I'm building a 340 stroker motor for my Dart sport. What is the relation ship between head flow and power output? Is there a simple formula to figure out how much flow you need to produce the power you want? If I use my small valve stock J heads what is the most power I can expect? E brock rpm heads? My goal is to make as much power and torque as possible with a max rpm of 6000 or so.
Horse Power Potential of Cylinder Heads
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mderoy340
Well-Known Member
IIRC 2 hp for every 1 cfm of flow
That would be the EZ formula and the one I would go by for simplicity sakes.
Also, valve size, or more actually theack there off will choke the engine & limit RPM.
The formula is not set in stone but a good general guide line.
Also, valve size, or more actually theack there off will choke the engine & limit RPM.
The formula is not set in stone but a good general guide line.
moper
Well-Known Member
2hp/1cfm for the lift range of the cam is what I use. Meaning if your heads flow 260 @ .600 and 250@ .500 and your cam is .495 after lash, you only have the potential of 500hp in the best of scenarios. That assumes everything else is right enough to not cost any power.
You need to say what the rest of the engine is made up of, and what the budget is. I.e. if your budget is $4K, and you want to run stock exhaust manifolds, "your results will vary".
You need to say what the rest of the engine is made up of, and what the budget is. I.e. if your budget is $4K, and you want to run stock exhaust manifolds, "your results will vary".
Budget is limited of course. I'm doing a 4" stroke 340 forged bottom end. 16cc dished pistons at zero deck should be 10.5 to 1 comp. Trying to figure out how much head flow I need to reach the full potential of the engine. Not a race engine just a fast street car good torque broad power band set up. Car has 3:55 gears auto trans. Will use TTI step headers and probably rpm manifold. Will spend the money to get what I need but don't want to spend more than I have to. Plan to do hydraulic roller cam so max rpms will be a little over 6k to be safe.
EL5DEMON340
Well-Known Member
Your going to at least have to go with 2.02 and some mild bowl work to get 230 cfm of flow from those heads. If you get 230cfm out of them you should be able to make 450 hp.
The problem so far is not so much the head flow but the thinking of needing more than what will work is my fear here. You can put to much head on a engine for a given performance level.
Describe the engine build, trans to be used, rear end gear & tire size as well as intended useage. With this info, we could better prescribe a head rather than possibly mislead you into a larger more well ported head.
At 410 cubes, the engine will want a head a normal CID engine like a 340 or 360 would want. At 410, it does need to breath some. The OOTB Edel. head will loose steam quick. How far it should be opened up is another matter. Depending on the build and useage, it could be some or all the way. Which with 3.55's, is probably not the way to go. But we will see what you have in mind and the build of the engine later.
Describe the engine build, trans to be used, rear end gear & tire size as well as intended useage. With this info, we could better prescribe a head rather than possibly mislead you into a larger more well ported head.
At 410 cubes, the engine will want a head a normal CID engine like a 340 or 360 would want. At 410, it does need to breath some. The OOTB Edel. head will loose steam quick. How far it should be opened up is another matter. Depending on the build and useage, it could be some or all the way. Which with 3.55's, is probably not the way to go. But we will see what you have in mind and the build of the engine later.
moper
Well-Known Member
Just my opinion but if money is a potential issue I would not bother with the hydraulic roller setup. If this has to run on pump gas I would also not use the 16cc piston with an open chamber iron head. If your heads can't flow enough you wont make good power in the rpms you're talking about. For some perspective a good set of as-cast factory iron heads that have a modern 5 angle valve job and back cut intake valves might get to 225-230cfm. Add in the smaller cam and you're just not going to do much with them. If you want to go for "max power" then look into a set of RPMs or similar aluminum. If your heads need work, and then need porting, you will be pretty close budget wise to a set of better heads that also give you a closed chamber to work with. You could also go with newer iron stuff but they are heavy and price waise are still pretty similar to aluminum. Do not plan to run any aluminum head out of the box - plan for a valve job on them at least.
If you have heads that will flow in the 240-250 range, and if the static is kept reasopnable for whatever head you go with, then you can expect to make some decent power. 450hp is mild for these. 500+ is easy with porting on better heads and a pretty mild camshaft.
If you have heads that will flow in the 240-250 range, and if the static is kept reasopnable for whatever head you go with, then you can expect to make some decent power. 450hp is mild for these. 500+ is easy with porting on better heads and a pretty mild camshaft.
It seems that his budget is good enough for we cams and a stroker rotating assembly, but not up for an expensive W9 set up. That head is listed @ 290cfms OOTB.
IF I had the money, that is what I would look for, 59*- W9's.
IF I had the money, that is what I would look for, 59*- W9's.
