Small Block HP - How Much?

[terry lee]

Last Saturday I ran into a guy with and EM Cobra, and we started talking engines and HP. He told me that his 302 put out 540HP, was very streetable and ran on pump gas, no bottle. My only comment was: you must have one hell of a cam, and got an affirmative nod. When he cranked it up I sure didn't hear what I thought was an engine putting out anything close to his claim. No big cam lope. Question is; is it possible to get that kind of power out of a 302, and keep it together? I know there is alot of BS out there, just curious if his claim could be accurate.

[Andy Dunn]

He might of had 540HP, but generally I think the engine would of been much louder than normal with an aggressive cam and minimally restricted sidepipes.

Here is a tech article on a 12.5:1 607HP 306. The keys are always heads and cam. The heads need to flow into the 300s on the intake. If you dropped compression to 11:1 and retarded timing, you would be in the low to mid 500s.

http://www.totalengineairflow.com/te...dermonster.htm

If I was a betting man, and I am I'd bet your EM buddy does not have 540hp.

[Brian Dinsmore]

I have to say if I had a dollar for every guy that says [and thinks] he has a 500 hp engine I'd have a GT40 by now.

I would have to think that the hottest naturally asperated 302's may make 475-500 at the crank. Maybe. And trust me you would know it had a cam in it.

Perception is Reality.

Reality is that I'm sure he thinks it makes 540 h.p

It dosen't! But then that just my perception.

HAPPY HOLIDAYS!

Brian

[coyled]

At 300 cubes with no nitrous, blower or turbo, 540 hp can be done. You would here it in the cam and pop from the compression. It would sound nasty, so I doubt its 540hp. Scott

[wtcobra]

"very streetable and ran on pump gas" and I bet he stayed at a Holiday Inn Express the previous night.

[B L & sons]

540 HP sure I believe hem.just not 540 HP all at the same time

[Bill Wells]

wanna bust his cherry...tell him to put it on a chassis dyno, pick a parasitic loss number, say 17% which is commonly used. tell him then that 540 engine hp would equate to 448 rear wheel hp using a 17% loss figure. if it gets 448 or higher you pay for the dyno (here about $125 ), if it is less, then its his lesson and his cost .! that will pick the flycrap out of the pepper and most likely humble him severely. saw this done once, laughed my butt off as the rwhp was woefully short of what the guy 'claimed' to have in the engine ! b

[RACER X #99]

Small blocks with that kind of HP sound real nasty and idle around 1,500 rpm. As much as I like sb Fords I am also realistic. Pump gas,very sreetable, no power adders, 540 HP I don't think so.
I have heard 475 HP 289's run with open headers and they are the loudest and nastiest motors you ever heard.
My $1.00
Cranky

[jayem]

I run a supercharged 289 with 8 lbs of boost, a 512 lift cam &
ported & polished heads with large valves. 390 hp, 440 lbs
torque. I wouldn't believe 540 hp. Jay

[Fred Douglass]

...the old adage that "there's no substitute for cubic inches"? There seems to be a lot of expertise on this site and you tend to agree far more often that, let's say, a panel of economists! Some article, years ago in Hot Rod said, numbers being equal on paper, (i.e. torque and hp), 450 hp form 450 cubic inches was a heck of a lot more grunt than that wrung out of 350 cubic inches. "Horsepower" v.s. "Ponypower", in other words.

Reading this, I assumed it was felt that the power from the big-cube motor arrived earlier than in the (necessarily?) higher-revving, more highly stressed motor. I thought the power data was equal, if it had the same numbers, it had the same power. Another article, in Motorweek, extolled the virtues of freer breathing, more radical cams, larger valves, etc. in smaller engines...and that power thus derived was IN NO WAY less real than that derived from big cubes...what say ye wise men? I would be very interested, as I'm leaning toward a "square" engine with c. 418-427 cubes (Dart block) ....

[Brian Dinsmore]

For Cranky,

289, open headers, 7000 rpm

http://www.norcal-cobras.com/videos/MVC-001V.MPG

HAPPY HOLIDAYS!

Brian

[scottj]

Fred,
Not necessarily a ye wise man but, if you want to go square with a Dart block why not a 447 (4.155 x 4.125)? I stay at 434cid (4" stroke) since efficiency and reliability are already compromised with the 434 combination. When over 400cid, the 4.030 bore isn't really an option by my way of thinking, for efficiency reasons.
Scott

[Excaliber]

Fred,,,interesting points there. Not unlike a recent thread concerning "rpm build time". Two motors being "equal" but ONE builds rpm faster than the other, thus finishing the 1/4 in a quicker time. Generally a short stroke builds rpm faster.

NOW,,,my guess is a BB will HOLD onto that power LONGER and EASIER at the same rpm when compared to a SB? Fascinating,,,,,

Of course we all know SB's rule when the smoke has cleared.

