j9fd3s

room for a long exhaust? i wonder what a longer intake does too?

ikari89

the longer intake will shift the peak VE point down, so yes for the lower rpm application you are going to want longer intake and exhaust runners.



was that what you ment by "longer exhaust/intake"?

Jeff20B

Yes, a longer exhaust and intake would be great. Unfortunately there isn't enough room for long primary runners... or maybe there is. I'll have to get the engine in there and start measuring.



The intake is short because it's carbed. Maybe a carb spacer would do something.

RONIN FC

If you cant lengthen the pipes much, then reducing the ID of the header and the intake(if possible) is a good alternative.



The key is velocity, and increasing the mass of the air column(by length) being rammed, or expelled, from the engine.

iceblue

Being carbed is going to hurt what you want. EFI and a custom fabed mani would do you best.

heretic

Where did your bridge ports close?



For what it is worth, a stock port with proper induction and exhaust will make peak power within a few hundred of 8k, depending on the engine. Most extend ports *will* make peak power above 8k. For an extreme example, I believe it was Mazdatrix that built an E/P engine that basically had NO power peak, at least not one that was useable. 10,000 rpm shift point and it could still make power past that if it could hold together. It's all in the closing line versus port area.



As regards your second question, perhaps it will better answer your first. Yes, at part throttle the power sucks due to charge dilution. But if you want more power the first thing you do is open the throttle more, so in comparisons about power (versus driveability) at a given engine speed, full throttle is assumed. Charge dilution is a non issue at full throttle. Intake manifold is at atmospheric and the exhaust is generally at or below atmospheric in the chamber thanks to the inertial "slug" of exhaust gases creating a vacuum behind them.



Look at the charts and do the math. You can't be getting high VE with enough exhaust dilution to kill power at the same time, and Mazda's research has shown bridge and peripheral port engines getting significantly higher VE than sideports as low as 2000rpm, which also pans out in the driving experience.

Jeff20B

Maybe some day.

diabolical1

now this is what i call a thread. extremely imformative and no one trying to start a ****-fight because they have differing info. the idea-mill in my head is churning now. i have some ideas for one of my next engines. i even see where i've made mistakes in the past now. i think i need to get a degree wheel.



thanks and cheers to you all.

RONIN FC

Oh, I remembered if your running a 4bbl carb, keep the secondaries closed longer to keep the velocity high in the primary ports.

guitarjunkie28

are you referring more to n/a's than turbos? i hardly ever see turbos peak that high.



to answer your question on the closing, i think it was somewhere around 65* or so.