Historic Sportscar Racing: Sebring Dec. 2015

[FJCamper]

Hi Fog,

We are working with the Kaddie Shack to modify a set of stock aluminum Kad manifolds as far as they can be modified, while the ultimate solution of a hand-welded steel tube manifold is in the works.

A Four-Kad system, each carb on its own manifold, has even been contemplated.

I finished disassembly and examining of our other 44 Weber today. My feeling that it was just a sticking needle and seat on one carb seems justified now. At one moment in our troubleshooting out at the track, it became apparent we had one dead carb, because blocking the velocity stacks with your hand on one carb (at that time) would just kill the engine.

Of course, there were moments when fuel was entering both carb float bowls, and the engine would try to run.

FJC

[sideshow]

If you are thinking a quad-kad system, take a look at short fresh air IDA manifolds. They don't provide enough room to do a split shaft, but it would be possible as four independents.

Of course that leaves linkage nightmare, that is where I gave up. The best idea I had was to use the Berg center chunk and drive four cables.

[Ol'fogasaurus]

FJ, do you have access to a flow bench? If not there are instructions on line on how to make one.

With a flow bench there are so many ways to test designs like putting a plentum on w/wo a balance tube(s) or runner lengh changes. Even putting a 4bbl on ) might be possible.

There used to be a product that I think was called "Extrude Hone" or something like that (I just checked and it is still around and that is its name). It is "abrasive machining"; gus used to use it for port clean up or enlarging them on heads.

I've never used it or seen it used but I remember when it first came out.

Lee

[FJCamper]

Hi Fog,

I don't have a flow bench or a dyno, and have to depend on those who do.

From my research, a set of dual Kads with 44mm throttle bodies and 36mm venturis, and 40 to 44mm intake valves will support up to 150 HP. Then, with our 25" tires, 0.93 4th gear, and 3.88 rear end, somewhere between 6500 and 7000 (redline) we have 140 mph in our HSR Ghia.

We have seen 123mph with 4.12 final drive, 34mm venturis, and a 6000 RPM redline in our Mexico Ghia.

The challenge, I would think, in designing a manifold is to have flow with velocity, not just one or the other.

FJC

[ps2375]

There used to be a product that I think was called "Extrude Hone" or something like that (I just checked and it is still around and that is its name). It is "abrasive machining"; gus used to use it for port clean up or enlarging them on heads.

I have looked into this at one time, and the cost was pretty steep back then. I seem to remember it being greater than porting by an experienced shop. But I'm sure it has it's place, like when working on a manifold with long curves that can be difficult to reach w/o cutting it open.

The challenge, I would think, in designing a manifold is to have flow with velocity, not just one or the other.FJC

That is the Black Art right there.

[Ol'fogasaurus]

I agree about using the honing paste on curved areas and I also would be concerned about it taking out too much metal in those areas also ... but "any port in a storm" (pun intended!)

One advantage to making your own intake manifold(s) and matching it to a head (combination) is that you know you probably have the best you can get. Also, you can tune runner and port length for the RPM range you will be working in the majority of the time; e.g., tork vs. RPM.

I was watching one of the "how to" shows on Spike and they were working on a Jeep. They modified the Jeeps intake manifold so they could use a self learning 4Bbl injection unit along with a RV style cam (high lift, short duration). The object was one HP per cu-in. and a tork curve that matched it.

On the dyno, after break in the best they could get was below the HP and tork they were after so they put on an old 4Bbl carb they had used on something else. After some rejetting and timing adjustment they got the desired HP they wanted and better torque.

My point being you can modify but you also need to tune and tuning can be part of the basic manifold design also.

For what it is worth.

Lee

I forgot to mention some things. They used an adapter that they had laying around to make the conversion to a 4bbl from a 2bbl manifold. The unit they used looked like it was one of the old conversions to rise the carb up and create more of a plentum chamber. They did not trim off the bottom, or so it looked to me, and it looked like the extension area might have gone down into the manifold more than it should have.

If I remember correctly they do (or had) a flow bench and I saw or heard nothing that said they used it. If that is true then it was a shame as it was a good lesson giving engine build.

They were working on a Jeep I-6 and it's intake is reminisent of the old slant 6 maniford that Mopar had; not like the "bounce" manifolds that are around or even the Chev style of manifold that made it rich in the center cylinders and lean towards the end cylinders.

More than you probably needed to know but it might give someone some food for though/something to think about.

Lee