Wrong Pistons? - Team Camaro Tech
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post #1 of 72 (permalink) Old Feb 4th, 07, 10:07 PM Thread Starter
 
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Wrong Pistons?

Guys,

About 10 years ago I purchased a 427 ($2,000.00) that was advertised as a fresh and balanced 13 to 1 compression assembly with aluminum heads. The engine was in a 68 Camaro (tubbed and lightened) that ran 10.80"s and was complete from oil to plugs. Last year I tore it down and began preparing to re-assemble using fresh bearings. After short blocking my 427 I realized that the pistons were .095 down hole. My intial reaction was that the pistons were 454 (.585 dome TRW) pistons with a 1.645 compression height and not 427 pistons with a 1.760 compression height, so I purchased a set of L2239 TRW's with a .485 dome and a 1.760 compression height correct or the 427.

I recently discovered that the original pistons were in fact a 427 TRW piston that had been cut aprox .080 - .090 around the flat parts of the piston and not on the dome. I believe this was done to decrease compression ratio as the 074 open chamber heads had been milled down to a 105 cc chamber.

Two questions:

1. Is it at all possible to expect any decent quench from a .585 dome piston .095 downhole?

2. Has anyone ever successfully used a closed chamber piston in the open chamber head aluminum 074 head?

Thanks,
Bill
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post #2 of 72 (permalink) Old Feb 5th, 07, 08:12 AM
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Re: Wrong Pistons?

My first thought is that your quench will be the piston to deck clearance plus the head gasket which is pretty high. With the piston decks cut like that, I would think someone intended to run in a decked block that was 0 deck.
If this is a race motor , I would do just that then check for piston to head clearances and adjust accordingly. Need to brings things back in line. Is this a short deck block? 9.780 range? Are you also saying that both pistons are in the hole, .090?

As for putting closed chamber pistons in an open chamber head,, I would think compression is low unless head has been cut a bunch?

I am sure you are keeping the stroke of both motors in mind .

Don
TC # 349
Zdld17:69 Z/RS,306, NOR141111, 9N554XXX, 12A, X3G, 59/59,723, AFR 195,CCC282/290HR, TKO 600, BU1122B1E Owner since Dec 1968

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Last edited by zdld17; Feb 5th, 07 at 08:23 AM.
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post #3 of 72 (permalink) Old Feb 5th, 07, 09:42 AM Thread Starter
 
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Re: Wrong Pistons?

Don,

Thanks. The engine is destined for a 69 Camaro that will see mostly 1/4 mile track use. The block is decked @ 9.790. The new 427 pistons end up at .005 below deck when installed.

The old pistons were installed in the block @ .095 below deck and it appeared that someone had prepared to run it like that. With the piston at that height the compression still works out to above 13 to 1 as the heads are now at 105 cc.

Using the closed chamber piston the compression ratio will still end up around 11.5 to 1 because of the milled heads. This is fine, but I am worried about the efficiency of the closed chamber piston in the open chamber head.

This is the crossroads:

Use the milled .585 open chamber dome piston .095 down hole with 13 to 1 compression ratio and questionable quench, or

Use the .430 closed chamber dome piston, .005 down hole with 11.5 to 1 compression ratio and correct quench

Thanks,
Bill
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post #4 of 72 (permalink) Old Feb 5th, 07, 11:43 AM
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Re: Wrong Pistons?

Bill , Is it possible to angle mill your heads to bring the .430 piston compression up to 13 or so?

Don
TC # 349
Zdld17:69 Z/RS,306, NOR141111, 9N554XXX, 12A, X3G, 59/59,723, AFR 195,CCC282/290HR, TKO 600, BU1122B1E Owner since Dec 1968

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post #5 of 72 (permalink) Old Feb 5th, 07, 11:55 AM Thread Starter
 
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Re: Wrong Pistons?

Don,

If you think something closer to 13 to 1 will work better with the closed chamber pistons, could we not play with head gasket thickness. The static compression ratio of 11.86 to 1 is the 43 cc dome piston @ .0055 deck height with a .040 with head gasket.