Ernie

[Richard Hudgins]

Originally posted by scottj
Fred,
Not necessarily a ye wise man but, if you want to go square with a Dart block why not a 447 (4.155 x 4.125)? I stay at 434cid (4" stroke) since efficiency and reliability are already compromised with the 434 combination. When over 400cid, the 4.030 bore isn't really an option by my way of thinking, for efficiency reasons.
Scott

Hi folks,

Another option is to go quite a bit oversquare such as 4.155 x 3.5 for a resulting 380ci. This will keep piston speed at 8000 in the 4600 fpm range. This speed is quite liveable and rod lenghts are very good, etc.

With proper heads and cam profiles, you could have a motor that would give you an effective powerband from 3200>7500 that would live forever. (A subjective term)

In addition, the combustion chamber area ratio would quite good and flame path and timing would allow a fairly high CR that could run on pump gas.

I would guess that 550 hp and 500 torque would be quite realistic with these sort of numbers.

Maybe Andy D. (The Butcher) could run some numbers on his trusty desktop dyno.

After all, current F1 motors are 3.8 x 1.85 10 cylinders for 3.5 liters and they produce 800 hp at 18,000. 5500 fpm piston speed with seriously exotic materials. Power band from 8000 to 18,000 is really cool.

[scottj]

Richard,

What you recommend is a very popular combination in dirt Late Model right now. It has the right amount of torque to get off the corner without blowing the tires off like the 434's will. The big motors need to have gear taken out so they hook up and then they don't have the acceleration on the straights. The 380's can use allot more gear and with an ultra-light rotating assembly, out accelerate the bigger motors once traction goes away. The ONLY reason I run 434's is because early in the night, when the track is hooked-up, they qualify better.
In dirt Late Model tune the 380 turns 5000-9000 rpm, 15:1 comp. 1.75:1 rod ratio, and makes about 800hp and 650ft/lbs.
If I was going to build anouther Cobra motor it would be a detuned 380.
Scott

[Mark Husar]

We have taken delivery of a 347 stroker built by a firm in L.A.. We run a roots with 8.0-1.0 compression and worked heads. The build sheet shows 410 hp with carb, 510 with 12 lb. boost and 625 with max boost. We couldn't get into the 500 range without help.
Mark

[jmarsey]

Just to give you a real example, My 331 made 548 hp - 455 torque @ the flywheel on 105 octane. Peak hp @ 7200

Basic specs:

solid roller / not radical
Roush intake with 750 cfm
Yates heads fully ported to my combination
R-302 block
0-balanced rotating assembly
10.5:1 compression
Major work with windage & oil pan

There is another 100 hp in this motor if I up the carb, cam & compression. 650 hp would be max for these heads naturally asperated. By the way, I would not call this a street motor.

I have 18 to 20k in my motor and as you can see, naturally asperated, a 302 starts to push the envelope at the 550 range.

[aumoore]

My 302 is a stock explorer long block with stock GT-40pheads, trick flow stage one hyd roller cam, edelbrock performer rpm intake, Holley 600 vac secondary and the Hunter 4 into 1 headers. On a chassis dyno it put out 267hp and 285 ftlbs to the rear wheels. If you use a conservative driveline loss of 15% that is 315 flywheel hp and 335 ftlb's at the flywheel. There were several aluminum head motors at that dyno day and There was a 289 that put out just under 280 hp to the rear wheels. The Stroker motors were running from 300 to 313 rear wheel hp.

A 540hp 302 with no power adders would sound like a late model dirt track motor or a drag motor. It would make a terrible street motor. Now a 460 could make 540 and be pretty docile but even then you would know it is not stock.

[SSSnake]

My 331 is just on the edge of streetable. It had a rather flat torque curve for the cam size and a nice lumpy idle. .545 lift, 234 duration at .050. The heads are slightly ported world products. It made 415 hp at 6200 rpm and was still making over 400 at 6800.

jmarsey
That 331 must be a real screamer. I could only imagine how that would sound through some open pipes

Glenn

[cobrashoch]

Freddy - Roughly speaking when the power curves and the torque curves are identical on a engine, they will run exactly the same, (straight line) assuming they have identical bob weights and the same rods. Makes no difference the size block you use, or if it's a Ford or a Chevy or whatever. Of course I am speaking in a broad sense, and that's exactly why I am big on supercharging. It's the best and cheapest way to add cubic inches without changing the bottom end dynamics of a engine radically. That is very important on lightweight cars like Cobras especially.
There is something to the revibility issues mentioned above on engines, but it has more to do with drivetrain geometries and blue printing mechanics than the size of the block. In a broad sense they run the same, unless you change to a turbine or change the fuel you use, or do something else radically different.
cobrashock