1987RX7guy

iTrader: (3)

Hey all, I wanted to know the total crossectional area of the 4 port engine as well as the 6 port engine. I think I might be able to do the measurement on the N/a but since my TII's engine is still assembled and has all the manifolds on it I can't do it right now. If anyone knows what it is please let me know. Thanks.

Santiago

EDIT upon reading the post it doesn't go into detail. I mean the combined area of all the ports. sorry about that.

andrew lohaus

is this some sort of port job you are brewing up?

1987RX7guy

iTrader: (3)

No no I want to know the total area so I can calculate how bit a throttle body(s) has to be to adequately support the port area in each engine. Then I want to compare it to the stock and aftermarket tb's for our cars. This will shed a little light into whether or not the after marked IDA tb's and manifold will be able to flow enough for them. If they don't then I would opt to not buy them. If they are bigger than the port size then I think it may be worth it. But it would be cool if I could use this for any porting I do in the future. But at the point in time I will be having BDC port my engine for me and I will be rebuild ding the parts after he is done with my street port.

andrew lohaus

ok but port cross sectional area is only one factor in terms of overall flow. runner shape and smoothness are just as important.

1987RX7guy

iTrader: (3)

Isn't it wonderful how a thread about a huge wing gets 281 veiws and I get 21. Damn rice!

oregano

iTrader: (1)

i mgiht be able to help u after this weekend. but not yet, sorry.

the big wing gets a lot of views cuz every one can relate. but when u start talking bout this stuff, most ppl get lost

NZConvertible

Only one rotor breathes at a time, and you don't need a ruler to see that the total cross-sectional area of the stock TB is considerably bigger that the total cross-sectional area of one rotor's ports.
Why don't you just compare the TB's then? 3x45mm is obviously a lot bigger (22%) than 2x50mm.

Pattsy

iTrader: (1)

The cross sectional area of the ports on the 6 port is roughly 12.432cm^2 by my measurements and math. Hope this helps some.

Pat

1987RX7guy

iTrader: (3)

I thought the intake phases of rotor one and two overlaped?

And I should have left out the comment about the IDA's as I have also seen some custom intake designs I could make myself with a welder(given I learn to use one )
Basically I don't want to eyeball it. Hard numbers are better for me and all of us I think.

Rx7Boi

Yeah but those 2x50mm with short runners will own the 3x45 with the stock manifold, plus the secondarys dont open all the way

Pattsy

iTrader: (1)

It was slightly more involved than eyeballing, but less than integrating the area of the ports. You can take the numbers with as many grains of salt as you deem necessary

g'night.

andrew lohaus

indeed hard numbers are great but the port area doenst directly corelate to total breathing ability of an engine. many other factors. take for instance a p-port. probobly about the same overall opening area--if not less--than a six port but it flows so much more air into the rotors because its a strait path and ussualy through very short intake runners. the only real way to get "hard numbers" about how much air flows through a given setup is to get it flow benched or use advanced modeling software. port area doesnt mean &hi# on its own. otherwise all you can do is make the intake track bigger, shorter, smoother and straiter by any means. you dont have to know exactly how much better something is to just know that its better. come on. some of these numbers you are always looking for just dont mean anything on thier own.

andrew lohaus

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rotarygod

iTrader: (1)

It sounds like he is trying to design an intake system with around the same total cross sectional area for the whole length to maintain high velocity. The throttlebody does have to be bigger though since the throttle plate, even when fully open, is still a restriction in the system. The whole point of this is so he can get as close to optimal as possible from the start without going to all of the trouble to find the one person in the world with a flowbench that will line up with a rotary. He also doesn't have to take his engine apart this way. He doesn't want too small of a throttle plate for obvious reasons and neither does he want too much area here since it will give no more max power and give low speed throttle a bit of an edge. Yes the intake runners make a difference in both size and shape. I think he knows that. A peripheral port makes more power not only due to short runners and a direct shot at the rotor housing but also because it is open for much more time which leaves more time to cram air in at high rpms. Just because an IDA style throttleplate is used doesn't mean that the same area as the stock throttlebody will yield the same results. It won't. The stock primary throttle plate supplies all the air to the 2 primary ports whereas the other 2 plates supply air to 2 runners. The single primary plate is more of a restiction to the system than the other 2 plates. By using an IDA or equivalent throttlebody, more air is distributed to the engine more evenly, even if the total area is smaller since no single throttle plate is responsible for more airflow than the other.

