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Oct 12, 2011 | 06:30 PM

#121

Herb Brooks

Senior User

Joined: Aug 2011

Posts: 186

Likes: 0

Now it "Majically" makes sense. I don't know about the back cut. will it reduce the seat surface enough to cause early wear or un reliable sealing? If not I say go for the back cut and be done. This type of thing is kinda like remodleing a house, "you know Honey for just a bit more>>>"
next thing you know your 20k over budget. If your comfortable with where you are sit down. BTW congratulations on a very informative and entertaining thread. Thanks

Oct 12, 2011 | 09:39 PM

#122

Gary Lewis

Thread Starter

FTE Legend

Joined: Jul 2010

Posts: 32,875

Likes: 48

From: Northeast, OK

Herb - Thanks for the compliment. There's sure a good crew providing support. These guys know their stuff.

All - I'm headed back to my home town tomorrow where the machinist-friend is. Am taking the heads awa the pistons. (If you got in after the piston discussion go back 2 or 3 pages.) Turns out the new, hypereutectic/eye-browed pistons have floating pins. Eric, the flow bench guy, said he thinks those require a mod to the rod. So, I'll ask my machinist. And, I'll ask him to look the valve seats over to see if any need touched up after the alleged "porter" did his thing.

I'll also ask him if he has any SBF heads I should consider. Dunno what he might have sitting around.

But, back to the pistons. I'm not convinced that the "new" pistons are better from a quench standpoint. Yes, they'll sit .020" higher in the bore, but they don't quite have as much flat area out of the combustion chamber to serve as the bottom of the quench zone as the dished pistons do. And, at first blush they may have more volume lost to the valve reliefs than the "dished" pistons do. I did get the burette in yesterday but have yet had time to answer that question, but will.

So, please chime in with regard to pistons and quench area. And, btw, Eric said to go for a .039" thick quench area, and get there by zero-decking the piston and using a .039" head gasket.

Oct 12, 2011 | 11:45 PM

#123

ArdWrknTrk

pedant

Joined: Jan 2008

Posts: 23,576

Likes: 39

From: EXTREME southwest CT

I agree with Eric.
Deck the block, and keep quench under .040".
But who knows, those pistons might be there already??? (I mean, that is the point of them)
I thought I had suggested this before.

Dish or no, the quench keeps detonation at bay by (A) creating turbulence, (B) offering too much relatively cool metal for the intake charge to burn in that area.

What you don't want is a taper where the flame front can force the remaining charge into the corner and the rising pressure will set off an explosion, instead of a controlled burn.

Oct 13, 2011 | 08:09 AM

#124

Gary Lewis

Thread Starter

FTE Legend

Joined: Jul 2010

Posts: 32,875

Likes: 48

From: Northeast, OK

Quote:

Originally Posted by ArdWrknTrk

When you say "those pistons might be there already" I assume you mean the dished ones, the ones that are on the rods currently?

My plan is to ask today how much it would take to change from one piston to the other. And, I'll ask how much to deck the block awa if he remembers how far in the hole the pistons are currently. Then, when things settle down here I'll mock up the engine and measure, awa cc the pistons and heads.

Btw, a guy responded to my WTB with GT40 heads that have been pocket polished and have double valve springs mounted. Will call to find price, but am thinking the springs are too much. But, I have new springs on my heads, so.... OTOH, another guy called saying a certain salvage did have 3 vehicles that should have those heads and they are ~$100/pair.

Oct 13, 2011 | 10:01 AM

#125

muscletruck7379

Postmaster

Joined: Apr 2003

Posts: 2,703

Likes: 4

From: Harrisburg, NE

Quote:

Originally Posted by Gary Lewis

As for preaching, in what way? Seriously, everything you said was constructive and not at all like preaching or ranting. And, btw, was the B&S a Model N? No, couldn't be, surely it was much later. I'm giving away my age, but I will say I spotted one of those 50' away in the museum across the street from the Dover Mile one day while waiting on the race to start.

I'm one of those guys that takes an hour to get a 10 minute point across at times... glad it came out right though.

and I actually had to look up what an N model briggs was! a bit before my time!

if the rods are full floating it means that they don't have to be pressed onto the rod, however you will need pistons that have grooves cut for the circlips that keep the pin from taking a journey into the cylinder wall.

i agree with eric as well about zero deck and 0.040" quench

Oct 13, 2011 | 10:49 AM

#126

85lebaront2

Old School Hot Rodder