Inliners International Forums General Discussion Engines zero decking

How much can be taken off a 250 block? I need to take off about .045 to get to zero with the 250 KB piston. Can this be done safely? This would yeild me about 9.01:1
If I use the 307 piston the deck needs to be cut about .030 to get to zero but the compression would be 9.29:1 which I'm kind of worried about.
Do you think I can open the chambers 3cc to bring down the compression? If I can open the chambers 3cc that would bring me back to 9.01:1
Any suggestions on which way to go?

thanks vince

I am running about .003 deck and .040 off the head with 307 flat tops. I get a some knock with reg. unleaded at low rpm under load. Anything after 2000 rpm is ok. With prem. fuel everything is ok. Still using stock radiator (50 Chevy) and have had no heating issues in this Texas heat even with AC on. These little 250s like compression so,squeeze it down,add a little more gas and pony up for some of that hi-test and have some fun...SCRAP

Leo Santucci in his book says not more than .030 of the block deck of the 292. That may not be the definitive answer and we will have to wait for Twisted6 to chime in.

3cc out of te combustion chamber shouldn't be a problem. You have the Integral head most of us are not familar with the Integeral head. You might wnat to go to Twisted6 web site. Look at the heads he has pictures of there, they are the non-integral heads. If the combustion chamber is pretty similar, then unshrouding the intake valves would help and at least 3cc.

Larry

Tell us a little about your vehicle, gearing,weight,auto, stick,stall on converter if auto,etc..
Does it need to pass smog?

What do you want to get out of it?
Better performance,gas milege,both?

personaly for a daily driver Leave the deck alone.
Take it off the head. The 194-250s Have the issue
over the water pump as it is. Due to the Lack of
thickness and crack the blocks on that corner. Yes
It can be Decked. Run the 307s take what you want
from the head to get the compression your after,
and only take what you need from the deck so That
The deck is true.
And the 1 Main reason Im saying this is IF?? you ever over heat the motor and warp the head and
Need to mill the Head again?? You will now have to figure out Where you're going to remove MORE
material to get the CCs Back to where you once had them.
Due to the compression I push I have never Zero decked my blocks, Only what it took to be sure I had a True Deck.And Knock on wood I have Never had a block issue over the water pump.
So this is just my 2cent oppion.

Thanks,still having computer problems here.
Can't afford hi-test.
I seen that in Leo's book but it didn't say which block.
'81van,4200#,OD,1800stall,3.42,27.5tire,must pass smog,both.
So I should run the 307 piston and just true the deck and head? That would give me a quench of .060 to .070 isn't that to much? I'll have to run the numbers and see what that gets me.
My plan was to deck the block to zero and take just enough off the head to make it true and use head studs to take some pressure off the block.

Thanks vince

One reason to leave the block as is and shave the head is because if you end up with too much compression after the head is milled you only have to change to another head and not get into block replacement or piston replacement.

With the right fuel ratio and igniton timing the 9.29 you are calculating shouldn't be a problem on pump gas although you might find it wants 91 octane or more. I'm right around the same compression ratio on my 250 and have always run it on 93 or 91 if that's all available. It might run on 89 but since it runs so good I'm not going to bother to try the 89. I'm also running a manual 4 speed tranny.

If you're worried about detonation, run water injection instead of doing all the machine work on the combustion chambers. I agree with Twisted 6 that you should mill the head, not the block to get the compression you want. With 9.3:1, you should be able to run unleaded regular with a water injection setup. They are currently available from Coolingmist for about $300 for a normally aspirated engine, and they REALLY work. I've used water injection on one motor with 11:1 compression, and it took all the knocks and pings out, but I did run premium unleaded with that high a compression ratio. If you want to check it out, log on to www.coolingmist.com for more info.

I am a firm believer in getting close to a zero deck height,in cars and motorcycles.

If you get a good quench area working for you,,, you will not need to run a water injection system, up to a certain amount of compression.

9.2 is not that high, but if your piston is sitting down the hole .070 @ TDC That can't be good.
It will most likely be a pinging monster!!

You can have an 8 to 1 motor that pings like crazy because there is no quench area(piston too far down the hole).

Then on the other motor you have a zero deck(or close to it) & have 9 to 1 that can run on the cheap gas.

It's all a matter of getting the quench area working correctly.

Two cents :-)

It would be nice for the quench to be about .045 for best turbulence and combustion.This requires a mock up assembly to check it all out. and then machine the parts for proper clearance.
Like mentioned above,close clearance will lessen detonation depending on the head design,generally,smaller volume chambers are better at this.
The L series chamber is similar to a small block V-8 head design?Then an actual 9.5 compression should be maxiumum on 91 octane fuel with an iron head.
Building an engine that gives all it can give is more than just a lumpy cam and carburation,it's all the small details making the difference.

