Mild 396 build

[Joe-JDC]

As I have said in a post here a few years ago, when I was getting my Automotive Technology Degree, I had to build an engine from scratch, and I also had to be certified in transmissions, rear differentials, front end alignment, AC, etc.  When I was in that college, I drove a '66 Fairlane with 289 4 speed.  I built the 289 with ported heads, intake, headers, etc., all the tricks, and had a 600 cfm Holley on the car because every one said it was the right size.  Ford Muscle Parts came out with their catalogs, and Ford recommended a 735 CJ carb for 11-13 hp increase over the 600 Holley on everything.  I took the 735 off my Shelby, and carried it to College and put my Fairlane on the chassis dyno.  I made pulls with the 600 and optimized everything.  Made 297 rwhp, and then installed the 735, for exactly an 11 hp increase.  It ran great with the 735, and I bought a 3310 and installed it.  Ran just fine.  The 289 can run with the best of them with a larger carb.  Geoff Mummert just finished 2nd in the EMC with a 289 SBF with what I believe was a 850 cfm carb.  I have dyno tested so many different sizes of carbs on the same engines that I can truthfully say that if the engine is efficient, and if it pulls vacuum above .5" at wot, then go next size bigger.  Joe-JDC

[frnkeore]

The following, said, tongue in cheek

So, form the advice I'm getting here, it's BAD to use a small carb (why would we use a small carb, when there are big ones out there) and it's good to use a 850DP on a stock 289, you'll get more HP in all rpm ranges.

I'm only to worry about max HP numbers and ignore the low and mid-range numbers, as your saying that they will be the same, no matter what and I can tell everyone about my big carb. Oh and don't even talk a MPG.

At least I can brag about the size of the carb that I'm using

[Drew Pojedinec]

Frank,
No one said there is anything wrong with using a smaller carb. The only thing anyone said was that there is often no negative to a well tuned larger carb.
Kinda seems like even when people say just that you do not seem to acknowledge it but go off again on your small carb opinion.

Who cares?  Original poster stated he tried a 650 and a 750, he liked the 750, so that is the end of it, he’s happy.

[frnkeore]

Drew,
My focus, right from the start, on this build, was/is a MILD street build and not a high performance engine. This engine is limited to 5200 rpm and falls off, extremely fast above that but, NOT because of the carburation. It has EXCELLENT performance, to that point though!

The OP says this, regarding my suggestion about a smaller carb:

"Yes, thought about it, however the throttle response with the 750 and single plane streetmaster intake were nearly identical to the 650 and dual plane preformer that we decided to keep it instead."

That statement tells me that there was a noticeable difference but, decided to run the 750, in spite of it.

Now, that could have been because of the DP manifold, the smaller carb or just because the smaller carb is jetted better. I don't know but, no one else does either.

The 750 is running fat on the dyno and only clears up near the max HP so, by the dyno results, how can it be said for sure that a higher velocity, optimized A/F won't make more torque? But, some say that it's not possible, at least, that's the way it was presented to me as I'm told there is no reason to try it. Maybe that's true but, then explain to me why a higher velocity, possibly better atomized  A/F mixture would produce less torque? Not to mention, that it might also produce, overall better MPG.

Now then, I appreciate Brent's expertise, skill and knowledge and I think he is one of the best builders anywhere but, I'm just as stubborn as he and if you tell me it's not so, you have to also tell me WHY, not just blow me off like, if I suggest something it's just wrong.

[winr1]

Brent

Those heads with a mild clean up and CJ valves, what cam would make the same numbers ??



Ricky.

[blykins]

Drew,
My focus, right from the start, on this build, was/is a MILD street build and not a high performance engine. This engine is limited to 5200 rpm and falls off, extremely fast above that but, NOT because of the carburation. It has EXCELLENT performance, to that point though!

The OP says this, regarding my suggestion about a smaller carb:

"Yes, thought about it, however the throttle response with the 750 and single plane streetmaster intake were nearly identical to the 650 and dual plane preformer that we decided to keep it instead."

That statement tells me that there was a noticeable difference but, decided to run the 750, in spite of it.

Now, that could have been because of the DP manifold, the smaller carb or just because the smaller carb is jetted better. I don't know but, no one else does either.

The 750 is running fat on the dyno and only clears up near the max HP so, by the dyno results, how can it be said for sure that a higher velocity, optimized A/F won't make more torque? But, some say that it's not possible, at least, that's the way it was presented to me as I'm told there is no reason to try it. Maybe that's true but, then explain to me why a higher velocity, possibly better atomized  A/F mixture would produce less torque? Not to mention, that it might also produce, overall better MPG.

