I have a fairly hot 302, but i'm still not satisfied, i was thinking of turning it into a boss 302, but i'm not quite sure what to do. Some say to just buy a set of cleveland heads and bolt them on, others say they are a special head and i just dont know what to do... anybody have any suggestions...?

Aaron
Oklahoma

 

install some AFR heads

 

You can't just buy a set of cleveland heads and bolt them on. They have to be drilled to allow water flow through the intake. They require a boss 302 intake or one of the clevor ones because you can't use 302w intakes without an adaptor plate. You will run into problema finding exhaust manifolds and headers for the application. As Kemical says best go with aftermarket heads. They will flow better without killing low end torque.

 

and be way lighter to.

 

The displacement sets how much torque you'll get, the cam generally sets where the power is in the powerband. The heads just allow more air to flow through, matched with the right cam makes the right power.

 

Different head will make different torque numbers, it's not just a function of displacement. Your port velocity is a big factor in torque production. I.E. GT-40P heads will make better torque on the low end than regular Iron GT-40's by better exhaust port design. (Which, BTW, I just discovered Hedman 89270 long tubes will fit P heads...looks like #2 primary might require a lil' dent...)

I agree, the aftermarket is too full of good aluminum and Iron heads to go thru the effort of boss heads.

If you're dead set on it, though, shop Ebay for a set of Australian cleveland heads, they have the closed chambers like a 4bbl cleveland head but streetable ports like a 2bbl cleveland head. They were actually on a 302C over there, basically a boss w/o the heavy block.

 

It's actually the intake ports on 4 barrel cleveland heads that killed the low end torque. They were just too large to get any air velocity at low rpms. Anyone who has worked on or driven one of the boss 302 mustangs can tell you what a dog they were at low rpms.

 

This is true, but in other words I was saying that....a 393 would typically put out about 30% more torque than a 351, just because of the stroke. Generally, the torque is set by the displacement, and the other components determine the position of the torque/hp in the powerband. The lower the torque is in the RPM range, the lower the HP and the more torque. But you could shift that torque curve up further in the RPM range and change the powerband to make it a high reving high horsepower motor. It would have a much higher torque peak too.

 

30 percent is a pretty lofty number for a stroker. By that right a 351 would have about 80 more lbs of torque than a 302, because basically a 351 is a 302 with an extra half inch of stroke (it just has a longer deck height to use pistons with more longevity, and that causes most of the other differences). But, alas, this isn't true, a 351 compared to a 302 has ~15 percent more torque. So yes, I agree, to make more torque you need a higher displacement motor.

HP is just a function of torque and HP. HP=TorqueXRPM divided by 5,252. Ever notice all dyno graphs miraculously have HP/TQ curves that cross at 5252 RPM? This is also why motors that make their HP at high RPM also sometimes have a higher HP number than TQ.

I agree the rest of the combo will affect your powerband. Heads that have large valves and huge port openings aren't conducive to low-RPM port velocity, but will scream on the top end, I.E. Ford's 4V Cleveland/Boss head. Screams in the 5000 RPM and over range, but doggy below that. Similar results from Yates heads, or TFS High Ports, or Edel Victors. Engine builders have been trying to make the best of both worlds, High-end HP and Low-end TQ for decades, including Variable Valve timing (V-TEC, VVT-I, etc.), Ford's IMRC variable-length runners, and other things, but the fact remains if you build a low-end grunt motor, you have a low-end grunt motor. Have your cake, or eat it. Or use a roots-type supercharger

 

Edlebrock (spelling) is now offering 351C heads in aluminum. I would not go the clevor the route. As mention way to many restrictions like intakes, headers and to top it off I don't think they will out perform a good TFS or AFR head anyways. The clevor thing was something they did when there was no other choice for a good small block head. Besides I don't think the cleveland head flows all that well on the exhuast side anyways. Some one else may know more than I do on that one.

 

These are typical TQ outputs of different windsor motors...

330rwtq for a 302-306
370rwtq for a 331
390 rwtq for a 347
390 rwtq for a 351
430 rwtq for a 373
460 rwtq for a 393
480 rwtq for a 408
500 rwtq for a 427
510 rwtq for a 434

I am wrong by saying 30%....i should of said 30ft-lbs. For example, at 2000 rpm a 393 will typically make about 30 ft-lbs more than a 351.


However, when I said the displacement sets the torque, I was reiterating what my dyno guy and I were discussing. It's my understanding that it doesn't really matter what heads you put on the motor, it'll still make that torque. Let me use an example to further explain. When I was building my 393, I was tight on money. So I was considering using the stock heads for a short period of time to cut the power down and save my transmission/axles from blowing up. I talked to some pros at the race shop down the street and they said putting the smaller heads on wouldn't cut the torque, it would cut the horsepower. That i'd still be making about 400 ft-lbs. It's all about the velocity of the air coming into the engine. A smaller port on the head will increase the intake velocity of the air and that helps torque. It limits the amount of CFM that can flow through the engine, which cuts the horsepower, but not the torque. Someone please correct me if I am wrong, but I am reiterating what other people more knowledgeable then me have said.

 

If cubic inches sets the torque, then why do you gain torque with a blower?

 

"displacement setting the torque" is not to be taken that literally. There are other contributing factors to what the final torque level is, but the displacement is what ballpark your in. Like if you have a 393, you're almost guaranteed over 400 tq. My dyno guy and the other guy at the race shop both basically said the same thing. They know that a 393 or 408 is going to put out about 400-430 ft-lbs. Assuming the rest of hte components are not mismatched, you'll get that torque because of the stroke of the engine. I'm not the best at explaining this, maybe someone else will pop in and lend a hand.

The blower increases an engines volumetric efficiency above 100% and is making say a 393ci motor actually as if it was a larger displacement engine. Putting on a blower is almost the same as increasing the displacement.

 

i agree with the aftermarket alum head answers. i have yet to hear anything bad about the afr heads. finding boss heads or messing with cleveland heads would cost as much as alum., if not more. if you want cleveland heads, put a 351C in it!

if you want high rpm performance in your truck and you don't need the low rpm torque, go with a good dual plane intake that starts making power around 2500 rpm. if that's not enough try a victor jr single plane! what kind of tranny and rear end gears are you running? cheers, garsten

 

I agree that cubic inches is a good baseline to determine how much torque an engine can make but it's only a baseline. Anything that determines volumetric efficiency (heads, cam, intake, rocker ratio, exhaust, blower, turbo, etc) can be more of a factor in final torque than cubic inches and must be taken in consideration. I saw an article on the new cnc ported tristed wedge heads where they were putting out 40 ft-lbs more torque than a set of moderately ported twisted wedge heads and much more than that over stock heads on a 347. That's gaining >40 ft-lbs by changing heads vs 30 ft-lbs from going to a 393 from a 351.

Don't get me wrong Justine, I'm not knocking cubic inches. I would love to have my 69 Mach1 with the 428 cobrajet back and if I could afford the gas I would have a mountain motor in my truck. Large displacement engines have huge advantages when it comes to making torque. You can make torque easier, cheaper, and in a more usable RPM range. I'm just saying that cubes are only one of many factors (and not always the main factor) when determining final torque numbers.