Inliners International Forums General Discussion Engines BLOCK DECKING

NEED TO DECK MY 292 CHEVY TO RAISE COMPRESSION. HOW DO I FIGURE HOW MUCH? HEAD HAS BEEN MILLED 0.60 BUT I AM USING STANDARD L.C. SPEED PRO PISTONS. LOOKING FOR SOME BETTER SLUGS BTW. THANK DAVE

as for decking the block You want to Zero Deck it with the top of the piston. Piston is TDC this where you want the Zero Deck hope this helps
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Dear Dave;

Your on the 'right track' do it with pistons.

Milling the deck is for making it "square" with the crankshaft centerline.

If you 'CC' a head chamber & give that figure to the piston Mfg. they can/will make the ratio you want.

This holds true for most engines as well.

Good luck, John M...

my 292 block is decked .030 on my daily driver...I use the full dish piston...head is milled .090....cam lift is .520....I could have gone more...mine is not zero decked....
anyone else have a decked 292 ?

Lee

the math worked out to approximately 9.3 CR...if I had decked more AND milled top off piston i could had gotten over 10:1 and still have a strong block deck and piston..ever see how much "extra" material there is on the 292 full dish piston?

this is why i suggest using the full dish piston..by cutting top and bottom you can 1) lighten piston and 2) deck block MORE than zero decking and cut off top of piston.....since top of full dish piston is just a ring/circle ,its ok to do and these pistons are VERY thick in that area- I have had this checked with an race engine builder-he says standard procedure for him......

Dave, from what I have read on the subject, the space or clearance between the top flats of the piston and the flat of the head is called quench or squish and for best performance should be .050" but not less than that. My 292 is equipped with propane pistons for 9:1 compression in a stock engine. The block was decked about .030" which brought the piston tops at tdc .015" below the deck. With the advertised gasket crush thickness of .040" that gives me a clearance of .055". I allowed some extra so that any errors in my calculations would not get me below that magical .050" clearance. The head was milled just enought to true up the surface. Regards!

Thanks for the info. I do have the 8.1 pistons so maybe i could think about milling them also. Is that a prodedure that can be done relatively simple by my machinist? I would definitely like to get in the 9 to 10 to 1 range. What horsepower could I expect with a 270 duration .520 lift cam with these pistons , my head has been milled 0.60.
thanks dave

Dave,

I think you misunderstood the advise given or I misunderstood what you just wrote. You cannot raise compression by milling your existing pistons. You must mean .060 rather than 0.60 on your head milling.

hello...well you can raise compression by decking block---however, you will have to mill top of piston also....so 1st mill/deck top of block...when you do this piston will "stick out" top of block...so to remedy this ,you need to mill top of piston-this is done alot-.....and when this is done you make dish is piston less and this raises compression.....
did i explain this ok?

Lee

and by JUST cutting off top of piston DOES NOT raise compression, but combination of decking block AND cutting piston top DOES raise compression

Lee - why would you cut the top of the piston?

I don't think you would want to cut the piston unless you were concerned with anything less than 0.045 inches of quench around the perimeter of the piston AND/OR valve clearance.

Ken

well....you want to cut the piston to raise compression.....understand?...if you have a dish piston-this causes a lower compression ratio, sooo if you make that dish smaller-by cutting top off piston, you can raise compression-BUT piston will be lower in cylinder at this point...so what you do is deck block-by doing this piston is NOT below zero deck height but hopefully up too zero deck height(you must do your math/analyzing what you cut off piston and deck )....at this point you have a setup that has higher compression....this is a standard way to raise compression....this is ALOT cheaper than a set off $100.00+ a piece pistons($600.00 a set AT least for forged flat tops)....this is a standard engine procedure to raise compression...
does this make sense to you?

this is GREAT for hot street or light racing BUT not full out racing...This is why i recommend the full dish piston for 292 applications-this can and has been done to most ALL engines and pistons...above is basic concept- to verify this, find a true performance engine builder near you-and ask about this concept- of course he will recommend just buying a different set of pistons until you tell him you are refering to Chevy inline 6 engines- then again either $100.00+ a piece for pistons($600.00 a set) or this method to Increase CR-...by milling head you can also gain compression...ever see the so called "new" design in V-8 pistons? called a reverse dome...do they look like a dish piston? do they look like a 292 full dish piston?...take a look and then this hopefully will make more sense...
hopefully this will help .....

by using a cam of.560 lift or less AND dish pistons, valve clearance is not a problem....to verify, check clearance

Ok - I get what you are saying - I decked my block to reduce the quench on my combustion chamber to .045 and then milled the head to get it flat and normalize CCs/chamber. I don't have stock pistons - I wound up with 9:1 compression ratio which is fine.

Decking the block without cutting the pistons would result in higher compression than if you did cut the pistons, but if you decked it so far as to cause a crash, I can see where you would have to cut the pistons. Thanks

thanks Ken,glad i could explain it ..by the way I like the slide show of trucks/vehicles you have on your Inliner profile..pretty cool

Dear Dave;

I would really think this over.

