Inlet manifold port matching

[Meatball]

Following on from my exhaust port match post

The inlet manifold im using is from a 5.5 griff with 45mm inlets from memory. My head ports have been opened by CRE my guess is that they are now much larger than the inlet manifold.

How would this effect the air flow if at all? i understand the other way around would be a problem.

Thanks in advance

[clive f]

you should be fine going from a small opening into a large one, but is it possible to open your inlets where they mate to the heads so that it is a smooth transition for the air flow, just in case giong straight into a larger hole causes any problems with the flow?

[spend]

clive f said:

you should be fine going from a small opening into a large one..

Which way round? Mass flow vs air speed (momentum for cylinder packing) is a black art Biggest restriction is the 38mm twists & turns in the inlet manifold IMHO. You can match the head to inlet so there are no steps, and also enlarge / flare the ports if you desire. Most of the porting I've seen is just smoothing the trumpet base and port matching the heads. Opening the internal runners of the inlet manifold seems to be rarely done - it is painstaking fiddly work. I don't believe 45mm trumpet base is poss (44mm IIRC) just as folks refer to 72mm throttles (normally 71mm?). If you deviate from round / rectangular you can do some interesting things, but you will probably need some weld/filling to get the best shapes possible.

[GreenV8S]

spend said:

Which way round?

A step out (air going from small to large duct) is pretty harmless since the separation bubble forms in the larger duct and causes relatively little restriction. A step in (air going from large to small) is bad news because the separation bubble forms in the smaller section reducing the effective size even further.

[Meatball]

I was looking for help from you 3

spend said:

I don't believe 45mm trumpet base is poss (44mm IIRC) just as folks refer to 72mm throttles (normally 71mm?).

your probably right


How would the engine benefit going from a step like mine to port matched as suggested?
any gains?

Im not thinking of pulling mine apart "at the moment" im just picking your brains


and whys my spell check not working?

[MADMAX2]

what brains????????????

[trackcar]

A step in the right direction is usually good news .. ie going from small to large bore .. means you dont have to be totally accurate getting the walls lined up but also a step in the right direction means virtually no flow lost to a properly matched port, but it helps prevent flow reversal so can help tame a wild cam at low rpm and can also help introducing fuel back into the airstream at low flow rates . so many good reasons for having a step in the right direction

[Meatball]

trackcar said:

A step in the right direction is usually good news .. ie going from small to large bore .. means you dont have to be totally accurate getting the walls lined up but also a step in the right direction means virtually no flow lost to a properly matched port, but it helps prevent flow reversal so can help tame a wild cam at low rpm and can also help introducing fuel back into the airstream at low flow rates . so many good reasons for having a step in the right direction

Thanks for that

I think its something i`ll tackle when i get around to changing the injectors.

[clive f]

spend said:

clive f said:

you should be fine going from a small opening into a large one..

Which way round?

you know exactly what I`m on about you plonker

Edited by clive f on Monday 29th December 09:13

[trackcar]

clive f said:

spend said:

clive f said:

you should be fine going from a small opening into a large one..

Which way round?

you know exactly what I`m on about you plonker

Edited by clive f on Monday 29th December 09:13

lol it did rather sound like argument for argument's sake I'm not really convinced by the rest of your post there either dave, how many heads have you ported and do you have a flow bench (or access to one?) .. talk of interesting stuff if you get away from round/rectangular .. and the inlet being a bigger restriction than the poor head ports .. evidence?

[clive f]

trackcar said:

clive f said:

spend said:

clive f said:

you should be fine going from a small opening into a large one..

Which way round?

you know exactly what I`m on about you plonker

Edited by clive f on Monday 29th December 09:13

lol it did rather sound like argument for argument's sake I'm not really convinced by the rest of your post there either dave, how many heads have you ported and do you have a flow bench (or access to one?) .. talk of interesting stuff if you get away from round/rectangular .. and the inlet being a bigger restriction than the poor head ports .. evidence?

not until I`ve made it Joo

[spend]

clive f said:

trackcar said:

clive f said:

spend said:

clive f said:

you should be fine going from a small opening into a large one..

