Jeep Strokers

I had a standard hesco aluminum head modified for a 1.570 exhaust and a 2.02 intake. The intake flowed about 250cfm @ .6 lift (25") the exhaust flowed only about 141cfm at the same conditions. I wanted more flow from the Exhaust, so i sent the head back to Hesco and the opened up the exhaust ports on their CNC mill. They made the ports round and moved the top of the port up about 1/4" The Exhaust now flowed about 155 CFM. I want to get the exhaust up un the 180-190 range (28") and the intake near 300 cfm(28") .

You cans ee from the picture that the valveguide extends quite far into the bowl. We are goint ot reflow the head @ 28" then see how close we can get the the target.

I took the head to the engine builder today. He had a stock 331 head lying around, What a difference in the size of the exhaust ports! maybe somebody has a picture of a stock 331 head to compare with the aluminum head.

Yeah the 0331 exhaust ports are the smallest compared to the 7120 and 0630. Apparently that was to heat the precats up faster. No wonder they spent the dough to improve the 99+ intake manifolds to bring power back up. That 2K head is costing you a bit more, eh? Let me know if I was in the ballpark after you're done. I wish I could have a go in the driver's seat of a Jeep that can do 160+(I know you're shooting for ~175).

I should have my 0331 finish ported soon, I will be interested in what I can do with the exhaust port.

Sure is a purdy head!

Here's a pic of my Alabama Cyl head with 0331 exhaust ports

The exhaust ports do not flow as good as you might think, even with a 1.570 valve and the large port, the exhaust only flows 149.1 [email protected] lift. The flow before opening up the ports was 136 CFM@ .5 Lift. The sticky thread here show a flow of 147 cfm with stock valves and some porting work. We will be changing the valves to Manley swirl polished units and reflowing the head. I will keep you posted.

The reason that exhaust flows so much worse than Intakes is also the reason that porting wont make dramatic increases in CFM, you're blowing exhaust past the flat face of the valve against the grain so to speak. The valve face has a much worse coefficient of flow in the reverse direction than is does in the intake direction.

Much of the work of evacuating the exhaust gasses is done by siphon effect AKA scavenging, this is why long tube headers are a staple of any performance build no matter what engine we're talking about.

If you analyze long tube headers they seem counter intuitive... Intuitively you want the exhaust gas to have the least restriction possible... short and fat primary pipes would seem to be the best way, or no exhaust at all open to air, with a port that you could fit your fist down... But that's not how it works... The smaller "hose" creates a nozzle effect that makes the spent gasses fire out with high velocity, by the time it's traveled down a "long tube" (usually 28 inches or longer without interuption or meeting other primaries) this velocity starts pulling a vacuum in the cylinder even when the piston is slowed and reversing back down, then the intake valve cracks open.... the depression inside the cylinder; creased by the high velocity gas (from the small ports) going down the long tube primaries litterally sucks intake charge into the cylinder during cam overlap, (some goes out the exhaust too but that's not the point)... creating part of the volumetric efficiency equation that allows efficiency to be above 100%...

In short, don't worry too much about exhaust, get it as good as possible without making the ports ridiculously oversize.

One of the reasons the 0331 head has smaller exhaust ports is that Chrysler corrected the overly large ports on earlier HO heads and fixed the lazy port floor that anyone with a bench can see for themselves, or read about in NOSIGMA's porting notes. Lazy port area's are counter productive and do nothing to improve flow. In fact they can worsen flow to the point that they create a vortex that effectively makes the port much smaller than even the 0331. This is known as choke, it's what happens when turbulent air starts to take up space that is supposed to be used by air that is streaming down the port. Think of it like an eddie in a river that the river current can't flow through smoothly thus lowering the effective space between the banks where the river can flow.

1bolt wrote: One of the reasons the 0331 head has smaller exhaust ports is that Chrysler corrected the overly large ports on earlier HO heads and fixed the lazy port floor that anyone with a bench can see for themselves, or read about in NOSIGMA's porting notes. Lazy port area's are counter productive and do nothing to improve flow. In fact they can worsen flow to the point that they create a vortex that effectively makes the port much smaller than even the 0331. This is known as choke, it's what happens when turbulent air starts to take up space that is supposed to be used by air that is streaming down the port. Think of it like an eddie in a river that the river current can't flow through smoothly thus lowering the effective space between the banks where the river can flow.

This is exactly the reason that I want to get my ACH with the 0331 ports on a flow bench. I would be willing to bet that even with the smaller ports that they flow at least the same or even better then the older, and "lazy" ports. Everyone thinks that because the ports are smaller that they won't flow as well, but I don't think thats the case.

If nothing else it should be a good low end torque producing head...

i have a 0331 head here. i think i am going to throw it on the bench and see what she will do.

steve

I've already done it and I think so has Alex22, CFM wise they flow a little worse, but CFM is not as important as the average joe thinks, even with intake flow CFM is only a guideline and a crude basis to judge improvements. CFM is like like looking as a 3 dimensional model in 2d without motion, it can be done but it doesn't tell the whole story. Port size and velocity as well as wet flow are important, maybe just as important as CFM numbers. You can make any hole bigger and force more volume of air through it, but if you make it more efficient by removing dead spots, and smoothing sharp turns the speed of the air speed increases and CFM also goes up...

As for the 0331 I think it will have a torque advantage through much of the rev range, and maybe give up a couple horse power up top... it's why I want to find out which factory castings don't crack. We already know the 0331 intake ports flow better than previous HO heads. For most jeep builds low torque is way more important than a couple peak horse power at the rev limiter.