Well. I've been doing this for over 13 years now. This is my 4th Fb. I've built two turbo FB's and 3 NA ones, my FC doesn't count as that's a completely different discussion. I've run both the RB long primary, Short primary, and at least 5-6 custom NA exhausts. My exhaust is by far not the be all end all for exhausts. It's been proven about 100 times that every engine will behave differently especially considering what port is used. They all have different requirements to achieve savaging especially depending on overlap and flow potential of the engine.. It's just annoying that the first thing every one suggests is the RB exhaust. It's been shown all over this forum the most people are making with the FB exhaust is 150whp. I have yet to see anyone make over 147whp with a RB exhaust. My whole point is that Fabbing a custom system correctly will net you more power than the RB bolt on systems. Another Difference with Kahrens car is that the FC exhaust is completely different then the 2" crap we get from RB. The fact that the FC header collects into 2.5" pipe instead of 2" makes a huge difference for top end power.

You have to understand how difficult this is always defending myself when no one else has proven that they've made this power in a FB. With relatively stock ports. Again the RB FC exhaust is a completely different animal and that's not what we're discussing here. I'm talking about the off the shelf RB Fb exhausts and how limited they are and it cannot make the same power as a well thought out custom exhaust not matter what style you make. I'm sure I could've made close to the same HP with a long primary system with a megaphone, but it would be louder than what i already have done and at what gain none if any.

My point is that there is more than one way to skin a deer, and the old faithfull swiss army knife isn't the best way. There are a few new devices out there that are easier and faster.

 

You don't have stock ports. "Relatively" doesn't count. That's like using the word "almost" to justify saying "the train almost missed me". It doesn't count. Yours are "cleaned up" which could mean anything. It probably does mean they flow better as the real secret to porting isn't in the size of the ports. You also don't have a stock intake manifold anymore. You have a Weber. Then again about 2/3 of the total gains on a streetcar will not come from porting. This is also a 13B which isn't a stock 12A motor which explains why (I'll quote you) "It's been shown all over this forum the most people are making with the FB exhaust is 150whp".

You have a GSL-SE 13B that has been built and with cleaned up runners running an aftermarket intake with a Weber carb. Is it surprising that we've never seen anyone with a stock 12A running a standard RB exhaust break 150? I don't think so. We've seen plenty of 13B's do it and I even gave you a link that showed a 13B do it on a stock exhaust manifold. Your numbers while nice are inline with what others have hit on 13B's before. Kahren hit 178 rwhp with a stock port, a custom manifold, and a restrictive airflow meter on a stock ecu! If you want to discount it for having a custom fabbed intake the we may as well discount yours for not having a 12A, having port work done to it, not having a carb that came with any rotary, and not using a stock manifold.

Now if you are saying you've never seen a stock port GSL-SE engine make more than 150 rwhp, again I'm going to tell you why. The intake! You keep going back to the size of your bores yet a GSL-SE engine and intake system is designed to make peak power at only 6000 rpm. There is no point going much over 6.5K. I know, I have one! The throttlebody is small and the airflow meter far smaller than even an early 2nd gens at a total of 4 square inches when fully open as opposed to 6. That's not much but probably not far off from how much total area you have. The difference being that yours isn't blocked by a spring loaded flapper door. You are also not losing power due to pumping losses over a very long intake system and with shorter runners you are tuned to take power up higher in the rev range. Just extending the GSL-SE powerband up a bit will yield significantly more power. Not rocket science. Your power peak was at 7.2K. Hardly comparable to a stock peak of 6K. The fact that you may not have much more flow area than a stock GSL-SE system just shows that the problem isn't with total flow. It's with total intake tuning. Your intake isn't as restrictive as you are making it out to be. You've got the results to prove it! The guy who had the 230 rwhp streetported 4 port engine had a power peak over 9K. See a trend? Compare torque numbers at each of these peaks and you'll start to understand what's going on.

The reason that it's hard trying to defend yourself is quite simply because you are highly skewing things here. There's nothing relatively stock about your setup in the least. You've also stated in another thread that you have an aftermarket ignition system and have gained off of it too. Show me a car that came with that setup minus the exhaust. That's why your power numbers, while quite nice, aren't as miraculous as you are making them out to be. It's also a part of the reason your constant bashing throughout the forum of RB is unjustified. You are selling off your system design to everyone with a first gen when practically no one has a setup similar to yours. I have stated that the design does have merit. However a direct copy of yours isn't the way to go about it. By your own admission "They all have different requirements to achieve scavenging especially depending on overlap and flow potential of the engine." Which car came with a setup comparable to yours?

