351w Build. how many horses? - Vintage Mustang Forums
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post #1 of 15 (permalink) Old 03-25-2019, 05:49 PM Thread Starter
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351w Build. how many horses?

Good day Gentlemen. just wanting to share my set up with you all and get your thoughts on HP/TQ figures. Don't have the motor build yet, most of the parts are on the way! from everything iv'e heard and read i should be a easy minimum of 400hp and 430tq to the crank. would be a lot happier if those numbers were at the wheels. what do you guys think?

early 80's 351W

keith black pistons. 030 over. dome with two valve reliefs. head volume(-5.00cc)
RPM air gap intake
Comp cam - 35-246-3. intake lift(519) exhaust lift(523) Intake duration at 50 is (230) and exhaust is (236)
heads are cast D80E heads i believe. They are fully ported and have 190 160 valves.
Compression should be around 10.5 to 1 when i'm done.
flowtech shorties.
not sure on which carb yet. any suggestions would be great.

and of course theres a few other things that can effort power a bit like efficiency in rockers, exhaust and such but i was just basing off the critical stuff. let me know if i'm missing something obvious. haha

what will this setup get me in ponies?
Thanks

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post #2 of 15 (permalink) Old 03-25-2019, 05:55 PM
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I think you'll be shy of 400. More like 380.
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post #3 of 15 (permalink) Old 03-25-2019, 06:06 PM
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Those heads have pretty large combustion chambers. Expect compression ratio to be slightly under 10:1 depending on how thick your head gaskets are.
I estimate about 380hp and 410 torque.

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post #4 of 15 (permalink) Old 03-25-2019, 06:21 PM
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What valve springs does it have?
Can they handle the lift of that cam?

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post #5 of 15 (permalink) Old 03-25-2019, 09:28 PM Thread Starter
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What valve springs does it have?
Can they handle the lift of that cam?
i'm getting the cam kit, which includes the new new springs and etc. also adding roller rockers to the mix. the heads are 69cc chamber heads but are getting plained and with those pistons il have to play around with gaskets cause i know i could be a tad over 10.5 to 1 with thin gaskets but aiming for just under. maybe 10.3 or so. why only 380hp? i've read up on people with stock gt40 heads that have acquired 380hp. i was told by a guy that my heads should easy be worth 50hp over gt40 heads(though i didn't believe him) I was thinking 35hp on that with the port work and valves would they not? just not happy with the numbers im getting lol.
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post #6 of 15 (permalink) Old 03-25-2019, 09:35 PM
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“why only 380hp?”

Because overinflated HP numbers have led to many disappointed owners.
Best to keep your initial estimates conservative.
Then, put the engine on a dyno and actually tune it.

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post #7 of 15 (permalink) Old 03-25-2019, 09:44 PM Thread Starter
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why only 380hp?

Because overinflated HP numbers have led to many disappointed owners.
Best to keep your initial estimates conservative.
Then, put the engine on a dyno and actually tune it.
fair enough, i appreciate the imput! if i stroke it to 393, and keep the heads i have what would you say i could acheive?
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post #8 of 15 (permalink) Old 03-25-2019, 09:46 PM
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The D8 heads are notta worth much and will seriously hold you back. The mildish cam grind will also hold you back. The profile looks a lot like the Pontiac cams a friend of mine used to run. They were long on duration and short on lift because of the heads he had to work with. He was racing the old ram air IV engines. A set of GT 40 heads would help you quite a bit on this or even better with AFR's or Trick Flow's(the cha ching is not too bad on these since they are ready to go out of the box).


Hard to say for sure. My fuel injected 351W made only 315 hp but 365 torque. It was in a 4 x 4 Bronco which pulled my boat and car trailer so the torque is what I needed more. I would add 50 or 60 hp maybe to my numbers to get what you will likely see with the configuration you listed. The torque will be fun though on the street. It is your top end run out that will be held back.


Stroking the engine with those heads won't help you much. Gots to let the engine breathe.



These are just my own opinions for free based on my meagre experience.


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1979 Ford F150 custom, 302, C4, AC, tilt wheel, main transportation

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post #9 of 15 (permalink) Old 03-25-2019, 09:55 PM
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390hp and 450 torque.

Face it. Those heads are not great. Even though they are ported.
Increasing the displacement will increase the demand for air. And if you want more HP you need a lot more air.

