Porting suggestions for an "A" series head

cygnus x-1 · 02-08-2010, 11:09 PM

Since several of you guys seem to be pretty knowledgeable about head porting I thought I might ask this here. I'm building up an A20 head for my 2nd gen Prelude with the intent to push it as far as is practical for this head. The intake valves will be going from 30mm to 32mm and the exhaust valve will go from 35mm to 37mm. This is about as far as the stock seats will go. I also want to mill it as much as I think I can get away with, probably 1.5mm to 2mm or as far as my machinist thinks is ok. Finally I would like to do some porting to help out the bigger valves. I've read everything I can possibly find about porting Honda heads many times so I think I have an idea of what to do. But it would be nice to have some opinions from others who are more experienced than I.

Background:
This is mostly a street car but I may take it to the strip on occasion. It's not really a DD so no worries about being a bit high strung (unlikely really). Compression will be between 10:1 and 11:1 depending on how much I can take off the head. Pump gas for now. Cam will be initially about 270-ish duration but I plan to go up to maybe 280 or so. A set of Extrudabody ITBs is also in the works but I may or may not get to that before this head goes on. Redline on this engine is only about 7000RPM due to short rods and long stroke (91mm). HP won't be too high because of the low redline but I would be happy with anything over 150HP. What I really want is a nice flat torque curve. Displacement is 2.0L BTW.

So here are some pics of a cut up head. I added some putty to the port floor as a mock up to see what adding some Devcon might look like. Good idea or bad idea? If I do any epoxy I'll probably fill in around the guides in the intake. Should the port roof be raised at all? The air coming from the intake will be pretty much straight into the head port so I'm not sure if it would help. I also want to keep the port CSA small for maximum velocity. I might also weld up the injector relief if I know the ITBs will be going on at the same time. The injectors will be in the TBs. Probably won't do much to the exhaust ports except maybe smooth over any casting flaws. An other suggestions?

Intake is on the right.

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rushi · 02-10-2010, 02:45 PM

I wouldn't use any bigger valves. What I'd do is to backcut stock valves and get a good valvejob done. My D15 exhaust ports flow extremely well with radius valvejob and radiused exh.valve edges. AFAIK, exhaust port flow is really an issue with A-series and looking those chambers, valves seem to be really badly shrouded.

For such of a low performance goals, I dunno would I do anything else to ports than those I mentioned and smooth the exhaust port roof (remove the guide/boss protruding into port). Well of course smooth/texture the intake ports but that's it. I think filling the intake port floors wouldn't hurt either. I suppose you know that Bisimoto/WebCams grinds cams for these engines too.

I don't like the chamber shape. It is about as bad as Hemi, no squish at all. Would require lots of welding/milling to get it good. High intake velocity should help here too.. Especially if you could create some swirl..

cygnus x-1 · 02-10-2010, 11:43 PM

Hi Rushi,

Thanks for the input. Comments below...

Originally Posted by rushi

I wouldn't use any bigger valves. What I'd do is to backcut stock valves and get a good valvejob done. My D15 exhaust ports flow extremely well with radius valvejob and radiused exh.valve edges. AFAIK, exhaust port flow is really an issue with A-series and looking those chambers, valves seem to be really badly shrouded.

The larger valves are already on the way so they will be going in no matter what.

The head I'm running now has had a 3-angle valve job and some port work done by myself. Mostly it was just a cleanup of casting flaws and polish the exhaust port and chambers. The valves weren't back cut though. With a Colt triflow cam (260/270 int, 274 exh) in it, it seems to do ok but I'm not super impressed. More on this below.

Have you posted any pictures of your radiused valve job? And on the exhaust valves, are you talking about radiusing the chamber side edge or the seat side edge (or both)? On the valves I ordered I specified to break the chamber side edge, but I can easily ad a radius of that would be better. How much radius are we talking here?

