Inliners International Forums General Discussion Hi Performance Good article about quench.

Nice write up about quench & the importance of machining the blocks & cyl heads to maximize HP & reduce the chance of detonation.

If you get a better quench area, usually, you can actually run more compresssion, run more boost etc.


http://www.enginebuildermag.com/Article/2266/surfacing_equipment_can_increase_horsepower.aspx


MBHD

Good information and short as well. How do you think those SBC numbers compare to say a 250 L6? Zero deck, flat pistons,.030 off the head, .035 gasket, naturally aspirated? Will that mandate premium gas?

They will be pretty close to the same increase in power as compared to a SBC.

I had a positive deck of .002-.004 w/the Felpro HP head gasket 4.125" bore. I did run 91 octane w/no detonation. (More info if needed)

If you are going to use a large chamber head, that will be less compression than a 194 cyl head.
Don't know what cyl head you are referring to.

You could run even low octane depending on what camshaft you use.

Say the combo you are going for, zero deck, 250 flat top pistons, .030" off the head & use a cam w/duration in the 260-270 degrees @ .050 on a 106 lobe center, you will be bleeding off a lot of cyl pressure. You will most likely not get into detonation.

But if you have the same combo & use a camshaft w/ 210 degrees duration @ .050 on a 114 lobe center, you will more than likely get detonation w/premium fuel.

It is all in the combination of parts all working together & carefull selection of parts, fuel distribution, timing & other things greatly effect how an engine is going to run.

Would need to know your whole combo of parts to further determine what you could possibly get away with while running pump gas.


MBHD

"I had a positive deck of .002-.004 w/the Felpro HP head gasket 4.125" bore. I did run 91 octane w/no detonation. (More info if needed)"


How, pray tell, did you achieve a 4.125" bore?????

That is the bore size of the Felpro head gasket.
I do not like that the headgasket has such a large bore, but @ the time it was the only high performance head gasket available.

MBHD

thats only about an eighth bigger on each side, just think of it as quench

It does not work that way.


MBHD

why not?

Read up on head gaskets & quench some more.
The area of the larger head gasket is dead space between the head & block is not considered a quench area, just dead space.

Quench, or squish area is typically the flat area on the top of the piston that's almost level with the top of the block deck. It must have a corresponding flat area on the deck surface of the head to qualify as quench.


MBHD

I did'nt know you knew that!

A very good article, but everything I've seen Vizard write is very good. The numbers are pretty consistent with the dyno stuff I've seen and my own DeuceCoupe Gonkulator computer that tries to capture it in simulation.

It's not like you gain 50hp just from a little more quench as is sometimes implied, but there is some gain, and mostly the quench and swirl then allows you to run more compression which gains even more. The sets of numbers tell that story.

Thanks for the link!

Both quench and squish (not the same) areas have heights that diminish as the piston approaches TDC, generally to .100 or less from the head's underside (and .100" doesn't work very well), which expels the trapped volume back into the remaining chamber.
These 2 surfaces (piston and head) are generally flat, parallel and horizontal - but need not be. Many hemi engines have a 20 or 30° angled quench ledge with head to match. Many 2-stroke engines have the 2 angles 1 or 2° apart. Heads have been machined into a concave radius closely matching the convex curved piston dome. The important factor in common is that as the distance closes mixture escapes in the right direction.

The edges of the gasket outline remain at constant shape and volume, which remains nearly static - and doesn't burn very well.

Does anybody know what the maximum is that one can mill off a 250 Deck? I got new pistons and they are down in the hole .057
Seems like all the new ones are like that. the old ones were only .032 in the hole. I want to zero deck it so I am thinking of taking off .057 off the deck of the block. Any opinions? I will be using the engine for just stock daily driver. But at this point it would have .098 squish with current block.
Any one know where to get thinner head gaskets than .041

Is there anyway you can install 307 SBC pistons?

307 pistons will be closer to the deck.

IIRC, Felpro HG are .038 compressed.

I believe I have some NOS HG that are thinner than .038 more like .035 ish?
Silver in color.
They are round bore, no valve relief notches, I forgot the brand name.
I think I bought them from Clifford years ago?

With .098" that is not considered any quench & could actually cause the engine to detonate from being down the hole so much.

With the low deck blocks being weak in the driver side fwd head bolt area & tends to crack with a stock thickess block, shaving it .057" will make it more weaker.

If it is a stock engine, you could shave the block, run a head stud in that corner & run less final torque, you could probably get away with it, but it's up to you.

I would get the correct height pistons, or even pistons that come out of the block some & shave the pistons down before shaving the block that much.

If they are available, the factory steel shim gaskets are .020"ish?
I might be thinking of the older 194 6 cyl head gaskets.
Anyone?


MBHD

Pistons like these would be better to start with. But definately more money. Less machining of the block to weaken it. These are not a race only piston.
http://12bolt.com/250292_products/250_pistons_57_rod_stock_length

OK great thanks for the tips and I'm drooling over those nice flat pistons. But I am going to go with the suggestion of getting some that stick out. So I got some 230 flat top pistons.
they have a compression height of 1.779 I think I can shave enough off of them and have enough thickness left and go with a thicker gasket possibly. I was thinking of shaving them only in the squish areas and leave the rest to stick up into the combustion chamber maybe with a ramp if necessary to increase compression. maybe then it will be too much compression. I will be having all sorts of combustion enhancing devices on the engine. HHO, Singh groove on head, plasma ignition, and some water injection of some kind, and ammonia, so I am not too worried about detonation with the high compression. I am looking to build a high mileage car, not so much for performance. Using many of the techniques from Eagle research books on improving mileage. I am currently treating all the engine parts except cylinder walls, with tungsten disulfide to reduce friction. It involves polishing and then embedding the tungsten disulfide into the metal to create a low friciton coating. Some companies out (microblue)there doing it for bearings and engine parts. I thought I would do it on my own as a budget art project LOL doing things outside the normal. I can post some photos later if anyone is interested.

If you need to shave the pistons and if you end up doing it with a milling machine, now would be a good opportunity to mill a dish on them that mirrors the combustion chamber in shape. If your numbers would otherwise allow for it, like if you need more CC after zero decking them. For reasons explained in this topic. Just thinking out loud...

OK I got the 307 Pistons in here today. looking to go with them. Now a question came up with the pin offset. seems like there is considerable ofset to the piston pin. which side do I put the offset to???? The narrow side towards the manifolds?? So I need to put two in backwards since they are for a V8?

Never mind I think I answerd the question on my own. thanks.

The notch or arrow on top of the pistons goes toward the front of the engine!