dbragg

iTrader: (7)

i had to take my intake manifold off againdue to it being rediculously loud after i messed with it a few months ago. once i got it off i realized why, the gasket i had on there was the wrong one. it was a 79-80 gasket and i needed a 81-85. i have a brand new 81-85 from mazdatrix.

i was looking at them today when i had them off and i noticed something. the 79-80 gaskets primary holes match perfectly with the primarys on the engine. yet when i put the 81-85 style on there the gasket holes are much smaller. would this be an issue? do i need to trim the gasket to fit? i just dont want it to effect air flow too much and i dont want it to eventually corrode due to gasket and go into my engine.

while i had the carb off i looked at the shutter valve and decide to remove the useless thing. the screws on the butterfly are crap. so ill probably just drill them out to get the flap off. im going to go ahead and pull the whole assembly off. i plan on using quick steel to plug the holes. do i need to make the inside of that runner flush without the indentions from the shutter set up? do i need to block off the hole that goes from one primary to the other?

now to the EGR port. i had initially planned on blocking it to fix my loud exhaust problem. once i got the manifold off and realized i just needed to install my new gasket to fix it im not if i want to block it off or not. the good about blocking it off, i wont have to worry about it and i can still run the 79-80 gasket that matches the engine ports. the bad, i dont want my intake to get too cold during the winter, this is my DD.

i will also be cutting the grooves into my intake manifold to try to help atomization. ill post pics of everything. thanks.

yes i search, on all subjects. i couldnt find what i was looking for.

vipernicus42

iTrader: (4)

You're correct, the gasket holes are smaller than the holes on the engine. From what I've been able to find, this is actually by design and should not be changed. Also take a look at how they compare to the holes on the manifold... I'm not sure what mazda was aiming for, but from what I've heard it's supposed to be that way *shrugs*

Dont' remove the butterfly from the shutter valve assembly. Notice that the rear primary runner is larger than the front, so that with the butterfly in place they both flow the same volume of air. Remove the butterfly and you unbalance the flow through your manifold. Leave the butterfly and its rod in place and fix them in the "full open" position somehow (I used JBWeld)

I don't know anything about EGR because my car never had it. According to the manual that's a Cali-only thing.

Jon

Rogue_Wulff

If you compare the 81-85 intake gasket to the ports on the intake, you'll notice the intake is smaller. Therefore, the gasket having smaller holes the the ports on the engine becomes a non-issue.
I can't really comment on the shutter valve, having never messed with mine, other than disabling it.
As for the egr port, if using the block-off plates, there's nothing flowing into it. Blocking the port on the engine is just a way to use the SA intake, which has not shutter valve.
The intake will not run any cooler with the EGR blocked, especially if the water passages are left open. Did you use those freeze plugs I sent you? I have the water passages blocked on my FB, but I don't drive it in extremely cold conditions. I have a truck for winter driving. I did have one problem of carb icing back during the winter. It was about 5F outside, and I started the car up for the first time in about 2 weeks. As it was warming up, it didn't want to idle or run very well after a few minutes. I simply shut it off, and waited about 5 minutes, then restarted it and it was fine.

dbragg

iTrader: (7)

i just realized the situation about the gasket. it matches the manifold, not the engine. problem solved.

viper-- so youre saying if i remove the shutter valve completely itll actually make the car perfrom/run worse? what about the hole from each primary runner to the other? what is to be gained if this is blocked?

rougue--yes, i got the freeze plugs into the engine. it wasnt as easy as id of thought, but theyre in there. i REALLY appreciate you helping me out when i really needed it. i wont forget it. so i have no coolant going into my intake to warm it up, but i have exhaust gases going into it to warm it up. im just wondering if i block of the exhaust port that goes into the intake if the bad will out weigh the good. my winters her arent that cold, but icing could possibly still occur.

vipernicus42

iTrader: (4)

Basically, when dealing with the shutter and related stuff, do your mods on the outside of the intake mani, but don't touch anything in the runners. You basically want to make it function as if the valve is still there, just stuck in the "full open" position. Don't plug the hole between the passages, but DO block the holes that lead to the outside of the manifold (from the outside with JBWeld or whatever).

PM me your email address, I'll send you the carb stripping tutorial I'm working on. It has a section on the intake manifold which covers it.

