https://www.rx7club.com/showthread.p...hreadid=237561

 

^

 

If you are looking for more than 25K, but less than 120K, then go with a small secondary bridge. Keep the bridge decently large and the engine will last. Most people don't make the bridge large, though, as they are not concerned with longevity at that level of porting, but that does not mean it is impossible.

This set-up allows you to easily add a turbo at any point, and will allow for a much more powerful engine.

BTW, in answer to your question, the engines will make similar power when prepped as you suggest, with a slight advantage going to the 4 port.

 

Glad to see you're back SCath. Your nitrous write-up on 1300cc will come in handy later (125shot if my car runs 13's N/A)

 

You should see my latest system. I never quit!

 

Get a website up man!

 

I broke my Halteched large streetport 4 port in NA. Even exhausting through an S4 turbo manifold and empty S4 turbo exhaust housing into a 3.5" turboback-

it made LOTS more power everywhere than my stock port 6 port running 2.5" racepipe.

That should be a no brainer .

Now, it did max out my 720cc primary inj by ~5,000rpm (couldn't get 1600cc 2ndaries online w/ out stumbling)- so that should be over 200hp by 5,000rpm!

The small bridge sounds like a good idea to me as well, but I would be more leary of Nitrous Oxide on a bridge port as compared to street port as the thermal shock to the thin cast iron bridge may really shorten its life span. Anyone w/ experience on this?

 

How did you break it exactally? Run lean and pop it?

 

I was worried about the thermonuclear shock myself, but am yet to have it break either of my bridged engines. It is one reason why I place my injector nozzles relatively high in the runners. (the other is to allow fuel atomization with the fuel with wet nozzles).

Nitrous oxide is jetted into the engine at -127*F, yet through all of my experiences with running it direct port, I have yet to see it cause a crack anywhere in the intake tract. My theory is that the incoming air charge is so heated from heatsoak through the intake manifolds that the nitrous vapour simply absorbs all of the heat from the air charge, and is much warmer when it actually enters the engine. Also, direct port mixes the nitrous oxide directly with fuel, which is typically warm. This would directly heat the nitrous charge.

When you consider direct port on V8's, though, the nozzles are extremely close to the intake valves, typically placed within inches of the heads. The valves are extremely hot, and get thin as they approach the edge of the valve diameter. They also hammer rapidly against the valves seat. Yet, exposure of fresh nitrous oxide on the valves seems to cause no chipping or cracking of the vlaves, despite the repeated hammering motion!
Again, I think the air charge simply heats up the nitrous oxide/fuel vapour.

I have considered installing a air temp sensor into one of the runners as close to the engine as possible to monitor the effects, but everyone knows the argument of time and money, something university students tend to lack an abundence of.



Any other theories as to why thermonuclear shock is not a factor?

 

How did you break it exactally? Run lean and pop it?

Broke it in NA...

No breaky till later when it got the turbo...

 

Scathcart- I hadn't thought of direct port Nitrous applications on piston engines. That does sound like a lot of thermal shock on the intake valves, but they hold up fine.

I trust the cooler running bridge in a rotary would be fine as well.

 

keep hope alive