Magic Quench Numbers

[Tom Kochtanek]

I need some advise from the wizards out there. What is the Magic Number for the desirable quench for a 409 stroked with a 427 crank?

My #1 piston at TDC is about .031" ABOVE the deck (I say "about" because I also need to know the best tool for measuring this vertical heighth). The gasket is composite and measures .048 uncompressed -- what will this compress to?

The real question is, how do I adjust this quench area, with gaskets or by milling the piston? I hope it's the former, since I have already had the reciprocating parts balanced :)

And if it is by using gaskets, where can I get the recommended ones for this application? Copper?

As always, I thank you in advance for your advise and consideration. This is my first ever engine build, and I am having fun :)

Cheers!
TomK

[CDNpontiac409guy]

Tom,
Did you have that block decked ? I mean REALLY decked:eek: ?
You should be sitting at .008" above. Gaskets compress to .038"-.042".
The accepted "ideal" quench distance is .028" - .032". This enhances the "swirl" of the air/fuel mixture at the top of the compression stroke.

For the record, the original spec is .008" below the deck. The steel shim head gasket compresses to .018" - .020".

.012" out of the block would be fine with the composition gasket... but that's about as tight as you'd want to go.

Ross has a reputation for getting these clearances very accurate. might have to check rod length:cool:

[Tom Kochtanek]

Aubrey:

I was thinking the same thing. I got this truck block at .060" and then a little, so it may have been decked before I had it done. Not sure what it took to get it to where it is, but will ask the machine shop tomorrow. Will also check rod length.

Is it possible to get gaskets that thick, made of copper or some other source, that could give me the correct height without changing anthing that has been balanced?

Best,
TomK

[CDNpontiac409guy]

Tom, on a "tongue in cheek" positive note.... You'd be surprised at how little 20 thou of aluminum would weigh:p .
Trouble is while doing this, you will lose .020" in piston to valve clearance. If I recall what you're using for a cam, you WILL want to check that:).
My stocker is at about .060".

[MRHP]

I hate to be the bad guy but.......My Ross 10:1 pistons turned out to be 11:25 plus! I hope the pistons you have were machined properly. I have heard of this problem with Ross pistons from a couple other people. It cost me a pretty penny to go to a larger cam and change all of my valvetrain to bleed off some cylinder pressure. Runs better now but what a pain in the a$$! I hope this is not your case! Let us know what happens.

[SSpev]

I've known several people that ran 2 gaskets. No problems I'm aware of. I think Smokey Yunick recommends .038 to .040 (sbc)quench.

Has the crank been turned? (rod pin, i know the mains are) Could be off set some. Is the block line bored? That will raise the piston in the bore. Rods been resized? Little on the piston, rod, crank, crank bore, and deck hight. Stacks up real fast.

[CDNpontiac409guy]

HHMM, sspev, maybe it was Smokey who was responsible for the widespread acceptance of composition head gaskets;) .
The GM spec on a high performance 409, ready to race, would be in at around .028".
I know the last engine I ran in my Belair was decked when I got it. Had .004" deck clearance, and I ran a set of GM steel gaskets ( because I had them on hand:p ). This was 1995.
That engine just plain SCREAMED:deal. VERY noticeably faster than a previous engine with the identical cam profile ( about 4 MPH in the 1/4 ).

My stocker ended up coming in at almost .010" positive... so I've got .028" - .030".

[SSpev]

That is probably true Aubery. I personaly think .030 or tighter is good as long as things don't start hitting ;) 2 things need to happen with the quench. Create alot of turbulance and have NO combustion occure in this area. Hence the tight clearance. Cummins diesels use around .040. But there WAY into emmissions not going faster:p

[Va348]

Guys

On deck to top of piston You really need to go by how much cyl. wall clearnce you have if you have street you can be closer.

A good Rule of thumb is .006 for .001 cyl wall clearance. I would not go tighter than about .026 Remember these new alu. piston they are using does not expand as much as old stuff.

On my stuff I ck. how much rock I have on top. There seems to be a magic # on race stuff.


Hope it helps a little.

Dale

[Tom Kochtanek]

Fellas:

It has been suggested that one approach might be to pair up a set of gaskets to obtain the required clearances. What would be the worst case scenario if this were to fail, assuming the clearances were met? This brings up lots of additional questions:

What type/brand of gaskets are we looking at here? Trusted or recommended sources would be nice :)

Am I correct in doing the arithmetic, that we need (.028" Quench + .031" Above the Deck) = nearly .060" gasket pair (compressed). I'll be interested to see if there is something out there to accomplish this, assuming it is a viable option.

