You know what? This guy is having a 20 B Pettit conversion done to his car. Good for him! Cameron Worth is doing it and he is arguably the best RX-7 tuner / mechanic around. Cam's street tire car ran in the high 9's at one point. (I have seen the time slip). The Banzi conversation weights about the same or better than same as the 13BREW did when new. The converted car will scream, have more torque and be simpler all around. Best of luck with the conversion and let us know how long it takes and how you are satisfied when you get it back.

For you V-8 guys out there...... go to another thread... Do a search as they say... or make a boat anchor out of your 50 year old reciprocating piece of "technology".

Then everything isn't equal, is it.

You're hung up on equal parts of air and fuel to each rotor. Think of it in terms of total air volume delivered. If you're delivering 1,000 cfm to a 13B @ X psi, then in order to deliver a proportional volume of air to each rotor of a 20B, you'd have to increase the output of the turbos to 1,500 cfm. You can't do that without raising boost or replacing the turbos with more efficient/larger versions, so it's not equal unless you apply the same changes to the 13B. Furthermore, if you did deliver 1,500 cfm to the 20B, the volume of exhaust gas produced would be proportionately larger as well, requiring changes to the exhaust to keep from restricting the engine.

You can never have a fair comparison once you start making changes to favor power production in the larger engine. If you make enough changes you will amost inevitably produce the targeted power increase above the original benchmark... but, if you made the same changes to the other engine, you'd increase its power by some degree as well. Giving the 13B the same 1,500 cfm with upgraded turbos and exhaust would narrow the gap down to much less than 50% again and you're back at square one.

It's as unfair as comparing my 396 LT1 to the stock 350 LT1. Putting the heads and cam from the 350 on my 396 would choke power off drastically, and the power produced would NOT be 13% more than the 350, because the intake and exhaust ports would pose a restriction to taking full advantage of the increase in displacement. It would be like increasing the volume of your lungs by 13% and then sewing half of your mouth shut. Over the same rpm range, you'd take in a marginally larger volume of air, and with appropriate fuel you'd make more power, but not proportional to the increase in displacement. A 454 trying to breathe through the same heads would be even more severely restricted.

Conversely, putting my heads and cam on the 350 wouldn't produce 13% less power than my engine, because the 350 doesn't have the displacement to take full advantage of the increase in airflow, and in fact, you'd end up with a significant reduction in low end power because you don't have the displacement to produce the same velocity in the ports at lower rpm. Here we're reducing lung capacity by 13% but increasing the size of our mouths by 50. Is that extra breathing capacity of any use if our lungs can't hold any more? Are you starting to get the picture?

You can hem and haw and say "more or less" all you want, but you will not get a gain in power porportional to the increase in displacement of two engines forced to breathe through the same components.

Ideally, burning 50% more air and fuel would produce 50% more power, but not in practice. You're assuming a lot of things, chief among them is that you can burn that extra 50% of air and fuel 100% efficiently, which is not the case, especially with a rotary. That alone negates your theory.

By the time you've managed a 50% power advantage over the 13B, it's not solely attributable to the increase in displacement but rather to the changes you've made which will eventually NET 50% more power. You will be wasting more power as heat and having to overcome more internal friction as power increases, so you'll have to burn more than 50% more fuel and air to net a 50% increase in power.

See above.

Maybe one or both of us misunderstood this discussion, but my understanding was that we are NOT talking about two engines breathing through the same components. As you already stated, one would have to modify the intake / exhaust / turbos to keep up with increased air flow.

I was talking about a more ideal scenario. But since you are pretty much supporting everything that I was discussing, I'll stop now.

Second only to yours...

Ahhhh, jim I see what your saying, I think we were just not communicating very well. I think your saying if you provide them both with the same cfm it wouldnt make 50% more. I agree with that, my point is that in a modified setting you should breath 50% more unless you choke it back.