 

To further elaborate from the standpoint of a GSL-SE since that's the engine you are using, you mentioned that you haven't seen anyone break 150 rwhp on a RB 1st gen exhaust. While you haven't quantified specifically if this is with a 13B or a 12A, I will go one step farther to provide you with some more insight. As I said before on the GSL-SE, power peaked on that car at 6K mostly due to intake design. Let's say we ran an RB exhaust on it. Pick one. Better yet lets say we use your car as a comparison. The goal is apparently to top 150 rwhp and it should be at 6K to be fair rather than your much higher peak rpm and expectedly higher power level as a result of it. At 6K with your setup before you went back and really fine tuned the exhaust, even with your superior in every way to stock setup, you got 145 rwhp at 6K. Not the 150 you want to see from stock ported 1st gens using RB exhaust systems! It was only after you pulled out all the stops that you finally broke it attaining around 165 rwhp at this point. A gain that is solely attributable to good tuning. Since most people using the RB system just want an exhaust that bolts on and usually don't go about retuning their cars, it's absolutely no surprise at all not to have seen 150 rwhp by anyone using an RB exhaust on a first gen. Especially since most of them have 12A engines. It doesn't mean it can't do it though. Remember the above is in accordance with YOUR test results!

 

Exactly.

I forgot to mention two rather critical things:

1. The air density with the new exhaust testing was atrocious. The gamma correction on the Megasquirt was 88% or even lower. What that means is, the air density was 88% of a standard 60-degree day. Temps were not that bad when I ran my *best* time with the "tiny" exhaust. I think it was around 50deg ambient

2. Ambient pressure was 95kpa, but my MAP reading would start to drop over 6500ish and it was reading 88kpa at about 8200rpm. So the (T2) throttle body must be a restriction. I noted this with the quiet exhaust but somehow my brain calculated that the increase in vacuum was due to exhaust restriction... durrrr that makes no sense. I did try a run with no air filter and that made no difference.

So we are a go for the 75mm throttle body, since apparently the stock throttle body isn't enough for 200+hp...

Actually, I *am* rather impressed, that the car was making more power despite the restrictive intake and very crappy air. (MATs in the 135degF range before a run, 115degF at the end - ambient was probably 95degF)

Details are critical!!!

 

I think you're mistaken on what I did. The most I could ever get out of the Rb even after multipule attempts at tuning and multipule dyno runs and tuning sessions, and adding my igniton crap was 140whp. The only change to the car was the exhaust and then I did 165. Then I changed just the main jets on the weber and set total advance to 30*BTDC adn i got 189. I went back to the dyno a few weeks ago added new velocity stacks, aluminum flywheel and a new clutch and backed it up with 190.5.

And you know what I really don't give a **** anymore. If everyone wants to argue and say they can make the same numbers as I can, **** it, street port a GSL-SE engine and throw a RB exhaust on it run a WEBER, ITB's, what ever fancies you. With a RB long or short FB system I gaurentee you don't put more than 180 to the wheels. Until I see it I'm done arguing.

https://www.rx7club.com/1st-gen-general-discussion-207/%2A%2A-1st-gen-dyno-sticky-%2A%2A-658265/

 

so the entire arguement, was that RB street long primary single dump header was not the best unit for over all HP?


I agree. I use one.

 

Well, sounds like a point all can agree upun.

So, why is the 2nd gen header better thanthe 1st gen header for the SE?

And, if using a 2nd Gen road race header, is there a bolt on pre that's worthwhile? I don't think going dual all the way out is possible on a 1st gen.

 

You mean that you don't think going dual all the way out using the 2nd gen road race header is possible right? I have dual all the way out right now with the 1st gen road race header.

 

so... i could put a second gen header on then run some 2.5 inch presilencer back to a 2.5 inch straight through muffler? something like that? would that be any better than running the normal SE header?

 

Naw, I know it's possible.... just wondering why the 2nd gen headers, even the model with a collector, is supposedly a lot better than the standard 1st gen header for the SE.

 

The difference is that the collected 1st gen header collects into a 2" pipe and the 2nd gen header collects into a 2.5" pipe. That's all. MUch better flow potential and there fore power potential. The uncollected Roadrace headers from RB are all pretty much the same.