I may end up swapping to a manual trans at some point. For now I'm going to stick with the 727. I was thinking of putting the engine together with my stock iron heads just to have it running sooner. I just don't want to choke it out. The stock heads have 42k miles so they could be cleaned up and used as is. There was nothing wrong with them. But as soon as your start throwing valve springs and parts at them it makes more sense get aftermarket heads. I get a really nice discount on anything from Mopar so anything in there catalog is on the table. But I don't really know how much flow I really need for an engine that is street torque build that will not see more than 6k. I don't want to run a 3500 stall converter and have no low end. I drive this everyday in the summer.
A stock 340 cubic inch to head flow is about 65% and a eddy head 340 would be 75% so those percentages on a 410 would be 265 cfm at 65% and 300 cfms at 75%.
280 or more at the cam lift your willing to go with should be in the ballpark.
280 or more at the cam lift your willing to go with should be in the ballpark.
fishy68
Tyr Fryr's Inc.
I understand wanting to get it running quicker but you state you don't want to choke it down and stock J heads will choke it down. I highly doubt it'll pull any where close to 6k rpm with them especially since you state you don't want to get into replacing valve springs. Roller cams generally require considerably more spring pressure than flat tappet cams so you will definitely have to replace the valve springs and most likely have the guides cut down and Teflon seals installed because stock J heads wont usually accept over .475 lift without spring retainer to guide contact.
BTW: your last statement about not wanting to run a 3500 converter because you'd have no low end is off base. Converters fall into 2 basic build groups, tight and loose. Nearly all of the pre 1990 high stall converters built were of the loose variety meaning they slipped a lot taking off. Converters have came a long way in the past 20-25 yrs. and today's designs can easily flash 3500 rpm and drive nearly like a stock converter (the tight variety). My Cuda had a 727 with a 3500 PTC converter and a very mild built 408 with a small Racer Brown solid flat tappet cam and I ran a traction limited 12.24 at 112 and to top it off it averages 13-14 mpg around town and 18 on the hwy when I'm not flogging it. If the converter was slipping there's no way it'd ever get anywhere close to that mpg. At idle (750 rpm) when you drop it in gear it takes right off without touching the gas.
famous bob
mopar misfit
:wack:
1 cfm = 2 h.p. ??? never heard that one! if my heads flow 352 @ .600 , w/ a .600 lift cam(after lash) your telling me that I got 704 h.p. ?? like to hear rrr take on this. you out there rusty?
moper
Well-Known Member
You have the potential of making it, yes. It's a combination of factors that get you to that generalized figure. There are engines that exceed that number and get as high as 2.5-3hp/cfm naturally aspirated at peak power. But they are more exception than the rule - hence the generality. The reality is if your cam was only .600, no you more than likely wouldn't make anywhere near that number. If the cam was .700, and the intake and exhaust manifolding was conducive to maximum horsepower, and if your machining and assembler are good, then it's pretty much a gaurantee you'd make it.
moper
Well-Known Member
A couple thoughts - there are no camshafts that would not require some sort of modification to the heads: spring seats cut, guides cut, etc. They may have exhaust rotators too which would have to go - and the exh valves are different in regard to where the lock grooves are placed on those so it means new exh valves. Plus - the stock work is not really that great. If you want to screw on bone stock heads and install a bone stock cam, you certainly can do so. But I don't see it doing much more than giving a bit more torque off idle, and not having much mid range (I consider 2500-4500 as "mid range" rpm). It will be it's own rev control so I'd say probably 4500-ish will be max rpm. Additionally - there's not much from Mopar Performance that will not require a lot of cash to get running. Your cheapest way out would be the Engine Quest Magnum heads. In stock form they have closed chambers, have the LA intake pattern, are cheap, can run the factory Magnum rocker gear, and will flow enough air to feed a mild stroker - they will outflow any stock LA type head right out of the box. You should be able to buy them, have them assembled with a spring to work with a milder cam (around .510 lift with a 1.6 rocker), and ready to run for the same money as having the factory 360 heads set up for performance work.
Like Moper said. Just because you have a cylinder head flowing 300cfm @ .600 doesn't automaticaly mean your making 600 hp. The quality of the bud is for starters. Second would be the combonation of parts used. A dual plane is giving up power to a single plane, which is giving up power to a tunnel ram, which all of these intakes need the right parts below it to show there abilty.
One could use a tunnel ram on the street and make a very modest amount of power. IE; 400hp in a 360. But the intake has the abilty to make triple that if the combo is right. Even if there is a set of fully ported heads under it. Low compression and mild cam's, small displacements and headers all lead to lower power levels.
In general, A stout high performance build can use the formula as a basis to get a idea. But if your limited or at a less than optimal level when the engine is built, power output will be lower. Things like not taking advantage of the heads flow abilty with a cam not lifting the valve enough. Cam duration has a huge roll as well. Etc. right on down the line for every part in, on and around the engine.