Now then, I appreciate Brent's expertise, skill and knowledge and I think he is one of the best builders anywhere but, I'm just as stubborn as he and if you tell me it's not so, you have to also tell me WHY, not just blow me off like, if I suggest something it's just wrong.

I have told you why, literally in almost every one of my responses..  You choose to not listen.  You have not listened to testimony, experiences, or data in the form of dyno results. I don’t know what else I can do.

Ricky, it would all depend on how well the heads worked. 

[frnkeore]

Brent,
You have to remember that my question is two fold and not just about torque and HP.

This was the best of the answers, I was given:

So then, what your telling me, is that fuel atomization and intake track velocity has no effect on HP, either good or bad and that it doesn't need to be optimized, for best results, either in MPG or HP?

They absolutely do!  Fuel atomization and intake track velocity have effects on everything!  However, *I do* optimize it on every single engine that leaves here and that doesn't mean, in any way, shape, or form, that I have to bolt on a smaller carb to do it.   The old internet wives' tale that you have to bolt on a small carb to get good  throttle response is a bunch of bunk. 

You basically agree with me here but, add the "Wife's tail" to it and don't address why a smaller carb, would not be beneficial or at least produce the same results or better mileage, at least until it looses the ability to feed the engine.

I will tell you, based on experience, that a 750 vacuum secondary carburetor is not a detriment to horsepower or mileage on an engine such as this.   This engine is pretty much at 100% volumetric efficiency and uses a camshaft that will pull very hard on everything above it.   

I don't know if you can call the 750 optimal, either if, the engine only pulls 503 cfm. I also note the 2900 rpm 405 ft/lb is richer (where I said it stumbled) than the 3700 rpm 406 ft/lb but, the VolEff is higher than the 3700 figure. Could it be because the secondary hasn't opened yet?

I will also tell you that unless it's an extremely gross negligent error in carb sizing, you will not see any differences in average horsepower.  I'm looking at two dyno sheets right now, on a 390 that I built, where I tried a Quick Fuel 750 and a Holley 1050 Dominator. 

Does this statement include pounds of fuel, per HP?

This engine made 539 hp with the 750 and 540 hp with the 1050.   This engine was not a 3/4 ton truck engine by any means, but looking at averages between 4000 and 6000 rpm, the average HP and TQ for the 750 were 497.5 and 498.5.  The averages for the Dominator were 497.9 and 499.3.  At 3750 rpm, the 750 was making 327.1 hp and 458.1 lb-ft.  At 3750 rpm, the Dominator was making 329.7 hp and 461.8 lb-ft.   

I didn't turn a screw on the Dominator and basically just bolted it on for giggles. 

Let me say, by no means do I expect a 2-circuit Dominator to be "fuel efficient" in comparison, but your point about a larger carburetor making less average horsepower really has no merit here.

I know you're gonna say, "Well, that's a high hp, high rpm 390 and it has nothing to do with the OP's engine."  You can say that, and I will disagree with you again.

Yes

[cjshaker]

About mileage, I'd try to explain that an air/fuel ratio means there is only a certain amount of fuel used in a combustion cycle, no matter the size of the carb, and that a 600 at 12:1 is the same amount of fuel as 12:1 with a 750, but I'm not keen on beating my head against a wall. 

[Sand hauler]

First off,my intention was not to cause any animosity in discussion.second this build is simply a mild, budget build using mostly left over parts from a previous build that I knew the history of. An old racer friend of mine would have called it a junk motor ,lol . This motor was simply built as a graduation present for my 18yo son for his 3/4 ton highboy he is trying to get back on the road. The cam and lifters of course, and 3/8 push rods are the only new parts that were added. A truly low budget build using good parts ment for reliability first and balance of torque and hp for playing and still used as a truck without getting over board on max performance racing motors. It is in my humble opinion that this was accomplished am looking forward to seeing and helping him fine tune and tweak it for his needs as he gets older and more experienced in the future

[Bolted to Floor]

First off,my intention was not to cause any animosity in discussion.second this build is simply a mild, budget build using mostly left over parts from a previous build that I knew the history of. An old racer friend of mine would have called it a junk motor ,lol . This motor was simply built as a graduation present for my 18yo son for his 3/4 ton highboy he is trying to get back on the road. The cam and lifters of course, and 3/8 push rods are the only new parts that were added. A truly low budget build using good parts ment for reliability first and balance of torque and hp for playing and still used as a truck without getting over board on max performance racing motors. It is in my humble opinion that this was accomplished am looking forward to seeing and helping him fine tune and tweak it for his needs as he gets older and more experienced in the future

Amen brother.....I think you did great.

[My427stang]

Great numbers, setup is a great match, nice work. 1 hp per cid on a street motor with those heads is an accomplishment

[Sand hauler]

Thank you sir I really appreciate it