this came on the 79 i just got. interesting intake i thought.
also got another modded carb along with a tin full of nikki jets.

 

That's a heavily modified FB intake.

Someone farked it up good, raising the heights of the primary ports is a huge no-no.

 

Also looks like they sealed the coolant passages... I was thinking of doing this as well, any drawbacks?

 

The two middle ports right? Something to do with flow reversion?

 

Other than low rpm intake velocity drops and low end torque loss, are there any other down sides to opening up the primary ports, especially at the top end?

It's easier to put 20mm freeze plugs in the housings, that eliminates the need for o-rings and coolant leaks. I'ts cheaper than tig'ing the intake pasages.

Interesting intake, someone spent some time on it.

 

Maybe the previous owner match ported it to his motor.

 

And it's a big no-no.

It permits reversion, *and* induces huge dead spots in the port, to the point where you can have backwards flow in areas even when "total" flow is forwards. (Whirlpools, like) The rest of the port is barely large enough to wiggle your finger in, and then opening it up like that at the end is trying to expand the area basically double in size while making a turn. Bad bad. And then you have the huuuge difference in length between the long wall and the short wall. Worse worse.

It's entirely a no-win arrangement. Reversion at low RPM, horrible flow at high RPM.


The downside to having no coolant in the manifold is that the manifold runs a lot cooler. This means that the fuel is more likely to wet out on the manifold when you open the throttle, so you need much more accelerator pump. I'm there right now, because I blocked off the coolant passages in the engine (freeze plugs, natch) because the housings were so corroded that there was no way an O-ring could seal. Plus it made fabricating a new intake gasket that much easier.

 

I agree.

 

the car pulled pretty hard the couple times i drove it, i was a bit suprised.
oh well, mikuni's going on tonight.

 

I have not heard this before, not doubting you, you sound like your knowledge is from conciderable experience. I can also see some merit in it. So the next question, would this type of porting/port matching benifit from the longer runners of the wrap around style intake for the dcoes and Mikunis?

 

It all depends on the manifold.

IF the runners are large enough, and IF the final turndown is several inches away from the manifold face, then there shouldn't be a problem. I however would not do it if it meant putting a significant taper to the port.

If it's a Lake Cities type manifold, by all means go for it.

I wouldn't make it any larger than .030" smaller than the engine's port, in any case.

I lost the article through various computer re-combinations (which, as rarely as I change my comptuer equipment, means it was from a *long* time ago) where Paul Yaw explained in detail why mucking with the primaries on a stock manifold was bad. He ended it by montioning making 190hp on a street port with a streetable exhaust without touching the size of the port exits, and 210 on an engine with a "not streetable" exhaust. Seems to me that opening the runner exits up on a stock manifold is 100% pointless because you're not going to be making much more power than that with that manifold no matter what you do with it...

 

what mikuni you go with?

 

44 phh. its on the car and running although i am having throttle cable problems.
revs up waaay faster now.

 

The Mikunis do tend to have a touchy pedal.