Hey Hank I have to disagree to a point. when I ran my 307s (12-1) with a 194 583-607 lift the pistons were fly cut .225 to clear the valves
When i spoke with the guys over at slefRacing about the compression ,And Only having the CCs from the Head we figured that motor was pushing somewhere between 13.9-1 & 15-1 And THIS was a daily DRIVE for the better part of 17plus yrs
I ran On the street with LCHEAPO 87 oct. This combo also Ran 15.15 All day long Nite or day with 3.08 gears & a 4speed. The Biggest issue was shutting it off With Out loading the clutch Then turn off the key. And It started with just a Bump of the Key. But When I ran the RIGHT Octang It would shut off just fine. BUT anyway my point is
Mine Never made a sound/Ping and I can SHOW you the top of the Pistons If you like. NO marks once so ever. And Im now useing the same set of Pistons in my NEW more But now the Dome has been fly cut even more to clear this new cam of 690-680 lift They have been also fire sloted.
My buddy here also runs a 250 with 307s at about 9.5 -1 on pump gas with a fair(mild) bump stick the car runs in the mid 14s on 91 oct.And the Block has not been decked.

PS oh yeah there maybe a mark or two FROM When I had a cam Gear brake ripped the teeth off it @5500 because when The motor was first Built they didn't put the gear on like i told them Which needed to be heated. but anyway Bottom line is when it broke I bent everyone of the intake valves and 7 push rods OOPS motor was less then a week old.

Larry what is the compression height of those dome pistons?I'm thinking you must of had a pretty tight quench to run that kind of compression on 87 without a ping.
I was shooting for a .041 quench(gasket thickness)with a zero deck on 87 octane.Might have to open the quench a little to get the compression down depending on how much I can open the chambers.

thanks vince

I have had these pistons over 17 yrs now So i honestly could not tell you. And now haveing been flycut twice for valve clearnce.Im not even a 100% sure what is left of the dome for thickness.I do know it still has at least.225 left of it. ANd I do beleive the dome was like .450 thick.
But like i said YOU COULD NOT SHUT it OFF with out loading the clutch. on 87 oct.

Vince, Hers's a link to Keith Blacks' web site (Silvolite pistons) and their 307 piston they list their compression hieght as 1.665. This compression height is what they advertise for their piston, it may vary with other manufactures.

http://kb-silvolite.com/spistons.php?action=details&S_id=240

If you go to the web site "Diametrical" listing you can go down to the std bore 3.875 and look thru what they have for compression hieght in that bore. You will also have to watch the pin diameter. The pin diameter can be worked with if you want to change from a pressed pin to a floating pin and there has been a recent thread on that. Also note what Twisted6 has taken off the top of his pistons. Hope this helps solve your dilemma.

Larry

Just a few comments.

You can find your compression to be 15-1 & the rings probably not be sealing.

I total up my cc's incorrectly on my motorcycle & found out I had 13.6 to 1 compression.
It started fine, idle was great, snappy throttle responce, but once it got to a certain RPM it just fell flat.

All that compression was just blowing past the rings.
BTW,, I was running 100 octane gas.

Having a compression ratio of 13.9 - 15 to 1 running on cheap gas tall gears & not pinging does not make sence @ all.
Unless you had a cam w/310 degrees duration @ .050 & a lobe center line of 102.

15.15 in the quarter?
Your friend having 9.5 to 1 & runs a half second faster than you?
It really does not make sense???

Is your car heavier than your friends car???

Could you give us a break down of your friends car & your car?

To me it just does not add up??

Unless your friends car is a drag car, lighter weight than your car was???

When you run that much compression, you would need @ least 112 octane, & w/15 to 1 that is methanol teritory.

Not trying to start anything here but to me it just does not make any logic.

Gentlemen;

If your 'shaving off' the top of the block to get more compression, that's not the way to go.

It works sure, but It's far better to have the pistons made the way you want as Larry & Hank point out. The piston (MFG) can/will adjust the wrist pin location to get you the compression you desire.

This is a big problem with the early engines which need that space in there to allow for things "streaching" at higher RPM.

The 63 + engines are different somewhat in that things don't "stretch" as much & can create more power than the 'early' ones when modified etc.

Remember; When these measurements are made the block/components are cold & this all changes when hot, running 6,000 RPM or more.

What's a point or two in compression compaired to blowing your engine??

Find the "happy medimum" somehow is my thinking here. There's fewer each day of these blocks, for us to play with.

Happy Trails.

