I pulled the 350 from my Beaumont and have the heads off now.This is all for a vortec head and cam change. I have a dial indicator to measure piston to deck clearance to try and achieve .040 quench with the proper head gasket.#1 is at tdc. My question is, where do I measure from on the piston, near the edge,centre? I have already tried from the edge and found that the measurment is quite different from one side of the piston to the other side when measuring near the edge of the piston to deck.It is .020 on one side and .007 on the other. By the way the pistons have stamped on them .030 and the # is H345NP.Now I am a complete rookie at this and just going by the info I have gathered from all the fellas here at Team Chevelle.These piston have 4-1/2 circle depressions which I assume are refered to as valve reliefs. Correct? I am going to try and find out what these pistons are today on the internet to figure out the size of reliefs these are.I would appreciate it someone could steer me in the right direction here.Once I get this issue resolved I have to try a locate the right compressed thickness head gasket and then try and figure out compression using Mr, Kellys' calculator and then seek help again chosing a cam for my baby.
I found out the pistons are TRW hypereutectic flat tops, 9.35 compression with 64cc heads. It also says 1.540 comp. dist. What does that mean?lol, sorry for all the questions but its the only way I am going to find out. With these pistons what figure would I use on Pat Kelly's calculator for valve relief size?

Once again thanks


Jerry

Jerry,
Try to get as close to the center as possible, but with those pistons its kind of hard. The reason there is a difference from one side to the other is because the piston is rocking a bit in the bore. You can push down on the high side until you get the same reading on both sides and that should be pretty close. Also, I think there is enough room right at the very front and back of the piston to get an indicator on it, but you still might want to move the piston around a bit and get a good average.
Yes the 4 cutouts are the valve reliefs. The Sealed Power catalog lists the valve reliefs as being 5cc.
The compression distance is the distance from the centerline of the piston pin to the top of the piston.
Hope this helps,

Thanks Bill. Bill, The dial indicator I have has a magnetic base so I placed it on the block and set the plunger of the indicator on the piston. This should be ok right? I will try and rock the piston to get as close to equal on both sides as I can. There is portion of the piston across the centre between the valve reliefs that is flat. Theoretically I guess if I can rock the piston to reasonably level I should get a fairly close measurement at both sides and centre.

Thanks Bill for taking the time to answer my questions, much appreciated


Jerry

Ok, I was able to measure the piston from front, back and centre and get a reasonably consistant .017. Now ,I need to find a gasket with a compressed thickness of approx..023. Any suggestions anyone


Thanks


Jerry

Jerry,
I think Fel-Pro has one close to that but I dont have a catalog here at home to check. If nobody else chimes in, I will look on Monday at the shop.

Thanks Bill


Jerry

I think the Felpro perma torque(fat blue ones) measure about .040 compressed and the steel shim ones are about .015. Howard

Originally posted by blumont:
Now ,I need to find a gasket with a compressed thickness of approx..023. Any suggestions anyone
ThanksGM has a composite SBC head gasket that is .028 thick.
I used it on my 10.3 CR, aluminum headed 383...works mint.
Part #10105117 and costs around $16 :cool:

Some things to consider, Jerry:

1. Have you actually cc'd your heads (all 8 chambers)? They can vary by several cc's from advertised and from each other, particularly if a valve job has been done. You should choose your head gasket to achieve a desired compression ratio, not a desired piston clearance, except to maintain the minimum required clearance. CC'ing is easy with a piece of clear, flat plastic and a 60cc veterinary syringe.

2. Check the deck clearance on all 8 cylinders. They can and do vary.

3. You say you've averaged several readings on clearance. Actually, all measurements taken directly above the axis of the piston pin should be the same. Measurements on the intake (top) or exhaust (bottom) side will not work because of the previously mentioned piston rock.

Ken

Didn`t GM have shims that were .018? That would put you at .035 which would be good.

Jim

Jerry,
Victor has a .020" steel shim gasket. Part number 1788SSB

Using a .028 gasket with .017 clearance puts me at .045 quench.The way i understand this is that this quench or squish area should be in the .035-.045 range, correct? I tried Mr Kellys' Comp calculator and come up with a compression ratio of 10.24-1. Is this going to work with 91 oct pump gas? My original objective here was to wake up the 350 in my ole girl.Can I match a cam to this that will relieve some of this pressure to make it pump gas friendly cruiser?