Jon

dbragg

iTrader: (7)

pming you my address now

id like to remove the butterfly, gring the lines in the manifold and then but if back, but the screws just dont want to budge and i dont want to round them off. oh well.

dbragg

iTrader: (7)

viper- read the shutter vlave section. i understood it all except where you stated to use JB weld on the actual arm of the shaft. you said dont get it on the washer or e clip cause itd cause a vasuum leak, i dont see how this could be the case.

im thinking i may just block off the exhaust port and use the 79-80 gasket and intake. that way itll make my life easier for grooving the manifold and i can get better flow.

BUT



everyone says if you port the 81-85 style manifolds to match the engine that youre actually hurting performance. well, if this is the case then wouldnt using a 79-80 style actually hurt you? wouldnt the smaller ports on the manifolds be better due to research mazda made between those years? thoughts....

vipernicus42

iTrader: (4)

Yes, I'd use the later manifold

Point #1 in bold here is what you're referring to when talking about port matching:

http://www.yawpower.com/Flow%20Testing.html

I didn't say not to get JBWeld on the washer or eclip, I said not to get it on the mating surface where the spacer sits. The spacer = that big black plastic thing with all the vacuum nipples that doubles as a heat shield. You don't want any JBWeld on the metal around the top of the manifold because then the spacer wouldn't sit level and no gasket can fix that.

Jon

vipernicus42

iTrader: (4)

There, does this make it more apparent?

dbragg

iTrader: (7)

dammit, youre right. the 81-85 manifold will be better. hmm, oh well. i guess ill just have to get creative when i try to groove it.

i totally understand what youre saying about the JB weld. it TOTALLY makes since. i mean, its obvious. its just when i initally read it i thought you were saying otherwise. sorry.

vipernicus42

iTrader: (4)

No problemo.

I can see where you're coming form. The washer is a "spacer" as well, so I guess I'll have to play with the wording of my tutorial to make it more clear.. and maybe draw those arrows.

Jon

dbragg

iTrader: (7)

yeah, i would reword it and possibly add the above pic. whelp, time to get off the net and to work.

Jeff20B

iTrader: (13)

aws140, what you see below is a '81-'85 manifold after some mods. More on it later.

I have a '79 manifold and it has the same size primary runners as '81-'85. Mazda used the same gasket from '76-'80 and since some of those models had a reversed runner manifold, with tall intermediate ports because they were secondaries, they had tall holes in the gasket. You can't use tall ports as primaries because they flow horribly at low RPM. It looks like a compromise that Mazda used to keep them backwards compatible all the way back to '76. Stick with the '81-'85 manifold. I did.



https://www.rx7club.com/forum/showthread.php?t=637323

Note: some of the info needs to be updated such as the '78 carb I mentioned was actually a later one from Japan meant for a catalytic convertor, and the flapper valve = shutter valve.

dbragg

iTrader: (7)

thats jeff--i finished locking my shutter valve in place with quick steel and using it to also plug the whole left by the actuator(?)

i polished it up a little with a wire tool. i want to throw it back on my car so bad. i havent driven anything other than automatics in over a month due to my surgery..uugghh. i have to wait though so i can groove the runners. hopefully ill be able to get it done sunday when my neighbor gets back from the beach, he has the tools i need to groove it.

thanks for all the help guys. glad i didnt swap to the 79 manifold now.

Jeff20B

iTrader: (13)

I've never grooved any of my manifolds. Let us know how it goes.

Oh, and I experimented on my bro's RX-4 engine with quicksteel in the ACV port. It didn't leak in the few thousand miles he driove it before the SC went on. Note this was during a rebuild and everything was clean.

His old manifold was quite similar to a '79 manifold where it lacked the ACV part of the casting, and had channels on both runners. I once adjusted the idle all the way down to 350 or so, just because I could.

Booyah

when I recieved all my racing parts in, the instructions specifically stated to NOT trim the gasket as it was designed that way.

dbragg

iTrader: (7)

ill post back in this thread the results of grooving the manifold

vipernicus42

iTrader: (4)

Wow Jeff, that manifold looks to be in pretty good condition. That RB block-off plate is crazy thick isn't it?

Mind if I use that picture in my pictorial to show a block off plate being used for the shutter valve vac spots instead of JBWeld?

Jon

Jeff20B

iTrader: (13)

Go ahead.

I've seen ACV blockoff plates range from very thin aluminum to 1/2" thick steel! It added a bit of weight to the manifold.