Bringing my engine to the limits of Street Prepared. I can run any intake manifold, throttle body and fuel / timing control system i chose. Only stipulation is that the motor must be a stock port engine.

Atkins Side Draft Manifold
TWM Side Draft 55mm throttle body
Megasquirt
FC CAS

ill have pictures along the way. Manifold should be here on the 30th. Then once i get paid on the 15th, ill be ordering my Throttle body. Megasquirt soon after. I'm still removing the horrible rust preventative scrap from all over the engine bay.

 

I'd like to see the dyno results when its done. I've heard that in theory a NA stockport 12a can only get to ~150 hp due to the port size and timing.

Whats your goal for this build? I know your maximizing but what kind of limit do you expect to top out at? Cool project.

 

The motor is for my hill climb car so i want to get as much as i can out of it. But the rules just limited me to a stock engine. The biggest reason i want fuel injection though is because i live near the lake, with a total different temperature range and for that matter, atmospheric pressure. The hill climbs are a few hours away and there are too many changes to the tuning i would have to make while at the competition and i couldn't "save" them as easy. Will the megasquirt i can make maps depending on my location for optimal performance.

Im thinking about skimping on the TWM throttle body and go with a Ford 5.9L throttle body. It would save me about 400 dollars and a lot headaches. I could adapt it to the Atkins manifold without too much difficulty.

 

That makes a lot sense. I wondered why racers were using MS setups even though they were NA for the most part. Good luck.

 

manifold arrived today.

 

ive read that 150hp number too, couple ideas....

1. if 150hp is the max amount of air the motor will flow (at what rpms?!), maximise the power curve under that. if the power peak is 7k, work on the 4-6k range

2. we used to see 1-2psi of positive pressure in the s4 manifold on the k2rd race car with the haltech, if its real, then you can do more than 150hp

 

Can you clean up the casting flash in the runners? I dont know if this would increase any power, but may help a lil bit.

 

nope. cant remove material more than 1" from the mating surface of the manifold in either direction and its for "port matching" only.

 

Test fitted the manifold. Seems pretty good. The manifold itself could use a little cleaning up on the inside. Especially the ports on the intake manifold flange. Ill get pics of this.

 

looks great .. can't wait to see what you put out of this setup. Alot of ITB's are in this section and I'm loving it

 

im hoping to get a much a possible from a stock port, non modified internally (ie unopened) 12a. Basically because the CSP rules say so.

 

the only issue i'm thinking is going to hold me back is the heavier rotors w/ the light flywheel. I think there might be more to gain from a 83-85 rotor set with an after market flywheel. If i rebuild the engine with later model rotors and the light OEM flywheel then balance accordingly, i think i would find some power.

 

Well Mr. Engineering Guy, do the math. Mazdatrix's FAQ section has weights for the flywheels and rotors. You can roughly guesstimate the mass's average radius, then all you have to do is figure the rotating inertia of the rotors (remember that besides rotating at 1/3rd speed, they orbit at full speed, I think those are additive) vs. the rotating inertia of the flywheels.

Rebalancing a '81-82 flywheel to work with '83-85 rotors is an old racer's trick. Personally I wonder if the .04lb weight difference between a '83-85 12A rotor and a Series 5 rotor is miniscule enough that you couldn't just slam a S5 N/A flywheel on there. That's the second lightest RX-7 flywheel evar.

My gut feeling is that the rotor weight differences aren't as significant as they first appear because if the weight loss comes from inside the cavities, then any missing iron is going to be replaced by oil, and while oil is a bit lighter than iron (proof: connecting rod bits do not float in the oil pan) it's still not insignificant.

Also, you won't see a power gain anywhere but on a Dynojet. Reducing rotating inertia doesn't make more power, it just requires less power to accelerate, so more acceleration makes it to the drive wheels. Lighter rotors *are* nicer from the standpoint of eccentric shaft flex and bearing stresses, though.