To those people who have got the dual sidedraft manifolds (TWM?) that put both carbs straight out the side of the block, I have a few questions:
1) How is the bottom end-torque?
2) Are they fairly drivable?
3) What carbs and specifically what choke sizes are you running in them?
4) How long (approx) are the intake runners after the carb.

I've tried searching this forum and a few others and I wasn't able to get any really definate answers from people who have driven them; just guesses. I'm seriously thinking of an EFI set-up based upon this sort of intake and I really want to know how it performs with carbs to get a rough idea of it's characteristics. My motor is a 12A but info from a 13B is also going to be very useful.
Thank you,
Grant

 

Don't own one but from what i've heard....

Very driveable. Lots o top end and very good throttle response.
Dual 40 Weber DCOE or dual 40 Mikuni PPH. Chokes.. anywhere from 28-32 depending on porting. Brad

 

Awesome. My efi set-up is basically going to mirror that with a few exceptions. The throttle bodies are going to be 38mm and obviously have no chokes, hopefully I won't lose too much bottom end. On the other hand my intake runners will be quite a bit longer because they should be between 6" and 8" depending on what I can fit between the block and the strut-tower. I'm also going to run the injectors in the outer secondary thottle bodies, and the two injectors in the primary runners are going to be further down and spray almost directly into the intake ports like the SE sort of did. The inner two injectors will be used during cruise and idle, hopefully that will reduce fuel pooling and increase drivability. Port jo will be a relatively mild port-job on the intake and exhaust (Anyone got mild templates I could copy?). Since the outer injectors will be used only during high-rpm they shouldn't decrease driveability by being so much further up the intake tract. If anyone has any input on these ideas please let me know.
Grant

 

Grantmac, you gonna run the GSRX throttle bodies?

Just wondering, I got a set and I'm going to try a curved, over the engine manifold, runners are about 12 inches, I might shorten them abit.

 

I'm either going to run GSXR600 throttle bodies or F4i throttle bodies. Really depends which ones come available on ebay for cheap. They both have the same 38mm butterflies so they should be similar, although the honda engine is more mellow so I'd be inclined to think they're venturi design will be a bit more streetable, although it's probably not noticeable. I'm going to run the runners straight out because I want the better throttle responce, and honestly it just looks cool! That and I'd have less problems with the fuel puddling in the intake runners. If I find the set-up lacks bottom end I may do a downdraft configuration with just 2 of the throttle bodies, but I'm guessing (educatedly) that it won't be too horrible with the injector placing I have. I'll sell the set-up to someone looking for more top-end if I find it's too high-strung for my application.
Grant

 

I was thinking straight out as well but the header temps are causing me some concern. I will need a good heatshield to keep the TB's cool. Also the position of the fuel rail and throttle linkage are a factor. Are you going MS or another fuel control?

 

As for header temps, I have researched this. I use the Lake Cities intake manifold which also positions the carb right over the header.

Header I use is ISC Racing stainless steel
JetHot 2000 coated

Factory Stock heat shield has a 1/8" thick pice of aluminum pop riveted to it. Whole thing is hung to the upper exhaust studs using simple brackets.

On the dyno for 40 minutes @ 6000rpms, the underside of the carb was 100-105*F per my pyrometer.

 

Thanks for the stats DriveFast7, I have a stainless header as well. Heatshield should be fairly straight forward to fab up.

 

I have used the short (Hurley) manifolds with twin SU HIF6 carbs on a 13B and there was plent of torque and very drivable. Throttle response and power was very good. My attempts to model the fluid dynamics did not work out accurately, but it would be interesting to see if anyone could do that. Eamon and I discussed the runner length but in the end he more or less made them to fit, and similar to 12A versions he had previously made. The manifold's horizontal distance from the engine to carbs is about 2.3 inches including gaskets (no spacers). The actual runners lengths are diagonal of course. Header heat was not a problem and I never got vapor lock even without a heat shield. I am looking for my old notes with exact measurements, but could re-measure if anyone is that curious.
You might check with MikeLMR; here is a link to his thread in another forum:
http://www.mazdarotaryclub.com/forum...&threadid=6861

And a couple other references:
http://ausrotary.dntinternet.com/for...ic.php?t=36800
http://ausrotary.dntinternet.com/for...pic.php?t=6133

 

Thanks for the links I've browsed through the one from Brittain a good few times for sure. What I'm thinking is to do the manifold pretty much straight out but with it angled up as much as possible without hood clearance issues. I'm also going to run stainless heat shields on both header (racing beat steel) and under the throttle bodies, if In need more shielding I'm going to try header wrap on the heat shields (but definately NOT on the header). I'm also going to try some ducting from infront of the radiator to get some cooler air to the area. As for management I've looked around and pretty much picked MS for cost and flexibility, also it appears I live near a MS guru so that should help.
Grant

 

I forgot to mention mine angles up as do many of the others. Reason is they need to clear the steering of RHD cars! I think with heat shields you should be fine and definitely so at road speeds. For a different car (non RX-7), I made a simple double-wall heat shield with a few mm space in between that worked better than a single piece of metal. Good luck with your project. BTW I drool over that guru racing setup every time I see it.

 

Well I took a tape-measure to my car today and I think I may have to go with a quad-downdraft configuration to get the intake tract length I want and still be able to run decent sized velocity stacks, not to mention a filter. Should still look pretty cool though and get some wicked throttle-response. Also going to try it with stock injector in the throttlebody set-up and if the idle stinks I'll go with staged injection with the primaries mounted as close to the block as possible.
Grant