Most well built street engines are probably around 1.8 hp per cfm but more exceptional engine's are higher and less exceptional ones are lower than. The 2 hp per 1 cfm is probably more of a race engine rule of thumb.
D-mailman
Well-Known Member
The Superflow formula is 2.06 hp per CFM exactly. That means the head flows enough to support that hp number but only if the combo is right. My 340 Duster went 12.25 @ 110.71 with 915 ported castings 2.02/1.600 valves Mopar 528 mechanical cam . The heads flowed 232 @ .525 You can do good things with stock heads but aftermarket has much more potential. JFYI .
Terry
Terry
I ordered a set of heads today p5153849. I'm pretty sure these are reboxed performer RPM heads. That should be enough to start with and then they can always be ported later. I will probably take them apart and check all the clearances, clean up the ports if needed and change the springs.
CPDave
Spin Cycle
When I was researching cylinder head intake flow's impact on power I ran across this set of thumb rules for relating HP to CFM:
Horsepower per cylinder =
0.43 x airflow @ 10" of water,
0.275 x airflow @ 25" of water, or
0.26 x airflow @ 28" of water (This last is 2.08Hp / CFM in an 8 cylinder engine).
You will note that one has to know the test conditions to derive the potential of a given head (i.e., how hard was the flow bench sucking on the head
). One also has to take into account other aspects of the test set-up like how often the flow bench is calibrated, whether putty was used around the entry of the port (or extensions on exhaust ports), and the size of the bore the head is being sucked over (large intake valves can be partially shrouded by the cylinder wall. Another point is that this does not take into account exhaust flow; you can have 320 CFM @ 0.600" lift on the intake port, but if the exhaust ports top out at 150CFM your never going to make the predicted numbers even if the rest of the package is optimized. Finally different shops (both being completely honest) can disagree on flow by 10%-15% on the same head due to all the variables involved in the testing procedure.
So yeah 320 CFM @ 28" of water can support about 665HP +- 30 or so, but the rest of the package has to match up to it and that also will likely require a race gas tune to get there(all of this leaves out the variables involved in actually measuring HP too :banghead: ).
All that said here's a real world example, the 318 combo that's in my '66 Dart:
'69 318 0.050" over bock, K1 rods, Scat 4340 crank, custom forged pistons (forget by whom right now), Hughes Engines main stud girdle.
EdleBrock LD4B Intake with a 0.5" semi open spacer and QFT road race 750
The heads are ported 1985 and up 318 ...302 castings with 1.94" intake and 1.6" exhaust valves by Ryan Johnson at Shady Dell speed shop in central
PA; they flow:
LIFT IN / EX
0.100" 66.1 / NA
0.200" 132.8 / 90.4
0.300" 189.9 / 126.2
0.400" 218.4 / 148.8
0.450" 227.9 / 152.9
0.500" 232.8 / 159.8
0.550" 238.0 / 163.9
0.600" 239.1 / 169.8
at 28 Inches of water (these will support no more than 497 HP). This motor previously made 330 HP at the wheels with the same cam & heads but less compression (was 10.1:1 now 10.25:1).
Comp Mech Roller Cam:
Lift-0.630"/0.630"; [email protected]"-254*/260*; and LSA-107*.
Harland Sharp Rockers. Magnum rocker adjusters, push rods, and lifters (basically pressure oiling the push rod/rocker pivot point from the lifters and through the push rods like a Ford or Chevy small block).
Headers used on the engine dyno were 1"&5/8" to 3" collectors, in the car I have the TTI early A-body step headers (1.625", 1.75", 1.875" to 3" collectors), 3" to 2.5" X-Pipe and a pair small Oval canister Borla mufflers dumping in front of the rear wheels.
Milodon road race pan, Brad Penn 20w50 Oil, Oberg canister filter, Oil cooler, and 3 quart Accusump.
On 93 octane pump gas at the crank:
RPM HP FtLb
==== === ====
3100 216 365
3200 221 364
3300 229 364
3400 237 366
3500 246 370
3600 255 373
3700 265 377
3800 275 381
3900 285 383
4000 293 385
4100 302 387
4200 309 387
4300 316 387
4400 324 387
4500 332 387
4600 340 388
4700 348 390
4800 357 391
4900 364 391
5000 371 390
5100 378 389
5200 384 388
5300 391 387
5400 396 385
5500 401 383
5600 406 380
5700 411 379
5800 416 376
5900 419 373
6000 421 368
6100 422 364
6200 424 359
6300 425 354
6400 423 347
6500 421 340
6600 419 333
6700 416 326
6800 415 320
6900 414 315
7000 413 310
Dave
And at the rear wheels:
Horsepower per cylinder =
0.43 x airflow @ 10" of water,
0.275 x airflow @ 25" of water, or
0.26 x airflow @ 28" of water (This last is 2.08Hp / CFM in an 8 cylinder engine).
