Guess The HP & Torque Contest

[lovehamr]

AL, I don't see how you can get that number from that calculator without using a silly low VE. I plugged in 427ci, 6200rpm, .9 VE and a mod carb = 845cfm. If I use 1.0 VE then I get 939cfm. Granted your motor may never reach 100% VE but to short it that much right from the get-go IS going to cost you HP. I'd lay $$ on that. In fact, going back and looking at the graph, I was being generous when I said that I thought the engine would nose over at 5800. Using those same #s it looks like it'll run out of carb around 4250rpm. I say 4250 because the graph shows it using 606cfm @ 4000 and 681cfm @ 4500.

[AL427SBF]

Agree if you use those VE and RPM numbers, if you come down to .85 VE and 6000 RPM you get a different picture. All of this warrants an explanation from my engine builder, I need to undersatnd his size selection criteria.

[Zoom This]

Gotta agree with the 650 carb combo. I went thru two 850 Holleys before going to a 650 Barry Grant Mighty Demon on my 418W. I lost 15 hp on the dyno but gained back 19 lbs. of torque thru the mid range and greatly improved throttle response. Nice trade as far as I was concerned. My motor is very much like AL427SBF 427 with the exception of extensive ported and lightly polished Victor Jr. heads and Vic Jr intake on a flow bench by Neil Ruegsegger, Danville, CA. On an Eddy current dyno I put out 478 hp at the wheels with the 850 Holley.

[lovehamr]

Zoom, when switching from Holleys to th Demon, did you ever try a larger Demon?

[DAVID GAGNARD]

Originally Posted by AL427SBF

Agree if you use those VE and RPM numbers, if you come down to .85 VE and 6000 RPM you get a different picture. All of this warrants an explanation from my engine builder, I need to undersatnd his size selection criteria.

Holley's own formula, basically the same as the one you posted is simple:
cubic inches X max. rpms, divided by 3456, multiplied by the VE......
assuming 90% VE and 6200 rpm max, your engine would be pumping 689.43 cfm's of air thu it..the general concencus is to have a carb capable of 50 cfm flow more than your max...so you would need a carb capable of flowing 739.43 cfm's or a 750 carb.......the 650 will work, and you'll have tons of low end torque and great off-idle response and if that's what you want, then you'll get it, but you'll be giving up in the upper rpm range......

a well built engine should be in the 95%+ VE range......

The 331 stroker I built in my garage had a VE of 96.04% at 6000 rpms on the dyno,at 3500 rpms, it was 90.98% and steadily climbed thru the rpm range to a max of 96% and I'm no great engine builder by any stretch.....

David

[olddog]

As I understand it, the intake manifold can make a difference. A lot of factory dual plane intakes seal to the carb in the center. Therefore each bank of cylinders can only pull through 1/2 the carb or two barrels.

When the plenum is open under the carb, each bank can pull through all four barrels. So depending on the intake design, an engine can pull more or less cfm through the exact same carb, with more being with an open plenum.

[AL427SBF]

All good input guys, thanks. I've emailed my engine builder and expect the root of it all lies with the trade of top end performance vs. low end torque and throttle response. That education is coming so stay tuned.

[JustOne]

You never replied to the question about asking if the heads were CNC ported or are out of the box. Which is it? If the heads aren't CNC ported, don't bother putting the engine on the dyno. Either swap them out or send them off to be ported before completing your engine build. Judging by the parts list, you are spending a lot of money on some high end parts, especially the bottom end. Heads and cam are the two components in this package that creates all of the power, do not spend a fortune on your motor and let those two pieces hold you back. The cam sounds a little small, and I would suggest that you will want to change it out if the motor does not meet your power goals. So, just change it now and since you are buying a carb, go ahead and get an HP 950 and then if you don't like it by, a second hand vac secondary carb off of Craig's List or e-bay, cheap.

Non ported heads and current Cam 485 hp / 510 tq
Ported heads and current cam 535 hp / 540 tq
Ported Heads and bigger cam 589 hp / 545 tq

J

[AL427SBF]

I think "Zoom This" summed it up pretty good, he found "his" solution the old fashion way, by experimenting. (I'm glad our motors are very similar). The Willy's 62502 (650 CFM HP Carb) can flow way in excess of 650 CFM (like upwards of 750) and has been put on SB's near 427 CID (slightly less) making 650 HP. I spoke to Willy's today and also got a call from my engine builder, they are both in sync with that carb being a real good selection for the 427.

Regarding CNC ported heads, what the engine builder says he has done is match the intake port to the heads. If that's another way to say it fine, if not - then I think what he has done is all that needs to be done for this build 'cause I'm out of money! I will say this, he has done a ton of measuring, balancing, honing and fitting with almost every moving part on this motor.

[DAVID GAGNARD]

Your going to have a great motor, no doubt. The talk of needing a larger carb was that your motor will see it's full potential with a slightly larger carb. I'm of the school that more often than not, people over carb their engines, we just think in this case you could use a little more carb to see the engine's full potential.....
But it all depends on what your looking for in the engine and what type of driving you will be doing.....
All in all, I think you'll be happy with your engine.......

David

[AL427SBF]

I agree, and full potential means different things to different people. This thread started out as a peak HP and torque discussion (@ 6200 rpm). Now I realize that was one dimensional thinking on my part. I bet most people assume the full potential of an engine is the highest HP and torque numbers you can achieve near redline. A better question would have been guess the HP and torque at 5252 rpm, where both plots intersect empirically, and always within a very narrow +/- range of the 5252 rpm level (real world). But now I wouldn't even ask that question, to me the full potential of an engine is the highest average power you can achieve over a usable rpm range like 2000-6000. Take the areas under those curves with different carbs, and then pick the one with the largest area under the curve. That to me is ringing out the full potential of an engine and over the usable 2000-6000 rpm range. I don't want to get into which you weigh more, HP or torque, save that for another discussion (but I like torque). Anyway, I bet the carb that gives you the greatest area under the curve in the 2000-6000 rpm range is not the carb that gives you the greatest peak power near redline. Don't know if that makes sense to you, but it does to me. Who wants to tackle throttle response and how that should weigh in on your carb decision?

[Gaz64]

All very true, especially for a street car.

500 ftlbs at 3000 with 400 hp at 5000 will provide a more driveable package than 400 ftlbs at 5500 and 500 hp at 7000.

[lovehamr]

Well dang AL, you changed the rules half way through! Also, if the modded carb will flow 750cfm rather than the stock 650 then that is the flow rate to use in calculations. As far as TR goes I'd have to say that you'll probably have all that you can use with your combo.

But if you are that big of a fan of torque then you shoulda' gone with a BB!

Sorry, couldn't help it man! O'course I could be a little biased...................

[Dominik]

I scolled up and down: Was the exhaust system mentioned?

While your area under the curve from 2 to 6000rpm is a concern, you can compensate for variations be shifting up differently.

So you actually want the biggest area in the rpm range you drive.
Which might very well be 2.000 to 6.000, same as me!

BTW, must we guess because Gessford built it ;-)

[Zoom This]

Originally Posted by lovehamr

Zoom, when switching from Holleys to th Demon, did you ever try a larger Demon?

I didn't try a larger Demon carb, although the carb expert who has raced with Demons since they were first on the market did say that an argument could be made for a 750 cfm carb, but the 650 will give better torque numbers. The miles per hour at the end of a 1/4 mile would be a little less with the 650 compared to the 750, but the 650 had a better chance to win the race based on all other things being equal due to better midrange torque. Afterall, that is what wins races....torque.

Bill

[greg schroeder]

my guess

512 HP
470 ft lbs

[JustOne]

I don't want to sound negative, but I do not think that having the heads port matched is nearly as good as a full cnc porting. You had asked the question as to how much power the motor would make at 6200. If this is where you want your motor to peak you will either have to have the Vic jr. Heads cnc ported, not just gasket matched or change to a different already ported head such as an AFR 205 or 225, or better yet a TFS High Port.
As is your combination will most likely peak around 5600-5700. If you are happy with this and this is what you asked for when having the motor built, then you will be very happy with a very nice piece that will serve you well. If you intended to get closer to the 600 hp number, then only a couple of items need to be changed or modified, and it is easier to have this done now then when the motor is in your car.
I have made a lot of changes to my set up, and I wish that I could have put it on the dyno the first go round instead of doing it later.

[AL427SBF]

Gary, finding the torque vs. HP vs. RPM sweet spot - that's what it be!

lovehamr, yep I did change the rules, I made it a more value-added exercise I don't think the Willy's is a modded carb, more like Willey's bending the rules to the max. extent possible. Just like the 12 Metre "America's Cup" racing yachts, you see how those boats have changed over the last decade? - they still have to conform to the 12 Metre class specs. As for torque, I like it early but it all evens out later with HP. Yeah your BB has a slight torque advantage but I get that back with less weight

Dominik, SS headers and MASTERTOUCH sidepipes, see bottom of page. As for the last part, you would be absolutely correct!
MASTERTOUCH327.COM

Bill, torque is greatly underrated in my opinion, the mission is to overcome Newton's 1st law.

JustOne, you're probably right about the cnc porting - but it's all mute because I'm out of money The 6200 peak power question has been superseded by a more refined approach to this -
(max area under the torque curve from 2000 - 6000 rpm) + [.9 x (max area under the HP curve from 2000 - 6000 rpm)] = perfect carb size