Thanks,
Bill
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post #6 of 72 (permalink) Old Feb 5th, 07, 12:32 PM
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Re: Wrong Pistons?

Quote:
Originally Posted by Billy.B View Post
Don,

If you think something closer to 13 to 1 will work better with the closed chamber pistons, could we not play with head gasket thickness. The static compression ratio of 11.86 to 1 is the 43 cc dome piston @ .0055 deck height with a .040 with head gasket.

Thanks,
Bill
I dont have my dcr calculator here at work, but will look at it at home later this afternoon. My thought was that If you have the additional clearance , angle mill the exhaust side of the head say .100 or so , depending on clearance, and try to fill up that comp chamber and use the thinnest gasket you can to get comp up. I did this before with a 468 using Ross 13.1 pistons but with open chamber heads, and angle cut heads . the motor will not run on any pump fuel for sure. I will crank out the hp but my concern is for your motor is clearance. You need to check it. You need to know what piston to valve clearance you will be running. Did you mention the cam you were using? Lift, duration etc.

click on this and load Pats program and juggle you scr /dcr
http://members.uia.net/pkelley2/DynamicCR.html

Don
TC # 349
Zdld17:69 Z/RS,306, NOR141111, 9N554XXX, 12A, X3G, 59/59,723, AFR 195,CCC282/290HR, TKO 600, BU1122B1E Owner since Dec 1968

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post #7 of 72 (permalink) Old Feb 5th, 07, 01:11 PM Thread Starter
 
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Re: Wrong Pistons?

Don,

First, thanks for your help. Much appreciated.

Comp Cams - Solid, 292/308 advertised and .635/.631 with 108 lobe sep.

I did look at the Ross 13 to 1's but I was concerned for piston to valve clearance with that dome size. The reason I chose the .438 dome over the .585 dome piston was for that reason. After realizing that the .585 dome pistons had been cut down I believe that the cutting of the piston was done to decrease comp ratio. Remember, the 074 open chambers were cut all the way down from 118cc to 104cc leaving a c/r of 15 to 1 at Zero deck. I am thinking they cut down the flat part of the piston to decrease c/r but did not touch the domes as they probably had the piston to valve clearance and piston to combustion chamber all dialed in.

The heads are currently 114 cc because we unshrouded the valve area and cleaned up the plug area. If they went from 118 cc to 104 cc, do you have any idea how far they may have been milled? I am thinking that the heads were probably hurt at some point and then repaired and surfaced. It is quite possible that the exhaust side is already down .100 or so. I am not concerened about octane ratings as I intend to use C12 or 14.

This was my logic:

If the .585 dome had to be cut back .090 or so, I figured by using the .430 dome I should not have any clearance issues. Unfortunately, the first thing I did was throw awy the old cam and lifters as I do not like having old cam/lifters hanging aroud. If I still had it I could tell you the lift that was run previous.

I know it is a bit of a cluster but I would like to feel as confident as possible before using the closed chamber piston.

.018 head gasket gets the c/r close to 13 to 1.

Thanks again.
Bill
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post #8 of 72 (permalink) Old Feb 5th, 07, 01:46 PM
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Re: Wrong Pistons?

Check your clearances is all I can say at this point. Sounds like you are going in right direction. Using the thinner gasket you got the cr down to 13.1, I guess it improved your quench? I know about how much head milling it take for sbc but bbc is differant on chamber, much larger but if I apply that to your 14cc head differance, I would say the head was ground .80-.100. Go from there.

If the heads were cut on the exhaust side , you may notice a little differance in the head bolt hole to bolt or stud, looking sorta of cocked? Ie. bolt hole not parrallel to stud or bolt. That may give you some indication. My guess is that if the piston decks were cut , I would think that someone was trying to put more dome in the head, ie increase compression. You did not say if your rods were stock lenth or not. I have done this before by using longer rods and milling piston decks but you really need to check your clearances. I took one piston hole with piston up and bolted head on, pored hot canning wax in the plug hole and let it cool. I got a perfect mold of what my cly was, quench and all, exact but on the ragged edge.
I was using Comp CB 312 roller at the time. I had a larger 750 lift from crane that we Comp cut back to their pattern. The car ran much quicker then.

