iron heads for a 408?

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754door

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Was thinking of porting a set of iron to flow at least 250cfm. I think I'am capable of doing that. But would 250cfm be enough to support 480hp in a 408 with a comp cams solid roller the .564/.570 cam. Then redoing the seats and guides. And cutting for the bigger valves.

In my head porting class I got a set of magnums to flow 244cfm at .500 and .600 lift. this is with 1.92int valve. I'am going to flow it again tomorrow after the porting I did today. Also are flowbench had clay stuck in the pedo tube because of idiots. And we cleaned out the tube and it is till 10 to 15cfm low. The reason we know this is a kid in our class brought his head and another head to his dads superflow 600 and it did almost 30cfm more. But after we cleaned the tube we got it down to only 10 to 15cfm low.

Our teacher ordered a new pedo tube. because there is still some clay stuck in the holes inside.
 
Stay with the 1.92 as this valve should be able to get you that amount of flow. A 408 engine really needs about 198 cc's of port runner and 315 cfm's or so, this head will never get this large without extensive rework.
 
The numbers a flow bench generates are entirely the result of the math and correction factors and the operator. If you cannot get the numbers the other kid's dad can, but you are confident your equipment is clean, sealed, and the calculations are correct for your weather/altitude, you have to belive the numbers it gives you. (it's a garbage in, garbge out...deal) That's why we never "race" flow benches. I know guys with poor calculations based on poor weather instruments, that get really good numbers...and the engine never makes what the head result says it should. The truest result is the engine on a stand or in a car going downt the track. Anything else is like looking at a thermometer reading to see if it's cloudy outside. As far as the numbers..244 is enough to support more than 500hp with the right cam. I think BJR's program doesnt assume past 100% efficiency. It might, I'm not real familiar with them in general...lol. So feel free to correct me Billy, but the numbers you list show a smaller cc, and a cfm figure that is just as you said: unattainable at least at 28". The basic thought process I use is the smallest valve and port cc that will get the cfm at 28" I want. Also remeber, the intake port extends from the back of teh intake valve, to the base of the carburetor. It's not just the head port. Anyway, roughly double the cfm is what most engines can basically do horsepower wise, assuming around 100-105% efficiency at peak torque. I know of street engines that are 108-112% efficient at peak torque. Efficiency is a factor of a lot of variables and is an empirical value resulting from testing. Not just number plugging into an algorithm like most cam and head spec'ing type programs. A head with 240cfm @ 28", flowed by a guy that knows his bench, and has good weather info, will make 480hp with a moderate (240-250 @ .050 cam. IMO, you're fine. BTW, that's a good number for Magnum castings and the 1.92 valve.... nice work.
 
Maybe thats why I don't assume anything. And you might need to get familiar with them. The programs I use are state of the art and used by many of the top racing teams today, maybe thats why I get the results that I do. And yes they go well over 100% efficiency and have had them in the 115-120 range. And believe me they don't give these away.
 
I figured they arent cheap...lol. I'd be interested to see how they do arrive at the numbers they do. Like what inputs, and how involved are the data entry tables. Like I said, that 198cc port flowing 315 cfm at 28" is maybe doable in a DOHC import.. not a single valve, snakey shaped pushrod V8 configuration. I'd have to call to make sure my memory is good enough, but I think a friend has gotten 330ish on Boxer Subaru heads (WRX), but those ports are only 1/2 as long as a typical V8, shaped perfectly, and have two intake valves worth of area.
 
I did a set of W-5's that flowed 323 with a 2.02 intake valve and a 205 cc port. I also did a set of commandos LP that ended up at 196cc's that flowed 324 cfm's. Give me your e-mail address and I'll send you some pics.
 
I know this is really picky, but the correct spelling is 'pitot' tube. Sorry, too much time in the aircraft industry.
 
Picked up a set of 596 360 heads today. Bought them off ebay and went and picked them up. Payed $10.00 for the pair. I will clean them up and check for cracks on monday and then flow them to get some all stock numbers. Then It will be cut for 2.02 valves.

What do you think I could get these heads to flow in fully ported form.
 
Picked up a set of 596 360 heads today. Bought them off ebay and went and picked them up. Payed $10.00 for the pair. I will clean them up and check for cracks on monday and then flow them to get some all stock numbers. Then It will be cut for 2.02 valves.

What do you think I could get these heads to flow in fully ported form.

According to what the above numbers say, when fully ported, wow, that can make for a mean street machine.
 
Stay with the 1.92 as this valve should be able to get you that amount of flow. A 408 engine really needs about 198 cc's of port runner and 315 cfm's or so, this head will never get this large without extensive rework.

Hey BJR,

Is this a general rule of thumb for a 408? Are you talking about an "all out 408" or a street/strip version? I am very interested in your thoughts re: this. I am coming up on now choosing the heads for my 408 and am still trying to figure out the best route to go for my application.

TIA.
 
