Engine and Transmission Tech

Racing fans,

How would you achieve max horsepower on the Rover 3.5 engine - using an Eldebrock manifold and 390 Holley carb - where the rules specify a .38 mm restrictor in a single air inlet to the carb ?

The shape of the air inlet and the induction hosing - under the hood of a MGB modern Heritage front chassis, with the .38mm restrictor somewhere in the length of the hosing before the carb - is the question.

Any ideas. Any suggestions ?

keep them on the track,

Phillip G

Phillip, you remember the snorkels used on the air cleaners of late 60's and early 70's V8's? some of them were amazingly small for the size of the engine yet they ran quite well. I realize what the engineers were aiming for was noise control, but by tapering the snorkel down to the restriction and making it the length and configuration that they did they were able to get it far enough away from the inlet pulsations to maximize flow through the restriction. I think the same principle applies here, except that if you can also supply cool slightly pressurized air to the restriction via a relatively large diameter hose and a proper venturi leading into and away from the restriction you should be able to maximize the flow through your 38mm restriction also. HTH

JB

Jim is on the right track, but I think Phillip's question deserves more discussion... so I'll throw out a few ideas and bump it back to the top of the message list. Please don't hesitate to tell me if you think these ideas are nutty.

1) IMHO, what you want to do is neck down gently and gradually to 1.5 inches (i.e. 38mm) from a much bigger diameter, and then neck back up gently and gradually to a much bigger diameter. In other words, you want to create a "converging/diverging nozzle" (Google that term for pictures if you're not familiar with the idea) so that any pressure change is gradual, turbulence is minimized, and airflow stays as close to parallel with the walls of the nozzle and hoses as feasible.

2) Keep this converging/diverging nozzle straight, and any hoses as straight as feasible.

3) Make the nozzle sections round in cross-section - don't squash them into ovals like the OEM's usually did back in the day.

4) Don't use corrugated tubing at all if you can help it - smooth walls are better.

5) Above the carburetor you need a plenum with a relatively large volume of air. The top of the carburetor really should have a short velocity stack so that air sucked into the carb from the plenum enters smoothly.

6) You don't need an air filter, but if you insist on using one make it BIG.

7) You'll make more power if you feed your engine cool air, so you might as well grab your air from in front of the radiator or from a headlight bucket if that's allowed. Having a metallic heat shield between the exhaust header and the induction system is probably a good idea too.

If a person could tune the air filter tract to resonate at the desired RPM, that ought to exceed 100% volumetric efficiency - the resonating air would create a standing high-pressure wave at the restrictor. But I have never done anything even remotely like this (well, except to help specify how my exhaust system would be sized. Similar principle).

Sounds like all of this engineering, is based on perceived, zero vacum leakage? roverman.