Don
TC # 349
Zdld17:69 Z/RS,306, NOR141111, 9N554XXX, 12A, X3G, 59/59,723, AFR 195,CCC282/290HR, TKO 600, BU1122B1E Owner since Dec 1968

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post #9 of 72 (permalink) Old Feb 5th, 07, 02:09 PM Thread Starter
 
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Re: Wrong Pistons?

Don,

Again, thanks. You may be on to something. It is quite possible that the combo had a longer rod in it as some point. Maybe that is why the heads were repaired. Possibly a rod let go and they did not have the time or resources to get another set, so went with a stock rod. Funny thing, somebody went to the time and expense of balancing the rotating assembly and then installing the piston/rod combo .095 down hole.

Anyway, yes the rods are now stock rods that we are going to prep as best and possible and then re-balance the new closed chamber pistons, rods and 7115 crank.

You went away from the idea of using the cut pistons and leaned toward the closed chamber piston at .0055 deck height and as close to 13 to 1 as possible. Does the 427 + .030 like the higher compression and what is the minimum thickness you would use on a head gasket with aluminum heads (all clearances considered)?

Thanks,
Bill
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post #10 of 72 (permalink) Old Feb 5th, 07, 02:17 PM
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Re: Wrong Pistons?

My 430 loved the higher compression, seem to crackle like most prostockers did inthe 80"s... think I was using the .043? or so Victor core gasket with the fire ring. From there I went long rod 468, then the fun started. there's hole shot photo in my photo bucket signature link, Had to put body bars on it as when the night cooled and track was sticky,, it has been on the bumper.

Don
TC # 349
Zdld17:69 Z/RS,306, NOR141111, 9N554XXX, 12A, X3G, 59/59,723, AFR 195,CCC282/290HR, TKO 600, BU1122B1E Owner since Dec 1968

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post #11 of 72 (permalink) Old Feb 5th, 07, 02:38 PM Thread Starter
 
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Re: Wrong Pistons?

Don,

The car looks awesome. Gotta love the crackle of the high compression big blocks. I will try to nail this thing down as close to 13 to 1 as possible. I just hope the closed chamber piston does not retard flame travel or cause chamber issues. Thanks for your help. If you can think of anything that may help, please add. If you would like to check c/r when you get home, here are the #'s"

4.230 bore
3.760 stroke
TRW L2239 43.1 cc pistons
.0055 installed piston to deck height
7115 crank
stock rods
396074 open chamber allloys 114 cc heads (2.19 /1.88)
9.790 deck height

Let me know what thickness head gasket you would recommend.

Thanks,
Bill
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post #12 of 72 (permalink) Old Feb 5th, 07, 02:46 PM
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Re: Wrong Pistons?

Will post later this evening.. I really dont see how the flame travel would be hurt when sticking a closed piston into and open head chamber. To me thats the reason of a good clayed cly check or even hot wax mold. later

Don
TC # 349
Zdld17:69 Z/RS,306, NOR141111, 9N554XXX, 12A, X3G, 59/59,723, AFR 195,CCC282/290HR, TKO 600, BU1122B1E Owner since Dec 1968

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post #13 of 72 (permalink) Old Feb 5th, 07, 02:50 PM
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Re: Wrong Pistons?

Can you mill an 074 head to 105cc? I would take a look before you go too far.
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post #14 of 72 (permalink) Old Feb 5th, 07, 02:53 PM Thread Starter
 
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Re: Wrong Pistons?

Don,

Good advice. Thanks and talk to you later. Nice wheel stand.

Bill
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post #15 of 72 (permalink) Old Feb 5th, 07, 02:56 PM Thread Starter
 
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Re: Wrong Pistons?

Oger,

I had the heads cleaned, pressure tested, springs installed and vac checked by a local speed shop. They were skeptical as well until everything tested ok. You don't like it? Please advise.

Thanks,
Bill
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