If you follow Mr. Lites advice you will be removing needed material(s) from the head & block to save buying the 'proper' pistons. This is a bad trade-off.

The 292" engine is a truck engine designed for commercial use and this is why it has a lot of "meat" in the block/head. The low compression pistons were probably a Federal mandate to comply with 'smog' regulations back then, which don't apply today.

It may take .045 to 'square'the block & if that's gone, you may have to start over.

A deck height of about .015+ is also needed to compensate for size changes in components during high temp/stress levels.

I would ask Steve that runs the "Mighty Six" & see what his thoughts are. His 1930 pick-up runs a 10.40 all the time with a built 292.

Good luck, John M.......

hello John....thanks for your comment...however the is a standard procedure used on engine building....this has been done many times to various engines...this concept may be new to you....Talk to engine builders about this...this IS is another approach to greatperformance...

John ,is this the 1st time you have ever read this concept?
as far as being being specific to the 292 engine-due to the fact that the 292 deck is thick, this decking procedure is a GREAT way to increase compression....as far as the pistons are concerned, look at the THICKNESS of the top of the piston.....

John, do you own a 292? have you checked the block? the pistons? have you ever decked a block? or cut piston tops? or had any of this work done for you?
I have research this procedure as i have described with 2 engine builders- both know the 292 and the specific pistons I am referring to....
John your comments are appreciated but my info is based on research.....I would not mislead you or anyone on the 292 and i am curious why you would question this....what are you basing your comment on? Have you done this procedure?

for those wanting to know, this is a tried and true procedure in the engine world and will work great on the 292 ...as I have shared, my daily driver 292 has .030 off deck, and .090 off head and I am using these full dish circle....I have taken this set up and checked to see how much more can be done and I will do this on my next 292 daily driver......
its nice to share comments here....
what i share here is based on experience or research...for those that are open to ideas that work lets continue to share....
Until you actually have a block, piston and do the measuring i guess this might seem an unsafe way to gain compression-but until you know its not a big deal....but now that you know this concept, research for yourself......

it is unfortunate John that you question me on this....but maybe you just dont understand this procedure...does it make sense yet?..this is a basic engine performance procedure

Lee,

If I may be allowed to mediate: no need to get defensive and certainly not offensive; they're called OPINIONS.

Baldy

hello ...thanks for comment Bald..opinions are good..

What I am referring to is a fact....
an opinion is not always based on fact

the info I have shared is fact...
not trying to offensive or defensive...

just sharing facts.....

some here like the facts i share.
I am only trying to share info to those whom appreciate it...what I have learned from the old timers is priceless....I am just keeping this info in the mix so those whom want facts can have it...for those that think this is opinion, well.....
seems from what i have to share is appreciated by some....
its not about you or me or anybody, its abut what works best for these engines.....
I am open to hearing ANYTHING contrary to the facts i state-
do you think i would mislead anyone on this?

Lee,

I would lose in a p---ing contest; before I couldn't get it over my shoes, now I can get it all over them.

Did it occur to you that I was perhaps referring to John's opinion?

Baldy

hello..no Bald it did not occur to me that you were not referring to Johns comment- thanks for pointing out....i am sorry if you are offended....Glad you pointed this out in your last Post-I would NOT have addressed my comments to you if you had make that clear in that Post and not your follow up Post...again thanks for your concern and I hope I did not offend you....

Lee,

I am not offended in the least, just don't want another carved pumpkin episode here.

Baldy

thanks for comment Bald..i dont want 1 either....

Well i will start by doing just this , but question? Is there a standard amount I can cut from pistons first before I install a piston at both ends of block to check for block decking dimension? say .100 off piston? what is the average? again these are regular trw 8.01 with a .300 dish. also i have milled the head .060, can i go back and mill some more? what about bigger valves? i want to do all this work now as i am building this for a boat and once i put her together thats it.. dave also have a chance to buy a 194 head, would this be a good way to go?

hello...good question...I can get back with you soon on more detailed answer, but till then, try this for your knowledge-bolt together to see what you have from top of piston to top of block area-squench area.....

then you know how much to zero deck.... I think .100 should be ok but only a guess right now....
as far as head is concerned, what cam lift are you going to use? this will concern what can be done to piston and block....
as far as 194, there is more compression due to smaller chamber but to get to good flow you need to open chamber up-but if you open chambers alot you get get more compression and good flow-you have to be careful with 194 heads-some have core shift that can cause problems when you install hardened seats and bigger intake valves....Again, what is goal of engine? whats it main use? what rpm range do you need/want?.....
back to piston and head....you are on right track-i havent done this but have checked it out...now i can check it our some more- also measure your deck height-from flat on main bearing cap(block flat spot)-10.875 is standard-that is 10 & 7/8".....

