On an 87 NA what and why would one of these setups be better? I'm thinking about weight, performance gains, etc. What are your opinions?

 

https://www.rx7club.com/forum/search.php

 

lmao....smart ***...I did, all I find is the how-to write up...


and just to point out when I posted here there wasn't another thread on the same page covering the same topic...

 

Hey what parts you need I have a lot of spare parts from this motor I had, intake manifold, throttle body, etc, etc....

I would really like to get rid of this pieces, make me an offer.

 

S5 intake manifolds would be your best bet...they flow a lot better than S4...and look a lot better

 

The S5 manifold is a tuned intake. I works great for stock or near stock engine levels. IMO once you start heavily modifying, especially internally , then it basically becomes useless. There have been a few that claim a HP gain using the S5 manifold, but that is on a near stock engine. Personally I think if you are planning a streetport in the future, keep the S4 manifold. If anyone else has any opinions on this Id like to hear it also.

 

Yeah stay with the S4 manifold. I beleive the problem with the S5 after mods is the VDI system.

Santiago

 

I believe that it is all about the intake runner length. The s4 intake is slightly better for a modded engine. I keep hearing that the best route to go for a ported engine or whatnot is to make your own intake.

 

The S5 manifold doesn't physically flow better than the S4 manifold. Look at the runner length, diameter, and how many bends are in it. How could it flow better? It can't. It's advantage comes from the VDI system. This not only overcomes all the other deficiencies but improves performance. Mazda got really lucky on that one! The VDI system is the ONLY thing that makes that manifold good and it is designed only around stock port timing. When you change the port timing what so ever, you need to change the VDI length to accomodate it. With the S5 manifold and a ported engine you now have runners that are too long, too small, and VDI is tuned to the wrong rpm. The S4 manifold has shorter runners but no VDI valve to hurt (or help) the powerband. The S4 manifold runners themselves flow much better but the dynamic chamber is designed differently. Still without getting too technical, stay with the S4 manifold for a ported engine. An S5 manifold will give a gain of 10- 15 rwhp on a stock ported engine at max rpm but it won't do very good on a ported engine.

 

Not trying to argue, as I agree with most of what you said,, but I really dont think that a 10-15 rwhp is what should be expected from a manifold swap. There is only a 14HP difference between the s4 and s4 engines stock, and that takes into consideration a higher compression ratio, llighter rotors and 1000rpm more to rev to.

 

Actually closer to 10-12 FWHP, rather than RWHP on a stock engine. And dyno tests show that only to be above 5500 RPM.

Bigger gains with a S5 manifold on a S4 block at RWHP would require a free flow exhaust, and most certinly a high performance air filter set up.

Now intresting that a free flow single exhaust (I haven't heard of anyone with real dyno sheets from a true dual and a S5 manifold on a S4 motor) the S5 VDI intake will provide almost identical RWHP to a S5 engine also running a single exhaust. I am sure this is due to the only very very minor torque increase that the S5 has over a S4 motor.

The higher compression is really a minor thing in the S5 rotors. The true advantage of the S5 rotors is the light weight.

 

I remember reading about this a while back and someone had mentioned that it wasn't just the peak HP that was increased,but the whole usable powerband and torque curve were overall better with the S5 manifold, on stock enigine.

 

Decide for yourself, blue: S4 motor, S5 intake, Red: same S4 motor, S4 intake:


BTW: even though the years are different, it is the same motor, just with the S5 intake manifolds, but the same exact exhaust and intake filter set up.

The lower end torque would probably be better if he had the aux/5th/6th ports working.

 

I guess not.

 

In the majority of the rev, the HP is actually a little lower. The power really doesn't come up until the higher RPM.