Hank the 15.15 was with the stock 3.08 gears and 3rd gear Never hitting 4th gear. And this spent most of its days a s a daily driver,When I finely got aroud to gettint the gears in that IT SHOULD of had when i frist built the motor it should have been running in the 13s. But as time went on and this started to show signs of some blow-by ( nearing the end of 17s running track & daily driving)the car ran a Best of 14.3 in 3rd gear with a set of 5.13s
And if you readit right I said It was a GUESS of between 13.9-1 to 15.1 We did NOT have FULL CCs we only guested We knew what the CCs at that time whatthe head had. But no clue as to what the Bore & piston had. It was a 194 head that had been Milled a few times Before I ever had Blew a head gasket which Burned a Notch in the head .010 deep.
Anyway It don't matter at this point. That 17yr old plus motor Has now been Rebuilt which Once i get the Valve cover done & side cover The New motor should be in sometime after the first of the year I Hope. With the same pistons now floated
and a little more milled off the top to now clear the New cam specks are .69111/.68057 dur.is a 269.2/272.7 lobe separation about 105.5 the valve over lap 58.9 crank deg. Now as for the compression I was after no less then 12.5-1
13.-1.I was going to gas port the pistons but didn't But a fire slot was done this time.
I have to open the block up to change out the head gasket Because they didn't not Install the right one. I will get pictures Of what the piston
Now looks like compaired to before. I also need to double check the Push rod to head clearance Because of the lenght being 10.400.

Now as to what the car weights With me and a full 18gal it tips in at 3000lbs This is a ALL STEEL
and all stock glass bodyed car with Tubs 8 point roll bar and all Inter.(including a back seat for two).SO a 14.3 in 3rd gear on a 17yr old plus Motor I do not feel was so bad.
This new combo should put me some where in the low-mid 12s we figure.without making the car lighter.
But we'll see and go from there.

Hey Larry,

I understand :-)

One thing though,,, you did not comment on your friends combination. The mid 14 car.

We are all wiser & smarter than we were 17 + yrs ago.
For sure your car will run better now & I know when my project gets done it will run better also.

Good luck!!

MBHD

the best i remember is it had a dual clifford with 600 holleys Not a clue to what or whos cam it was and I beleive he had either 4.11 or 4.56s in it at the time. Both are cars are 64 chevyIIs His car is a bone stock daily driver.Bench seat the whole 9 yards. Only main difference is his is a 2door post, were as mine is a factory SS There is a Pic of his car in the racing link a white chevyII with flames Gary R.

Larry,

I have heard the post models are lighter,, is that correct?

MBHD

generally speaking the sedans are lighter than the hard tops, due to the extra reinforcement in the frame or body for stiffness. In fact the 63-64 Dodge or Plymouth four door sedan was lighter than the two door sedan. Convertibles out weight all the above.

Larry

In comparing GM mid-'60s A-body cars on a Pontiac site that I frequent, I found out that 2-door post models were a mere 5 pounds lighter than their hardtop counterparts.

Not a big difference, but the post cars are lighter.

Yes they are but not by much at all. Frame wise There is nothing different That i everseen or found out. I have owned them all from 62-70 Two of them being SS,One being a four door No wagon as of YET lol Both my 64 & 69 were SS cars my 69 being a BB 396 bored to a 427 10sec car many year back But also a 4speed. My 64 SS was stock L6 power glide on the floor.

I agree with the B-man and Twisted 6, I think the weights are pretty close.

In 63' the SS became an option on the Chevy II Nova 400 and it was pretty much just for looks: bucket seats, updated intruments, real nice steering wheel ect..

The 64' the SS still came with the 230 unless it was ordered with the L32(195hp)option or the L77(220hp) both of those options used the V-8 and the
big 4 row rad so they probably did wiegh more.

I drive a 64'hard top (non SS) ) and I don't see any extra reinforcement underneath.I have always heard that the models with posts had the stiffer body's and were better for all out drag-racing.

Yes they are more in favore Because of the Post at the rear Qt window and Door..Before I added in the sub frame connectors an roll bar I slit The side Qt window at the valance and Body about a 1in rip in the sheet metal.Right at the base of the window Very corner.This was due to the Body flex. But no biggie now all fixed LOL.

Cool!! now I know where to keep an eye on when I get rid of my open diff. BTW you left out the 73-74 Nova hatch backs. I had the 73, it was the only SS I ever owned...I miss that car.

Over the weekend I was reading Leo's book and on page 69
Recommened Clearances
piston to top of block. (deck height)

.000-flush with steel rods.

.020-high RPM/aluminum rods.

G10-250,
That is correct,, & that is the way to go!!!!

MBHD

Thanks MBHD thats where I'm headed, just got to figure out how I'm going to get there.lol

G10-250,
Tell us what parts you plan on using & your steps on getting a zero deck.

Do you have the KB pistons now, or are you just going by compression height stated in catalogs?

Have you physically installed your pistons & checked these measurements?

