Well I built it. Hot Rod Magazine had a build up in the May 2000 issue for a 380 HP 351W.

I followed the "recipe"
351W .040 over
Comp Cams Magnum 280H - Straight Pattern Grind, 230 Degrees at 0.050 and 0.512 inch lift
GT40P Heads with Stainless Valves and High Lift Valve Springs
Edelbrock Performer Intake Manifold & Carb
Ford Duraspark II Ignition
And I threw in Roller Rockers for grins.

The cam degreed in right on top and I measured the push rod length for the new hydraulic lifters.

Dual Exhaust is thru Ford Motorsports headers and 2-1/2" tubing to a set of Cats and Cherry Bombs. (Sounds real good).

This was a new motor build up and calculated compression ratio was 9:1

According to the Dyno run in the article HP peaked at 380.7 at 5500 RPM and Torque peaked at 395 at 4400 RPM.

I installed the engine in a 1980 F100 along a C6 with a B&M Transpak and a 3:50 /1 ratio 9" Rear and took it to the Chasis Dyno.

I was surprised that the HP and Torque curves did not even come close to the article.

Chasis Dyno showed peak HP at 222.1 at 4300 RPM and peak Torque at 293.8 Ft/Lbs at 3500 RPM.

Torque builds quickly to near peak at 2100 RPM and stayls relatively flat up to 3500 RPM where it starts to drop off.

Even considering parasitic loads from accessories and loss thru the Automatic, I still think I'm about 100 HP Short and 100 FT/Lbs of what I expected.

Does anyone have any ideas of where the HP went?

Thanks in advance
Jerry Tomasello
Crosby, TX

 

I am a novice at best but my first question reading your article was how much compression did the article in hot rod state. Yours was estimated at 9:1 how much was the articles? This would make a bit of difference. Where your dyno is located versus where their dyno was located could make a difference such as height above sea level etc. Another question arose what did the fellow (person who dynoed your motor) think when you give him the specs and then he dynoed it, if he is a good engine builder his impression would be a good measure of the end result. If you have the money throw in a higher stall not too much higher next step up and some numerically higher gears (3.73:1) and see what happens, not trying to insult you I am sure you have already thought of these things, they woudl increase the output but not help solve your problem neccessarily, sorry to hear about it maybe you will figure it out good luck sounds like a good street motor if it is at it's peak in power unless you figure out the hangup then it would be very nice good luck again keep posting if you figure it out I myself am qurious to the answer

 

JW

According to the article they used stock pistons. In fact this was a junk yard pull and they only did the upper end modifications as listed.

I think the original compression ratio was advertised at 8.3:1, but the Ford GT40-P Performance Heads have a 50cc combustion chamber which is much smaller than the stock heads. According to my copy of Desktop Dyno the calculated compressions ratio is 9:1.

Also I believe that all Dyno results are corrected to sea level.

Jerry Tomasello

 

This might sound dumb, but did you factor in hp loss through driveline, loss through an automatic trans? I am sure most dynos can give you net hp and gross engine hp estimates... Do you have both figures?
Mark

 

Mark

According to the Dyno Guy, you can figure about 15% loss for a Standard Trans and about 17% to 20% loss for an automatic.

At worse tht would put rear wheel HP at 380 X 80% or 304 HP.

Still quite a bit above the results I got.

Jerry Tomasello

 

One thing your probably over looking is that the magazine probably dynoed there motor on an engine dyno with open headers and only a waterpump. There can be a major loss upwards of 20% when you add in an exhaust system and accessories (fan, altenator, power steering). This would bring your 380 HP down to: 304 HP, then another 20% for your auto tranny: 304 becomes: 243 HP.

There can be large differences between an engine dynoed with open headers and no accessories and the same engine in a vehical with all the accessories and a full dual exhaust dynoed on a chassis dyno.

I wouldn't be too dissappointed with 222HP at the wheels, the 351W was only rated at 149HP (at the flywheel) in 1980.

 

CC

According to the article they Dyno'd the 351W with 3" exhaust flowing thru Flowmasters. So I know there will be some difference there.

Excessory loads on my engine would be Water Pump, Alternator, Power Steering Pump.

Thanks for the comments

Jerry

 

>JW
>
>According to the article they used stock pistons. In fact
>this was a junk yard pull and they only did the upper end
>modifications as listed.
>
>I think the original compression ratio was advertised at
>8.3:1, but the Ford GT40-P Performance Heads have a 50cc
>combustion chamber which is much smaller than the stock
>heads. According to my copy of Desktop Dyno the calculated
>compressions ratio is 9:1.
>
>Also I believe that all Dyno results are corrected to sea
>level.
>
>Jerry Tomasello

I'm not sure if this is the problem, but the GT-40P's have 58cc chambers, about 2CC less than a non "P" GT-40.

 

JW

Sorry. I mis-typed on my last response.

According to the data I got from Central Coast Mustang the GT40P Heads have a 59cc Combustion Chamber. This is what I used in Desktop Dyo to get the compression ratio.

Thanks
Jerry Tomasello

 

Were your number corrected for altitude and atmospheric conditions? I suspect there's were.


