This is the intake not ported and with a 1205 gasket (*corrected). The heads are 1206 but with rounded corners, AFR 1095 Comp series. The intake is closer to a 1204 I think? Seems a bit gratuitous for an anti-reversion step, no?



The interesting thing, is that I think the CSA of the runners with a 1206 jumps to something around 2.8" which according to simple calculators projects as way more RPM than I need to turn. I'd be happy shifting for max power at 6500, so a peak around 6-6.2k. Currently the motor peaks way below that. I realize intake CSA isn't everything, but don't want to drop a lot of dough to make a further mis-match.

I also have a brand new XFI 280 cam on the shelf... just not sure I want to put it in yet though.

383cid
AFR 195 Comp heads
LPE219 +4deg advance ground in
LT's dual 3" exhaust
ProFlo XT intake with 90mm TB (Edelbrock says it can go to 1206, I've been running it with a 1206 gasket, just with horrid mismatch.)
403rwhp/417rwtq

(If I don't do the cam, I should probably at least put 1.7 rockers on there to get some more air flow.)

 

To be honest I think alittle port matching will help gain a few ponies here. I know my one friend has made big power with a miniram 1204 port on 1205 and 1206 heads before but you really want a smooth constant transition from plenum to valve; a gradual taper is desired.

I'm not a fan of high rockers on cams to get lift. Its harder to get proper valvetrain geometry. I'd just keep the 1.5-1.6 rockers and run proper cam lobe if you need more lift for the setup.

Combo is making big numbers for the cam and intake so I think a port job will only help alittle. Intake is likely not flowing near as much as the heads and alittle bit of flow support may help bring up the hp numbers. Not always guaranteed to work this way but is possible.

280 xfi cam should put you in the 6500 rpm shift region. Do NOT run more than a 1.6 rocker on that cam. They are pretty hard to control as is.

 

Orr, thanks for the response.

First thing first, that is actually a 1205 gasket. Not a 1206, so they really are 1204 ports right now.

I would hope it would eek a bit more HP out of it but who knows. I was playing around with rough calculations for CSA though and I got this:

Equation is: Peak torque rpm = (constant x ave CSA.)/ci of 1 cylinder = rpm

Current setup: 3.5" CSA in plenum tapering down to 2.2" CSA at port exit
Ave Intake CSA: 2.8"
RPM for 383: 5158

Ported to about 1206:
Ave Intake CSA: 3.07
RPM for 383: 5656

Exhaust is 1 3/4"
CSA: 2.19
RPM: 4034

Current TQ peak: 4500
Current HP peak: 5350

So due to the large plenum entrance, I wonder if you can get by with a smaller intake exit?

I wonder, what porting would do here? Does having a larger RPM split drag the curve upward or does it flatten it out into unusable RPM (I don't turn usually past 6500)?

And yeah, I have the 280xfi just haven't decided if I want to put it in or not... hmmm

 

Also depends on air flow velocity profile. you can have a measured cross section of XX inches but if the flow is not smooth across that area, it could act smaller than XX inches.

For rough estimations on port CSA for rpm limits I use PipeMax. A simple software program that seems to work well but not all engines model exact on it.

Does give ok estimations on head port cross sections to support RPM.

A bit of taper does help in the runner shape but the flow is going to be limited by the minimum area set by the entrance to the head. Most heads are limited at the pushrod pinch or the throat. Typically you want the min csa to be at the throat of the head port but sometimes its limited at the pushrod pinch. So it would be nice to see the intake opened up through out to help transition the flow into the min csa region of the head port.

Atleast smooth out the casting flaws to eliminate any troublesome turbulent areas. Dont polish it much just smooth it out with a cartridge wheel after using a burr to open the port out alittle.

I know for a fact those heads are large enough to support 6300 rpm peak power with a good cam lobe. Just extending your rpm range that much with the larger cam will net a good hp gain. IF the intake can support it, then it will make power.

 

So in regards to head port CSA -- RPM. It seems usually these are what the formulas are getting at for intake flow, really head flow more than intake manifold flow. Does pipe-max tell you a different CSA number for intake manifold CSA as opposed to head intake runner CSA?

I also know that the pinch point in the AFR 195s is something like 1.96", which would yield peak torque at 3610 RPM. But maybe that is wrong, I know the valve is 2.08."

I think they should be at the least cleaned up and maybe taken to a 1205 or something. (60 grit cartridge roll?)