Project: Cherry Bomb
 

Here's my project car. It's an '85 12a 5-speed with 105K miles, and has not been modified in any way. I've changed the plugs, wires, and dis. cap. The only optional equipment are A/C (which I removed), and alloy wheels (which I added). So, it's the lightest factory stock RX-7 you could buy in 1985.

My baseline 1/4 mile et's are as follows:
Average: 16.75 @ 83.9 mph
Best: 16.66 @ 84.8 mph

All my testing is done with a G-Tech Pro performance meter.
Future plans will include:
Weight reduction
LSD
All new suspension
Relocated battery
DLIDFIS
Modified carburetor
Electric fan
Underdrive pulleys
Smog removal

Oh yeah, I forgot to mention . . .
All new exhaust

What about future plans for an exhaust system and direct fire leading ignition? Both are a must.

looks like a well thought out start, did you make your own or buy a prebuilt exhaust?

Good luck with it.

True that! I'm looking at the RB Power Pulse exhaust. That alone could net me the biggest gain (save for the LSD).
I have a couple spare ignitors, and I know I need new coils. So, I be adding a DLIDFIS very soon.
I'm also looking at E85 conversion.

Thanks for the input.

Sounds like a plan, except you won't be gaining any power from a LSD. I might have misunderstood you on that one though.

Plan sounds good so far, have a couple of questions/suggestions. The underdrive pulleys will give very little net gain for the price and are of real value only if you are spending a lot of time in the higher rpm ranges. And a stock engine is not built to run at 8k+ for extended periods of time, nor is the torque/hp curve there.

If at some point you rebuild with the needed mods for running over 8k, then I would install the pulleys.

Since you sound like you are going for max performance, while the RB header is a good system, it does not give the most hp output. Depending on your budget, you can buy an SDJ header, very pricey, and have the rest of the system built with 2-1/4" mandrel bent tubing, a Borla pre-silencer and muffler of your choice. Such a system can be built for a little more than the complete RB system. Not buying the underdrive pulleys will help offset this cost.

Lsd is a good upgrade but will not be as big of a performance gain as you might think. It will help with launches and bring down your 60' times though. Header. full exhaust system and carb/intake gives the most gains, the lsd helps apply it to the pavement, along with the right tires.

Engine output aside, I think the factory open differential and tall gear ratio are holding me back bigtime.
I expect only incremental gains from most of the items on my list. Taken individually, I think exhaust & LSD stand to give me the most noticable improvement.

I got the pulley idea from my days driving Mustangs. You're right, probably not worth it.
My budget is pretty tight, I can't afford to drop long cash on any one thing right now. I'm still looking at exhaust options (ironic, considering exhaust is probably the weakest element of my stock setup).
I know I need a good carb/intake combo. I have a spare 12a that slated for a streetport rebuild. I'll probably go balls out on that one. But for now, I need to work with the factory Nikki, and stretch the full potential out of it.

The only shorter stock gears are from the SE with the manual tranny, they are 4.1. All other stock ratios are 3.909, including the SE auto. Anything shorter is aftermarket and lsd is a given to put them to use.

Exhaust and carb will give the biggest gains. Shorter gears and lsd simply make better use of the gains. Shorter/wider tires can be as effective as changing to shorter gears sometimes.

alright, got you, I thought you meant hp performance, not car performance.

I was planning on a 4.44, either sourced from a Mazda pickup or a vender.
However, I am wondering if there's a way to correct me speedometer with the gear change?

4.44 should give good gains. Would work even better with a TII trans. Closer ratio...Taller 5th. Don't trust just anyone to a ring and pinion swap. It usually harder than they think. Maybe pull the speedo drive from a 4.44 RPU.

it looks like to be a good Project can you get more pics?

PLENTY MORE photos coming soon.

I assume you're talking about an FC Turbo 2 transmission, correct? Is that gearbox a direct bolt-in?
Actually, I was gonna do the swap myself. I know it's complex, but I learn by doing.

so i looked at your pic and i have a 79 12a and i thought what the heck is that mine dosnt have it. is it a A/C or what.

sorry inadvance for ignorance
http://img503.imageshack.us/img503/6170/engid1.th.jpg

Dude! Count yourself very fortunate that you don't have one of those little bastards!
That's the oil cooler (commonly known as the 'beehive'). Your '79 also has an oil cooler too, but it's a completely different and far superior design. The beehive is not terribly effective, prone to leaking O-rings, and notoriously difficult to remove and fix. (mine weeps oil, and is going away very soon)
Believe my, you don't want one.

Oh good i saw it and i'm like "OMG Whats that? what am i missing?"
but it turns out its a good thing

It sounds like you have a great plan ahead of yourself. Like trochoid said, skip out on the underdrive pulley and go straight for exhaust. Exhaust, carb/intake, and ignition will net more gains than any other three things (provided the rat's nest is removed).

You have a great looking car too, by the way.

Update: 1st Mod, 1st Test
 

I bought all new tires, and changed the oil. My front tires were pretty bad, causing a vibration in the wheel (yeah, they were that bad).
Then . . . I removed the rear sway bar, and tried launching from 3000 rpm.
Results:
New Average - 16.63 @ 83.6 mph
New Best - 16.53 @ 84.6 mph

Saturday, I'll swap out my rebuilt carburetor and do a timing adjustment. Next week, I do mechanical secondaries and assemble parts for my DLIDFIS.
Oh yeah, I need new brake pads, too.

BTW, don't laugh at my pictures. The underside of my car is a little ratty, and I have loads of tools but no garage to work in. So, I gotta build stuff in my driveway. It's like that, OK?

Carb swap . . . engaged
 

Well, I'm 40 minutes into my Nikki swap. Here's how it looks so far.

The gasket between my nikki and intake manifold looked like that too before I went Holley with a Racing Beat intake manifold. It looks like it was in awful shape.

I think its really great how you are logging your times after all the mods you are doing too.

actually the behive design besides the common leaking and everything work great to keep oil temp. around the same as your coolant
if your vehicle came with a behive I wouldnt remove it
just add a fmoc to drop the temps a little more
plus with the behive comes a nice tall radiator
They definatly work or else mazda would not have put them in there

Yeah, that thing is just there to catch all the parts you're gonna drop workin' on your carb.
My idea was to test the most common mods posted in this forum. People keep asking "how do I do this, how much power does it add?"
Horsepower figures are not much use to us anyway. Elapsed times are KING!

Well, here's how it looked when I had to quit for the day. My buddy's truck needs some work, and we'll lose daylight in 2 hours. So, I'll finish up tomorrow.