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Author Topic:   Bumping up compressoin
hobby10k
Dirt Freak

Total posts: 226
posted January 24, 2005 05:21 AM  
Ok I have determined that stock internals (can) last on 13:01 comp. Now my question is what all will I haft to ajust to make a safe margin for the engine moving from 10:01-13:01 comp? such as timing, plug temp, jetting etc.
See a friend of mine said that he ran his engines at 13:01 comp and had problems with burning up a piston every other race. now I just want to set myself in a (safe) area to run in.
Now the engine is a 355 with a 2brl carb and intake etc. and obviously will be running race fuel. also would a 406 be the same? cause looking into maybe building a 406.

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leapinlizard
Dirt Freak

Total posts: 402
posted January 24, 2005 08:02 AM  
Burning pistons sounds like a tuning problem rather than compression.

brownstone
Dirt Freak

Total posts: 284
posted January 24, 2005 08:49 AM  
lizard said it right the compression alone will not cause piston burn.

Burn has to do with too much timing, not enough fuel, or vacuum leak ( sucking air )

If you are buring check jet size, and consider backing down timing slightly.

dirtbuster
Dirt Forum Champ
Total posts: 2007
posted January 24, 2005 08:58 AM  
I agree that piston damage is prob timing or fuel related not compression. Unless you are not running enough octane compression alone wont do it. With 13:1 i'd plan on about 110 actane, even with the 2 barrel just to be safe.

[This message has been edited by dirtbuster (edited January 24, 2005).]

stockcar5
Dirt Forum Champ
Total posts: 578
posted January 24, 2005 03:32 PM  
if the center of his pistons were pounded out then it was detonation (which can be cause by to much compression for the fuel you are running) with 110 on a 2bbl you'll be fine. sunoco 110 is one that will support 13.1 with their 110. i think vp lets you go a little higher.

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Mr. Badboy
Dirt Full Roller

Total posts: 29
posted January 24, 2005 05:52 PM  
We fire slotted a block on an alcohol fired motor last season, and saw the damage on the block and head between number 3 and 5 cylinders, and down the side of one piston and cylinder. We thought on the rebuild things were good, and took the car to the dyno to get it tuned. We were so far off in terms of fuel supply that we were going to burn another motor. The dyno saved the day, the $400 spent was cheaper than the cost to rebuild the motor.

hobby10k
Dirt Freak

Total posts: 226
posted January 25, 2005 01:40 AM  
Yea I know what caused the burnt pistons in my friends engine, I was just wanting to know where to set everything at when I do bump up my compression so I dont do the same. is there a safe margin to start in as far as, jetting, timing, and plug temp? and Of course I will be using 110 for fuel.

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BrianW
Dirt Freak

Total posts: 385
posted January 25, 2005 10:29 AM  
quote:
Originally posted by hobby10k:
Is there a safe margin to start in as far as, jetting, timing, and plug temp? and Of course I will be using 110 for fuel.

Yes - but you won't get an accurate answer from here - taking it to the dyno with a wideband O2 sensor will "tell all" as far as "safe" jetting. Timing will depend on basic engine design and how well the flame travel is in that engine. Figure really safe is 30* of total timing (or locked-in timing), OK 32* and unsafe at 34* - again baslines - you might find out your heads don't have good flame travel and swirl and make max power at 36*, but you'll never be able to tell without instrumentation to read the changes you make.

Raz_900
Dirt Forum Champ
Total posts: 635
posted January 25, 2005 09:12 PM  
I'd go 2 heat ranges colder on the plugs and up 3 jet sizes if it's a Holley. Back the timing off 4 degrees and work from there. Unless you take it to a dyno for a tune. Too hot of a plug will also burn through a piston in short order.


dirtbuster
Dirt Forum Champ
Total posts: 2007
posted January 26, 2005 07:30 AM  
If you let us now what heads/pistons you have that would help a bunch. Timing is really dependent on those things.
Also what plugs you are running now.

[This message has been edited by dirtbuster (edited January 26, 2005).]

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