You really need to have the parts at hand to measure correctly!!

I will help you out.

MBHD

Thanks, I'm sure I'll be bugging you for help.

No parts bought yet.Still waiting for my slow ***
machinist to call me back to tell me if the crank and block checked out OK.

I'm acually not sure if I'm going to go with the KB or Speed-pro pistons in the 307 flat top flavor.
Once I measure the crank,rods and pistons I'll match them up.
Then bring the deck down what ever I need to get to zero and use head studs.

Larry
If I read your post right you started with 12-1 pistons then fly cut them for valve clearance. This would lower your compression ratio not increase it. Normally anything over 13-1 would run on fuel such as alcohol. I have a 254 cu in six running 10.3 -1 and with timing set for performance it will ping some on 89 octane but runs fine on 92. I run a comp cam and msd ign including disributor 6A box and blaster coil.

Most vehicles that come from the factory with a compression ratio above 10-1 are marked on the fuel gauge to use premium fuel only.
Big Bill

big bill those pistons are rated 12:1 in a 307 motor. You got to throw that rating out the window.

As you will also NOTE i had a 194 Head on this motor. But with a Bump of the key It would fire right up. YOU JUST COULDN"T shut it off. And Like i said before If you'd Or anyone would like to see the top of the pistons I'll email you the pics. THIS Motor NEVER once Pinged. and I was running 87. Yes I know it shouldn't have run. MY BB That had 12-1 wouldn't even start at 45mph and pushing for a HR The Best it would ever Do was Back fire I even Blew up a NEW set of Mufflers,when it back fired out the tail pipes.ANd This motor ran on sunoco 240 Pre. When they used to sell it. I'd mix it with NoLead One day I got much NoLead and It wouldn't even start.
When I finaly relized what was Up I mix 5gals of 240sunoco Prem. and 104plus octange booster Dumped it in the tank and a little down the carb and It fired right up at a bump of the Key.
So i figured back then (17yrago) If the octange was to low this L6 would have never fired Up WEll to my surprize it did. It Just wouldn't shut off with out loading the clutch.
So this to Proves one thing is That Our L6s don't run Or ACT anything Like a Vthing More ways then one.
SO yeah the motor should have be pinging It's Butt off Or the Valve should have been rattling Like Crazy BUT Nope not a word From Either.

Well I finally got to see the Speed-Pro piston and the valve reliefs are a little different then the KB piston.The KB has 4 individual reliefs,the SP has 4 reliefs but they are not individual they are kinda opened up into pairs.
Called speed-pro and they don't have the cc's for the reliefs.Has anyone measured a speed-pro 295ap 307 piston? The KB is 4cc's, the SP looks to be a little more and might work out for me a little better.

We don't have sunoco out here,what is 240 premium rated at in octane?

If it has a single or dual trofts for the valves they usually has more cc's in the dish.

MBHD

They No Longger sell the 240.this was back in the Mid to late 70s. But if???????? I remember right it was 110??

"troft" thats the word I was looking for.
It has 4 valve reliefs with trofts connecting them into pairs.Probably 1 1/2 to 2cc's worth.
Hard telling without really measuring.
Might be the way for me to go,less I'll have to take out of the chamber to get where I need to be to run 87 octane.

Man, wouldn't it be nice to have the 240 back at the pump.

Guys
Compression Ratio is based on the total volume in a given cyl. at top dead center it makes no difference how many cyl you have. the following is the total cc s that will give you the compression ratio on a 250 cu in chevy bored .030 over. this includes deck height space, cyl head space, and the thickness of the compressed head gasket minus any piston dome plus any valve relife to get total ccs for compression ratio.
9 to 1 86.85cc
10 to 1 77.20cc
13 to 1 57.90cc
15 to 1 49.63cc
I most likely miss understood the post, and I am not criticizing anyone just making an observation. If I hurt someones feelings I am VERY SORRY as I did not not mean to.
Also Sunoco sold 190 through 260 to anyone. In the old days we used to get some dealers to break the seal on the pump and sell us the straight fuel that the pump mixed with its 190 to make higher grades they called it 280. 280 worked very well in a blown Hemi running 25 psi of boost. I never did know the exact octane rating of 280 it was claimed to be everywhere from 104 to 120 depending who you talked to. They also used a different method of determining the octane rating then, than they do now
Big Bill

Guys
This is not an exact figure because the higher a compression ratio goes the more it is off but we used to say that for every 10cc of total head volume you removed your compresion ratio went up one. This is a close figure in the 9-1 to 12-1 range NOT EXACT but it is a good place to start if you don't want to do the exact math. To my knowledge late model six heads went from 60.32 to a max of 74.00 so using the above figure you can change your compression ratio about 1.4 by swaping heads.
Big Bill