Which way round?

you know exactly what I`m on about you plonker

Edited by clive f on Monday 29th December 09:13

lol it did rather sound like argument for argument's sake I'm not really convinced by the rest of your post there either dave, how many heads have you ported and do you have a flow bench (or access to one?) .. talk of interesting stuff if you get away from round/rectangular .. and the inlet being a bigger restriction than the poor head ports .. evidence?

not until I`ve made it Joo

As usual you two have completely lost me heyho play your games....

[Pasco]

spend said:

clive f said:

you should be fine going from a small opening into a large one..

Which way round? Mass flow vs air speed (momentum for cylinder packing) is a black art Biggest restriction is the 38mm twists & turns in the inlet manifold IMHO. You can match the head to inlet so there are no steps, and also enlarge / flare the ports if you desire. Most of the porting I've seen is just smoothing the trumpet base and port matching the heads. Opening the internal runners of the inlet manifold seems to be rarely done - it is painstaking fiddly work. I don't believe 45mm trumpet base is poss (44mm IIRC) just as folks refer to 72mm throttles (normally 71mm?). If you deviate from round / rectangular you can do some interesting things, but you will probably need some weld/filling to get the best shapes possible.

This makes perfect sense to me Joo

Shirley laminar flow is the ultimate goal in this instance ?

Opening up and smoothing out the inlet manifold and matching the ports etc is a positive step imho

[trackcar]

ok.

[spend]

trackcar said:

ok.

Thats a change from gobbledegook Can't you make your mind up what to post?

[Pasco]

trackcar said:

ok.

Hey Joo whats with the OK comment ?

Sorry if my opinion offended you but unless you can tell me otherwise it make perfect sense to me mate

Please enlighten me why you think this is not worth pursuing.

[trackcar]

gobbledegook was what i think it is but discretion got the better of me so i just posted ok lol. it just sounds like someone trying to sound technical but not actually saying anything of substance at all. i would love you to explain it further though dave

[Pasco]

trackcar said:

gobbledegook was what i think it is but discretion got the better of me so i just posted ok lol. it just sounds like someone trying to sound technical but not actually saying anything of substance at all. i would love you to explain it further though dave

Blimey Joo far from me from wanting to fall out with you but that's a ste comment imho weather it was aimed at Spend or Me !

[GreenV8S]

I don't know about the rest of it, but I kind of doubt you're going to get laminar flow at any point in the intake manifold, and anyway it's not really what you want. What you want is an attached turbulent flow with a nicely energised boundary layer. Laminar flow would detach at the first hint of trouble even assuming you managed to achieve it. Having surface roughness can actually help the flow stay attached (by encouraging mixing within the boundary layer) so silky smooth highly polished is not necessary what you want. I would have though the important thing is consistent cross section area reducing smoothly through the corners and corners kept to a minimum with no sharp corners anywhere.

[spend]

GreenV8S said:

I would have though the important thing is consistent cross section area reducing smoothly through the corners and corners kept to a minimum with no sharp corners anywhere.

Hmmm.. I worked on the maxim of enlarging the corners to 'straighten them out' by increasing the outer radius and shortening the inner, which seems at odds with your statement. I can't visualize how a bend and constriction would maintain an orderly march of the O2 squadies
Certainly agree with only flowing changes (no pun intended ) and gradual change in cross section. You can extend those same tenets to the inlet manifold runners IMO, the std 38mm dia is comparable to the LR std @44x25mm head port which will have been enlarged somewhat in most of our heads?

I still think you want to try and make the charge speed up in the head port so that you get the benefit of momentum overfilling the chamber, I would pretty much leave alone the (decent) TVR heads anywhere around the valve/guide area because of that also. Getting that final 'funneling' down to speed up & swirl is really hard I reckon and the hump inside the TVR inlet ports seems to have been carefully sculpted for that very purpose.

All in all it certainly gives you a strong desire to do away with convoluted hoses - blame Tim Lamont for that

ETA: Missed a slash

Edited by spend on Tuesday 30th December 02:15