It's interesting that you bring up valve shrouding. One thing I was thinking about was maybe trying to reshape the intake port/bowl transition to try and bias the flow to the insides of the valves; in an attempt to minimize flow to the shrouded areas. Maybe that doesn't make any sense since the shrouding would really do that on its own. IDK. I do know that there is one guy that has done a ton of work on these heads and he always reshapes the chambers to remove the shrouding. I've been a bit hesitant to do that for fear of lowering the CR too much. Stock CR is just above 9:1 on these so any loss is not good. However maybe the flow gain is worth more than the CR savings. And I suppose with the bigger valves the shrouding will only get worse.

Here are a couple pics of the valves at 0.1 inches of lift. Does the shrouding look bad? I don't have enough experience to make a judgment.

Originally Posted by rushi

For such of a low performance goals, I dunno would I do anything else to ports than those I mentioned and smooth the exhaust port roof (remove the guide/boss protruding into port). Well of course smooth/texture the intake ports but that's it. I think filling the intake port floors wouldn't hurt either. I suppose you know that Bisimoto/WebCams grinds cams for these engines too.

Well, as far as performance goals I don't actually have any, except "as much as I can get".

About the best I've been able to manage so far with my current reworked head is around 125HP at the wheels as calculated from datalogs with my Megasquirt. I don't know how that would translate to brake HP. These engines stock maxed out at 122HP at the crank, so I'm definitely better than stock. I'm just wondering how much I can push it.

Anyway, removing the exhaust valve guide protrusion I did on the last one, so that's a keeper. With the port floors I mostly just want to make the short side radius a little bigger since it seems to be fairly short. Do you think that will lower the cross sectional area enough to be a restriction or not? I suppose I could rig up a sort of crude flow bench to see if adding to the floor makes a difference.

I know about Web/Bisi and I'll very likely get my next cam from them. While we're on the subject, one interesting thing about Web is that their regrinds have higher lift than other companies (Colt, Delta) regrinds. Do you have any thoughts on whether it would be better to have more lift vs. duration or the other way around?

Originally Posted by rushi

I don't like the chamber shape. It is about as bad as Hemi, no squish at all. Would require lots of welding/milling to get it good. High intake velocity should help here too.. Especially if you could create some swirl..

Right, the chamber design is definitely not modern. For awhile I was considering welding up the chambers but the pistons have a slight dish in them so it would be pretty much impossible to generate any significant squish. It would also take so much welding that the seats would likely need replacing and the chance of warping would be high. Not to mention the cost.

However, the casting I'll be building on does have a couple small pits around the water passages that will need to be welded up. Do you see any areas in the chambers that could benefit from maybe just a small amount of welding while they're at it? Like maybe the big open space by the plug hole?

Regarding swirl, Colt's triflow cam is supposed to generate swirl by opening one of the intake valves sooner and for longer than the other. I have no idea if it actually works but it sounds at least plausible.

Again, thanks for any input, good or bad.

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2DrSE-i · 02-11-2010, 11:32 AM

I'm no head guru by any means, but just by eyeballing i think i have some observations

The intake ports are UGLY. Not sure what its called, but where the air enters the head (on the intake side) and then splits into two ports (to get to the valves) looks very restricted. Could the head not gain by opening these ports up, and smoothing the transition a LOT? maybe adding a bit to the division, but edging it more severely?

If this helps...
O to olo on the intake side

I really need to learn the technical terms before trying to post LOL.

This will be great info for me to, building an A motor in the future myself

What does the exhaust side port look like?

cygnus x-1 · 02-11-2010, 07:31 PM

Originally Posted by 2DrSE-i

I'm no head guru by any means, but just by eyeballing i think i have some observations

The intake ports are UGLY. Not sure what its called, but where the air enters the head (on the intake side) and then splits into two ports (to get to the valves) looks very restricted. Could the head not gain by opening these ports up, and smoothing the transition a LOT? maybe adding a bit to the division, but edging it more severely?

I don't know if it has a technical term but I would call it a divider. It doesn't look that bad to me though. Being fairly blunt is ok. Think of the leading edge of an airplane wing. They're quite rounded and cut through the air just fine. It could stand to be a little thinner possibly in the floor side. I would do this in conjunction with filling in the port floor to create a sort of "D" shape as the port transitions into the bowl. A wider shallower bend will tend to create less shear in the flow as it turns the corner. This is hard to explain, a picture would be better if I could find one.

