396 Stroker Motor Lacking HP

[MUSTANG65FBK]

So I bought a 351w stroker motor about a year and a half ago, the motor is a 1993 block which I wouldn't do again because they only came stock with 200 hp, it's been bored and stroked to 396 cubic inches and was supposed to be putting out 400 hp at the flywheel. The motor has cast iron 1970 351w heads 69cc with 9.7:1 compression ratio, roller cam although it's only like a 206/221 cam, edelbrock rpm air gap intake, holley 670 street avenger carb - do I need a bigger carburetor?, JBA swap headers, x pipe, 2.5" exhaust and side mufflers. So long story short, I take the mustang down to The Mustang Shop in Auburn, WA and get it dynoed on their mustang chassis dyno. Started out with 240 hp at the rear wheels and 319 ft/lbs of torque, added bigger floats to the carb and rechecked the timing which was way off, and the best I got was 283 hp at the rear wheels and 378 ft/lbs of torque. I've heard that you have basically a 20% loss in power between the flywheel and rear wheels so that would put my flywheel hp at approx 330 which is 70 short of what they claim it to have. So right now I'm talking with the shop that built the engine to see what my options are and they want me to take the engine back out of the car, ship it back to them since they are in Spokane and have them put it on their engine dyno because they are certain that my setup should make 400 hp at the flywheel. I don't know if any of you have done a 351w into a 65/66 mustang but it is a pain in the *** and I'd prefer to not have to take the motor out again, ship it back to them and have them give me some BS story that yes it is in fact running 400 hp. So my questions are, I asked the shop if I could get a partial refund on the motor since it's 70 hp shy of what it should have and then I could buy some parts and do it myself which they agreed to but I haven't come up with a figure yet. Or I could have the shop buy some parts and have them shipped to me since they could get parts for much cheaper than I ever could. Finally to my point... I want new aluminum heads and a cam. The Mustang Shop said my cam was way too small and the heads were way too restrictive to put out 400 hp at the flywheel, what brand/size heads would you recommend putting on the motor? And if I replace the heads, what other parts am I going to have to replace? Same with the cam, I want something that has a rough idle and some lobe to it because right now you can't even hear it, but not to where I won't be able to run my power disc brakes. And if I replace the cam that I've got with something bigger, do I have to replace the lifters, timing chain or anything else? I was thinking of some AFR 185's or 205's and then a comp cam 35-770-8 which is their extreme energy cam that has a rough idle and is a lot more aggressive than the cam that I have now. I wouldn't expect that the shop would purchase both but maybe they could get a good deal on the heads and I could get the cam or something. Any advice would be great, thanks

[supershifter2]

carb is too small. put an 830 cfm holley double pumper on it. the cam is small. the windsor heads are way too small for your 396 chebby engine. put afr 205 heads on it. basically its a low performance engine > the heads, cam, carb, compression should be upped to 10.5 or as high as you can get it with the pistons you have.

[My427stang]

Well the carb is too small in the end, but its not too small for the cam and heads you run now.

That's basically an RV-cammed 396 inch motor with small block heads, 330 hp is about right. Definitely not a 400 hp motor unfortunately

To make it run, get some smaller chamber AFR heads and more cam, something in the mid 230-240 @ .050 range. If money runs out, keep the carb for now, but eventually it'll like a 750, and would LOVE a 750 double pumper after the heads and cam.

BTW, with a set of nice heads and the cam you chose, it'll be brutal compared to what it is now. Only thing left would be to recurve the distributor

[shaneh]

The shop you got it from has been sniffing too much gasoline if theythink that thing will make 400 hp with those heads and cam.

[ScottsGT]

Originally Posted by supershifter2

carb is too small. put an 830 cfm holley double pumper on it. the cam is small. the windsor heads are way too small for your 396 chebby engine. put afr 205 heads on it. basically its a low performance engine > the heads, cam, carb, compression should be upped to 10.5 or as high as you can get it with the pistons you have.

X 1000!

I would have suggested some of the larger Trick Flows. but since you did not build the motor using pistons fly cut for the canted valves, stick to the AFR heads. Don't know what kind of piston top you have, but at this point it's not worth the trouble to go through when AFR will be just fine for your combo.
A motor is a pump. You are restricting what gets into the cylinders and out with those small heads and carb.

Imagine trying to run a marathon while breathing through a straw.

I too cannot believe the engine builder suggested those high numbers if they knew which heads you were running. (Not doubting what you said, doubting the engine builders experience)

[frdnut]

What type of camshaft are you running now?...I will assume its a hydraulic flat tappet?..If so yes you will need to replace the lifters if you decide to go with that camshaft. 35-770-8 - Xtreme Energy? Mechanical Street Roller Camshafts, No upgraded distributor gear necessary. .You will need the solid roller link bar type lifters....I agree with what the others have said..The top end parts would be very mild on a 351 let alone a big block sized 396.

[jdub]

I would not bother sending the engine back because with those heads, cam and carb it sounds like it's right where it ought to be.

[Maxum96]

Just to echo what the others have said, you'll never make big power with those heads and cam. Also it makes no difference what year block 351w you use as to what it's horsepower potential is. Some year blocks are said to be stronger in some areas than others. My 393w makes about 600hp at the crank. I could swap all my parts into your block and it would make the same horsepower that I make now.

[6t9mach1]

I'd be pretty happy with 282 rwhp with that combination. Thats probably about 330-350hp at the crank. My computer software said 315hp at the crank but I also did not know all your cam specs and much else about the engine.

As other have said your heads and cam are way to small for a 396 cid engine. If you go with an inline type head like an AFR, 205cc's is the smallest I would go. But this brings up another issue; your transmission is a T5. A T5 is not going to live long behind a big cubic inch stroker motor that is built to its potential. If you want to get much crazier with the engine you are going to need to upgrade your transmission or it will not live long. With those cubes and a properly set up engine with the correct components, 500hp is easy to do but like I said your drivetrain is going to need some work as well as the frame of your 65 which is not built to handle this type of hp. So there are other things that need attention, IMO, before you start messing with the engine.

[6t9mach1]

Maxum, what cam did you end up going with? Something off the shelf or did you go custom? I cant remember.

[sportsroof69]

My block is a '93!


It's pretty well been covered,and your carb is right for that setup. With new heads and cam, you'll need more.

[bartl]

Nothing wrong with that block. The engine just needs more air (carb-cam-head work). Can't say the limited choice in headers helps much (small primaries).

Got a pix of your dyno sheet?

[Maxum96]

Originally Posted by 6t9mach1

Maxum, what cam did you end up going with? Something off the shelf or did you go custom? I cant remember.

It's a CompCams solid roller with .616 lift on the intake and .622 on the exhaust side. 285 and 291 duration on a 108 lobe center.

[jdub]

Originally Posted by Maxum96

My 393w makes about 600hp at the crank.

What type of fuel are you running? Are you able to get away with 91 octane on the 11:1 compression?

We're practically neighbors. I hope I get a chance to check out your car someday.

[68Fastang]

I would recommend the AFR 185's with and 850 cfm carb with a comp cams hydralic roller(grind #291THR7). That combo should easily net you the 400hp at the wheels with the rough idle your looking for. As said above, I think the parts in your current combo where correctly chosen as a package. It's just a 300hp package, not 400hp. You'll also want a header primary size of 1 3/4" with a 3" collector. Your 2.5 exhaust would work as long as you have a good, free flowing muffler. With the right muffler and an x pipe, you'd be surprised how quiet a 3" exhaust can be. Just my 2 cents.