are you going to go for a shaved bay look?

 

Loving the exhaust so far. What are the plans? Is it all going to collect into one pipe, or will you have them collect into two pipes, then travel to a large dual pass muffler, with twin 2.5" pipes as the exhaust "tips"?

 

ive always liked the s4-s5 chassis, but your work needs to be showcased in something more befitting.

 

Really like your exhaust! Have tried myself to do some exhaust in Solid and it almost resulted in a fist trought the screen, and the keyboard over the knee

 

Can't you put the radiator on the same place but then in front of the holding brackets?

 

Because cooling is always an issue with such a big motor
oil provides a lot of cooling for a rotary, i would suggest you to mount dual oil coolers.
I did it last year and now i have to use an oil thermostat otherwise the engine runs too cold.

Should work wonders for that nice 4-rotor i think!

 

that's like telling someone what they should or shouldn't like. some of us actually like FCs you know.. also has probably the best bay for a 4 rotor room wise. on top of it all i don't think i have seen a 4 rotor FC yet, so why not. it was/is my plan but it won't be the first anymore.

 

i think fcs are the best looking rx7, i want to put a four rotor in my vert

 

FC is the most good looking Rx7 so far...

 

Well, I'm going to try to clean everything up, remove most of the unnecessary clutter and make sure it looks tidy, but I'm not going to invest weeks to smooth every detail out, it's not going to be a showcar.



This is the rough plan so far:



I think this will fit the FC chassis well, it might be a bit loud depending on how well I can make those mufflers work. But ah well, with the big foam air filter it's going to be loud as hell anyway.
I've been doing some research and flow simuations on the exhaust, it's pretty difficult to get the simulations right because there are a lot of unknown factors, but I still found some interesting things.




Meh, opinions opinions, I like the FC, it's a pretty solid car, cheap to buy and own, lots of engine room, good for drifting, parts are pretty easy to get, and I actually like the look of it.


Ah yes, it's pretty tricky, I use a 3d sketch, and then use a sweep to form each header pipe. It took me a few tries but it worked

Well it doesn't really fit there, besides I'm not going to be using a stock radiator, and I want a hood vent so it's going to be all custom made anyway.

I know already have 2 FC oil coolers waiting to be put on the car

 

it was meant to be a compliment...

 

hmm I think your exhaust is going to be a bit small. Really thats similar to what most the turbo 13b boys are running right now, and you really need as little back pressure as you can acheive.

I always thought you would be running dual 3" systems.

 

I ain't no specialist, but here's my 2cents worth.

NA rotaries depend very heavy on the correct exhaust system. On my 13B NA Bridge Port motor, my engine builder refused to start my car with the single system I had on initially. It was a dual Ø57mm for ±1m from the exhaust ports, then into y-piece with Ø60mm collector, into a megaphone from Ø60mm to Ø76, over 100mm, into a Ø76mm single pipe. The single pipe was ±1.5m in length.

He didn't want to start it, he said my Apex Seal Spring will collapse very quickly, as he experienced that on a earlier situation.

I am not saying your idea wont work, I just wanted to bring it under your attention that if the exhaust gasses cant escape, replacing 12sets of Apex Seal Springs can be costly.

Regards
Adin

 

Ah, thats the first time I've heard of collapsing seal springs due to backpressure, I wonder if this is true why turbo guys don't have any troubles since they have a ton of backpressure.

Anyway, mad mike's 4-rotor also uses a 3,5" single exhaust, and he's running with more hp than I'm ever going to, and that seems to work fine, same story with the 787b, that thing doesnt have a huge exhaust either, and it seems to be pretty reliable to say the least.

 

Please do understand that I am not saying that what you doing is wrong, it was just a point that I wanted to share.

From my understanding of the turbo cars running single systems is that the pressure inside the engine is much higher then at the tip of the exhaust, which is at Atmospheric Pressure, therefore the flow is better since air flow from a high pressure to a low pressure area. On a NA setup, the pressure in the engine is much less then the turbo engine would be, therefore the exhaust design needs to be adequate to aid in the extraction of the spent gasses. And the fact that rotaries don't have valves to keep the spent gasses from re-entering the engine, that can causes numerous kinds of problems. But, thats just my understanding of why the differance between a NA & Turbo exhaust system.

On the 787B: the short system works, and it works well, I would just like see how the system is put together. I am sure that is 4 runners into a y-piece and into a back box.

