Plenum Mods
I read that one can improve breathing on a SDi by shortening the 8 standard tubes inside the plenum by 10 to 25 mm. Is there anyone who could shed some light on this? And also, what will the pay-off be since one cannot always gain without a down side? The engine is a 3.5, 9.35:1, Viper hurricane cam and fully ported and flowed heads on a manual 'box in a very light car.
Could a well sorted Holley 390 outperform the old flapper injection system? Thank you, Johan |
Moderator Curtis Jacobson Portland Oregon (4577 posts) Registered: 10/12/2007 02:16AM Main British Car: 71 MGBGT, Buick 215 |
Re: Plenum Mods
Well... I researched that topic and included some of the results when I wrote this article:
Service and Troubleshoot Rover 14CUX Electronic Fuel Injection Quote: I know other people on this board have first hand experience with this and with the other questions you asked (carb etc.) - I hope they'll comment. Johan, you didn't comment on how your car will be used. Real racecars operate in a relatively narrow rpm band, and a carb can be tuned well to suit that car for a particular weekend of racing. It's harder to tune a carb to suit all the traffic, weather, and road conditions you'll experience with a street car. That's where EFI shines. |
BlownMGB-V8 Jim Blackwood 9406 Gunpowder Rd., Florence, KY 41042 (6470 posts) Registered: 10/23/2007 12:59PM Main British Car: 1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS |
Re: Plenum Mods
That plenum volume is close to the displacement of the engine, runner volume is about half of cylinder volume I believe. Some theories hold that runner volume equal to cylinder volume yields maximum torque, I think this was the theory behind the old Red Ram intakes on the early Dodge Hemi. I think you have some room for tuning but the system is already optimized for street use.
JB |
roverman Art Gertz Winchester, CA. (3188 posts) Registered: 04/24/2009 11:02AM Main British Car: 74' Jensen Healy, 79 Huff. GT 1, 74 MGB Lotus 907,2L |
Re: Plenum Mods
Johan, look on-line at the mod's done by the specialist companies, and the dyno results, for each particular build. Bigger trumphets = more flow, not shortening. Velocity is relatively low at entry. You want to build velocity constantly, towards the intake valve. What does "Real Steel" say ? Good Luck, roverman.
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Re: Plenum Mods
WOW!!!
I am impressed and thank you all for the contributions! I should have explained my reasoning...I was considering the mod only to allow more "turning space" between the lip of the tube and the roof of the plenum box..just like when one cuts the choke tower off a Holley to create a bigger gap between the roof of the air cleaner and the carb body. To answer some questions...the 3.5 is in a small Triumph Dolomite on a manual LT77 box with a Ford Capri LSD rear axle, ratio 3.08:1. Now...another question please...what has the experience taught you guys...to balance-pipe or not...?? I "upgraded" the dual exhaust system laste year and put 2" pipes and silencers into car because it failed a 100dB track day sound test and the old silencers had very little guts inside. The gent who made up the new system used internal fits at joints...in other words wherever there is a joint in the pipes the diameter reduces....I thought if I fit a balancer pipe I effectively "open up" another route to help lessen the restriction to flow. Ha-ha, but it really feels as if the car has lost some of its grunt. The balancer is also about 2" in diameter and is quite close to the rear of the engine. Any comments on that? I have a similar system in my Triumph saloon in South Africa which works really well...or so I thought...now I am playing devil's advocate here...if my Dolomite got slown down like this, maybe I should chuck the balancer out of the SA car...hmmm... Thank you again to Curtis, Jim and Art |