Even if the 20b and 13b have the same turbos and both are running 10psi the 20b will be injesting close to 50% more air. The reason is since you have 50% more breathing capacity its going to take 50% more air to "back up the system" and pressurize the manifold. This is why on that thread the 20B guy was making 630+rwhp with a T72 at only 14psi of boost, in a 13B it wouldnt make anywhere even close to that power at 14psi. The reason is 14psi on a 13b is a lot less cfm than 14psi on a 20B due to the amount of cfm it inhales with every rpm.

Its very similar to that LS1 guy (Rob I think) that was making over 700+rwhp with a single T76 and at some crazy low boost like 14ish psi. The engine was inhaling so much air with every rpm the turbo was basically flowing as much as it could but only creating about 15psi in the manifold because the engine was inhaling most of it.

So basically what I'm getting as is even though they might both be running the same turbo and the same boost, the 20B consumes way more air so the turbo has to flow a lot more than it does on a 13b to create that pressure. In a modified setting (like Cam's conversion) your going to let the engine breath and take in the air it needs. It would be imposible to use the same manifold on both setups, the 20B manifold has to be bigger just do to design (which you know).

Anyway, I think we all understand eachother.

STEPHEN

Anyway, I think we all understand eachother

sure.....that will happen just as soon as the sun stops rising in the east and setting in the west ;)

Why can't we all just get along :D

well to be back on topic, Yes plz keep us updated on your journey of the 3 rotor. Now continue!

... can't stop what never started... the Earth rotates :)

You mean the Earth doesn't reciprocate?

Rotate yes, reciprocate no.

The forum is back!

I have a few pics to upload later of my trip down to Pettit. Pettit has also agreed to take picstures of the process so I'll be able to keep everyone updated as we go along.

Where's the pics?

Pettit Pictures
 

Hello,

Here are my first pics of the 20B conversion. I've already posted numerous pictures of my car - to find them, search under my name (david hayes).

Cam took me out in his 20B and I took a few shots of his car. It drew a lot of attention at the race track:

Wheel Pics
 

I decided last week on my wheels. Because my RO_JAs don't come in a width size larder than 10'', I'm going with Forgeline WC3s in 18X9s for the front and 18X12.5 on the back. I'm rolling the front lip (doing this when I get the car painted) so 9s shouldn't be a problem.

See attached pic of the wheels. Any good tire suggestions? I currently run Toyos which have been fine but let me know what is the best.

You shouldn't have to roll the fenders for 9's. I've seen a FD with 10's on the front that the fenders had to barely be roll'd

I run 17X 9.5's on the front of mine, and 17 X 10.5's on the rear. No rolling.

I think it depends on your offset also...some offsets with 9.5s or 10s will definitely need the fenders rolled.

I ran 17 X 9.5s all around, 48 offset all around, on 255/40/17s in the front, and 275/40/17s in the rear. Granted, it was stock suspension, but no rubbing, no rolling of fenders, nada.

damn a 20b is just too insane to think about.... so much potential its not even funny..

Is there any reason not to roll the fenders? Since I'm going to have body work done and a new paint job, thought I'd go ahead and do it.

FYI - check out my sig. A lot of the items will now be for sale through Jeff in sales at Pettit.

I don't know... I don't believe you can just unroll them, and leave them as such later on, and if you could, it would most definitely show where the metal bent. Given that, I was always curious why if rolling the fenders is quite permanent, people just don't cut away part of the fender?

Why you sending us on a wild goose chase?

David, remember we, we spoke post-20B conversion over phone, I have the Red FD with the wide front fenders and live on southside of town. Im running Volk Racing CE28N's, 18x9.5 Fr and and 18x10.5 RR, 255/35/18 and 285/30/18 Bridgestone S-03. The only thing i needed for the rear was the toe links and trailing arms kit for those to fit. Before going with the wider front fenders, i still cleared my 9.5's (but with 235 fronts), so you should not run into any issue with the 9's up front as long as you have the propper offset.