Another option is to mill the tops of the pistons the needed amount, the limitation being the new distance between valve and piston, as CPG pointed out. But wouldn't that be the case if it were "gasketed up" as well? Would we just be milling one section out of the tops of these pistons, or is it the entire surface?

So many questions for the newby! Thanks for your continued interest in my saga. Please, I beg you, let's keep this a single instance and not make this into a discussion about "How many gaskets were on factory set ups?". Think of this as a single case (mine) that needs viable solutions :) :) :)

Assuming I do this correctly the FINAL assembly time, you will hopefully see this engine in KC in September. And then I can thank you all personally for keeping me involved and enthusiastic about these "WX" projects :)

Thanks again!

TomK (slightly nervous about the options)

[dq409]

In the instruction sheet that you get with your Ross pistons they have two types of piston skirt designs with two different minimum cylinder wall clearance specs, A and B.

Modified type engines, including drags,
A= .008 to .009
B= .004 to .005

In talking with Roy my machinist about this he says that he questioned Ross about this and Ross says that both styles should be clearanced at the "B" specs!

Why Ross has two different specs when they themselves state that both styles should be .004 to .005 is the question!

[59elcooldsuv]

Gentlemen:
Seeing how my current project is the first time I've been inside a W motor -

Can you tell me EXACTLY where you measure this deck height?

My first guess is that you measure it on the side of the cylinder that is closest to the intake manifold. (?)

On "normal" engines I'm accustomed to measuring in the middle so as to get above the wrist pin & not let the piston rocking affect the measurement. The pistons that my machinist ordered from Egge have a bit of a dome, about an 1/8" high and about the same angle as the deck. The original ones were flat, so I think I'll get a compression increase, no matter what.

I think I'm going to draw 3D volumes in Autocad to represent the piston dome & the "chamber on top of the cylinder" and let the computer tell me the theoretical volumes. Then press some play-doh into the valve depression in the head & measure it's cc, unless one of you can tell me how many cc a 250hp 348 head would have, then I won't need to go shopping for a beaker with cc marks.

I would appreciate your thoughts on this issue to edikate a virgin.

[fatride]

As you know I'm a big advocate of running the correct quench. Seems like some machine shops just plain forgot to ask what gaskets you plan to run. My pistons (Ross 10.5:1) are .015 in the hole , with a steel shim head gasket = .035 quench. I feel safe with this number. I recomend steel head gaskets for one reason, it allows you to keep some deck height. To get the correct quench and run a composite gasket means you would have to zero deck. That leaves you no were to go if you needed to deck the block again!

[Loafer409]

"unless one of you can tell me how many cc a 250hp 348 head would have, then I won't need to go shopping for a beaker with cc marks."
====
Ask and ye shall receive... 10.3 cc

Look here....09



http://nhra.com/tech_specs/engine/index.html#chevy

select 1958

[Va348]

Tom

Do yourself a favor and deck your pistons. It would change Bal but about 5 grams. And its going lighter so no big deal.Where you get in trouble is if going heaver. Ever who bal your eng. probably used 4 grams for oil.So now it will be 9 grams. I use 8 for big blocks. A lot of Shops are using 15 to 20 now.

Ck your valve cly now. I like .080 and .100 Can get a long fine at .060 and .080 Ex is most important ,piston is chasing it.

Jury rigging will most of the time be trouble. Deck pistons!

Dale

[CDNpontiac409guy]

Yes Tom, I'm with Dale here.
I'm looking at one of your pistons right now ( you know... same kind;) ).
Because you do NOT remove material from the valve relief, I can see that the surface that will have to be milled down is a very minimal area. At .020", I would think that the weight of the aluminum taken off would probably be more like 3 grams:p
As Dale said, not a concern. The actual weight of the residual engine oil inside the piston, ect, calculated into the "bob" weight which is used for the pupose of balancing the crank, is at best, a moving target.

So... remove that bit of material, do your clearancing, wash everything up, and do a complete trial fit.... making sure you check the piston to valve clearance at approx 10 deg BTDC & ATDC.
Knowing the cam profile that you have, and if your springs are at around 150 pounds on the seat, I think .070"-.080" would be quite acceptable.

This isn't a big deal, Tom... just one of the standard delays:rolleyes: ;)

[bbqcruising]

Tom, I talked to Jack Gibbs who specializes in these stroker motors and He told me that Victor makes a head gasket that is .054 not compressed.Some other interesting stuff. Ross told him to determine how much your deck has been cut, measure at 10 and 2 oclock from the crank mains to the deck. They state this value should be 9.6 inches. Aubrey is correct that factory spec was .008 below deck. Jack said in the 60's he saw that value to .001 above. If you go with .008 below deck and a crushed value of the factory steel gasket of .018 it looks like GM had .026 in mind. Jack also stated that they did start using double Gaskets in 63 for insurance purposes. He said that .030 off the top of your pistons would be about 5 grams as Dale stated. By the way, he gets those head gaskets from Show Cars. If you would like to call him his number is 530 934 4336. BBQ

[Tom Kochtanek]

This exchange has given me much information to go with. I had a call into my machine shop (they decked the block and did the heads) but he was out for the day. I plan on posing the same Q's but am now armed with all of your collective experience.