I have a set of Mopar Performance ported iron heads rated at 275 cfm @.500- .600 lift with a port volume of 166 cc's. How will this relatively small port volume affect power production? Do I need port volume of about 200cc's. The rest of my combo includes: 408 shortblock, 750 Holley, a "junkyard" Eddy RPM intake, 1.5 Comp steel roller rockers, belt driven water pump, 9.1 KB pistons, TTI step headers, Comp 242*/248*@.050, .549/.544 lift hydraulic roller cam, MSD 6AL ignition, 2.5 exhaust,4spd manual, Super Stock springs,9.25 axle with 3.55 gears. I hope to get 450-500 hp. All going into a '71 Duster. Any critiques, comments?
 
Was thinking of porting a set of iron to flow at least 250cfm. I think I'am capable of doing that. But would 250cfm be enough to support 480hp in a 408 with a comp cams solid roller the .564/.570 cam. Then redoing the seats and guides. And cutting for the bigger valves.

In my head porting class I got a set of magnums to flow 244cfm at .500 and .600 lift. this is with 1.92int valve. I'am going to flow it again tomorrow after the porting I did today. Also are flowbench had clay stuck in the pedo tube because of idiots. And we cleaned out the tube and it is till 10 to 15cfm low. The reason we know this is a kid in our class brought his head and another head to his dads superflow 600 and it did almost 30cfm more. But after we cleaned the tube we got it down to only 10 to 15cfm low.

Our teacher ordered a new pedo tube. because there is still some clay stuck in the holes inside.


i have a comp solidroller one size bigger that the one you are looking at in a stock stroke 340 with some heavily ported eddyheads and it runs real hard, that cam you are looking at will smake some stupid torque in a 408!;) prepare for alot of tiresmoke!
 
I may go with the one you have duster340 not sure yet. I 'am hoping for around 500hp. and 500+ftlbs. Then I will add a 100shot on top of that. I want it to be a super sleeper. There is a 57chevy with a 550whp big block chevy that I want to beat around my neigborhood.
 
I'm more interested in having a flat torque curve than top end horsepower. I mean you "use" torque more often in regular everyday driving but can't really feel horsepower unless you're at the track.
 
sr, Head wise you have what you need, assuming the numbers are accurate. However, the other parts choise will limit output some. The cam is relatively small, good for flat torque, but also good for sharp power drop offs. But with smaller vo,mue heads, I think it is a good match. I would spec a larger carb and intake tho. The 4" arm engines I'm used to that run the std Performer RPM ususally drop off a little after 5500 or so. And drop fast. Also, the carb is on the smallish side. I like wet flowed ratings of 770 or bigger, and dry flowed of 850 or bigger. These things eat up carburetor size. A similar 418 with a set of mildly done RPMS, an RPM, a 3310 Holley, and smaller flat tappet (235/240@ .050 solid) made 450hp/490tq at the crank. It was like shutting off a light switch above 5400 tho. hp peak was 5200.
 
My 596 360 heads that I got the other day flowed 196cfm at.500lift and like 129 on the exhaust. This is all with factory seats and valves everything was just cleaned and than flowed.
 
Hey BJR,

Is this a general rule of thumb for a 408? Are you talking about an "all out 408" or a street/strip version? I am very interested in your thoughts re: this. I am coming up on now choosing the heads for my 408 and am still trying to figure out the best route to go for my application.

TIA.

GTX,
Sorry for not getting back to you before now as I've been very busy. This would be a street strip version as for all out racing you could go up to 20% more in port volume and flow. The port size and flow is all in relation to piston speed which is determined by rod length, shorter rods faster speeds and longer rods slower speeds. Short rod engines need larger ports and more flow and long rod engines need smaller ports and less flow. As the differences in the BBC and the BBD, the BBC has a 4" stroke and 6.135 rod and a 290cc port in a 990 square port head and the 440 BBD has a 6.768 rod and a 182 cc port in a 452 head. Yet the power is similar and the Tq. also.

The optimum crank angle is 10-12* past TDC for best Tq and Hp. This is where the rod ratios come in play and this is why Mopar likes a 1.80-1.85 rod ratio. And I know someone is going to say well the 360 is 1.72 rod ratio, this is true and this is why you have seen alot of these engines in trucks and vans and large passenger cars as the rpm's would have been kept lower. The only way to help this out in a larger stroke engine is to move the piston pin location, but this can get expensive.(custom pistons)

My 404 ci engine needs a 196 cc port runner and 315 cfm's of air flow, the heads that I have on it are 184 cc's and flow 316 cfm's with a 2.08 valve but this is a BBD. If you can get the flow without haveing the port volume then the engine will respond better and ET quicker as port velocity will be better. And this you'll see in the 60 ft. times.

The heads that I would use on a 408 would be the 190 or 177 commandos, if you can afford the 190's this would easily get the job done and get the flow that the engine would need. I did a set of these and they flowed 324 cfm's and were 196 cc's with a 2.02 valve. A smaller head would give more Tq and low rpm Hp which is more desireable for street, something like a head in the 160-170 cc range and flows like 270-290 cfms @ .600 lift. This would mean that the low lift flow #'s would have to be very strong, something like 170/220 @ .3/.4 lift. Hope this helps you decide on what you want for heads.
 
Moper,
What was the piston speed on that engine? I think if you look or have a way of finding out that the piston speed was over 4600 FPS and this is why the HP fell off @ 5400 rpms.
 
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