like and prove everyone who ever told you it won't work wrong.

1320stang · Aug 27, 2005

No, the stall is right, or it should be right, it's a $500 JPT converter (I think it's JPT), I know after shelling the previous tranny, getting this one redone, we could have bought a $900 bolt together Neal Chance converter and been done with it. First car was a 3000# '69 R-code Mach I and this car is a 2900# '68 coupe, both with cages and subframe connectors. The tune is right, I think it's somewhere in the chassis setup as the former car has been a drag car for years, whereas the latter is a street legal car, although it hasn't seen the street for about 3 years.

We're using less gear, but we're using what my chassis guy told us to use, he's worked on both cars so.....

D.Hearne · Aug 27, 2005

brianj5600 said:
If you want wow factor and don't mind giving up some performance and drivability, get 2 or 3 carbs.

I challenge you to come down here, drive my Ranger with it's three carbs, and tell me it's somehow missing something. There are NO drivability issues with them, period. Nor is it lacking in performance. Just dumping the clutch and nailing the gas at the same time will tell you that, or let it out slow and putt along, either way they work as well as anything else out there. And as I've said previously, they need no constant fiddling with to keep them tuned. If thats the case, they weren't tuned correctly to start with. Only someone who's never satisfied with something, will keep fiddling with something like this till they get exascerbated and swap them off for a single carb, and I can guarantee them then, they wouldn't be satisfied with that either.

Mr_Merciless · Aug 29, 2005

If the motor is 9:1 why not put a huffer on it? Or a Novi supercharger? Stay away from Nitrous only good for 15 seconds at a time and refils are a pain. Forced air is free. However what is the crank made of? Cast, forged or billit? My gues is it's stock and this will cause you to drive over it if you really try to put the power down.

iskwezm · Aug 29, 2005

Mr_Merciless said:
If the motor is 9:1 why not put a huffer on it? Or a Novi supercharger? Stay away from Nitrous only good for 15 seconds at a time and refils are a pain. Forced air is free. However what is the crank made of? Cast, forged or billit? My gues is it's stock and this will cause you to drive over it if you really try to put the power down.

what makes refills a pain and who says its only good for 15 seconds at a time????Hold the button as long as you want,Since when is forced air free????The kit alone is gonna run $2k+ so technically its not free and nitrous is more cost effective for the power.I ran nitrous for many years on my dd truck to my quad and sea doo,its never been a problem to me

DarkoStoj · Aug 29, 2005

I have some world windsor sr. heads lying around I'm going to throw on it, and with those heads I'll be at 9.5:1 compression.

I was thinking of running a comp cams 282 solid flat camshaft dur 236@.50 .578 lift with 1.72 rockers and a 110 LSA

victor jr intake with a speed demon 750 mech secondary carb.

How would this combo match up? I have a tremec 3550 so I don't have to worry about the stall.

When I have more time I'm going to throw on a 150 cheater since I have it sitting on the shelf just waiting

also, the bottom end is a stock crank thats been turned with eagle I beam rods and TRW forged flat tops. How high can I safely spin the motor without having to worry about going booooooooom

D.Hearne · Aug 29, 2005

Mr_Merciless said:
If the motor is 9:1 why not put a huffer on it? Or a Novi supercharger? Stay away from Nitrous only good for 15 seconds at a time and refils are a pain. Forced air is free. However what is the crank made of? Cast, forged or billit? My gues is it's stock and this will cause you to drive over it if you really try to put the power down.

Ditto, the AIR is free, the FORCED part will cost you. As for the crank material, that part of the equation is moot, the failure will be the block or the main caps, not the crank, unless it's one of the early 50 oz/in units. Those are the only ones I've seen that had a tendency to break.

Hissing Cobra · Aug 29, 2005

Ronstang said:
Blah....multiple carbs can be great. Want to put a single 4bbl on an engine of equal specs except the 48IDA Webbers on mine? I would blow you away....and with ~1700 cfm.

I agree. Both my twin brother and I run the dual quad setup on our cars ('79 Cobra/'85 GT.) We both made over 300 rear wheel horsepower and both of our cars run in the 12's. They are both very streetable and behave excellent on the daily cruises and trips to work. We did it for the "WOW" factor but have also managed to have respectable times in the quarter mile too.

If you persevere, anything can be done. Ours are tuned to perfection and are right around 12:5-13:5 on the air/fuel on the dyno readings. This is on 93 octane with no detonation whatsoever. The key to our combos is the removal of the chokes from each carburetor (who needs them if you're not driving the cars in the winter?) and the elimination of the crappy progressive linkage. We run a straightened rod from one carb to the other so that when we're cruising, each carburetor is working on the primary side. We're cruising around on 4 barrels but it is NOT a problem. During wide open throttle, the secondaries open at the same time. There are no lean spots during the transition.