I did zip over to my buddy's shop where we are assembling the engine to take more measurements. Unless I am reading this incorrectly, I have #1 piston at TDC at .031" out of the hole (above the deck) and -- get this -- #7 at TDC is .039" above the deck. I plan to do the other side to see if this is a pattern. Then we have a discussion with the shop that did this work... I need to be certain of these measurements first.

Will keep you posted as things develop. Thanks for all your input. I plan to do this correctly, assuming there is a single correct way :)

Cheers,
TomK

[SSpev]

Oops. I posted resized rods add to the stackup... WRONG (what was I thinking:confused: ) Anyway, What rods are being used? I recently had a problem with stock BBC rods. I was 0 to .015 out of the hole. The rods where .010 differance long to short.

[Tom Kochtanek]

Tom:

I am going with Eagle BBC rods, and since they are now out of their holes, I aim to check the lengths to see if something odd is going on. Thanks for the tips, everyone!

More later,
TomK

[oil4kids]

Does anyone have an actual number on how much grinding the bottom of the block can take to clear the rods before getting into the water jackets

[59elcooldsuv]

Originally posted by Loafer409
Ask and ye shall receive... 10.3 cc
Look here....09
http://nhra.com/tech_specs/engine/index.html#chevy
select 1958 [/B]

Way Cool! Thanks Loafer.
BTW, when it says "block volume = 70cc" does that refer to that wedge-shaped cylindrical section of combustion chamber in the top of the block? Should I theoretically get that number if I ask my autocad to measure a space I draw to those dimensions?

[Loafer409]

That would be my understanding, but there are others here that can give you a more definitive answere then I....CPG???

[SSpev]

Here are the measurments, in cc, on my 348 in the 61 (avitor)

--------------1 --- 2 --- 3 --- 4 --- 5 --- 6 --- 7 --- 8
vlv pocket - - 10.5 12.4 10.9 11.5 12.0 11.7 11.7 11.1
cyl chamber - 69.9 68.3 68.3 70.0 66.9 69.5 67.3 70.0

average 68.8 and 11.5

With an average deck height o .031 and steel head gasket 9.35 CR avg.

[fourspeed409]

I have heard that the eagle rods are a decent product but they must be double and tripple checked for proper length. As for your out of hole measurements varrying, if your rod length checks out ok then check to see that the deck was milled paralle to the mains.
Shane

[CDNpontiac409guy]

Good point, Shane.
And if that block was NOT milled square to the crank ( which is the WHOLE IDEA behind doing it )... then the machine shop owes Tom a crack free 409 block:eek:

[Tom Kochtanek]

Thanks again for your continued input. I did connect up with the machine shop that did the deck/head/crank balancing work, even talked to the guy who did it (Earl). Earl said he doesn't have any means to determine just how much he took off when decking (he can do that for 90 degree blocks), but he did recommend checking the rods carefully, and suggested that the factory 427 crank just might contribute to length in a single hole (not sure if that's the case yet). I'm out of town for the weekend, so maybe next week, after work in the evenings...

When I do get to take it all apart, we'll do the grinding work at the bottoms of the holes to allow clearance for the rod bolts. Then after another good cleaning, we refit all 8 pistons without rings and check the protrusion out the deck for each hole (after I verify that she turns freely :)). After taking those measurements we should know a lot more.

Boy, after doing this one right the rest of my W builds are gonna be a piece of cake! CPG got me going in that other thread when he mentioned how easy is was (comparatively speaking) to stroke a 348 with a 409 crank. Maybe I should have started there and worked my way up :)

Cheers,
TomK

[dq409]

Originally posted by Tom Kochtanek
CPG got me going in that other thread when he mentioned how easy is was (comparatively speaking) to stroke a 348 with a 409 crank. Maybe I should have started there and worked my way up :)

Cheers,
TomK

NAHHHH !!! Always start with the toughest project first !!! Then from there everything else seems a breeze !!!!! LOL !!!

[Va348]

Tom

You may want to ck length of rods and piston and put short piston with long rods. With the Ross piston I do not see over a .001 variance. I have seen the stroke off on stock cranks by as much as .008.

Put that rod& piston in say # 3 cyl. and see how it mikes out. if deck is tapered will will not show but a couple thouands,if crank stroke it will most like to be more. You all so need to put a feeler gage on ex side of piston on shirt to keep it sq. with bore. If you have say .005 cyl clearance use a .003 or .004. A bore that big any rock will be a Big diff. as much as .010 I would guess.

