well this point might be lossed on the efi crowd due to the type of intake we use but was wondering on a dual plane intake what would be the benefits of applying this theory to an engine.first as you all know the 4 middle cylinders have shorter runners from the intake opening what if you were to change the way the engine makes power?being that the intake has short runners is it possible to give those four cylinders a shorter connecting rod and large valves with huge ports to make horsepower?second the outboard cylinders have longer runners what if you were to give it a longer rod small valves and high velocity ports just to make tourqe would that give you the best of both worlds?i know cam timing would be an issue as well as the longer rod,small valve part would hinder the engine at high rpm's just an idea if anyone has touched on it.

 

i'd go for a sheet metal intake with more equall runners. on the street and even bracket racing the preformance from the unequall intakes isn't usually a problem. i think your engine would have balance problems.

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ICON Motorsports
1st & 3rd
MM Black Diamond 538 F&AM

 

This is done but it requires much more r&d than the average person can perform. Your talking about fundamentally changing the intended rpm band by a significant margin. If you get it wrong the .bsfc will be terrible (actually, even if you get it right, bsfc will be good on some cyls and bad on others at the same rpm).
Most combinations don't allow you enough room in the engine area to implement these changes. The intake would need 4 runners that are below 4 inch and others 12+ inches. You would also need to size exhaust and camshaft (a true dual pattern) specs accordingly. Look at the examples in new cars, intake manifolds (and cam duration in some cases) that are effectively long at some point and short at hirpm (viceversa for cams). They use all kinds of electronics to implement this function and inmost cases and, rarely do you see more than 20hp over the previous version of the same engine.


A better approach (when carefully applied), is to use alternating hi/low rpm elements on different parts of the engine.

Use a small carb with big heads (keeps velocity).
Use a big cam with dual plane intake (see above).

Use big exhaust with small duration cam. This can be applied to many areas of engine configurations.

[This message has been edited by jcb999 (edited June 21, 2001).]

 

I believe i remember a letter in either chp or car craft that addressed a topic similar to this. They said that an engine built in this manner (big valves, short runners, lotsa cam, big header tubes for HP, opposite for max torque) would have multiple torque peaks (duh) but would also have a very pronounced dip between the peaks. They also said that someone built an engine with 8 different combinations, one for each cylinder, with each one moving slightly up the torque band. The result was a billiard table flat curve that made power everywhere. It also took more money than the large majority of us will see in a lifetime

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DG

1984 Z28 LG4/A4
Mods: are you kidding? They cost money.
Powered by Eclipse, Kicker, Rockford Fosgate, JL Audio, and MB Quart.

 

reason i asked this cause saab came out with that ****ameme engineeremotor that lets the cylinder head travel effectivly changing the compression ratio at different rpm levels for instance 700-2800 would yield 12.5 to 1 for tourqe as the rpms increased the ration would drop back leaning out the mixture to make hp has anyone seen this idea?

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