Ok I have read a couple threads on this subject but I still have not found a clear answer on this. I have a couple of 12A factory intakes and wanted to experiment with porting and polishing the intake. Is this a waste of time?

 

Of course not. If its your first time and I wouldn't port them on usable irons. If they're not usable do it, great practice. I haven't even ported before but you will need the most practice you can get. Try it and then when you think you are ready port your engine

 

Well find some bad housingsfirst dont use good ones.

 

He is talking about the intake manifolds guys.

 

^^lol sheep

 

The only reason to port would be to smooth out the casting ridges and increase the runner size. Polish would be a nono. Hopefully Carl will pop in and give you some advice on how much to open the runners up.

 

Oh, misunderstood, I see now.

 

I just noticed that the intake runners are real bumpy and would like to smooth them down. Would this give me a better fuel flow from the carb through the intake ports of the irons?

 

If you smooth the intake too much, the runners will wet out with fuel. Some roughness is desired as it will establish a turbulent boundary layer and helps keep the fuel mix suspended in the air charge.

 

Out of curiosity, and because I've been drinking, would angled, shallow grooves in the intake help out to increase turbulence and help create a vortex like movement through the intake that would improve the quality of the mix?

 

look at this thread:

https://www.rx7club.com/1st-generation-specific-1979-1985-18/cutting-grooves-intake-manifold-555308/

i plan on doing this sometime soon hopefully.

 

LOL, drink less, read more, it's better for your health and knowledge.

 

From what I've read polishing is a "no no". And as far as porting, Less is more with a stock port motor. Match the intake to the gasket and call it a day.

Ridges (as described in link below) do seem to help low idle and extreme low rpm torque. Worth wile IMO. But definitely won't give you any big HP gains. Or MPG gains with my recent exp. Don't expect any huge gains from it.

Good luck!

https://www.rx7club.com/showthread.p...=1#post6401882

 

Never ever polish. Polishing actually hurts flow. You want to use maybe 80 grit sanding rolls for the final "finish", at the smoothest.

Never port the outlets any larger. This will kill flow because of the shape of the port. I've had lots to say on this before...

Never match to the gasket, either. For one, you always want a step "outward" in the direction of flow. For another, if the gasket is bigger than the ports in the two parts you are mating (normally the case) then you will get a big "bulb" in the port runner that will hurt flow as well.

 

I'm sure your right I don't have squat for exp with these motors. Only seat of the pants feel from before and after.

But I think porting mine helped quite a bit.

I didn't touch the primaries, I should have mentioned that, only the secondaries and I opened them up maybe 1/8" all the way around. I used my trusty harbor freight digital caliper and checked the ports on the housings and they were quite a bit bigger than the ports on the intake. They were a lot more circular as well and the intake ports were nice and rectangular. If I wanted to match the intake to the motor I would have had to go close to a 1/4 inch all the way around on all ports and rounded them out quite a bit. Wish I took better pictures when I did this.

Anyway opening up the secondary jets and intake ports slightly seemed to give me more top end pull. The car felt pretty dead past 6500 before seems to pull to 7ish now. Could just be the cold weather...

That is just my exp with it. On that note I haven't had this car since new. The housings might have already been tampered with.

 

Thanks alot vxturboxv! I appreciate your help. I will just do it since I have a couple just laying around and then I will test them out. Just need to order some more intake gaskets and o rings for my stock.

 

If you're going to do a lot of screwing around swapping intake manifolds back and forth, get some 19mm (I think?) freeze plugs and use them to seal off the coolant holes in the rotor housings. It might be slightly larger than 19mm, I remember having to spread the plugs out a bit with a Strategically Sized Socket in order to get a tight fit.

But, once plugged, you can yank the intake manifold without opening the cooling system. If you have no emissions equipment, pulling the intake manifold becomes the fast way of removing the carb, too. (The F-U carb nuts get very easy to access when the manifold is off of the engine!)

I would not recommend this for a street driven car, though. I *had* to do it because my rotor housings corroded badly at the O-rings and it was a perpetual coolant leak. Now drivability sucks when the engine is cold, especially when it's below 60 degrees.

 

Yeah the last time I did the "freeze plug mod" my last engine started making a loud squealing noise so I will pass on that mod. Plan on rebuilding it soon. Replacing coolant is better than replacing an engine plus it is cold here and my RX-7 is a daily for now until I get the roll cage installed.

 

I highly doubt the squealing was related at all to the noise.

The reason for running coolant through the intake manifold is to heat it up for better fuel atomization and therefore drivability.

 

And on that note, An inline fuel heater will do a better job of heating the fuel for atomization. This was my original plan but the cost of the inline heaters are ridiculous. So I just replace the o-rings this time around. I figure some better gas mileage can be had by doing this as well. But I have nothing to prove it.

I was going to try this unit....
http://www.kenneke.com/veggie.html

 

The problem isn't the fuel atomizing out of the carburetor, the problem is the fuel hitting the cold manifold walls and condensing. The manifold has a lot more mass than the droplets of fuel, so making the fuel 130 degrees instead of 50 degrees will not help very much.

 

The freeze plugs for the intake are 20 mm. Part # is Dorman 555-101.