I will get more info...hope this helps so far....

ok..here is some info...I just cut a full dish 292 piston in half.....

from top edge of piston to 'bottom"-what you see when u turn piston over and look into- measures approximately 7/8 of an inch-..3/8 of an inch (half) is from top of piston to inside of dish, 3/8 of an inch (half) is thickness of piston from bottom of dish to underside of dish...hope this makes sense

from top of piston to top ring land is approximately 7/16- almost a half inch!!!!!-THIS is where you can cut...top is VERY thick-

i will get back to you again....

The Core shift is prone on ALL heads(194,230,250,292) But it has showen to be more of a issue with the 194 head. So In some cases You can end up going right into a water jacket, By Just Trying to get a New hardened seat Installed..
BUT this is a whole nother Topic and Not related to Block decking.}[oooooo]

hello..thanks for comment,....I have found core shift and thin castings by using sonic testing on the 194 heads...and have even hit THIN walls working on old 194 round track heads....If I remember correctly, you have seen this yourself, right?


i have seen less core shift on 230-292 heads...the 1's I have cut up have thicker castings too.....but i am sure core shift occurs in all these castings

Sonic test are good BUT if YOU want the FACTS as You put it Lee. AND One already Know the head is trash CUT IT up It's a lot more FACT finding then the sonic test. So Yes Lee I have Seen this MySelf.

But If your not sure what Your dealing with Yes Sonic Testing is a good way to find things out about Your Block Or HEAD/s
hum i guess I cut up heads and Edited photos to Put up on a web site and Never looked at them roflm_o
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hello..wellll Larry, I have done both-Sonic tests and cut up heads to find out what these heads look like-also I have seen many at PES cut up and not cut up........I wont cut up a good head!!!!!-i just sonic test to find out if it is a good candidate-if its good and has room to cut for hardened seats I use it..if there is no core shift-and this can be found with sonic test-i use it.......I have and will continue to cut up ONLY bad heads....this is how I have learned....its amazing what you can find on many of these heads.....I gather as much info as I can by sonic tests and cutting up only bad heads that are cracked-I just dont use heads that prove to have weak/thin casting walls if sonic tests show this....I wonder if you know what you are dealing with sometime...I just gather as much info and facts about these heads and engines and it seems some REALLY appreciate it some dont....
Not sure what you are going off on here.......do you sonic test heads? How many heads have you built? are you running a bolt in head yet?.....
why does have have to be like this?

some truely enjoy my comments...I thought you did too until recently.....

Yes Every Head Gets sonic Tested Once it has been cleaned and Fluxed. No I don't do the testing my self. It be Nice Just a few more toys I'd Luv to add to my List. It sure would Beat Paying to Use someone else toys/Machines LOL

OH ps No I don't cut up good Heads Either Now that would be a waste of a good thing.Later I'm done on this. }[oooooo]

This has been the most painful thread to read-no wonder i dont venture back to this forum but once an annum.

There seems to be a common problem with all of the annoying threads in this forum and its to do with the inability to articulate clear thoughts or ideas which really grinds threads to a screaching halt.

Articulation or the lack of, is not what occured here.

Giving potentialy dangerous information to a novice is!

Would you have us remain silent & allow it??

John M.....

Well, said John. How is one to learn if you accept only one version of advice and are not open to others.It might be agonizing to make a decision when more variables are introduced, but at least after studying the info and asking questions you are less likely to make a costly mistake. Nobody here force feeds what you MUST do
with your project. The decision is still your own.

I certainly agree. Also, have seen membership more than double since have been a member, so welcome to the many members that have'nt yet been formally acknowledged! Have learned a lot, and the mixture of knowledge from the 'youngsters' and the 'oldsters is totally amazing.

Well I will agree with you guys.
And just have to ask. ok?? str8six if it is so annoying and painful to come here and read these forums WHY bother to come back? no body made or makes you come back. now do they?? now did i have the ability to articulate that clear enough for you?? Just my 2cent question. And Now for my 2cent Comment Unless your a PAID member you realy don't have much to complain about Your using the BBoard for free.so thank you for stopping in to say Hello. }[oooooo]

The administrators really need to highlight the more liberal use of the search button. Of course im not forced to come back, i simply make my semi annual drop in looking for some interesting content and find pages of threads that have all been covered ad nauseum which is unfortunate. "I saw it at PES" which if queried would probably net a higher thread count than the sheets on my bed.

Thank you for your profound observations.

We all look forward to them with next years visit and I'm sure the 'Administrators' do as well.

John M.....

i think you are going the long way around to get compression. if it is for the street use lp. pistons. they are 9 to 1 then with the head milling and the over bore you would be close to 9.5 or better.

Dear Bob;

Absolutly!

BTW; This is a marine engine for a 'plesure craft' and not the place for expermental techiques.

I've not seen a subject so misunderstood.

JM.....