250 Head on 200 Back from Machine Shop

[pikesan]

Just got done reading this thread: viewtopic.php?f=1&t=60392&p=462755&hilit=exhaust+porting#p462449

Very cool thread.. obviously alot of well informed people on this board and I appreciate that. I just got my head back from the machine shop and I'm wondering what work I should do to it.
It's already had a 3 angle valve job and milled 0.25 (if I remember right). The pistons are at .005 deck height and I was targeting 9.0:1 compression ratio. The rest of the engine will have Comp Cams 268-like custom grind (loved that cam in my 302), header and dual exhaust and so far unknown carb.

My question...
Should I open up the exhaust ports to match the gasket? Either bigger or just radius what's there.
How about opening up around the valves and polishing or at least smoothing the combustion chambers. I can't believe how rough they are!

I'll do all this myself. I've got more time than money to spend. If I left anything out, ask away!
BTW, just got the bottom end put together after going 40 over with all new parts from Egge.com. Very cool guys to deal with.
Thanks!

 

[rbohm]

My question...
Should I open up the exhaust ports to match the gasket? Either bigger or just radius what's there.
How about opening up around the valves and polishing or at least smoothing the combustion chambers. I can't believe how rough they are!

yes, you do want to do some pocket porting to clean up the valve bowls, and you want to port as far into the ports as possible. same with the exhaust, which is where you will get the best power increase from the log head unless you send it out to be extrude honed. you want to match the gasket opening, and blend that back about 3/4" into the port. as for the combustion chamber, you want to smooth out the chamber as much as possible, but dont bother to polish the chamber for a street engine, as it will load up with carbon soon enough. you also want to equalize the chamber volumes as much as possible.

 

[Gene Fiore]

I would not match the exhaust gasket with the exhaust ports in the head :nono: ...the gasket openings are huge by comparison to the size of the exhaust port...you will lose too much velocity and this would not be a good thing. Just smooth the inside of the exhaust ports and remove all rough flash but don't change the size of the ports.

 

[CZLN6]

Howdy All:

Since you have more time then money, (I can relate) I'd highly recommend smoothing the combustion chambers. The smooth surfaces will be less likely to have hot spots that could cause pre-ignition, and smooth surfaces are less likely to carbon up as badly as rough surfaces. Finally, a smooth surface will reflect heat into the combustion process, causing a more efficient engine. I not only smooth the chambers, I polish them. All that I had occasion to inspect were alot less carbon caked than the stock, rough surfaced chambers. What's it worth? I don't really know, but like you say, I've got more time than money.

Keep us posted you your progress.

Adios, David

 

[pikesan]

Hi David
this board is lucky to have you. Thanks for the input. I think I'll do exactly what you said. The only bummer is I'll have to pull the valves out.
Anyone know of a combustion chamber clean up kit they can recommend?

 

[82F100]

Pikesan,
http://search.eastwood.com/search?w=hea ... 7AodDzzZ-w