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Discussion Starter #1 (Edited)
Im having a discussion elsewhere about those infamous 340np pistons that are down in the hole .020. Someone is suggesting that those pistons would be fine with higher compression heads and a standard undecked block and it would run fine leaving the piston approximatly .045 down in the hole minus a gasket. They also suggested to run a standard .039 gasket and running a 60cc head which puts the quench at like .084. I was reading an engine builders book and it says excessive quench of .060 could cause serious detonation. This someone is suggesting the engine will be fine with the excessive quench on this engine since it was too mild to even feel the affect of excessive quench. Thought I would get some feedback from the pros here because I really want to know the lowdown on this.

355
scat 9000 crank
scat 9000 i-rods
345np 030 cast pistons
LT4 hotcam
1.6rr
canfield 197cc heads
Converted lt1 intake
Headers
dual 3inch
 

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Excessive squish won't cause detonation but minimum squish helps reduce the tendency to detonate. You need to invest in a burrete and start measuring volumes then figure out your actual CR.

Your combination looks like a mishmash of acquired parts. I have no idea what you are thinking of accomplishing. good luck.
 

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Discussion Starter #3 (Edited)
This isnt my engine but someone is suggesting that this was an ok setup. I had a feeling it wasnt the greatest setup myself. If you check my sig you can see this is not my engine. Im using this example from someone elses parts list so maybe i can learn something.
 

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shaggy said:
This isnt my engine but someone is suggesting that this was an ok setup. I had a feeling it wasnt the greatest setup myself. If you check my sig you can see this is not my engine. Im using this example from someone elses parts list so maybe i can learn something.
Your sig says one thing, but how do I know if you weren't building another engine?
All this rash of Quench and Squish postings sounds like misunderstandings being derived from Chevytalk postings. I wish I had the cast concession over there. I'd make a fortune from all the broken legs caused by jumping to conclusions.

Excessive squish dimension doesn't cause detonation. Some engines don't even have quench type chambers. They don't detonate with no squish at all.
What they are saying is a quench headed engine with less squish (more height) may be more likely to detonate than one with more squish (less height). This statement is more true if the CR is high and less true if the CR is low.

Don't make the faulty leap of logic from "more likely to detonate" to "causes detonation".
 

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Discussion Starter #6
So would an engine with a quench of .080 and compression in the 10:1 ratio run ok? Thats really what im trying to find out.
 

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Discussion Starter #8
DriveWFO said:
You gotta factor in the cam too.

That was listed up top. LT4 hotcam. The person has a shortblock with those mentioned pistons and the suggestion that was given was get smaller cc heads. I wondered what the pros here would have suggested is all.
 

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Paul Wright said:
All this rash of Quench and Squish postings sounds like misunderstandings being derived from Chevytalk postings.
My question in the Best of Tech thread comes from wanting to better understand my existing setup. I've got stock dished, 4-valve relief pistons, .025" deck height, .028" gaskets (4.10" diameter), and the Vortec chambers.



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shaggy said:
So would an engine with a quench of .080 and compression in the 10:1 ratio run ok? Thats really what im trying to find out.
Yeah, everybody thinks they have 10:1 if they have flat tops.
I don't suppose this person actually measured the volumes with a burrette and computed the CR did they. I don't suppose the measured the Intake closing and calculated the DCR did they? This kind of guessing and online calculator figuring will almost certainly bite this person in the arse.

I've come to the conclusion that not everybody can build engines. My gut feeling is this guy built it out of a collection of Ebay deals. But you know what? This may sound harsh but some people are too lazy, cheap or incompetant to build a good engine.
I gave up trying to help EVERYBODY with a problem, because some, quite frankly, are just too stupid to learn.

Why are you worried about it?
 

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Discussion Starter #11 (Edited)
Im not worried but I just seen someone giving suggestions to help the person out and it just didnt seem right. I said he should probably look into getting different pistons or decking the block and someone else said just throw on a .039 gasket and smaller cc heads and call it a day. Then I thought would that be something Paul Wright would say? I also would like to learn something to boot. Thats why I post these ridiculous questions all the time.
 

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,,,sound harsh ???

LOTFLMAO

One of the best "old sayings" I've hurd would apply here;
"If you try to teach a pig to sing,,you and the pig will end up frustrated":mad:

shaggy,
Looks like your friend hasn't measured squish / piston to head clearance at all,,,ie; .060 or .080???:confused:

A large "piston to head clearance" of .080 or .060 will only cool the mixture in this area,hence the term "quench",to the point of lost burn.
The engine can gain efficency by closing the PTH clearence to the minimum allowed by the parts combination,,say .035,cooling/quenching a minimum amount of the available mixture, adding volume as needed to the chamber to keep the CR the exact same.

In other words,,Gaining cylinder head volume by adding PTH clearance to obtain desired CR is an inefficent method of action.:eek:
A tite PTH clearance with the combustion chamber CC'd correctly for the desired CR is always the better combination.:D

RED67:chev:
 

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Discussion Starter #13 (Edited)
That was basically the answer I was looking for. Just wondered how the engine would respond under those conditions.
 
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