andrew lohaus

ok it makes sense if hes trying to keep it uniform for the sake of high velocity. and relative to the rest of the intake the port oppening obviously is important. it wouldnt make sense to have a sewer pipe lead up to a pin hole. (i though he simply was looking for a tb with just slightly more cross section than the ports on the assumption that that fact alone would make it better than the stock tb, which isnt necissarily true.) but shouldnt the intake gradualy narow at a certain rate for max power (i assume this is the end he's going for). also for what its worth many of the rx7s out there making stratospheric hp#s are still using the stock tb. the tb isnt whats holding the engine back, its only having 1.3L that does.

rotarygod

iTrader: (1)

The whole point isn't making "stratospheric" power levels, it is trying to get as close to max potential for what he has. Nothing wrong with that. The high power turbo cars can force more air in. The really high power cars do typically have a different intake. The primary throttleplate on the throttlebody is more of a restiction than the other 2 plates so yes the throttle plate is a restriction. An easy way to fix this at the expense of a little low end power is to hog out the dynamic chamber to use one large plenum. Now the entire engine is being fed through an average of all 3 plates rather than by 1 plate feeding 2 ports and 2 plates feeding the other 2 ports. More uniform air distribution. Optimally the intake cross sectional area should reduce at a rate of 10% total over the entire length of the intake runner.

1987RX7guy

iTrader: (3)

Yes but I can't polish the intake tract or ports because they are supposed to have a slightly rough surface. I forget the true reason behind this but I remember something about it promoting the fuel stay suspended in the intake charge and providing some turbulence. But given the materials I can use to make an intake plenum it will have to be smooth because I don't have any casting equipment or a mold. I planned on using a barrel style intake bolted to the stock(port matched) LIM with the proper size throttle boddy to provide enough air to all the ports.(based on crossectional area)

j200pruf

iTrader: (4)

You can polish the runners, but don't polish them to the point the runners have a mirror finish.
And Santiago, If you want a different intake manifold for your TII, just get an IDA mani with some TWM throttles, it will be a lot easier, and probably cheaper than building one.
There could definatly be some gains in building a custom intake manifold for a N/A, but I am guessing thats not what your doing this for.

1987RX7guy

iTrader: (3)

I have seen the IDA's but I am doing this for the TII. I need my N/a to retain as much reliability for now. And going with an IDA setup would cost me roughly 1k dollars. I think I can make my own manifold for half that. I just need to understand how to make it and why it needs to be that way. The total area covered by the ports would be the first step IMO.

rotarygod

iTrader: (1)

So this is going on a turbo. That's cool. I made my aluminum upper manifold based on my engine porting. My runners are slightly shorter than the stock runners and they feed into a single plenum that is fed by a 75mm Mustang throttlebody. If I were designing it for an n/a I would have used a smaller throttlebody. It was a little touchy on the throttle on the low end but when the turbo spooled up it was fantastic. Rather than basing the throttle plate area off of the total port area, base it off of total runner area. It is much easier this way and will still give you what you want.

I would go ahead and get the sanding wheel on this inside of the runners for as far as you can. Smoothing the rough cast surface does have a benefit. Just don't polish it so smooth that you can see your reflection. Even the sanded surface is still rough enough to keep dispersion and flow rates high. There are alot of people that assume that since you don't want it perfectly smooth, the rough surface it comes with must be best. In truth it is only like that because the manifolds are made with a sand cast and that is the imperfection in the casting process. The new composite engine manifolds out there are much smoother than the aluminum ones internally but still aren't totally smooth and slippery.

NZConvertible

What gains/losses did you see?

1987RX7guy

iTrader: (3)

At which point should I measure the port runner area?

rotarygod

iTrader: (1)

Due to the larger single throttle plate and the fact that all 4 runners receive air at part throttle, the power fell off some on the low end (below about 4K) and streetability went down. This is under part throttle though. When the engine was floored and the turbo spooled up it really got going fast. The improvement in airflow also aided the top end quite a bit. Low throttle driving around town wasn't as easy due to the lack of intake velocity. It was a play car anyways so I didn't care. I guess it could have been worse but the Haltech makes tuning a wonderful thing. Sadly that car is in rotary heaven now. I still have the engine though.

I would just be fairly general about the measurements. Just look at the runners where they join between the upper and lower manifolds. The gasket is larger though. Measure these for area and combine them for a total area number. Then add about 20% to the size in area to account for throttle plate losses. This doesn't mean that it will work exactly as you want it to but it should be a good starting point.

Hey NZ: No hard feelings over past bickering. We're both pretty hard headed!

NZConvertible

That's pretty much what I expected. I don't think I'd bother with this for a street car but I'd definitely be worth it for a track/strip car.
Hell no, holding forum grudges is silly. I just respond to the info in front of me regardless of who it's from. And where would the fun be if we all just agreed with each other?!

1987RX7guy

iTrader: (3)

Cool I think I am going to look into buying some LIM's and port them myself then measure how larg they are and add it all up. Time to get back into formulas. Blah!