 

Hyper, if I have learned anything from this thread, it's how to get over 200 HP at the crank (and damn near at the rear wheels) from a NA 13B. Fre flow headers, better coils, and updating the intake from the stock EFI. Not sure if I'm ready for Webers, but headers and coil will happen soon. Thanks!

 

why dont we throw one of the shack headers on and see what #'s you get..

 

That's only if you wanna see MAX POWAH!

 

A lot of people i know are running rb systems.
This was interesting to read

 

except RX-7 owners are dead broke.

 

I told Robert a while ago I'd throw one on and test it back to back against my exhaust. I'm all for a Rotaryshack sponsorship.

 

I'm already handling that ;D

 

i'd love to see a decent exhaust come from you guys. if it could work well with a stock SE i'd definitely go for it.

 

Alright then, let's make this happen. Let me know when you want my address to ship the header out. Heck I'd even be willing to pay for shipping.

 

uno mas
http://www.youtube.com/watch?v=MdmIgmxvjuc

 

Update:
Well My RE header finally cracked so I got one of the last 2 ISC headers to replace it. Just got her on the car and I thought I'd show you all what I found when I got everything apart.
1 the center section hung way too low.
2 the dynomax muffler couldn't take the pounding of the exhaust and came apart inside.

Now I'm kinda at a cross roads because I'm considering not using the whole expansion chamber again. here are teh pics and here is why,

 

Yo Adrian! Sorry.

Yes, your exhaust did hang down pretty low. I've been building Gavin's 3" exhaust and I made sure to keep it tucked up. I'm just about finished with it and I'm about to start on my 3" system.

If I could make some suggestions, go with an RB 3" universal presilencer in the cat location. It won't blow out so easily. There's a reason for it; there is a design feature you may be interested in, plus it's RB, so should last a while on a rotary.

I spoke with somebody at RB yesterday about their presilencers and why the 3" universals don't come with an expansion chamber/anti reversion chamber like the 2" and 2.5" versions. He said the 2" and 2.5" were designed in the mid '80s and the actual reason for the expansion chamber is literally to allow for the expansion and contraction of the perforated core inside during heat cycles, and it is a slip fit design to keep the core from cracking. That made perfect sense to me because I had to repack a dead empty 2" RB presilencer last year and when I cut it apart, I only cut through the outer shell leaving the perforated core intact. The perforated core was able to be pulled out of the end cap inside the expansion chamber. I then wrapped it with stainless pot scrubbers, coarse steel wool and lastly fine steel wool. Slipped it back together and welded a bead around the cut. Sounded much better on the GLC compared to the old half dead RE glasspack I was using as a main muffler.

The point I'm getting to is about the 3" universal presilencers. They have a slip fit like the 2" and 2.5" but no need for an expansion chamber. If you ever get a chance to see inside of one, at one end it has a short length of pipe like a sleeve. This is the slip fit to allow the core to expand and contract. The other end is obviously welded. Their 2.5" and 3" universal mufflers also have this slip fit sleeve.

My exhaust will consist of an RB road race header (hey it's what I have), to a dual pipe flange, then to a custom 30° collector to 3", then to an RB universal 3" presilencer (I went with the "large" version since I'm NA but Gavin went with the medium version), after which there will be a short 45° angle pipe to correct the angle, and then into dual 4" round 3" core Magnaflows welded inline, then a flange, then up over the rear end, then into an RB 3" universal muffler. I'll probably do a dumpy to aim the noise down since I'm NA.

I decided not to do an expansion chamber yesterday after talking to the guy. Now I see you may not keep using yours. Any ideas how your system will be set up next?

 

hyper; that's kinda what the piston muffler did on our old FC race car, the case was just too weak to handle the rotary...

jeff; with a presilencer, 2 resonators and a muffler, i think it'll be nice and quiet! i joke, make the front half of the car out of radiator and the back half out of muffler...

 

lol well I'm 2 rotor right now so I'm literally fitting as many mufflers as will physically fit under there. I'll probably not do a dumpy but instead get some sort of resonated tip just for that little bit of extra muffling it's probably going to need until I add another rotor. I'm also going to do the exhaust pressure test with my boost gauge hooked to the O2 sensor bung (the short fat bolt in the rear oil line hole on beehive engines is the same thread as O2 sensors, and I have one with an NPT fitting for an oil pressure gauge to use with the boost guage for this test).