Inlet Ports On Custom Manifold

[mattbenselin 0]

Hi a little advice is required on this subject please...

 

 

As you can see in the first picture the inlet ports on my head (they already a little bigger and ports flowed) don't line up with the inlet manifold design. This manifold is not my design but it's the only thing I got.

My question is should I leave the head be...or...should I remove some metal so the port shape matches that of the manifold runners? (indicated in red below) I would obviously smooth the port as much as poss. to create a better airway. I know there are water channels there for the original manifold too so how much could I take off?

 

 

If I do remove some metal will this have a negative effect, ie slow air speed? Or will the enlarged port flow more air because of the size of the runners?

I should mention that the manifold runners are straight, that is they do not angle down or anything from the flange, they are 100mm long and are used to mount 40mm bike carbs.

 

Thanks for any help, Matt

Edited October 31, 2008 by mattbenselin

[projectpug 0]

I am no expert on porting heads but if mine was mismatched that badly i would definately try to smooth it out a bit.

[unariciflocos 49 1 Cars]

I'm doing the same bike carb conversion, but I'm definitely going to mill the inlet ports. From what I know such edges cause turbulence and drastically reduce air flow.

[DamirGTI 327]

I would most certainty ground down those highlighted areas , yes .. in fact it's an essential job , in order to achieve good/quality air/fuel mixture distribution from the inlet manifold into the ports , inlet manifold and head contact areas must be mirror image ! if you leave it like this it'll rob you a good bit of air flow making turbulences around that square edges in the inlet ports ..

 

Mark the excessive projecting areas on the inlet port entry's as accurate as you can trough the inlet manifold (or you can use gasket to do so ..) , but fit the manifold on the head , on the studs and tight it ... mark the edges , then remove the manifold take a grinder and blend the inlet ports from inside out up to the end mark on the edges which you've marked , ground the edges in order to achieve smooth transition/radius - but don't go mad with grinding ! .. then refit the inlet manifold back and re-check if it's fine, or you may need to grind some more ..

 

Look over here for some more info :

http://www.guy-croft.com/viewtopic.php?f=2&t=7

http://www.guy-croft.com/

 

Have fun !

Damir

[Sandy 189]

Very difficult to do in situ without stray swarf, I'd advocate taking the head off ideally.

[mattbenselin 0]

Hi thanks for the advice...

 

...the head is off anyway as the whole engines being given the once or twice or thrice over! I've spoken with Guy Croft who concurs that the head should be machined to match the manifold. I am taking the head up to his in a couple of weeks anyway for him to skim, clean, shim and work his magic!

 

This might sound a little contradictory to myself but....no one has suggested I get a Bogg Brothers manifold, or have another made which better suits the head ports?

I know this is a costly route and seeing as I have a manifold already an almost trivial one, but the benefit of having a manifold which better suits the inlet ports, and is built to the quality few can match is surely the best option? Also and to me quite obviously, once I port match this head to this manifold, I can not use another! I'm not trying to convince myself one way or the other, money is a big factor and its something I don't have a lot of right now, especially to buy manifolds with!

BUT what do people think, what would YOU do?

 

Thanks, Matt

[DamirGTI 327]

If you'll be taking the head to Guy's workshop ask him advice regarding that inlet manifold as well (take the manifold with you and show it to him..)

 

Damir

 

(say hello to mr. Guy for me ! he's been most helpful in the past years during my projects , could say all the best about the man )

[jonir 0]

hello i think its better to leave head as it is, what comes on fitting the manifold.

i'd think its better to try modified the inlet manifold to fit whit the head.

what i have seen these heads, is that the ports are just been cleaned off all edges

and the biggest job is right before valve.