Porting 4AG: My 1st O/S valve porting job

[MorGo]

Why increase the chamber cc's and then have a huge domed pistons to make compression?
And you ruined the chambers.. research "pressure recovery"..
Yes,the chambers need to be modified but not like you have done.

[oldeskewltoy]

Why increase the chamber cc's and then have a huge domed pistons to make compression?
And you ruined the chambers.. research "pressure recovery"..
Yes,the chambers need to be modified but not like you have done.

I was given the pistons specs(dome volume 9.5cc) and told to work the chamber based on that pistons volume.

I took your advice and did some searching on "pressure recovery". Speed talk, Darren Morgan seems to have the handle on this.....

I have to admit it is a VERY interesting subject.... Most of the search showed this discussion on speedtalk, I've since joined. I'm not so sure how a 4AG chamber could get the absolute correct shape, based on the original casting. It was even brought up that there aren't any(many) decent 4V heads, most need to be welded and ported.

I'm also pretty sure there isn't a way to gain 3+cc of volume and and get the chamber shape they suggest.

I'd be interested in seeing how you would increase the chamber volume by nearly 10%(3.5cc increase), and having(keeping) an appropriate shaped chamber....

[MorGo]

Ehh.. what I don't get is why you have to modify the chamber to get compression down? In street engine some 12:1 comp is just fine (my 4A-F with 11,5:1 runs just nice with Russian 95 octane)
Always reduce the dome instead increasing the chamber.That makes lighter piston and generally neater chamber.NA 2T-G/18R-G are quite poor just for that reason;need huge dome to make compression.Install flattops and some boost.. ;-)
4A-engines suffer from small bore to be really powerful engines;30,5 mm intakes are not too big and some 32 mm start to suffer shrouding (diminishing benefit)

[oldeskewltoy]

Ehh.. what I don't get is why you have to modify the chamber to get compression down? In street engine some 12:1 comp is just fine (my 4A-F with 11,5:1 runs just nice with Russian 95 octane)
Always reduce the dome instead increasing the chamber.That makes lighter piston and generally neater chamber.NA 2T-G/18R-G are quite poor just for that reason;need huge dome to make compression.Install flattops and some boost.. ;-)
4A-engines suffer from small bore to be really powerful engines;30,5 mm intakes are not too big and some 32 mm start to suffer shrouding (diminishing benefit)

My 4AF runs pretty good on 89 octane(about 10.25 to 1)... that is another story (4AGZE 8.9 to 1 bottom end, under a 1st gen - crappy intake port 4AFE head. I flow matched the poorly designed #1 exhaust port to #4, and then matched #2 and #3 to the first 2 - http://www.toymods.org.au/forums/tec...p-porting.html

I DO understand (and agree with) the smaller chamber is better theory... after all I'm using it in my "little" 140+whp 4AGE... on all stock internals(pistons, rods, crank) except wrist pins, cams, and valve springs. Chambers on this engine are 33cc


Back to this head for a bit........ the common high comp 4AG pistons out there are severely peaked(domed). My clients pistons at 9.5cc is HUGE, but I'm TRYING to work within the confines of my client. You've admonished me for a "ruined" cylinder head... and yet within my limitations you haven't offered me any methods other then new pistons that could've been done. Do you have any recommendations on the head work based on the piston my client is using???

[MorGo]

Ahh,you are forced to use something that doesn't belong the build!
Well,even then I would looked hard how to reduce the piston dome (of course not compromising the piston strenght!) instead roughing out the chamber.
But I understand where you are.Oh how I hate customers! (that have zero knowledge and force you doing something stupid..)
I quess you have done what you can and it's not your fault considering what was given.
BTW,your port work seems nice! (well,some things I would do different but then again;I don't know everything!)
12 years with flowbench and I still found myself amazed of what the air does (or not!)

[MWP]

Interesting reading, thanks guys.
I wish i had known about the pressure recovery theory before i attacked my 3SGTE (gen4, Caldina) head.

I did wonder why they changed to a convex shaped area between the inlet and exhaust valve walls when all previous 3SGTE's had a very concave area.
The convex shape change would have quite a large effect on pressure recovery.

It seems i made a couple of wrong choices in the way i worked the chamber:



I could have done with removing less material from between the valves like TK has in the following photo
(see the concave shape in this earlier head)



Ah well, lesson learnt.

[oldeskewltoy]

I did some sample measurements and the peak of the chamber measures out to a little over 15mm total depth...... the spark plug sits about 7.4mm tall........ "Houston, we have a problem"

I've asked the client to send me one of his pistons so I can see how his pistons fit my chamber work..

If the pistons interfere.... I'll be bringing it all to my buddies (Loynings) to get their take.... and try to figure out an effective solution if one is needed

We indeed have a problem! The piston is resting on the spark plug electrode..

about 2mm to tall........ Next week it is off to Loynings to see what can be done.

[PrettyCoolWagon]

Hey Dan,

Do you think using spark plug indexing washers could solve the problem?
http://www.moroso.com/catalog/catego...?catcode=41011

This write up pretty much explains it, ..intended more for improving burn rate/efficiency but can also be done to stop piston/spark plug interference.
http://www.sr20-forum.com/naturally-...ark-plugs.html

[oldeskewltoy]

Hey Dan,

Do you think using spark plug indexing washers could solve the problem?
http://www.moroso.com/catalog/catego...?catcode=41011

This write up pretty much explains it, ..intended more for improving burn rate/efficiency but can also be done to stop piston/spark plug interference.
http://www.sr20-forum.com/naturally-...ark-plugs.html

hmmmm, easy enough to test... the .064(1.6+mm) equals 312 degrees (so says Moroso), so I could back the plug off and see how much that helps....


Well... the plugs stop contacting the pistons between 180 and 270 degrees back rotated......

[liteace]

any more progress on these pistons? alot of aftermarket high comp honda pistons have a spark plug space for it usually.

[oldeskewltoy]

any more progress on these pistons? alot of aftermarket high comp honda pistons have a spark plug space for it usually.

The client is fully aware of the situation... and the possible solutions.... 1) plug indexing, 2) "fire slot" machined in pistons (roughly 18mm wife by 1.6mm deep), 3) "Racing" spark plugs without overhanging ground electrode.

[30psi 4agte]

Nice thread Oldskewltoy..... Well laid out and informative. I wouldnt be too concerned over how you have reshaped your chambers. Allbeit not perfect but you have worked with what you had to do.

Good job mate