LS6 crate 454 piston help - Chevelle Tech
2002 General Tech questions from 2002

 
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post #1 of 16 (permalink) Old Nov 10th, 02, 12:17 AM Thread Starter
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Does anyone have an idea what pistons went into an early XXA 454 crate motor? I've heard either domed or non- domed making 10:1 or 11:1 with a domed piston. I can't run on less than 100 octane so I'm assuming they are the domed higher comp ratio pistons. Heads are 990's/118cc. What dome volume in cc was used?
Any help is greatly appreciated
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post #2 of 16 (permalink) Old Nov 10th, 02, 6:15 AM
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I belive those pistons have .090-.100 dome

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post #3 of 16 (permalink) Old Nov 10th, 02, 11:01 PM
pdq67
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May be wrong, but if it an LS6, then they should be the .270" ones.

But the engine instead of being a true 11 to 1 CR., is more like 10.25 or so b/c it isn't blue-printed from the factory...

Hope this helps. pdq67

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post #4 of 16 (permalink) Old Nov 10th, 02, 11:17 PM
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An old GM Performance Parts catalog shows that the pistons were part number 6262976 and were forged aluminum domed pistons for the LS6 engine, part number of 366250.
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post #5 of 16 (permalink) Old Nov 11th, 02, 2:06 PM
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LS6 crate motors have open chamber heads and the original LS6's had closed chambers.

------------------
My 70 SS396
Engine pic
My Black Cherry 70 SS454
The launch 13.13 @ 101.490/1.92 60 ft. with radials,2.73's,and thru the mufflers
1.90 Best 60 ft.
101.84 Best MPH

1968 Oldsmobile Cutlass convertible
1973 GMC Sierra 454 p/u
1985 Cadillac Eldorado (daily driver)
Chris Corwel,TC Member # 785
Member # 141 AMCA
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post #6 of 16 (permalink) Old Nov 11th, 02, 4:45 PM
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Chris is correct. Also, seems to me that you should be able to get by with 97-98 octane even if you had closed chambers and 11.25:1. What kind of timing are you running and is it possible somebody bolted on a set of 291's?

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post #7 of 16 (permalink) Old Nov 11th, 02, 5:24 PM Thread Starter
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Thanks for the responses. I didn't set the timing but I assume pretty much normal @ 10-12 degrees initial. I've seen the casting numbers on the heads and they are for sure 990's. Here is the rest of the combo:
Block stamped XAA
Casting # 14015445
Edelbrock 1413 800 cfm with spacer
3933163 intake (de-codes for L-78, L-79) alum Hi-rise
Crane gold race roller lifters set for .024 intake and .028 exhaust(stock for 362 cam)
Dynamax 1 7/8" headers thru Dynamax mufflers
Pertronix "Ignitor I" ignition
3:31 posi
I get it to stop pinging with one part 114 racing fuel and three parts pump 91, which comes out to be about 97 Octane. (I correct my previous post re: 100 Octane)
I have no idea if the motor has ever been torn down and changed in any way. I bought the car exactly as it is.
Thanks for the help
VH
1970 SS454 El Camino
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post #8 of 16 (permalink) Old Nov 11th, 02, 7:12 PM
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I run a crate LS6,and have no problems with running 94. You might want to check your timing!
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post #9 of 16 (permalink) Old Nov 12th, 02, 12:29 AM Thread Starter
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Thanks CFR. With all due respect, the guy that tunes my motor is a 25 year veteran of NHRA racing from Gassers to Top Fuel, so I gotta believe he got the timing right. I'm just trying to get an idea about the pistons that went into these early crates. I guess I'll know for sure when I take it down. Maybe the previous owner juiced a little because it needs 96 or 97 worth of Octane. Which is fine with me, it takes me back to the good old days. Thanks again for the responses
VH
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post #10 of 16 (permalink) Old Nov 12th, 02, 4:11 AM
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You'll need to verify the initial timing, the amount of mechanical advance and what RPM it comes in at along with how much vacuum advance is available, this could easily be 20º. In other words, you could have the initial timing set at 10, fine, but the dist could give 30 mechanical and 20 vacuum, giving you a total of 60 and a nasty pinging problem.

This engine is really marginal for todays gas, it was made to run 100 or so. I recommend you have your dist gone through at a shop where they have a dist machine and know how to use it. A short, late curve with limited vacuum advance might make all the difference here.

Tom
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post #11 of 16 (permalink) Old Nov 19th, 02, 2:22 AM
dsr
 
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HI Volney
In 1990 I bought a new XXA LS6 crate engine part #366250 It came with the closed chamber pistons & open chamber heads witch gives you 10.23to1 compression. The original 1970 motors had closed chamber pistons and closed chamber heads & 11to1 compression.I ran it on Sunoco 94 octane for many years 40,000 miles and didn't think there was any problems (motor ran fine and no ignition ping) until I had the motor rebuilt this past summer. The engine builder said I had damaged the piston skirts due to detonation??? I replaced the pistons and dropped it down to 9to1 to avoid any further problems with detonation. Dave
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post #12 of 16 (permalink) Old Dec 4th, 02, 11:28 PM Thread Starter
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Thanks for the replies. I guess the bottom line is that these motors used the same pistons as the original LS6 motors, and the compression dropped to 10.5:1 with the use of the open chamber 990 heads.
Welcome any further comments
VH
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post #13 of 16 (permalink) Old Dec 4th, 02, 11:34 PM
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No, should have been about a point drop in CR. From 11 to 1 to around 10 to 1 or even slightly less... pdq67

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post #14 of 16 (permalink) Old Dec 5th, 02, 5:54 AM
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The 14015445 block was not available until 1978 so this is not really and "early" crate engine.

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post #15 of 16 (permalink) Old Dec 5th, 02, 7:48 PM
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Steve Johnson is right on target with the part numbers. I bougt a 366250 engine and immediately took out the pistons. I loaded in the 9.1 pistons from the 1971 low compression ls6 motor and never looked back.

I still have the original pistons if anyone wants to buy em. Brand new, never run, standard bore. I also have a complete standard size main and rod set and a new set of standard rings.

For what it is worth the pistons are 11.00 with closed chamber 108 CC heads and 10.2 with the open chamber 118 cc heads that are (were) delivered on the 366250 crate motors.

I think you might be right on the edge with 10.2 cr on todays junk gas with iron heads. My 454 runs 9.1 to 1 (nominal) compression with the pistons I have and I have never had any trouble with detonation. I even run air conditioning and I can lug that sucker right down to almnost stalling with the air on in high gear. Then I just step on the gas no fuss no ping it just pulls away. For my money the extra point and one half cr just is not worth the aggravation.

As for the tuner having 25 years experience and all that well I dunno. Perhaps he is just trying to dial in all the go fast he can to look like the hotshot tuner? I just tend to rely on the old "If you want it done right you gotta do it yourself" philosophy.

Any takers on the pistons?????



[This message has been edited by oman (edited 12-05-2002).]
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