Ken, you say I should choose a gasket to get a desired comp. ratio. A thicker gasket will decrease my compression.This would of course increase the quench area to above what I understand is the desired limits.Are the 64cc vortec heads I have too small a chamber for my situation? I am not rushing to get this engine put back together, I am trying to learn something here as I go. I am going to check clearance on all cylinders as per your recommendation. Ken, could you elaborate a little on the procedure for cc,ing the heads.

Thanks Bill, I read that to use a steel shim gasket there could be concerns over sealing if the deck is not flat enough(proper term?)where as composite gaskets are more forgiving, right.
If there is any other info you fellas require to help me out let me know

Sorry for the long list of questions but I do really appreciate the input here

Thanks
Jerry

Jerry, I made a few assumptions and came up with a CR of 10.3:1 with your .017 deck height and a .023 gasket. This would be too high for 91 octane. With a standard .040 gasket your CR is still too high at 10.0:1.

The piston clearance doesn't have to be in the .035-.045 range. That just the minimum. In fact, more clearance would help the combustion process, by giving more room for the flame front to spread.

That 1.540" compression distance on your pistons is the distance from the center of the pin to the top of the piston surface, not counting any domes or depressions. It is used for calculating what your deck clearance will be. So, adding them: 1.540 comp. distance + 1.74 (half the stroke) + 5.7 (rod length) = 8.980". With a Chevy small block standard block height of 9.020", your pistons should be .040" down in the hole. If this were true, your CR would become 9.5:1, which is about right for 91 octane. So, maybe your block has been shaved .020", or perhaps your measurements are off.

Sorry, I gotta get back to work. I'll explain cc'ing later.

Ken

10.2 for compression WILL run on 91 octane ...............i know it will cause i built the motor......runned with a summit cam 234/244 @ .050 with 488/510 lift the engine was a 60 over 350 with dome pistons even! and there is no knock or ping.....its ran with a 3000 stall and 3.73 gears and has ran a best so far of 13.36@103.44 mph (with no tune and was the 1st time out in street trim) thru the mufflers and street tires..... even with the junky smog heads that are 76 cc......


run the .020 steel shimmed head gaskets and make sure you spray them down good with copper coat spray and dont be afraid of the sealing things you hear........i have thrown steel shimmed head gaskets on engine blocks with over 100,000 miles on them and have yet to run into the sealing problems people always talk about.....and even ran nitrous on a few of them for kicks.....

so dont turn away from the steel shimmed i run those on about everything i build just to keep the compression up.......just make sure everything is cleaned very well and you torque your heads correctly

and dont be afraid of the compression get all you can........can you live with a 3000 stall? if so then go with the 10+ compression and get the cam in the 230-240 range to help bleed some of it off....

if i was building this motor i would go the steel shimmed head gaskets......your heads and run the summit cam 234/244 @.050.....run a nice dual plane intake like the edelbrock rpm and a 750 carb....with a 3000 stall.............you will be in the deep 13's with ease.......maybe even 12's if the combo is tuned near perfect......

i can hear it now bla bla bla........im just telling you straight out...been there done that talking from experiance and the one who builds them......not alot of bs talk from reading and from hearsay......

Thanks for the part number Bill. I am going to spend more time measuring piston to deck this week to make sure I get it right. Ken mentioned that the pistons should be .040 down the hole and I know it is no where near that unless I am makin some real big errors here taking measurements. I suppose the block could have been decked at 1 time.Also thanks to Ken, ddeenis and others for input

Anyways I will keep trying

Thanks again
Jerry

That Summit cam is likely on a 114 lsa, thats why the DCR allowed it to run on 91.

I hope your chambers are bigger than you think. 10.25:1 is, IMHO, 93/94 octane range, unless you run a ridiculously big cam. I.E., DCR best be in the 7.75-<8.0:1 range.

Well Gene, I am going to remeasure everything to see what I come up with. I am starting to get quite concerned whether I can use these vortec heads or not. I was going to need help selecting a cam anyways but this combination I end up with has to be able to drive on the street and have vacuum for power brakes.It will probably never see the track(well maybe once when I get it going) This is where the whole scenario is starting to get darker and darker for me. lol. I am not sure but maybe at this point I should be listing all the info on the car so someone might be able to help me out.

Not to make matters worse, but just an FYI...
On both sets of Vortec headed motor projects that I've been involved with, actual combustion chambers cc'd out at 62cc. Heads were factory, never been surfaced. :(
But, the bright side!
Vortec heads don't require as much timing...34* total works great.
I ran a -5cc flat top piston (same H345P), .015 deck and a .028 gasket with a XE274 on premimum pump gas with NO problems. Power brakes worked fine, too.