Here's a couple of pic's.

Here's my dyno graph and some timeslips.

zookeeper · Aug 29, 2005

Nice motors! It looks like you're running Edelbrock/Carter carbs, so I'm guessing you're running 500cfm carbs? Also, you're using straight linkage? That would sure simplify things for me, but have you modified the accelerator pump squirters? How much compression and what cam are you using? I'd appreciate any info you'd care to provide.

Hissing Cobra · Aug 29, 2005

zookeeper said:
Nice motors! It looks like you're running Edelbrock/Carter carbs, so I'm guessing you're running 500cfm carbs? Also, you're using straight linkage? That would sure simplify things for me, but have you modified the accelerator pump squirters? How much compression and what cam are you using? I'd appreciate any info you'd care to provide.

Thanks! Yeah we're both using the Edelbrock 500's. Our intake manifolds are different as he's got an old school Offenhauser and I've got a new Edelbrock unit. We both run 1" spacers under each carb too. We both bought calibration kits for each carb and tuned them religiously until they were just right. We then went to the dyno and both carbs were right on the money. Mine actually ran too rich in the upper RPM range so I leaned it out jet size on the secondaries and that brought it up into the 12:5 range. The guy at the dyno was pretty impressed.

My cam is an Elgin Pro Stock solid lifter flat tappet camshaft. It's numbers are 238 INT/248 EXH @ .50 and 536 INT/560 EXH. It's slightly larger than my brother's (I'm not too sure on his specs but I know mine is the next size larger.)

Our heads and compression are different. I use AFR 185's (58 cc's) that are right out of the box with no porting. He uses '69 351W heads that he's ported/polished and added bigger valves. My compression is 10:8:1 to his 10:3:1.

Guess what? Even though I have more cam, compression and heads, his made more power than mine and is faster in the quarter mile! I made 307 rwhp to his 311 rwhp. My torque is 279 to his 287 and my quarter mile times are 12.70's-12.80's @ 107-110 to his 12.50's-12.60's @ 107-109.

Anymore info that you need?

retro50 · Aug 29, 2005

Hey Hissing! Your cam is not 238int/248 ex at .050. It is 248Int / 258 Ex at .050. The lift was correct though. My cam is the earlier specs you posted with 238Int-248Ex@.050 .512-.536 lift. I agree the dualquads work pretty good and look mighty impressive. I've had mine on the road for 8 years now, and i've never had a problem with them. I once tried a Edelbrock Victor Jr. on the same engine (no other changes) with a 650 c.f.m. double pumper Holley. What a sorry combo that was. I lost all of my low end torque and it was LAZY for normal driving, At wide open throttle it was great though. That was the only thing it was good for. I didn't have enough motor under that combo to really take advantage of it. By the way the pistons in both motors are K.B. 116 Pop-up pistons with .200 domes. Darkostoj: I say give it a try you have nothing to lose. At the worst it will cost you a little bit of labor to swap it out and some new intake gaskets.

Hissing Cobra · Aug 29, 2005

Thanks Bro!

10secgoal · Aug 30, 2005

Mr_Merciless said:
If the motor is 9:1 why not put a huffer on it? Or a Novi supercharger? Stay away from Nitrous only good for 15 seconds at a time and refils are a pain. Forced air is free. However what is the crank made of? Cast, forged or billit? My gues is it's stock and this will cause you to drive over it if you really try to put the power down.

Who's going to use any power adder for more than 15 seconds straight ?! Maybe an import with 20psi running in the quarter. Any power adder is bad for any motor for that long. It's the added cylinder pressure that comes from and added HP that causes problems. All this crap being thrown around by non nitrous users gets just a little old. Nitrous is more expensive in the long run anyways.

I guess each motor is different Hissing5.0. He is just going to have to test each setup at the track. I have the same heads as you. But a dual plane intake, and a hydr. roller cam with 224 @.050 and .542 lift. The compression is only 9.2-.3 to 1. But runs a little harder in the 1/4. I also tried the victor jr, that intake was just too big. Was great after 3800 though. Duals do look kinda cool though.

race-rodz · Aug 30, 2005

agreed... NO2 is more expensive in the long run.... figure $35 to fill bottle, so after 70 or 80 bottle refills... your going backwards from what the supercharger and related componets cost.

i will take my power adder on the easy payment plan of $35 a refill... thanks

Bullitt · Aug 30, 2005

HissingCobra, are those HP numbers through an auto?

seem low for a combo like that.

definetally can't argue with your ETs and MPH though.

1000cfm of carb on a mild 302?

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