To much head

[Taylorman]

What does having heads to large for your engine do for performance? Say you have a 454 with 355 cc intake runners. What would this cause?

[steelcomp]

It would be a dog. You'd have a serious lack of intake runner velocity, and a poor carb signal. Basically, you'd put your foot in it, and nothing would happen, till, say, 7500 rpm. At that rpm, there's finally enough air going through the intake runners to give the carb a good signal and properly atomize the fuel. :coffeycup

[SmokinLowriderSS]

Steelcomp has it right. The runners are so large that a lower revs the fuel droplets fall out and "puddle" in the intake, also, poor suction signal on the carb so lousy feeding at idle and off-idle unless the carb is pretty heavilly undersize to try to compensate. Even then the intake air will be very sluggish. Would be less of a problem for a direct port-fuel injected engine but would still not like it. At high-RPM tho, the larger runners allow enough air to move that they feed really well. Takes like 5-grand minimum to wake them up tho, and likely will not feed well untill above 6K.
One of the design intents of the orriginal big block chevy's (the "Turbo-Jet" from 1965) was to get inlet port velocities to be steady for the entire runner length, at speeds aproaching 16,000 feet-per-seccond. (from my Hotrodding Big Block Chevy's book section on Cyl heads).

[SmokinLowriderSS]

My large ovals are 255cc according to Mor-Tec. (353049 heads)

[DeputyDawg]

Hey Taylorman, don't listen to these guys. All you need for that motor is a 14-71 or a big PSI screw blower and your intake velocity would be great! Just kidding man, Steel summed it up perfectly!

[steelcomp]

Hey Taylorman, don't listen to these guys. All you need for that motor is a 14-71 or a big PSI screw blower and your intake velocity would be great! Just kidding man, Steel summed it up perfectly!
Now yer talkin!! :D All of a sudden, those ports aren't so big after all. :supp:

[SmokinLowriderSS]

Don't forget a set of 2.3" intake valves and a set of 2" exhausts. Bet with that huffer she'd breathe just fine at 2500 RPM or so. :jawdrop:

[78Eliminator]

Taylorman, are you thinking about new heads or were you just curious?

[Taylorman]

No, it was just a question out of curiosity.

[cstraub]

Port velocity is critical. I see it everyday guys with marine engines go way to big on heads. A 310cc runner head can support a 540CID engine to around 6200 rpm without maxing out the runner. So when your going to run a max of 5500 rpm why do we need a head capable of 6200 rpm? Slow air makes peaky power, fast air makes broad useable power.
Its critical to match runner volume, cross section to the CID of the engine and the intended rpm range.

[Daytona100]

What about if your running a blower? Does it matter as much when your forcing the air in?

[cstraub]

Daytona,
No, on blown applications you can get away with "overheading" but don't make the mistake of over camming in this situation with a Huffer and large heads. A small cam is all that is needed.
Chris

[Daytona100]

How much cam would you consider overcamming? Cant think of the grind number but its a crane with 553 intake lift and 573 exhaust. Powermax hydrolic cam.

[cstraub]

I can tell you that a 345cc headed 572 with a 10-71 doesn't need much more then .570" lift and around 240 @ .050"
Chris

[Daytona100]

Thanks for the info. Should have it running this weekend. Kinda curious on how its gonna run.

[SmokinLowriderSS]

Those specs look fair to me, but I've never dealt with a blower setup myself. i'm running a bit more cam than that on an N.A. setup 454. .565" lift, 280* duration at .008 (seat to seat). I think the duration at .050 is about 232*, solid, strong runner with really broad power delivery.

[rrrr]

Too much head? There's no such thing. :jawdrop: :D

[FILUCKY]

Almost never see too much "head" on a motor but i definitly see to much cam and carb! :hammerhea

[SmokinLowriderSS]

Almost never see too much "head" on a motor but i definitly see to much cam and carb! :hammerhea
Now THERE is a true statement. I have seen a lot of people who seem to think just put the cam in or the carb on and it will be used to it's max. effect, improvement guaranteed. I see a lot of it in manifolds too, "overmanifolded"? :idea:

[steelcomp]

Almost never see too much "head" on a motor but i definitly see to much cam and carb! :hammerhea
I've seen almost the exact opposite. Usually it's a combination of both...too big a head AND cam. Just about any aftermarket head is too big for what CI engine most guys run, and the rpm range they run it in.

[FILUCKY]

I guess i'm mostly refering to the most common build, stock long block with a 292 cam, tunnelram and a pair of 750's, and then they wonder my it only goes 60 mph... :notam:
Thor has some new "C" style heads out that are flowing (worked over) in the 585cfm range. I'm looking into trading in! :)

[steelcomp]

I guess i'm mostly refering to the most common build, stock long block with a 292 cam, tunnelram and a pair of 750's, and then they wonder my it only goes 60 mph... :notam:
Thor has some new "C" style heads out that are flowing (worked over) in the 585cfm range. I'm looking into trading in! :)
Just curious...why do you need that much flow??

[FILUCKY]

Looking into builing bigger motor. Just read about a guy running these heads on a 598 (I think it been alittle while) dynoed out 1404 hp on gas (N/A of course and no nitrous) :) And i'm going to be lucky shooting for 1100 hp with my setup i have now. But this is just wishful thinking at this point i would think that it would run me about 12k to upgrade. :frown:

[steelcomp]

Looking into builing bigger motor. Just read about a guy running these heads on a 598 (I think it been alittle while) dynoed out 1404 hp on gas (N/A of course and no nitrous) :) And i'm going to be lucky shooting for 1100 hp with my setup i have now. But this is just wishful thinking at this point i would think that it would run me about 12k to upgrade. :frown:As long as you can turn that kind of RPM, you'll be OK. If not, look at the HP of this motor at the RPM you're going to run. I would imagine it's power band is pretty narrow. That kind of HP isn't usually found at very reasonable levels. Is this for your jet??

[FILUCKY]

Yes this is for my jet, i think you would be suprised by how low of rpm these motors start making lots of power, my current setup runs very strong at only 7200 rpm. I do know of a guy that sets up Chevy motors to run in the 8500 rpm range and then he runs some kind of gear reducer and a big cut impeller but i have only heard about it not actually seen it. I've only been running these style of motors for the last year so my knowledge is very limmited but learning something new every day. I've been told by a few guys running these style engines that they have gone bigger cubes and kept almost the same power but lowered the power band to a more freindly range. :messedup: