I was just wondering which intake manifold is better for making power in a NA. I have heard that the S4 is better for torque and the S5 is better for house power. Just wondering. Thanks

 

The S5 flows better and makes more power. Mostly due to the valve that retunes the intake runners at 5500 RPM. Someone just posted dyno results on the forum not too long ago and showed a nice power increase over the S4.

 

This is true only on stock ports. Once you go with a ported motor, the S4 is the better option.

 

Do you know how come? Would it be better for my motor since it is ported and running a TII middle housing?

Thanks

 

Thats interesting...because i have a S5, and i put down 167rwhp. (I'm making even more now. Probably around 175-180rwhp..but have nothing to back up the claim except hp calcutations due to 1/4 times/mph.) I'm yet to see a s4 put down anything like that......need some dyno graphs to back up the claim. CJ

 

Not an S4 engine, an S4 intake manifold setup.

 

Heres my opinion based on my little bit of comon knowledge about airflow. The less restrictions equals more , faster flow wich equals more horspower (top end) Dont know about torque. Dont care either. Im interested in top end and with the S4 intake runners the middle manifold seems to be perfectly streight wile the S5 VDI setup has a bunch of curves and twists for airflow to get stuck on and create turbulence. That sucks. If this is true than some day I will upgrade to S4 middle intake. Thnx

 

The inside of a s5 manifold has alot smoother bends than you would think. Not to mention, they're madrel bends. Also, a s5 with the vdi in high rpm mode, is quite a bit shorter than a s4. Anytime you have a shorter intake manifold, you'll make more peak power. Assuming that the runners are of the same size

Kinda funny, the s4 guys want a s5 intake manifold, and now the s5 guys want a s4.

I agree that a straight manifold would make more power, but it needs to be shorter in length. CJ

 

oh ok. I didnt think the S5 was shorter. Yeah thats one of the maine reasons why manifold porting gets you more power is because your shortening the path. Mainly on the lower VDI part.

 

Mid next week, i'll have all my dyno sheets up on the web. I have a peripheral port 13B, street port 13B, my FD with a down pipe, and my 90 FC. I can't seem to find my 167rwhp run.....but i do have my back up run of 166.4rwhp. I'll post them. CJ

 

The best NA block is the S5 block...The higher compression rotors and lighter rotating assembly make the S5 block a better starting point. Actually, you don't need the whole block...just the rotating assembly.

Now, if you DON'T port the intake ports and the exhaust ports, stick with the S5 intake. It will make more power with the VDI.

If you do port the engine, the PORTED S4 intake will produce a higher PEAK HP number than an S5 intake. This is due to the straighter runners of the intake.

Porting the S5 intake and intake ports negates the effect of the VDI, thus resulting in less 'charge' being forced into the combustion chamber. Think about it: If you port the intake ports, the intake stroke of the rotor stays open longer. Thus the "bounce effect" of the VDI occurs latter and has less time to pulse into the opposite intake runner.

Of course we are talking about PEAK numbers here...The more you port the S4 and S5 NA engines, the more you move the power band up the RPM range. Heavily ported engines have low HP and torque down low and become useless on the street.

About now your probably wondering how I came to these conclusions, because we all know the Dyno is the only way to prove anything. All I have is the Dyno charts of about 10-11 different people that have done NA porting and Intake swaps. I've made my own conclusions and posted them here.

My own 86 has been an on going experiment and I've been through the following setups:
S4 block with S4 intake - no porting - Header/Catback
S4 block with S5 intake - no porting - Header/Catback
S5 block with S5 intake - street porting - Header/Catback
My favorite setup to date was the S4 block with the S4 intake. Why? Not because it made the most HP, but because it had the most torque down low. I've never been able to launch my car the same as I did with the S4/S4 setup.

The next time I rebuild my engine, I will be going with an S5 ported block and a ported S4 intake.

 

That's some interesting info guys. I never thought about a ported motor changing the rpm at which the vdi was tuned. I also never thought that an S5 would outperfom an S4 intake. I'm going to be up all night staring at my box of rotary leftovers wondering which is better now.

pp13bnos are you sure the S5 runners are longer? I'm not debating this since I don't have an S5 intake. It just looks the other way around. Do you know the exact difference?

 

Nowone seems to have good proof. So you guys are saying that as long as I dont have an internal street port than a S5 with just manifold porting is better UNTIL I get streetported? If so than good.

PPNOS_ yo this is something that I have known for awile but nowone realizes really. I asked RX7.com what RWP the S5 gets and they told me 125 average. Well if these are getting 160FWP than thats a 35hp difference wich puts you just at 200 FWP. SO anyone with 165RWP hit the 200 hp mark.

 

The s5 intake manifold, has a shorter intake length when the VDI is the "High mode" or after 5.5k.

I've thougth about have Rob@Pineapple build me a mid intake that is ultra short...giving me even more topend. But then i would need something to do away with the stock rev-limiter. As i'm making peak from 7,500 to about 8,200. And the stock rev limiter steps in at 8560 (According to the s-afc.) Later, CJ

Von- I'm not shure what you're getting at?

 

Guys,
I am currently running a s5/s5 set up on my race car with steet port and a very open exhaust. Documented HP is 200rwp. Do you think it could be better with the s4 manifold?

 

have you thought of going s6 top intake manifold for better air flow
is you go to short in a n/a the shorter the manifold the quicker it will rev but you can loose torque thats what i found with a side draught and a ada setup

 

Which is the better option if you've disabled the 6 ports and VDI?

 

^

 

^

 

^

 

In my opinion, i'd stay with the s5. CJ