I'm wondering if I should open my new Air Gap RPM manifold to match a 1206 FelPro gasket like the intake ports on my AFR heads, or if I should leave the intake manifold ports as they are and just throw a 1205 gasket on there. Will there be any noticeable difference between leaving the manifold stock vs matching it to the heads? It will be a smaller port going into a larger so instead of the other way around where the intake charge would be hitting a wall around the port if the head was smaller. TIA

 

mike - You should read the fine print on the AFR head instructions. They are not as big as 1206 and it warns about you port matching them. When ever you get into high end heads I would not let just any smow without a flow bench and good track record make any changes.

That being said the rule is: The complete intake track for a single cylinder should continue to decrease in size because of the increase in A/F velocity. If you go from a small manifold runner to large head port the decrease in velocity will cause fuel to change from vapor to droplets.

I have big 1206 intake that had lots of time spent port matching it to some heads. When I went to 210 cc with smaller ports it's not ideal, but your creating turbulence which aids in keep the fuel suspended.

You best bet is talk to someone at AFR. Your 1205 air gap might be close enough in port size to really work nice!

 

The problem is that the AFR's are already gasket matched to a 1206 so I'm wondering if I should do anything with the intake to get it closer or just leave it

 

My Vic Jr. intake is gasekt matched to 1206 as well as my heads, this is something you could do yourself, I would do it.

 

You would have to contour the air-gap ports way up inside. The time and effort might make it cheaper to just buy a real 1206 intake manifold that could be matched up with minimal effort.

IMO - The top single plane is probably the world products. Followed by some of the signature series. I've been very happy with Weiands team - G's The 7200 - 7800 rpm models have significatly smaller plenum and runners compared to the 8000-8500 rpm single planes.

The Team-G's take minimal time to port match where the Edelbrocks are lots of time

 

George, why would I need to go way up into the runner? I thought that I would only have to go about 1" up when blending, but then again that's why I'm asking


I currently have a Victor Jr that I'm replacing with the Air-Gap. I don't see 7k +rpms often so I thought I'd try something that is close to a single plane intake but with the torque benefits of the dual plane

 

The complete intake track for a single cylinder should continue to decrease in size because of the increase in A/F velocity. If you go from a small manifold runner to large head port the decrease in velocity will cause fuel to change from vapor to droplets.

I tried to increase low end TQ years ago on hot rodded motor with big 230cc heads. It's not going to happen trying a dual plane. I tried using a Weiand Stealth dual plane.

The intake port runners are a tuned length and size. They actually only increase power over a narrow rpm range by using the ram effect to increase cylinder filling. That's how you can make a motor over 100%VE

If you mess with the last inch of it you could be making a venture shaped manifold port. I really think that these companies put some time and testing into these modern design manifolds. So if you modify them it's sketchy as to whether you ruined them or not.

I fought the dual plane Stealth and decided that it's the whole package from carb to intake to heads to cam to compression that determines the motors dyno run graph. Just by putting a small wimpy unit in anyone of those places is not the answer to adjusting a motor for it's power characteristics.

I've run single planes for probably 100,000 street miles over the years on all kinds of motors and they do work on our sub 7000 rpm motors

 

Could you refresh my memory of your cam specs? If your cam is not too big advancing it 4 degrees can have a significant change in how a motor runs. I've been running my stuff 4 degrees retarded to help the top end and it works.

 

From the sounds of it I should just leave the intake alone then. I assume I should then use a 1205 gasket with it.

Here's my Comp Cam specs. The part number is 12-000-9 which is the mechanical roller blank and the grind numbers are CS 4875S/4876S SR112+4. The lobe separation angle is 112 degrees. This cam has 4 degrees ground into it to improve the lower rpm torque so when it's installed at 108 degrees it will essentially be straight up at 112 degrees. The lift is intake .616"/ exhaust .622" with 1.6 rocker arm ratio. Duration @ .050 is Int. 248 & Exh. 254 . The cam timing events @ .050 are 16 52 63 11.

 

I only spray the head side of the gasket with permetex red. If your heads is 1206 it needs that gasket.

Your cam is hotter than what I run right now in my 427 ci and hotter than any of the three in my 383 ci that i ran to 7500 rpm nearly every day of it's life.

232/240 112
236/244 112
240/248 112

None of them had ground in advance. The first on my list is off the shelf Crane SR cam. The 236 & 240 intake duration were on the edge because of large cc heads. When it came right down to it the 232 was probably the best all around cam. I didn't mind driving it 2800+ miles in two days or smoking the slicks at the drag strip. The second two were very race orientated and instead of 7500 rpm capable would power the car into the rev limiter. If I had my foot on the floor and watching the road I would hear the sequential misfire before I could shift.

The 236 and 240 are in motors right now and the 232 has dents in one lobe or else I would give it to you to try. I could get the one lobe fixed that the roller beat up. Maybe you have a cam regrinder in your area?

 

Thans for the offer, but I've been very satisfied so far with my engine aside from the oil burning issue. The cam has worked out really well.

I'm picking up the heads this week and figured I'd try the RPM Air Gap while I had it apart. It's gotten great reviews where people found the top end to be identical with open plenums intakes but the lower midrange was improved, so of course I have to try one out

 

I had the RPM Air Gap on my 355ci with a CC 270H hydraulic cam 224 deg duration and 110 deg LS and 1.6RR for about .500 lift. I got 285RWHP and 327RWT on the dyno.

I then changed cams to CC 282s solid cam with 236 deg duration and about the same .500" lift with 1.5RR and swapped in the Vic.. Jr. intake. I got 295RWHP and 331RWT.

I don't know what you can take from this but it shows me you don't lose a whole lot of torque with that particular single plane. THe Air Gap is a great manifold but if you ever want to rev it out the Vic. Jr. single plane will come out on top all the time not alot but a win or lose at the drag strip that is why they are preferred