85Gen1

hey i was wondering if any on you could give me some good information about boosting my 12a rx7. ive done turbo set ups on other types of cars such as eclpse and talons but ive never done it to a carb. my main question is do i need to send out my stock carb to be prepped for boost because im only planning on running 5lbs of boost and just running a bonnet? thanks for the help!

Directfreak

iTrader: (2)

I really don't have the answer you're looking for. But, for 5lbs of boost, you can just run a draw through setup and not have to modify your carb at all.

85Gen1

ya racingbeat said for those stock rotors they can only hold 5 pounds but i wasnt sure if they were trying to sell me stuff or that is truly what they can hold. but thank you for the advice. sadly i already have a custom intercooler kit i built so im kinda stuck with blowthrough

Twilightoptics

iTrader: (1)

Search time.

Gert the carb boost prepped. Stock 12a in good shape and good tune can take 12psi all day long.

No one has an accurate depiction of what to do to a nikki specific boost prep other than 2 guys. Robert from Rotary Shack, and another guy I forget his name. It's kind of a secret.

For any positive pressure, the carb needs works. Send it out. Search some more.

85Gen1

ok thanks for the information! i emailed robert at rotary shack to see what has to be done

PercentSevenC

It's not a secret anymore. (Not that it'd be particularly hard to figure out if you know how carbs work.)

https://www.rx7club.com/showthread.p...1#post10321601

Note that the "secondary mod" bad 83 refers to is converting to mechanical secondaries. You can search for the writeup on that.

Twilightoptics

iTrader: (1)

Just the normal choke stuff, mech secondaries, and richen the secondaries? Seems like there should be more to it as there is more to it on every other carb.

I'd also like my vacuum advance question answered. I'd hate to turn a 18mpg car into a 10mpg car only for a few ponies.

rx71king

iTrader: (6)

your vacuum advance will not work under boost.....but if you ran a draw through it would....i have bin thinking of making a nikki draw through kit using s4 or s5 turbo.......what do you guys think?.....so all you would need to do is jet up the carb and bolt it on...

Twilightoptics

iTrader: (1)

Draw throughs are a terrible idea for a wankel. Compressed air makes heat and in turn detonation. Heat is the rotary enemy as is detonation. Run a blow through and run an intercooler.

That said. I under stand the vacuum advance wont work under boost. It wont work under NA WOT either. Hense the "vacuum." It's strickly for cruise purposes. I don't know if the vacuum diaphrams will live under positive pressure situations. Hell, or if it'd even reverse the pull of the dizzy. Guess I can break out the mityvac and test.

rx71king

iTrader: (6)

i ran draw through for years 12psi .....my engine lasted 5 years of beating it every day...it all in the tune and how you lock your dizzy....none of that welding crap..

PercentSevenC

Boost prepping a carb isn't exactly rocket science. It surprised me just how simple it was to prep my DCOE because everyone talks about it like it's some sort of black magic. The Nikki is actually easier than most 4-barrels because it comes stock with solid floats and can easily be converted to mechanical secondaries, and you don't have a power valve to worry about like on a Holley.

I haven't experimented with vacuum advance yet, though I've been wanting to for a while. Let me know how it works out for you, because 10 MPG does certainly suck (though I'm not sure how much having the extra timing would help in my particular case). If nothing else, you could always acquire a stock 12AT distributor (are they even any different?).

Twilightoptics

iTrader: (1)

Since there's no change to the engine, and typically a little more power helps economy in an underpowered situation like our..... I'd think if you could get the cruise timing back to where it should be when under a vacuum, milage should only suffer when you're getting on it.

coldy13

That's the problem, just try to stay off the gas, I dare you I could get around 20mpg highway with my old setup with a locked dizzy. I had to play with the mech secondary linkage a bit to make it so I was only on the primaries while cruising. Since you should be using the stock primary jets, it doesn't suck down the gas until you open the secondaries. I think my secondaries were around 235-265 to get the AFR down to 12.0 at 14psi.

And yes, you can run 12psi all day long with a good tune.

Twilightoptics

iTrader: (1)

Mmmm that gives me encouragement! 60mile round trip a day to work, milage is important! I've got everything but the FPR and a little welding between the flanges for the manifold.