What are the advantages and disadvantages of a port matched inlet manifold?

 

What kinda set up?

I just port matched my intake on my RB intake,I opened the hole ALMOST as big as the gasket,It should help the fuel flow better,

 

anytime you can get the fuel/gas mixture into the engine undisturbed and quicker the better your car will run!, more air flow capabilities, = more power, some people say there is improved throttle response as well!

 

That's not what I've heard, at least not for a stock port engine... what about all this talk of intake port reversion? If you port match the manifold, there's no lip there to dissuade things from flowing the opposite way. I definitely am no expert on the subject, but RB strongly cautions against doing exactly that in their instructions for my Dellorto manifold, and I believe it's for that reason.

I'm sure I've seen discussions about this... I believe the crux of which were not to do it with a stock engine. I personally would not do it.

 

Well, my Weber manifold was enlarged to almost the same size as the gasket also. I did note that it didnt require much material to be removed at all though, so the ports were almost that big to start with. Anyway, I dont have anything to compare to, but my Weber seems just fine through out the RPM range. I just need a little bit of jetting and she will be perfect .

~T.J.

 

SiverRocket- like you I recollect that there was 'expert' advice arguing that the ports should be mismatched to assist in air/fuel mixing. Inspite of searching I have not been able to get confirmation, certainly RB as you say are against it.

 

Wasn't there a thread on Mazspeed? I distinctly remember reading some in-depth discussions within the year... likely on Mazspeed rather than here.

I don't know... while I don't have any personal experience, I'm gonna go with RB lol. I think I've heard of people throwing away manifolds after they've tried this... again I have no hard evidence though lol.

So hey... try it if you've got a spare manifold, but don't count on it having positive results.

 

i have tried a ported intake manifold on a stock motor and it made a big difference!! look inside a stock manifold, its super restrictive , and matching it to the motor as close as you can will only help!

quote;SiverRocket- like you I recollect that there was 'expert' advice arguing that the ports should be mismatched to assist in air/fuel mixing. Inspite of searching I have not been able to get confirmation, certainly RB as you say are against it.

what kind of expert advise is that???LOL!!the onle thing a mis-matched intake manifold would do is cause fuel puddling, and slow intake velocity not to mention less total flow capabilities. all lead to less power not more!i have seen ported manifolds work better on every type of engine setup, turbo , n/a, ported, or stock!
i think somebody gave you some bad info!

 

All of my manifolds are matched in runner size to each other with the excepton of the lower manifold to engine. I always leave the runners in the manifold slightly smalller than those in the engine. Its not like there is a huge area increase just a slight little lip. It does not restrict incoming air in any way but does serve as a speed bump for reversion. Fuel isn't going to puddle here. Air is moving too fast. You can make both runners the same size just put a slight angle on the engine side. One of the few times Paul Yaw ever posted on this forum he commented on this. He also does the exact same thing on all of his engines. He probably knows more about airflow through a rotary engine than damn near any one else alive. It's fantastic advice!

 

Do you possibly have a link to that thread?

 

Hey guys, I have been through this and if your motor is of a stock porting configuration and you port match he intake to the motor you will lose a LOT of low end power and torque. Reversion is real and should not be underestimated. Example: On my '85 12a stock port I decided to use my '73 rx-3 intake manifold. Now if you think the '79 manifold is the best 12a intake you've never seen a '73! They are so sweet one might think its an aftermarket piece. i had high hopes, so i enlarged the runners very slightly and port matched to the gasket leaving a 1/8" lip on the bottom since i was already aware of reversion. Well the result was not what i had expected. The motor was a dead dog until 4000. Torque was no longer produced by my motor and of you tried to drive it like a normal 7 , you would end up looking very silly, but after 4500 or so it felt like it wanted to rev to 9K, very free revving in the top end (makes sense) so on a ported motor that is raced this may be ok, but for your daily driver that's stock ported, you dont wanna do this. I had the ported injtake in my 7 for 3 months and i had learned to deal with the narrow, peaky powerband. When I put an '83 intake on it felt like it was supercharged, All of a sudden I could shift whenever i wanted, take off in 2nd, shift to 3rd at 2500, etc. Torque was back! And it was there all the way to redline. me thinks the problem is a combo of reversion and weakened vac. signal at the carb due to decreaced velocity at lower revs. Anyhow I learned a lesson, hopefully it will help others and save sone innocent intakes from being butchered. :>}
By the way, the setup is: '85 12a, yaw carb, 12lb f-wheel, RB streetport exhaust (long tube style) DLIDFIS, etc.

 

For an N/A engine, The effects of killing intake velocity by having too big a runner cannot be understated, also helping the reversion wave is bad idea and must be dealt with. Intake manifold porting is very tricky, and many times counter-intuitive to what you think might work. 10,000 is a victim of this and is sharing his experience, which is exactly what happens when you do what "looks" right.

 

:bs: You have no idea what your talking about. Not trying to flame you, but your passing on bad info. Everything you said in this post is completely wrong and erroneous. Maybe you misunderstand where and how this mismatch is supposed to exist?

 

Mr Yaw is correct in the advice you have passed on here. If you look at the housings you'll see that they flare out right at the manifold interface, and when you put the gasket up to it, youll also see that the gasket is smaller than the face, but the same size as the runner cross section (on the secondaries). This "mismatch" is the reversion dam. It's safe to go to this size (gasket). On the primaries, as tempting as it is to open them up for the tall ports, DONT DO IT! This will KILL velocity, the sudden pressure change will cause fuel to drop out of suspension, and you will increase reverse flow (reversion). These are BAD things. Reversion is your enemy at low rpms, hence one reason to leave the big dam in the primaries. There is more time at low rpm's for intake reversion to occur.

 

Actually, Paul Yaw didn't touch the manifold exits at all.

And he's right, too. The primary runners would be trying to make a 90 degree turn with a VASTLY different short side and long side radius, while expanding, at the same time. Plus, the primary barrels are farly small anyway so there's no real *need* for the primary runner exit to be hogged out.

The manifold runner exit is the *last* thing to be touched. It's already bigger in area than the carb venturi *without* the booster in place... it's also larger than the main part of the runner... what advantage would enlarging the runner exit possibly have?

"I have made 190hp on a streetable engine, and over 210hp on a loud exhaust engine, without touching the manifold runner exits".... hmm I wonder why people think it's such a big problem then eh?