OK, I am helping a freind build his rx7 for SCCA and we are looking at the difference of carbs vs EFI on a 6-port N/A. THe main reason is that a carb has a lower min weight.

This is going to be a track car, with little street time, so MPG is not that big, mostly power, reiablity(sp), tuning and cost( to do and cost of upkeep)

Any help would be great, and if you got a kit, posting the link would be nice.

Thanks
bryan

 

EFi injectoin will yelled more power, but will cost a bit more if done properly. You can use a IDA type Throttle body fitted for fuel inection.. with ems injectors etc.. will run around 2-3k.+ tunning.

Carb is ALOT cheaper to do.. could be done at 1k with everything new.. or if yu search on ebay or forsell section could be done about half that... including fuel setup as it is much cheaper for low pressure fuel pump and fuel lines.

Some good link for carbs set up are:
www.racingbeat.com
www.mazdatrix.com

 

Efi > *

 

Ive seen this on other forums for 80s cars :P.

Carbs are not nearly as accurate with fuel metering, use accelerator pumps, etc - and 'tuning' them isnt nearly as precise or with the amount of options EFI has. You just turn a screw and get a rough AFR - and size the fuel pump cam based on just trial and error (it literally squirts fuel outwhen you suddenly drop the gas so it wont run lean and bog).

It can work, especially if the intake manifold is set up properly, but its just not nearly as efficient and powerful. It IS a lot cheaper, though.

 

So if the EFI has a weight penalty, then what would that suggest to you about carbs?

 

If you are building for EProd, check the current rules. They just gave carb cars 42mm chokes and made the weight the same at 2350lbs. If this is your class I'm hearing guys argue about who's making more power, that's good. I'm going EFI in mine mainly because of tunability. EFI will get you more power in the mid-range because of the accuracy it has feeding fuel.

 

Don't understand your point Evil...sorry. Do you mean carb's are inherently less able to make power because of the lack of ability to adjust them precisely and while are a cheaper short-term option are therefore useless for precision tuning and thus tuning/ignition/power/mileage/startup, etc?

 

Racing rules always give a weight penalty to whatever is an advantage.

BTW, jgrewe had a good point - always ask the people who race in the class. Sometimes there are small loopholes or small advantages. Granted, they will eventually get plugged (probably by a weight penalty, lol) but sometimes that's all you have to go by, and Miss Cleo is no longer in business to tell you what will be the best thing to have next year.

 

carbs have the inherent restriction of the venturi, so the fuel injected route always has the ABILITY to produce more power.

However, you say you can have a lower min weight with carbs, a nice DCOE or IDA carb setup would probably do you just fine, look at the setup the formula mazda cars run, the star mazda setup, one piece manifold with DCOE carbs. They put out 180RWHP on stock ports.

How much lower is the weight limit with the carb vs efi? Carb will be cheaper and with the lower weight would probably be a better choice. Just be aware that you will have to tend to the tune at the different events, varying altitudes and temperatures will not be compensated for automatically.

 

Yea that is the class he is looking to build for. Last information we had off SCCA was the carbs have a 200ish pound differemce but I know that was for the GT classes. IF you runing in Eprod then I guess you have more up to date info, we still waiting on the rule book to be mail.

Quesiton, if your running in EProd, what do you have done and how you ranking, also are you running EFI or carb? Also what part of FLa you located in, cause i am moving back to N. GA which is where the rx7 is now and going to be raced.

Thanks

 

Check the SCCA website it has up to date rules under Club Racing- Rules and Cars. They update it monthly. At this point we are running a 'vert in EP with an IDA. I got involved with the car last year, and I've helped develope the car. Its starting to pay off, we got our first wins last event at Sebring(Reg. race). And that is with a guy that is 71 this week who doesn't push the car harder than he needs to. The car is just starting to get up to National race speeds.
I'm building a coupe for EP right now. Pretty much taking advantage of all the rules will allow. Glass body panels, lexan, totally stripped down to the shell, extensive cage, Its starting to look like a car again so I'll post pictures soon. This car will be EFI, we will be testing them head to head and I think both will end up EFI. Even breathing through the stock TB and manifold that have to keep, tuning will be better. And I really hate carbs anyway.
We're heading for Daytona Aug 4-5

 

Yea post pictures of the car, or Pm info. We both are in a 20ish so I know he push it for what the car is worth. We haven't started looking into fiber and lexan yet, still need to weld a cage in it first to see what the weight is and where he wants to remove the weight. I worked with Carbonfiber so, I looking into cost of making CF panels in place of major weight problems.
Question what compression/motor are you running? We going to be running a stock 86 'block" for sometime, he said something about rebuilding another 86 block with 88 rotors.

 

Sounds like you have a good start. I've posted different things I've found as I've lightened my car under 'Adding Lightness' threads. We make our own body parts and you can see the 'vert athttp://www.mazdafiberparts.com A friend started throwing the site together a while ago but never got to far. No biggy, we aren't really set up for production anyway, and we hope we don't need to make to many parts for our own cars