Technical IR manifold theory

Just for shits and giggles, I ran the numbers on my combo, rounding down it would call for 42mm venturis, so if the venturi should be ballparkish 80% of the throttle plates 48's mm dellortos would be on the small size. From what I am reading, booster signal deteriorates if the venturi size exceeds 80% of the throttle plate size, you want to be around between 72% and 80% of the throttle plate size.
56mm Bergs would probably be ideal, but thats BIG $$$
Metalshapes, you built your intake from a rochester fuel injection base right? You could probably build a decent intake from an Edelbrock TR-1YX or early Weiand tunnel ram.

 

I built an IR intake for my 320 inch GMC six with a Howard 12 port head. No books. No science. Just a drill press and torch. Had 270 CFM (OEM on Rambler V8) Holley carbs. Then I switched to 500 cfm Holley's. On the dyno it had lots of reversion. Big cloud of fuel above the carbs. Made stacks for it and ran it in my '32 Ford coupe. Got the XXO/VGAlt record in '84. Then I sold the engine to George Cambell and he put it in his Salt Circus roadster. Did very well in his car. Wasn't really fast but it did OK.

 

Science isnt always a bad thing...^^

 

Science is usually a good thing. But you have to be smart enough to interpret it. The rest of us just cut and try.

 

This is my second set of Webers on this engine.
The first set was home made from a early Vette lower FI intake, Citroen/Maserati DCNF's and adapters & linkage I made myself.
The second set is a IDA setup that was probably matched for a 302 Formula 5000 or similar.
I kept the venturi's the same, and they were a nice match for my 400 Cubic Inch Donovan.
Its a beautifully torque engine that will still rev. ( just over 500/500 both torque and horsepower )

I've never owned anything like it...

The one tip I can give that really seems to make a difference, is spend plenty of time on the linkage.
I made a progressively acting linkage for the IDA setup, and that made a lot of difference.
( slowly acting for the first half of travel, and then quickly from 1/2 to WOT )

 

I'll do a build thread about the Morgensen Special when I'm going to restore it.
Here is a pic of it, taken in 1954.

 

George, specs on the cam.

Lift: .525/.555
Duration: 288/296
Lobe center: 106
Solid.

 

Thanks Alex, And further to this, pretty much what I figured...Note Davids comment below that the 383 wanted 1 degree less with IR.
And David runs 106 in ALL his 383's, so one degree lees means a 105 LSA. I will hazard a guess, that based on my calculations, the 383 wanted 1 degree less because the 48 IDA's actually constituted an inlet restriction on the 383. Typically, an engine with a restricted inlet tract will want a slightly narrower LSA.
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Re: Vizard's secret '128' cam spec # revealed
by David Vizard » Mon Mar 14, 2016 2:52 pm

falcongeorge wrote:Question for David, pretty sure I know what its going to be, does using an IR intake affect the optimum LSA for a typical 2 valve wedge combination?

Yes but not as much as I had expected. Tried different cam LCA in a Pontiac 455 and a 383 SBC with 48 Dellorto's on. The Pontiac was no different to a single or two plane. The Chevy wanted one degree tighter and the difference in power was only about 7-8 hp. Would like to have done more with IR but ran out of time. However I suspect I may have an opportunity to do a lot more with an IR system on a 289 Ford later this year so we will see what transpires

DV
David Vizard
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Re: Vizard's secret '128' cam spec # revealed
by falcongeorge » Mon Mar 14, 2016 2:57 pm

David Vizard wrote:falcongeorge wrote:Question for David, pretty sure I know what its going to be, does using an IR intake affect the optimum LSA for a typical 2 valve wedge combination?

Yes but not as much as I had expected. Tried different cam LCA in a Pontiac 455 and a 383 SBC with 48 Dellorto's on. The Pontiac was no different to a single or two plane. The Chevy wanted one degree tighter and the difference in power was only about 7-8 hp. Would like to have done more with IR but ran out of time. However I suspect I may have an opportunity to do a lot more with an IR system on a 289 Ford later this year so we will see what transpires

DV
Thanks David. I was guessing it didnt make any difference.

 

David Visard is still around?
Cool...

 

Hes on Speedtalk regularly. He has cut way back on the seminars. For those that dont know, David Vizard started his career on Mini-Coopers and Ford Kent motors, so needless to say, he has TON of weber and Dellorto IR experience under his belt.

 

I had my 3c ida's on a stock 231 Buick v6. It ran better than the 2bbl and gave the same gas mileage. I had to choke them down to 24mm but they ran very well. I then built the engine and when I ordered a cam I was told that reversion was caused by excessive overlap. I ended up with a Crower 282-fdp
Intake lift .478 duration 282*
Exhaust lift .486 duration 287*
LSA 107*
overlap 26*
solid lifters
The engine has seen 6k but with the adjustable pushrods I try to hold revs to 5500 rpm. While chopping the plugs at top end I haven't seen any raw fuel on the tops of the carburators (reversion). The ram tubes are 2'' long and I feel the engine runs better without them but the tubes put the occasional backfire during cold starts above the carbs. Gas mileage is about 20 mpg driving around.