Regards

 

i can't wait to see how this turns out!

-sean

 

Im also not saying your point is invalid, Just trying to figure out what exhaust will best to use.
About the turbo engines I was referring to the apex seal problem, some turbo engines have exhaust (between engine and turbo) pressures several times the intake pressure which i imagine would put a similar load on the engine than a n/a engine with loads of backpressure.
As for the rest of the exhaust I don't think you can compare turbo with n/a exhaust, turbos have more pumping losses and higher egt's which i think increases needed exhaust size.

 

3.5>dual 2.5" should be about right for an n/a 4 rotor.

i've never seen collapsed seal springs even on engines that had clogged cats, i have seen it on tunes that were far too lean though. the stock n/a cars had almost too much restriction yet they would commonly go 200k miles with the exhaust wings, dual cats and semi restrictive mufflers. i really wouldn't worry about it, but of course for optimum performance it may need some tweaks after it's all said and done.

people often look at a 2.5" pipe and think it's too small, not keeping in mind that is about the equivalent of a 3.5" single. the same people probably run single 3" exhausts on their n/a thinking it is giving performance gains when the reverse is most likely true.

it might be slightly restrictive for an n/a PP motor but only barely.

also a fan of duals on n/a cars, as they need the extra surface area for muffling that sharp exhaust tone.

 

Seeing such a beautiful engine mounted so wrong in a car makes me a sad panda... :-(

I myself am mounting my poor mans 13B several inches back to further improve weight distribution. The only reason it's mounted so far forward is unneeded under-dash crap like heaters and stuff.

Riz.

PS: Don't worry: I'm jelly as **** on the engine!

 

that might be possible if it was a dry sump and cost about $3-4k more..

yes it is a little nose heavy, about as much as a battery relocation and weight reduction would take care of. the car was 49/51 with all the accessories, much of which will be gone, taking weight off the nose.

if he plans on mainly using it as a toy and for drift anyways.. being a little nose heavy would actually be ideal, if it was being built strictly for competition then weight balance would be something to worry more about, also nothing a few weights in the rear couldn't offset.

i also cringe at the thought of a rev happy motor sitting that far back pushing that much power with the flywheel only inches from handicapping you for life without adding another big chunk of weight, ie a scatter shield.

 

You summed that up pretty good.
It's actually not as bad as you might think, I'm really confident the front of this car will end up weighing similar or less as a normal single turbo car. A turbo, intercooler, needed piping, power steering pump, battery, heavy intake manifolds, heavy exhaust, shielding, wastegate, blowoff valve, solenoids ect. also weigh a lot all together.



Got the e-shaft back from the grinders by the way. They had to spend some time to get it right so it got a bit expensive, but it turned out really great. The picture doesn't do it justice, all the bearing surfaces are super smooth and more important, everything is dead-on accurate . Still isn't done though, it needs to be balanced.

 

Still, it will be mounted relatively high. Choosing a tranny with a shifter location more forward, modified driveshaft, custom bellhousing/adapter and mounts would make the car so much better, for a relatively small investment compaired to the build of the engine.

Scattershield FTW! But I get your point. I just feel the car is kind of unworthy of the engine? You know what I mean? I find it hard to understand why John goes through this much trouble, and then just mounts the car in a way that seems the easiest.

Is that the goal? A stock-like FC with an insane engine? If so: I haven't spoken. Can't wait to hear it run!

Riz.

 

pretty much, why not. that was my goal as well. to build a 4 rotor about as cheaply as possible, make it fun and the rest doesn't matter. mounting it like a stock 13B makes life simple and the car still works like it should.

i suppose i'd rather enjoy the car before i could afford to drop $40-50k into it and am too old to do with it what it was intended for just to make it a little more well rounded. most of these DIY builds are not sponsored by big shops with $100k budgets.

next hurdle will be the starter, auto starter won't fit and the manual starters are too weak for the 4 rotor. might get a stocker to work but it will be unreliable, perhaps finding a motor that fits the casing with larger stator/windings? can bump voltage to the starter with a separate battery tied to just the starter but it will cook it relatively quick pushing 18-24 volts through it.

 

yeah for a 1 man thing you have to pick your battles. building and tuning the engine is going to be enough of a challenge, besides the rest of the car can be the next project

 

2 x 12V battery's together on a 24V starter of a truck enough power to bring everything around.