i have an 85 GSL DD. a friend of mine has a 79 manifold that he isnt using. i thought about installing that manifold on my 85. i just want to know what i would be gaining and loosing. i know about the EGR hole. i already plan on blocking that off with some of that steel in a tube stuff. the only problem is im not 100% sure i have a 79 gasket. a brand new 85 gasket just came in from mazdatrix today. would i be able to use this gasket if i modify it a little?

i just dont want to install the 79 if ill be loosing low end and gaining top end. this is a DD, so i want driveability.

i have already searched and saw one thread, but it didnt have much info. so spill your guts here.

 

The primary difference in the 79 intake, is the lack of shutter valve. I have heard they *can* flow a little more air, but I doubt there is much difference. The lack of the shutter valve, and it associated crap, would tend to make me believe the early manifold has a better airflow pattern, especially in the higher RPM range.
IIRC, there is a fitment issue when mixing carb/intake from early and late 1st gens. Something about the OMP linkage. I just can't remember if it's early carbs on late intakes, or late carbs on early intakes....

 

I have an 79ish manifold on my car with the newer FB carb on an old jap motor from an SA, and it seems pretty much the same. As for the big EGR hole I used a block off plate that came with my RB header, I had to drill a new hole to make it fit and for some reason the old motor and manifold has studs every where instead of bolts. Since the studs on the EGR were half way threaded I needed some really thick washers to put inbetween the bolt and the block off plate, and I found that the corner seals from my old motor worked perfecty (ghetto I know). I think you also need another block off plate that goes on the side of the manifold that faces the firewall, not 100% sure I could be wrong on this one. After that I used assorted vacume caps for every thing else and it worked easily. As for the gasket I don't think there will be a problem the difference between your's and the earlier gaskets is that yours has a little extra gasket on the bottom for some port on the bottom of the 81 and up maifolds (pics on the bottom. Since I bought the car with the engine already blown I can't give you a before and after comparison, but the jap motor supposedly has more agressive porting and it seems to drive very nicely with no lowend issues.

early style 80 and below 12a gasket


newer gasket 81 and up 12a


I don't know if the port sizes are different, or it's just the pics being different sizes, if they are different I think its more important to match the gasket to your motor rather then the manifold so you don't risk peices of gasket falling in the motor.

 

I forgot to mention that I run premix so I never delt with the OMP system.

 

ill have to examine the manifolds some more. mine is coming off anyways. i just didnt know if itd be a good idea to swap the manifolds while i was at it. thanks for the info. keep it coming.

 

The SA manifolds are more even and smoother inside, since there is no shutter valve in the rear primary.
When Paul Yaw built my old carb and intake,he used an 84 manifold and simply removed/filled the shutter ports,copying the design of the 79-80 units.Theres nothing fundamentally wrong with the 81-85 manifolds,there is just more junk in them.Replacing one stock manifold with another will probably not gain you much,if anything.If your planning on porting/smoothing a manifold for real performance,the 79-80 is a better choice just for its simplicity.

 

well, what i plan on doing is modding the inside of the runners with grooves to allow for better atomization of the full. the grooves will keep the fuel from "puddleing" on the walls of the manifold.

 

I opted to use the SA intake for my blowthrough, for the added flow.. There are some modifications to making it work on 81-85 engines. I removed all the egr castings from the intake, and then added the differance to the bottom of the SA intake to match the FB.

 

both manifolds already have the EGR block off plates on them. the main thing id have to do is block off the EGR port on my 85 engine. ill give the 79 a closer looking over tomorrow and i may go ahead and pull of my carb and manifold as well.

 

The main reason I removed the casting off the intake was to gain clearance to mount the S4 turbo in the same place as a 13B. Nice and tight beside the engine.

 

You must be thinking of something else,perhaps the port air injection passage or the ACV.......the 1980 CA cars are the only 1st gens with EGR.

 

i ran a 79 intake on my 85 for a while with no problems... i can't say for sure that i gained a whole lot buy doing so, but i was always told there was a difference in the runners... 79 being the better of the two... i also blocked off the coolant ports to keep the heat out of my intake... good luck!!

 

Blocking off the water passages was another mod that Yaw did to mine.
It has its disadvantages though,especially in colder climates.In the winter,my Yaw carb would freeze solid in only a few highway miles......and that was in CA winters!Were talking only 40* or so,not even freezing outside.I had to route warm,underhood air to the intake,carbs need some heat to atomize fuel and prevent iciing.

 

i want to add to this. i saw the 79 carb again yesterday in person. the actual ports on the manifold are the same size as the ports on the 85 manifold. the gasket is the only difference. since this is the case ill probably be cutting grooves in the 79 manifold and installing it on my car in a few months. i need a break from doing work on my car and im about to move for college.

 

The reason for the tall port gasket was for the rare reverse runner manifolds. I've never seen one for a 12A and only a couple for 13B.

 

so youre saying the runners on the 79 manifold should be different than the runners on my 85 manifold?

 

No. Mazda used the same gasket from '76 to '80 because it was cheaper. Then for '81-'85, they went back to the '74-'75 gasket. It was cheaper than coming up with yet another gasket.

 

Get ahold of RX7carl and see what he has to say on the subject since he has done alot of flow testing.

I know on my SE(still FI) my upper and lower intake have been ported and it made a substantial difference in performance.