Thanks Bill, reading your post it seems I made another error. I was using +5cc for those pistons when using the DCR calculator. Was the gas you were using 91? That at least sounds a little encouraging. I also wonder if the high altitude I am at here affects this in any way. We are at 5000+ feet here, up in the clouds

Jerry

Jerry,
That would be with 93 octane and we're right around 1000 ft.in elevation.
I believe, with a careful choice in a cam, you'll be fine. And very pleased with the Vortec's performance. ;)

Use +5 for the CR calculation on the DCR calculator. Select the flat or dish button. The program will assign the correct sign. This is because some mfgs use negative for domes and other use negative for valve pockets and dishes.

Well,I remeasured and remeasured piston to deck on all 8 and now I am befuddled. Measurements range from .005 to .041. I then placed a good straight edge across the deck and you can see a difference in places.And sooo what does this mean? Have the block machined? Just for a point of interest I checked the old head gaskets and they were approx. .045. It had on 78cc heads and ran great.I did notice some of the piston tops were quite black and sooty and am not really sure if thats to do with the diiferent clearances or not.Maybe I should just add up all the clearances and divide by 8 to give me a average eh! graemlins/clonk.gif As it went with the rest of the car restoration process nothing is as simple as that. I am going to wait and get a little input from you fellas and then decide on my next move

Thanks for the help


Jerry

Jerry,
It is not at all uncommon to see a stock block with a .015-.020 difference from one end to the other. Also, if the crankshaft was reground, and the guy running the grinder was "lazy", the strokes could be off as much as .010 from one journal to the other.
Now, I am going to buck the trend here....unless you are planning on racing this car in some type of class that requires every last 1 or 2 horsepower....stop worrying about it, use the Fel Pro .038" gaskets and put the darn thing together ! I am betting that very very few people would actually notice the difference in the performance without actually running the car at the strip and comparing 1/4 mile times and mph. If any of you guys were to look at as many engines as we do in the shop, and see how badly they are machined from the factory...you would be amazed. And yet they run great. I am not saying that its a total waste of time to blueprint the engine, if you are building it from scratch...but in this case, I dont think the costs involved would be worth the results.
Just my opinion,

Thanks again for the help Bill. As I mentioned earlier I am not racing my ole girl , just wanted to wake her up a bit. I am going to do as you suggest

Thanks

Jerry

Don't the vortec's use a different head gasket? I just got the whole setup and the head gaskets are different than any I have ever seen. They are .028 thick.

Most factory small blocks will have around .025 deck clearance, I've never seen one with as little as .020. Those pistons are .020 short rebuilder pistons, so I'd expect your engine to have .040 --.050 deck clearance as built. Often the stroke is a little short on reground cranks.

How are you finding TDC on the individual cylinders?


As is often the case I'm in agreement with Bill here. Just put it together and run it. At 5000 ft you're not going to have too much CR, although at sea level this combo would require a huge cam to be usable on pump gas.

Tom

Tom,I was using a dial indicator with a magnetic base. I set the base on the block and the plunger of the indicator on the piston and slowly turned it over to get the highest point that the piston reached. I then checked measurement with indicator and even a feeler guage. I took all measurements at center of piston. Now I will admit I am a complete rookie here and when dealing with thousandths of an inch here I could be off a little but not enough to give me the large difference in each cylinder(I think).Did I measure these in a correct way?


Jerry

Jerry,
If at all possible I would suggest using a depth micrometer in place of the dial indicator. It is far more accurate and much user friendly. We tried to use a dial indicator and found it nearly impossible to consistantly (thats the key word)obtain accurate readings. Use a piston stop to find TDC, measure off the axis of the pin bore (they should be equal)then average the readings from the major and minor thrust sides. Do cylinders 1,2,7 & 8 first to determine if you have slope in your deck. Depending on those readings you can measure the remaining cylinders. Here is a link I found on how to use a depth micrometer.
http://www.cimibooks.com/main/store/tradetheory_sample1.asp
Hope this helps,
Bob

I too agree you should just put it together with the thicker head gasket. The Vortec heads can tolerate a lot of compression on pump gas without ping. A buddy of mine is running a true 9.6:1 Vortec headed 383 in his heavy Suburban with a tiny hydraulic roller (less than 200° @ 0.050" and 109° lobe separation) and it does not ping at all on 92 octane unleaded.