Good luck. Reminds me when I did my first 427 sm block in very early 70 took a wk to get it to turn over working at nights.

Dale

[Tom Kochtanek]

I spent this afternoon taking more accurate measurements on all the components. The news is not good, and I'm a bit stumped.

First I measured the six Eagle BBC rods that I had not yet mated up to pistons and affixed to the crank. They were identical in length, but not 6.135" as expected. I first measured the top where the wrist pin fits, and it was .994". Half that would be the center of the circle (.497"). Same for the lower end, measuring 2.330" or 1.165" from center. The length between was measured at 4.480". The sum would be .497" + 1.165" + 4.480" equals 6.142", or exactly .007" longer than I expected (assuming 6.135" is correct). I measured these several times each to be sure. So there is some of the distance I need to account for.

Then I put in pistons/rods in cylinders number 2 and 8 (no rings) and accurately set TDC for each and then measured the verticals. I switched the two setups (putting 8 into 2 and vice versa) to see if the numbers stayed the same. Reason was I was suspecting that perhaps one of the 427 crank journals might be off a bit from the factory. We turned the mains, but the journals only needed polishing. The result was the same both ways, which leads me to conclude that it's not the crank that's giving me the length out of the bore. Plus it indicates that the block is in fact "square", correct?

The bad news is that when I took measurements the other day (the day I first initiated this thread) I basically eyeballed TDC. I was way off. I mean not even close. Plus I learned to rock the piston outwards, and that makes another .006" or so difference. Here's the kicker -- the more accurate distance out of the head at TDC is much larger than I first claimed. I did these measurements over and over again for holes 2 and 8 and consistently got .060" ABOVE THE DECK. I didn't do the other side or the holes in between, since I was a bit taken back by these new (and huge!) numbers.

Perhaps this block was decked (and decked, and decked) once too often, twice too much? Hard for me to tell. I asked the machine shop guy who did it, but he had no way of telling (so he claimed).

Are there solutions to this, other than starting over? Assuming .010" above the deck might be the most we would want to go, I need to make up the .050" difference PLUS the quench distance (.028"), correct? Is this even possible?

Can we possibly consider milling maybe .020" off of the pistons, double up on the gaskets, and get proper clearance? I would need to make up something like .058" with the gaskets if the pistons were cut down .020".

Or is this the wrong approach? Your comments are most welcome.

Bummed,
TomK

[CDNpontiac409guy]

Tom,
You COULD go as much as about .014" out of the hole, but that's it.

.060":confused: :eek:
.007" longer rods ?

Something's goofy here.

Do you have another block on hand ?
If so, why don't you set your stroker crank in it, rotate it so the throw ( rod journal ) is at it's closest point to the "inside" deck ( where you got the highest reading on you piston issue ).
Take an accurate mesurement of the distance between the journal and top of the deck of the block... at it's very shortest reading.
Repeat for the other block.
Check the difference.
If your readings don't show a difference of at least .040"....
Your pistons are defective.

[SSpev]

Cutting the piston is a very good way to make up some differance. Done all the time. Already mentioned here, I think. Your pin hole, in the rod, is .994. Can I assume you are using floating pins?? (press stock pin .990- hole .988) Rods are bushed??? Bushing could be located wrong and macined wrong. You can have the rods rebush with offset bushings to shorten the rod. Still got a ways togo though. Oh, on milling pistons. Ross uses BBC slugs to start. Look underneath and you can see the valve reliefs for the BBC. My are this way. I was talking to Bluescreemer and wully bully 2+ years ago at super chevy and one of them referanced this. There is a THIN spot. Care needs to be taken when cutting these pistons. I think they found out the hard way.

[Skip FIx]

MOck up all the rods and pistons, measure the deck then shave the pistons. Easiest since you already have everything and its not completely assembled.

One of my recent Pontiac motors was decked with one set of rods that were resized short and not straight. When we used another set of rods they were 0.015 out. Got a 0.050 gaslet for it as it was completley assembled short block beofre the machine shop checked it.

[art38]

Fatride,
I was worryed a little. I had just measured my Ross 10.5 pistons and had .015 below deck and was told I had the wrong rods. Are the rods 6.000 or 6.010? Anyhow I guess I'm going with .022 steel shim gasket. Remember this is a truck block. Any idea of what C.R. will be.
Art38

[fatride]

Art, Comp should be 10.1:1
:)

[art38]

Fatride,
Is that with the TRUCK BLOCK? If so then I'm happy happy happy. :D :D :D
Art38

[fatride]

Yes Art that's with the truck block.
:D