Sheetmetal Intake

I've been doing some research on building a sheetmetal intake, and have even taken the plunge and started in on things.

My "hotrod" isn't a 30s or 40s odd-ball something or other.. a bit more modern, but at the same time rather odd/uncommon.

I'm building an International Harvester 304V8. I've been running this motor for 8 years in a short-course "desert" style racer.

There are few "hot-rod" parts available for this series of engine, so you have to rely on the "old" methods.

(My tow motor is an offset-ground (stroked) IHC 392)

This engine has been ported, the bottom end lightened and balanced, decked extensively to get out of the boring 8:1 stock squeeze, etc.

The stock dual-plane cast iron intake manifold weighs around 60lbs. There is an aluminum casting version that recently became available that's ~20lbs, but aside from injector bosses and the availability of a 4bbl, it's a recast of the original in aluminum (still a dual plane).

I've been talking of building a sheetmetal intake for years, and a buddy finally called me on it, and even came by last weekend to make sure I got started on it.

After far too many hours with the plasma and die-grinder cutting out the intake flanges (Ugh, next time, I send it out to a water-jet).. here's where I'm at.

(This is a spare block and heads, not the ones I'm going to run)



The rectangles go across for the water passages, and I'll add a longitudinal to make an "I" shape to almost finish the coolant setup.

I need to add a mount for the thermostat and bypass housing to the front, which won't be too bad other than perching the cast-iron stockers on top of my light-gauge intake.

You can see my first two mock-up runners. 1.5x1.5x.065 square (intake ports are ~ 1.375x1.375).

I might lengthen them slightly to actually touch. That'll work for the center 4 runners at least.

Or I'll cut a little angle into the flange side and lower the carb a bit - I needed to get to 12-15" in runner length to tune the intake, and I'd rather keep the carb low and just settle for ~40lbs savings and a single-plane.

Searching through the HAMB, there are several good sheetmetal intake designs, but they're almost all dual (or triple) carb setups.

I'm leaning towards just a single, 600-700cfm square-bore.

(I've been running this motor for 8 years with a 500cfm 2bbl perched on the only factory intake available. With the previous setup, it would float the valves at 6300rpm but it would pull right up to 6300rpm. This overhaul involved heavier valve springs (from ~100lbs seat to 140-150lbs) to allow more RPM, but the carb wasn't quite choking the engine before).

Dual carbs would be more difficult to tune, and this engine isn't a big-inch (bigger than 304, but less than 345) monster. I also need this to operate in some filthy environments, and 2x the carbs means 2x the cleaning and overhaul on 'em.

I was planning a "V" bottom plenum. It would be EASY to build a full-length V bottom ("log" style, I believe you call it) and mount the carb over the center 4 runners.

I'm concerned about fuel distribution to the front and rear cylinders, and overall performance with this setup. I wouldn't be with dual carbs, but again, I'm not interested.

My current thought is to put the 4 center runners together much like I have pictured - straight into each other - and then lean the 4 corner runners in to the center.

Should I try to cut them all off such that I get a "V" bottom, or would a "diamond" (two 90-deg opposed Vs) be preferable, having the plenum ramp "up" on either side of the engine, as well as the front and back?

This would then be the bottom of the carb box / plenum, with the 4bbl perched atop.

Would a little gap in the center (between the front and rear runners of the 4 center ports) be fine, or should I shoot for leaning the 4 centers together into one bunch, too?

The engine is setup to run 2,000rpm through at least 6300rpm (historically). I just put new valves in it and the heavier springs, but keeping the current cam grind and everything else (so 2-7?).

The TF727 has a high stall converter and the heavy duty guts to hold up to the abuse (thus far, I've only broken one case and imploded one set of guts) and thus real-bottom-end isn't necessary.

It idles high as it is (was).

My hope is for a functional racing manifold when I'm done, not just a fashion statement.

I'm open to any advice or criticism, including the ones that start with "Why would you hot-rod an International dump-truck motor??"

 

very cool i love oddball motor builds.

 

Maybe somebody here can dredge up some old photos of a Crower U-Fab manifold in either finished or in kit form.

 

If I could make a sugestion, you would build a multi pannled plenum, something with 8 sides, and then match the runners to that. Or, build a 2x4 plenum, and use a single plate at top. Or, you could build more comple runners like in the picture below. Take a look around at the websites of the various sheetmetal intake manufacturers (Hogans, Wilsons, etc).

jn6047

 

Oh, and by the way, I love the idea of your intake and your engine. I've got a 392 for my project that I had work done at Campbell Automotive in Edmonton Alberta several years back. They did extensive head work, balanced the bottom end, added a bigger cam (Sig Erson), and stiffer valve springs. They were very impressed with the stock bottom end, being that it is a skirted block with steel crank and forged rods. Unfortunetly we were unable to dyno it because I could find my spare fly wheel, but they figured I had a real torque-monster on my hands. I asked him what he thought it would be, and he said just guestimating that it would have around 400hp+ and 500lbft+. One day when my truck is done I'll be taking it there for chassis dyno.

There is also a company that makes roller rockers for our IH engines that work on the stock rocker shaft. It's a company that makes tractor pull equipment. Can't remember the name but do a search at binderbulletin.org and you should find it. I've got a Mallory mag pick-up distributor coming for mine, and I plan to purchase the IH Only intake.

Check out binderbulletin.org, as there was another guy that did a stroker 304 with a sheetmetal intake there (but he was planning 2x4 if I remember). As well, there is a fellow in Ohio by the name of Jeff Clouse. I spoke to him a few years ago. He has a BDS 8-71 on his 392 with BDS fuel injection (first EFI they did). He was getting 700+hp on the dyno and 7-10mpg in a lifted Scout II with 44", steep gears, and the blower underdriven! I beleive he had forged 7":1 pistons and a relatively stock bottom end. There was another guy that was competitvely pulling (DLH Machine) that was getting close to 600hp naturally aspirated with mostly just custom machine work on his 392. He stepped up to BBC to be more competitive, and he said that $ for $ he could build 2 of his 600hp 392s for the cost of a slightly higher HP BBC! Lots of potential in these engines given enough thought and machining, but the ceiling seems to be aroudn 600-700hp due to restrictive exhaust ports.

jn6047

 

if your going to do a tunnel ram style intake the rule of thumb is to have the upper plenum just under half the cubic inches of the motor,, ie 300 cid motor; 150 cid plenum.

who is thumb anyways??? and why do his rules apply to just about everything??

 

I had this made..It's for a Hemi, Dodge..It has the upside down "V" down the center of the plenum..
Duane.

 

With the long reach to the ends, you may think about switching to round exhaust tubing then flare the ends to match the ports. You can buy pre-bent tubes pretty cheap. Once all eight are welded together, it becomes very rigid so wall thickness isn't all that important.