I'm getting ready to build an REW-based engine for my FB to replace the stupid carbureted S5 turbo setup it currently has. Might run the stock twins non-sequentially to get it going, and then I'm planning on going single later. It's such a light chassis and has so little traction that I don't care about making huge numbers. I admit it'd be fun to try for the magic 400 WHP mark, but I really don't need that much power, so that's not very high on my priorities list. It's a street car first and foremost, so I don't want to get too crazy. A little crazy is fine.

So, should I port it? I'm not really interested in porting the intake manifold or modifying runner lengths, and have no plans to go to an aftermarket one. So would a streetport on the intake side be counterproductive? If not, how far should I go? Open them earlier? Close them later? Both? By how much? Or just leave them stock? The primary ports look pretty small to someone used to the old-school 4-port stuff, but I don't know if it's actually a good idea to open them up with the stock intake manifold. It's worth mentioning that I'll be keeping the stock redline.

I'd appreciate any thoughts or opinions. Also, if you have any links to other threads dealing with how porting affects the tuning of the stock intake manifold, I'd love to read them. It's kind of a hard subject to search for.

 

Port Timing
IO = Intake opens
IC = Intake closes
EO = Exhaust opens
EC = Exhaust closes

North American REPU 3B 13B 1974-77
IO 32° ATDC
IC 50° ABDC
EO 71° BBDC
EC 38° ATDC

North American 76-85 12A and 76-78 13B
IO 32° ATDC
IC 40° ABDC
EO 71° BBDC
EC 38° ATDC

84-85 GSL-SE and RE-SI 6 port 13B
Intermediate (Primary) intake
IO 32° ATDC
IC 40° ABDC
Secondary intake
IO 32° ATDC
IC 30° ABDC
Auxiliary ports
IO 45° ATDC
IC 70° ABDC
GSL-SE exhaust
EO 75° BBDC
EC 48° ATDC
RE-SI exhaust
EO 71° BBDC
EC 38° ATDC

FC 6 port
Intermediate (Primary) intake
IO 32° ATDC
IC 40° ABDC
Secondary intake
IO 32° ATDC
IC 30° ABDC
Auxiliary ports
IO 45° ATDC
IC 80° ABDC
exhaust (with diffusers)
EO 71° BBDC
EC 48° ATDC

Second and Third Generation Turbo 13B and Cosmo Secondary
IO 32° ATDC
IC 50° ABDC
all turbo exhaust
EO 71° BBDC
EC 48° ATDC

Racing Beat "Street Port"
IO 25° ATDC
IC 60° ABDC
EO 84° BBDC
EC 48° ATDC

^I can't confirm these RB port timings as I have no templates handy. The other listings for stock ports should be accurate.

 

Now that that's out of the way, you know my thought is go ahead and streetport it. You've got EFI now to tune utnil it runs best. You're also more likely to get to that magical 400HP mark. We'll be able to turn up the boost without worry pretty easily on this setup, so while this doesn't directly justify streetporting, it doesn't work against it either.

You're just worried about the idle quality and driveability of a streetport since your current setup sucks. Well I say don't worry. There are plenty of folks streetporting FD engines and keeping nice idles.

So now the question becomes if we're porting, how far should we go? As you can see from the list above, all stock ports open at 32°. Now if you look here, these were opened a little sooner and closed a little later.




The primary is what I'd be more concerned with, since this is your idle. We don't have to go this big. Note these are from a 20B. FDs start closer in shape to the finished streetport.

 

I went pretty large with my streetports (2nd gen) and loved it. It doesn't sound like you're looking for a 25mpg daily driver, and idle with a streetport really isn't that bad. As mentioned above, go a little more conservative with the primary ports and you will be really happy. I personally love the sound of a moderately ported rotary at idle

 

Yeah, I'm not worried about the idle. I was able to get the current large streetported motor idling smoothly at 850 RPM with a Weber carb and a locked distributor, and with EFI and proper ignition control it should be all the better. Mainly just want to know what changing the port timing does to the powerband with an unmodified stock intake manifold.

My concern with the primary ports is that the manifold runners look relatively small, so I'm wondering how far it's okay to take them.

 

Well, earlier opening will increase your VE through pretty much all of the RPM range (as far as streetporting is concerned); closing later will move your powerband further up in RPM. If you don't extend the closing edge too far, you will have a nice power curve sooner in the powerband with a moderate streetport, without having to rev more then you're comfortable with.

The intake manifold will not be a restriction at the power levels you are aiming for, at all. Not to mention, the stock FD intake manifold is designed to help in lower RPM power/torque with it's long runners and lack of plenum. You'll have no problems. DO IT!!!!

 

In a car that light it will be stupid fast (for a street car) either way.

 

The engine is apart right now, so it's the best time to port.

Hey Trots, thanks for your advice. What do you think about the secondary street port pictured above? Would that be good for what Percent is aiming for? I really like the closing line, so we'll do that. What are your thoughts about that specific opening line?

For the primaries, we'll also close them to the same line because I've found the idle is not disturbed much on other engines with this much closing timing. I'm only concerned about the opening line. We could open them at 32 degrees, same as any secondary or any 12A. Or we could go farther like the 20B primary posted above. I wonder how THAT would affect the idle. Thoughts? Thanks.

 

As for exhaust, I'd like to go with Trots' recommendation. Hope you don't mind me posting this here.

This should help spool even a T72.

 

Those secondaries look very nice, that is definitely along the lines of what I would do with it. Like I said, when staying streetport, you can never really open them up early enough to hurt your powerband, just be sure that the leading edge of the side seal stays supported the whole time, and the trailing edge has a nice transition over the closing port face and you'll be mint. As for the primaries, I'd do what you said and just open them up to secondary spec and be done with them, just clean up the casting a bit.

 

Dude, you're awesome!