Bear tracks

 

Like Beartracks is suggesting, I think there's a lot of big numbers being blown around these days because of false input into the dyno. You have to adjust for current atmospheric conditions. Humidity and temp are the main factors, with humidity being the most crucial. All readings are supposed to be corrected to sea level at some specific barometric pressure ( 28.something, can't remember anymore ). It's easy to fool the dyno by inputting false numbers ( worse than they really are ) and out comes a big corrected number. A chassis dyno is very different than an engine dyno. It measures power at the rear wheels which is greatly reduced because of loss through the transmission, u-joints, and differential, no to mention all the accessories and exhaust being connected. 200 plus horses at the rear wheels doesn't sound that bad. Compared to a questionable figure from a magazine ( refered to as comic books in the engine building trade ) buildup, I'd say your okay.

 

I've seen just about every dyno trick
used to make the engines owner feel like
he has more power than reality, and the
magazines are the worst. Temp, humidity,
barometric pressure all contribute to
making power, not correcting for any
one of these factors, you have more power.
I chassis dynod a car i owned a couple of
years ago, in the middle of winter, made
good hp/torque, I rebuilt the engine with
more compression/bigger cam/more carb/better
heads/headers, and made a total of 15hp more,
in the middle of summer...

Bates

 

Great post, very interesting. But something still seems odd. From the parts listed one would think that that motor should make more power at the wheels that it dynoed at. A friend of mine took his 1999 Ford Expedition with a 5.4L (all stock) to work with him (works in the wind tunnel testing at Ford) and has access to a chassis dyno and Ford rates the motor at 260hp at the flywheel, his dyno pull posted 212hp at the rear wheel. The 5.4 is a great motor but its running through manifolds, single 2 1/4" exhaust with cats, very restrictive intake track. Your motor should post at least 255hp at the rear wheels. Was there many others getting their motor dyno'ed along with you? How reasonable did their results look? I dont know, put some more miles on it and take it back and run it again.

 

I'm no expert, but here goes.

Your torque peak is a little low in rpm range for such a big cam. And the horses should be at a higher rpm too from my thinking.

Didn't hotrod use an rpm intake/carb? Not much diff anyway from my experience. But 10-20 horses adds up fast, especially where your cam will want them in 4500-6000 range.

You have a lot of cam for as low rpm as the peaks are suggesting. I'm thinking you might have a little problem either with the combination or with the heads themselves. Weren't they designed for the 302? If so they will lack the port volume for the extra cubes to breath as well as they should. Did you port the heads at all? Just opening up the pockets and gasket matching the intakes can make a huge diff.
How is your timing set up? Did you change the advance rate? What about jetting? Were you right on or a little rich/lean? How many miles do you have on it? If it's brand new you will be getting a huge amount of friction from the rings/cylinders until they get worn in, unless the machine shop used very fine stones on the walls. Even then, I would put some miles on it and tune it. If you got 600 carb try a bigger one. Play with the combination a little.

I still think somethings wrong with the combination. I know that fords usually like dual pattern cams. If I'm not wrong comp says to use more compression with that cam and a lot of carb/head work if you can. I would expect to see a peak hp in the 5500 range with that much duration.

About the drivetrain. Is the tranny new. They have to wear in a little too. and the good ol c-6 is notorious for sucking 50-60 hp to turn. Add in 5 hp for the driveline itself. 15-20 for the ring and pinion. Do you have big meats on it? Seems like 4x4 or one of those mags dynoed 35's against 31's and found 15-20 hp less with the big meats. Add all that up and 100 hp is gone easy. That still leaves you with an honest 300 or so. Still seems a little weak to me.

If it was mine I might buy one of those cheap cam/lifter kits from summit with about 224/230 intake/exh duration and similar or more lift and try that. I know it doesn't make sense, but if you play with the desktop dyno or any other dyno you will find that sometimes smaller cams make huge torque increases with little or no loss in top-end power. That usually means you need better heads and/or more compression. That or try working the heads over. (Not that hard I've done plenty for other people and my own. Just buy a couple good porting books and go slow and easy with the right tools.)

Lastly If I remember right Hotrod ported their heads or used another head to make over 400 hp....Maybe they had an ace up their sleeve. It's not hard to make good hp when you have top pros turning the wrenches and putting in every trick they know how to do. Icing the intake is a good trick. So is spraying a little nitrous into the carb stack when the dyno is pulling.

 

JROCCO


One question I have is what did the fellow that dynoed your truck think? If you gave him your engine specs and he was pleased with the run then it is probably on track even thought the paper doesn't correspond. And something else to consider if you add in say 3.73 or 4.11 gears it will bring the torque figure up and put you in your rpm range real fast, as well as adding a higher stall these things would be icing on the cake. Do you have access to a engine dyno maybe it would be a different story? My brothers s-10 blazer with a 468 dynoed at 470hp and 520torque on an engine dyno yet he only ran a 12.89 in the quarter and it is all due to the 3.08 stock rear he is running at the moment throw in a 3.73 or higher and I will almost guarantee a second off that time. Good luck if you have set it up correctly and everything is in order then you should be fine, just isn't the same when you don't get what you are looking for on paper. If you figure anything else out please post I am interested in your dilema again if you have time ask the fellow who dynoed your motor what he thinks cause he should have a good idea of what to expect. Good luck, I reread your original post I bet that truck does sound good through the glasspacks as it should have a slightly rough idle.