intake port to intake manifold. match or mismatch?h

[CHT]

With stock port openings and the big intake manifold ports which in the 460 amounts to a 1/4inch plus mismatch.

That is I think way too much, Ive used up to .125" on all surfaces on an IR and was quite a bit faster. Single 4s definately like less.

In any application/use that suits the port and bowl size in the head, they work better all round with the mismatch in place. Funneling the port out to suit the intake dose nothing to boost performance, yet fitting the big intake on the small port with mismatch in place out performs the same head port with a matching size intake!,

X 2

In all but the highest rpm applications, a mismatch seems to go a long way toward cleaning up un vapourised fuel and helping mid range torque without hurting or even increasing hp.

And bingo that's precisely why it works!

[cjperformance]

With stock port openings and the big intake manifold ports which in the 460 amounts to a 1/4inch plus mismatch.

CHT .. That is I think way too much, Ive used up to .125" on all surfaces on an IR and was quite a bit faster. Single 4s definately like less.

Agreed, but this is what the miss match ammounst to with stock small port head and stock large port intake manifold! It works way better than when hours are spent funneling out the head port to suit, so its generally not worth spending time here at all!, but maybe it will work better better again if the head port is brought out to within .125" or so of the large port intake manifold.? Something to try next time...

[Five9dak]

With a boosted combination is the concensous to match? Specifically a positive displacement or small turbo application where boost is applied through the whole rev range.

[CHT]

With a boosted combination is the concensous to match? Specifically a positive displacement or small turbo application where boost is applied through the whole rev range.

I think that's really up to the individual and how they feel about it. I've seen blown 30psi + with a fair mis-match and you would never know unless you saw it. Sometimes they buy a head and then a manifold and hey presto mis-match. I've seen the mis-match deal work in all applications.

[Boz-Race Engines]

With a boosted combination is the concensous to match? Specifically a positive displacement or small turbo application where boost is applied through the whole rev range.

I think that's really up to the individual and how they feel about it. I've seen blown 30psi + with a fair mis-match and you would never know unless you saw it. Sometimes they buy a head and then a manifold and hey presto mis-match. I've seen the mis-match deal work in all applications.

x2 same

[cjperformance]

The miss match really is no problem in (as I said before) pretty much any situation but for the most high rpm max top end HP applications.
AND in a world where it is not always practical or affordable to spend untold hours on development, the mismatch is one of those things that really can help out. Not that the engine is 'bad', but where tuning etc is not absolutly optimal for the comb, the mismatch and its resultant turbulence in the intake port can just help out and clean up poorly atomised fuel. what the mismatch may or may not cost in lost pure top end HP, it can more than make up for throughout the biggest percentage of the useable rpm range. N/A or Boosted.

[CHT]

The miss match really is no problem in (as I said before) pretty much any situation but for the most high rpm max top end HP applications.
AND in a world where it is not always practical or affordable to spend untold hours on development, the mismatch is one of those things that really can help out. Not that the engine is 'bad', but where tuning etc is not absolutly optimal for the comb, the mismatch and its resultant turbulence in the intake port can just help out and clean up poorly atomised fuel. what the mismatch may or may not cost in lost pure top end HP, it can more than make up for throughout the biggest percentage of the useable rpm range. N/A or Boosted.

And consider texture, that plays a big part in it too.

[Boz-Race Engines]

And consider texture, that plays a big part in it too.[/quote]

X2 AGREE

[Calypso]

I've used to think about the mismatch this way:

If you have IR intake, it's beneficial to have "trumpets" in the end of the duct, because air likes to go in from the sides of the duct rather than from the center.
Big intake to head mismatch, where head entry is smaller than intake exit, is a bit similar situation as I see it. At the discontinuity air wants to enter from the sides more than it otherwise would, evening out velocity profile and possibly pulling in fuel that has been wetting the walls and collecting to the step. Small rounding in the head entry could be beneficial to make it resemble the trumpet a little from flow point of view.
It would be similar phenomenon that exists in more continuous way in the funnel shaped duct. It would be interesting to find quantitative info about size of the step (or angle of funnel) impact to velocity profile.

I'd bet that having a small rounded step "in the perceived wrong direction" meaning head entry is smaller than intake exit, will generally make more power than having it vice versa, which tends to be more typical approach (head entry slightly bigger than intake exit). But what do I know, I haven't tested it, and it's easy to get anything wrong without testing in such a complex system.

[CHT]

I haven't tested it,

oh it's worth it alright. Ive done it over and over. Does also help keep the runners clean all the way up. Cant burn what already burnt then reintroduced eh!

[Boz-Race Engines]

i think it is well and truley worth the effort to do, some good results to be had

[CHT]

OT but I have a radar for exhaust carbon in the inlet, I cant stand it. I've seen many a guy strip a motor down fast,and they dont look and study what did or didnt happen, there's a lot to be learnt right there in front of us.

[cjperformance]

The miss match really is no problem in (as I said before) pretty much any situation but for the most high rpm max top end HP applications.
AND in a world where it is not always practical or affordable to spend untold hours on development, the mismatch is one of those things that really can help out. Not that the engine is 'bad', but where tuning etc is not absolutly optimal for the comb, the mismatch and its resultant turbulence in the intake port can just help out and clean up poorly atomised fuel. what the mismatch may or may not cost in lost pure top end HP, it can more than make up for throughout the biggest percentage of the useable rpm range. N/A or Boosted.

And consider texture, that plays a big part in it too.

Absolutly!!

[cjperformance]

I've used to think about the mismatch this way:

If you have IR intake, it's beneficial to have "trumpets" in the end of the duct, because air likes to go in from the sides of the duct rather than from the center.
Big intake to head mismatch, where head entry is smaller than intake exit, is a bit similar situation as I see it. At the discontinuity air wants to enter from the sides more than it otherwise would, evening out velocity profile and possibly pulling in fuel that has been wetting the walls and collecting to the step. Small rounding in the head entry could be beneficial to make it resemble the trumpet a little from flow point of view.
It would be similar phenomenon that exists in more continuous way in the funnel shaped duct. It would be interesting to find quantitative info about size of the step (or angle of funnel) impact to velocity profile.

I'd bet that having a small rounded step "in the perceived wrong direction" meaning head entry is smaller than intake exit, will generally make more power than having it vice versa, which tends to be more typical approach (head entry slightly bigger than intake exit). But what do I know, I haven't tested it, and it's easy to get anything wrong without testing in such a complex system.

Im with you there for sure.

[Bob Hollinshead]

I thought the mismatch only helped with a sharp edge to create turbulence and promote a remixture now we throw the trumpet bell theory into the mix to increase airspeed and/or volume.... I'm all confused now Very interesting stuff and I can see I'll be trying a few different intakes on my oval port engine if I ever get the thing together. Some dyno testing data sure woud be cool. Bob