Originally Posted by 2DrSE-i

This will be great info for me to, building an A motor in the future myself

Hooray!

Originally Posted by 2DrSE-i

What does the exhaust side port look like?

My cut up head doesn't show the exhaust port section very well. I should mill it straight so it does. In fact maybe I'll do that this weekend.

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cueball · 02-11-2010, 10:48 PM

[quote=cygnus x-1;76197]

Have you posted any pictures of your radiused valve job?

D15B2 All-Motor build

first page shows pics

Smeado · 02-13-2010, 05:42 PM

Hello to all!

Ok i feel obligated to post here, since i lurk here almost everyday and soak up knowledge but usually don't have much to add to the conversations. but as a fellow "A" series guy I too seek the advice of the OCO gurus on head porting. I have been working with Cygnus and a few others to try and get the most out of our old school heads. here are some comparisons of the stock cylinder head and the deshrouding i have started.

I also made a 2D blueprint of my head using my cutup head and my ID probes to get as many measurements as i could, it also has the valves, springs keepers, and guides that i am going to use so the valves are different than stock with a smaller diameter. I have all intentions of epoxying the guides and was wondering if you guys would recommend Devcon Aluminium since it will (hopefully) expand and contract with the head, or Devcon Titanium since is has a much higher heat range and tensile strength?

thanks again to everybody on the board for all the good advice,

Smeado

The_Beave · 02-13-2010, 06:08 PM

Have guides custom made to accomodate proper OD of the guide and the smaller ID of the valves.

The de-shrouding you've done is a decent first step, but, it's really not quite enough. You have a lot more to go in order to, at the very least, get the material from the head out of the way 45 degrees from the seat. This is basic "geometric" de-shrouding.

You seem like your afraid to open up the chamber circumference. Don't be. Just don't encroach on the headgasket, which you can clearly see the line of the headgasket. That gives the valve more room to breath, and really won't effect headgasket seal.

Do you guys have an MLS headgasket or is it composite?

Performance Porting · 02-13-2010, 06:14 PM

a little more deshrouding all around will go a long ways

cygnus x-1 · 02-13-2010, 11:44 PM

Hey Smeado! I was wondering when you might get in on the action.

Originally Posted by The_Beave

Have guides custom made to accomodate proper OD of the guide and the smaller ID of the valves.

I think what he was talking about was filling in the void around the guide where it pokes into the intake port. I was planning to fill it in just for the simple fact that it bugs me. I could also build in a little bit of a divider to direct flow around the stem if it would make any difference. IDK.

Here is a pic of what I did to the exhaust ports on my current head.

Originally Posted by The_Beave

The de-shrouding you've done is a decent first step, but, it's really not quite enough. You have a lot more to go in order to, at the very least, get the material from the head out of the way 45 degrees from the seat. This is basic "geometric" de-shrouding.

You seem like your afraid to open up the chamber circumference. Don't be. Just don't encroach on the headgasket, which you can clearly see the line of the headgasket. That gives the valve more room to breath, and really won't effect headgasket seal.

How far away from the valve edge do you think would be enough? I have considered putting this head on the Bridgeport and doing some strategic milling in the chambers. This way it would be easier to make them all the same. I would need to get a tilting table though.

One other thing that I think will make a big difference too is some serious skimming. I've been studying this casting and I'm almost positive it could handle a 2mm skim. Not only would it help to open up around the valves but it would bump the compression up nearly 2 points. That would more than make up for the loss from deshrouding.

In fact I think tomorrow I might just throw this chunk back up on the mill and knock part of it down to see what happens.

Speaking of milling, I did open up the exhaust port to get a section view. The blue line shows how far the lump around the guide sticks down into the port.

Originally Posted by The_Beave

Do you guys have an MLS headgasket or is it composite?

I think someone may have had an MLS made at one time but I forget who now. Other than a custom gasket it's either an OEM or a Fel-Pro. Both of which are composite.

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