Racingartist

I am thinking of doing some mods to my 83 RX7 that I race at track day events. The car was a PRO 7 class race car under SCCA sanctioning with a 12A. I am building a header and am thinking of building my own intake manifold and make the runners about an inch longer than stock. I will be porting with a large port or maybe a Bridgeport and will get a race beat racing rebuild kit. I am hoping for 200 HP to 250 HP. What do you think am I going the right way by these mods? I use to build and crew chief on sprintcars and pit on Weston West stockcars. I know piston engines the rotors are new to me but look like a lot of fun.

nff

if your gona run a big port job youll need a higher flow carb or do some work to the nikki (if it has a nikki on it) others will be able to help you better on that front. also what rpm range are you hoping to get to? 8.5k+ a shield should be installed in case anything goes boom. transmission gears up the rear end dosent sound like a fun thing. and if your going that high race clearance and hardened internals would be a good idea too.

if the cars a scca car already you should see what its all got on it first it may already have a lightened flywheel. and some fairly interesting stuff. how dose the car run? at idle dos it brap brap at ya? if it dose congrats you got a bridge. lots of youtube vids of the sort. let us know what its got on it. or even better vids

Racingartist

Thanks for taking your time to answer my posting. I am thinking of faricating my own intake manifold and using a Holly carb not sure of the CFM needed. That class (Pro7) runs and pretty much stock engine. I have a spare racing clutch and pressure plate but the flywheel is iron. There my be an alumium flywheel on the car but I haven't checked yet. It has a modifyied Nikki carb on it now and one spare. The car has a exhaust temp gauge and and all the other needed gauges. When I ran the car last July I didn't like the speed it seemed to be down on power but that may of been the way I was driving it. The guy I bought it from said that the engine thats in it was a back up engine and I have two other engines one disassmebled and one up of a stock RX7 that most likely needs to be rebuilt. The engine in the car now I was told was down on power but it did run pretty good. What RPMs should the Rotory be ran at?
In the next few months I will make a video of the engine running and post it thats a great idea thanks.

nff

well by what racing beat says stock internals are good till 8500rpm. after that stock may fail. and with a bridgeport you'll be running past that to get peak power. personally i think the trany would fail before the engine. unless its a TII trany then it should be good.

also a good place to post a thread would be the NA tuning section. the guru's over there would help you more since this is obviously a tuning/racing thread.


oh and if you do start porting it make sure to port the exhaust also since its no use just porting the intake if the exhaust causes a bottleneck

Racingartist

Thanks I have ported a few Fords and Chevys in the past we got 850 Hp out of the last Chevy on Alcohol so this sin't my first rodeo. It is my first time working on the a Rotary engine. I planed on porting intake and exhaust and I will fabricate my own intake manifold I want the runners about a inch longer to make some more top end power.

CobraStngSVT

I'm not sure what your plans are and for what organization... but make sure you comply with class rules before you go doing anything.

For instance... in IT7/ITA (which I run as well) you cannot modify the intake manifold, you also can't run a lightened flywheel or do any porting, etc...

I can get way further into this to try and help you sort it out if you want but let me know. The mods your talking about doing would bump you into STU but even then you can only do a street port.

Like I said let me know and I'll go further into detail.

Racingartist

I am 63 years old and I thought that I retired from racing back in 1988 but a co-worker talked me into building a Chump Car (1978 Olds Cutless) and the old racing bug bit me again. So I did so trading and now I have this RX7. It was raced in SCCA Pro 7 class. I just want to run some track day events to have fun driving a race car again and by doing this way I can do what ever I want to do to the car. So being and old guy I want to see how much power I can get out with a little playing around with a rotory engine. I started racing in Hi school F modified now they call it B sportsracing. I then built a dirt car for a friend then some stockcars (dirt) and got into Winston West racing and built supermoditys and sprintcars that was 1964 to 1988.

nff

go apeshit then are you thinking of sticking NA or do you want to got turbo?

Racingartist

I will be running a carb if I win the Loto I will go turbo. I plan on running hardend gears in the rotors and counter weights and a racing oil pump and oil pan baffel. I hope to start this around the end of this year. For now I will build a header and do some modifiying of the stock intake. I have two spares and first I will hog out one the other I will cut apart and add some aluminum runners to it. I will be using the flanges and adding my own runners.
On a different note what RPMs should the stock engine run at? With a piston engine depending on how modified the engine is we run them from 6000 to 8500. I know that they are getting 9500 out of the CUP Cars now days.
I was thinking that maybe running the engine thats in the car now around 8000 to 8500 maybe 8700. When I ran the car for the first time last July I didn't look at the tac I was shifting when I saw the light come on. I was having trouble with the fuel pump and spent most of then time trying to get out of everones way.
I did run the car later that day with a new pump and spent the 20 minute event feeling out the car still shifting with the light. A few days later it occurred to me that the last driver was a very young girl without any racing experience so the light may have been set to come on a very low RPM.

nff

stock engines run till 7-8k depending on the year. S5 and up go to 8 before the car starts yelling at you. where as below s5 is 7k if i remember correctly.

cfamilyfix

iTrader: (15)

If you want to make your own intake mani...here are some pics from forum member rx71king...

https://www.rx7club.com/members/rx71king-71689-albums-first-attempt-making-12a-intake-4954/

Racingartist

That is cool and exactly what I was thinking of doing Thanks.

CobraStngSVT

This sounds like an awesome build! Keep us updated with pics please.

Racingartist

I have been working on my race car and so far I built a Stainless Steel header with 2" tubes and I ported out a stock intake welded up all the vacuume ports and filled in the pockets so now I have smooth runners I did leave them a little rough so the fuel charge will stay mixed and I modifiyed my Nikki so it's now manual secondaries and I am building a 2" spacer plate that goe's inbetween the intake and engine to make the runners longer. I we post picture later I have to go to work now.