You will note that one has to know the test conditions to derive the potential of a given head (i.e., how hard was the flow bench sucking on the head
). One also has to take into account other aspects of the test set-up like how often the flow bench is calibrated, whether putty was used around the entry of the port (or extensions on exhaust ports), and the size of the bore the head is being sucked over (large intake valves can be partially shrouded by the cylinder wall. Another point is that this does not take into account exhaust flow; you can have 320 CFM @ 0.600" lift on the intake port, but if the exhaust ports top out at 150CFM your never going to make the predicted numbers even if the rest of the package is optimized. Finally different shops (both being completely honest) can disagree on flow by 10%-15% on the same head due to all the variables involved in the testing procedure.So yeah 320 CFM @ 28" of water can support about 665HP +- 30 or so, but the rest of the package has to match up to it and that also will likely require a race gas tune to get there(all of this leaves out the variables involved in actually measuring HP too :banghead: ).
All that said here's a real world example, the 318 combo that's in my '66 Dart:
'69 318 0.050" over bock, K1 rods, Scat 4340 crank, custom forged pistons (forget by whom right now), Hughes Engines main stud girdle.
EdleBrock LD4B Intake with a 0.5" semi open spacer and QFT road race 750
The heads are ported 1985 and up 318 ...302 castings with 1.94" intake and 1.6" exhaust valves by Ryan Johnson at Shady Dell speed shop in central
PA; they flow:
LIFT IN / EX
0.100" 66.1 / NA
0.200" 132.8 / 90.4
0.300" 189.9 / 126.2
0.400" 218.4 / 148.8
0.450" 227.9 / 152.9
0.500" 232.8 / 159.8
0.550" 238.0 / 163.9
0.600" 239.1 / 169.8
at 28 Inches of water (these will support no more than 497 HP). This motor previously made 330 HP at the wheels with the same cam & heads but less compression (was 10.1:1 now 10.25:1).
Comp Mech Roller Cam:
Lift-0.630"/0.630"; [email protected]"-254*/260*; and LSA-107*.
Harland Sharp Rockers. Magnum rocker adjusters, push rods, and lifters (basically pressure oiling the push rod/rocker pivot point from the lifters and through the push rods like a Ford or Chevy small block).
Headers used on the engine dyno were 1"&5/8" to 3" collectors, in the car I have the TTI early A-body step headers (1.625", 1.75", 1.875" to 3" collectors), 3" to 2.5" X-Pipe and a pair small Oval canister Borla mufflers dumping in front of the rear wheels.
Milodon road race pan, Brad Penn 20w50 Oil, Oberg canister filter, Oil cooler, and 3 quart Accusump.
On 93 octane pump gas at the crank:
RPM HP FtLb
==== === ====
3100 216 365
3200 221 364
3300 229 364
3400 237 366
3500 246 370
3600 255 373
3700 265 377
3800 275 381
3900 285 383
4000 293 385
4100 302 387
4200 309 387
4300 316 387
4400 324 387
4500 332 387
4600 340 388
4700 348 390
4800 357 391
4900 364 391
5000 371 390
5100 378 389
5200 384 388
5300 391 387
5400 396 385
5500 401 383
5600 406 380
5700 411 379
5800 416 376
5900 419 373
6000 421 368
6100 422 364
6200 424 359
6300 425 354
6400 423 347
6500 421 340
6600 419 333
6700 416 326
6800 415 320
6900 414 315
7000 413 310
Dave
And at the rear wheels:
CPDave
Spin Cycle
moper
Well-Known Member
I agree with absolutely everything you said especially the comments about flow test and dyno results. I'm usually a skeptic when it comes to guys and shops chest thumping and touting those figures and all that's why.
But I don't agree with this: " (these will support no more than 497 HP)"
If one builds a combination that is highly efficient - not just in airflow but in combustion and limiting pumping and frictional losses - you can exceed that number. Such an engine in a V-8 factory-type package is a compromise in terms of longevity and costs, but that figure can be exceeded fairly significantly if you control the things that work against power getting to the crank hub. That's the line of thinking behind any successful Stock Eliminator engine builder and many FAST class builders.
But I don't agree with this: " (these will support no more than 497 HP)"
If one builds a combination that is highly efficient - not just in airflow but in combustion and limiting pumping and frictional losses - you can exceed that number. Such an engine in a V-8 factory-type package is a compromise in terms of longevity and costs, but that figure can be exceeded fairly significantly if you control the things that work against power getting to the crank hub. That's the line of thinking behind any successful Stock Eliminator engine builder and many FAST class builders.
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