There is nothing wrong with a 380hp 351w with iron heads. It’s a fun torquey engine. And with some careful tuning you might get 400hp.
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post #10 of 15 (permalink) Old 03-25-2019, 09:55 PM
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Shooting for a horsepower number is kinda like saving money on car insurance by switching companies... If you believe everything you hear about saving money then I should switch to Geico, then switch to Allstate, then to Progressive and FINALLY to Liberty Mutual and by the time I get there they'll be paying ME to get car insurance.

There's more to "performance" than simply a horsepower number on a chart AND horsepower doesn't necessarily equate to the kick in your pants you get from acceleration.

For instance, say your engine DOES produce 400 horsepower at the crank, but at 6,500 rpm and only produces 250 horsepower at 2,500 rpm. What if MY engine only peaks at 360 horsepower at 5,500 rpm but horsepower output is 300+ from 2,500 rpm and up? Which car, with everything else being equal, is going to be faster? Which car is going to be more enjoyable for cruising?

I often get discouraged by what I call "catalog shopping" when prospective "builders" pick one piece then another based on claims made by the manufacturer and "advice" given based on someone else's experience with a part even though the situation may not be exactly the same.

If your goal is "stoplight racing" and the ability to leave that souped-up Civic in the dust when the light goes green what's going to be more important? A Comp Cams decal in the quarter window, a "lopey" exhaust note and the satisfaction of knowing that your engine dyno'd at 400 hp at 6,000 rpm or seeing the Honda in your rearview mirror?
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post #11 of 15 (permalink) Old 03-26-2019, 01:28 AM
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Stock heads are the killer no matter how ported they are (barring exceptions). You would gain 50-100hp by going to any aftermarket 185+cc head.

This shows you what is possible within the confines of 351 cubic inches:

https://www.hotrod.com/articles/buil...d-351-windsor/

You can see they gain about 100hp between an OEM iron head and an aftermarket head.

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post #12 of 15 (permalink) Old 03-26-2019, 05:07 AM
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Ported or not, I'd ditch those cylinder heads and get some good AFR or TFS heads. 185's minimum, 205's if you go stroker.
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460 rwhp / 489 rwtq SAE

TFS 205cc 11R heads || Vic Jr. intake || Holley 950HP || 14" 6 piston / 13" 4 piston Wilwood brakes || T56 Magnum || SPEC 2+ hyd clutch || Detroit Locker || 3.70's || Aluminum DS || TCP R&P || TCP 1 1/8" front sway bar || TCP front adj coilover's || TCP Panhard Rod & rear sway bar || Maier rear leafs || Bilstein shocks || Forgeline GA3C wheels - 18"10", 19"x12" 325/30
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post #13 of 15 (permalink) Old 03-26-2019, 07:32 AM
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I ran the same cam you’re running with a set of TW185s on a stock bottom end 351. I don’t have any Dyno numbers but it ran 12.80s.
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post #14 of 15 (permalink) Old 03-26-2019, 08:21 AM
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Woodchuck's dead on. It's far more important WHERE the power's made in the powerband instead of just 'what is peak?'.

A great comparison here is a Boss 351 vs. Boss 302. The 351 only makes about 10 more horsepower, believe it or not, but it'll wafflestomp a Boss 302 in almost any race you care to name. Why? Because the 351 produces much greater torque at a much lower RPM, and sustains it throughout the powerband. The 302 has to rev to much higher RPMs to hit its power peak.

There are a lot of engines that produce 'modest' horsepower numbers, but will absolutely put you back in the seat. Having a broad range of torque production is far more important for a street car, as it will deliver good performance any time you hit the gas pedal, instead of needing you to wind it up and get into the 'sweet spot'.

That's not to say that you can't build a really hot 302 though, with broad-shouldered torque too! Just worry about how the combo works together, and focus on a high, flat torque curve as much or more than peak horsepower at high RPMs. A normally aspirated 302 making 350 lb-ft or more is not easy to do, but with good heads and well matched parts, it's possible.

The venerable "5.0" Fox Mustangs of the 80s were legendary for being fun, fast, and making tons of tire smoke, but they only had 225 horsepower or so. Not too many Hondas making an honest 600 horsepower can catch them.

Last edited by Grimbrand; 03-26-2019 at 08:23 AM.
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post #15 of 15 (permalink) Old 03-26-2019, 08:44 AM
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I wouldn't change to GT40 heads - your valves are already bigger. If you consider different heads go with AFR or something similar. You'll also save a few pounds.

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