Ruadhd2

HI.

I have a 1989 RX-7 13B engine. The engine has good power at the middle and high end of the power band, but idles poorly and runs very rough at low rpm and low power.

The engine has a new Holley 4 bbl carburetor with vacuum secondaries. The carburetor looks large for the engine, and may be rated at 850 CFM. A performance shop installed the carburetor, stating this is what is used for racing. The car also has headers with a straight through muffler and side pipe. It is very loud.

I will happily trade low-rpm drive-ability for some loss of ultimate power.

I will be trading out the straight-through muffler for one that actually muffles.

If I were to stay with a carburetor, what would you recommend?

If I were to go with fuel injection, what would you recommend?

thanks,

Steve

Hypertek

iTrader: (3)

seems like it would be a headache to convert back to fuel injection.

Did you convert it to carburetor or was that the action of a prior owner?

Evil Aviator

I recommend taking the car back to the "performance" shop and have them tune the carb properly or convert the car back to stock form and give you a refund.

Otherwise, I would recommend something that you could tune yourself or pay somebody else to tune. The best parts in the world will run like crap if not tuned properly. Therefore, you need to ask yourself what you are capable of doing yourself and what you will need to pay for, and only you can answer that question.

Here is a carb guide. Note that the Holley will not run correctly on an RX-7 unless modified by a shop that knows what they are doing. Racing Beat sells Holley carbs that they specially modifiy for our cars.
http://www.racingbeat.com/manuals/intakeguide.pdf

Ruadhd2

Looking for model number

Ruadhd2

This is on a Lotus 7 variant, called a Rotus. Here's a link to pictures.

https://picasaweb.google.com/drsms22/KillerBee1990Rotus

More Information. This is a 13B engine with lightweight rotors and lightweight flywheel and a Racing Beat modified Holley 600cfm carburetor with Holley Intake Kit model: 84-92 6-Port.

More refined questions now that I know what we have:

1. It is had good top end power but idles poorly and runs roughly on the street. How to improve smooothness of power deliveray for low to moderate rpms?

2. Racing Beat recommends 1. Long primary header - dual-tube connecting pipe - rear muffler(s). (i.e. Road/Race Exhaust System)
2. Streetable Header/Presilencer - y-pipe - rear mufflers.
3. Downpipe/Presilencer - y-pipe - rear mufflers.

I need to get this car quieter, much quieter.

arghx

iTrader: (3)

you might want to try the 1st gen section considering there is a greater base of carb knowledge there

AGreen

iTrader: (11)

An 850cfm is large for a street driven rotary. The "performance shop" gave you a carb that'd undoubtedly work well for racing. That means the car never really sees low rpm/idle situations. That's why on most fuel injected rotaries that make high HP, the secondary fuel injectors are quite large (850cc and up) and the primaries are smaller (generally no higher than 720cc).

You should ask around on the "Old School and Other Rotary" section of the forum. They'll have ALL the answers you'll need.

Love the Rotus. Original

Evil Aviator

Rotus 7!

Is that what you have? That should work well if your engine is street ported. Do you know what kind of porting the engine has?

Check the 1Gen RX-7 forum and also the various write-ups and videos on the internet. Personally, I would take it back to the performance shop for tuning.

Your car will probably need a few custom-made parts. See the Racing Beat recommendations below. Yes, the small tube diameter is optimal, but you can gradually increase the diameter toward the rear of the car if you want to use cats/mufflers with a 2.5" tube. Note that their short primary header is actually not the correct length according to their own data, lol. I like the long primary exhaust a little better anyway, although for a Rotus 7 you may want to go with the short primary due to size restrictions.
http://www.racingbeat.com/mazda/perf...gurations.html

Make sure that you use exhaust components that are capable of withstanding the high heat and pressure of a rotary engine's exhaust. Also, do not use "turbo" mufflers or mufflers with huge 115mm+ tips as these will be too loud on a non-turbo car. Here is a list of good quality brands of exhaust components that will work well on a rotary engine: Apexi, GReddy, HKS, Racing Beat, and Rotary Performance (Bonez). Do not use popular piston-engine mufflers like Flowmaster because they will blow out.