Piston to Wall clearance

[jenkins71]

Hi Guys, just got m block and pistons back from the machine shop.

I gave them the pistons that were in there, L2266's (flat-tops), and the ones I wanted to use, used L2295's (hi-compression domed).

That measured piston-to-wall clearance and found the flat-tops to have .003" clearance, and the L2295's to have .007" clearance.

Is the .007" too high? My book says .008" is the limit. What would you do?

Also, what is a good compression ratio for a 440 street/strip torque monster?

Thanks!

 

[69Bee]

By "Your Book", do you mean the service manual? If so, that is for stock, Chrysler, factory pistons. These are aftermarket pistons, and as such, have their own clearance spec.

If the L2266F's are new, my Speed Pro book says the MINIMUM clearance should be 0.0015". They are also coated, so you cannot directly measure the pistons, unless the skirt coating has the small window. The front of the box gives you the required specs, and measuring point for the pistons.

The L2295F pistons have a minimum clearance of 0.005", and do not look coated (according to Summit website pic), and can be measured directly at the specified point.

Be careful when you measure the pistons; the piston and mic are supposed to be at a room temp of say 70 degrees F.

 

[Cranky]

I've seen the 2295's run at .003 before but things need to be straight and true and don't over heat the engine but .007 will work too. I like compression and know how to deal with it on the street. Cam is important when you plan on running pump gas on the street but it can be done but you can also make a low compression engine run damn good too.

 

[super-bee_ski]

.007 to.008...
Only 1,000th so the toleance is close (Tight)

That being said...
.005 to .007 is close...

You are A-OK...

 

[Meep-Meep]

I'd stay away from the domed pistons for street use as nothing good will come of it. 9.5:1 max and 175 PSI for a pump gas street engine IMO.

The .007" might sound like a diesel when it's cold but that sound will go away when it warms up. I ran up to .011" and that really sounded like a diesel when cold! Loose clearances not recommended for longevity by the way.

 

[jenkins71]

I'd stay away from the domed pistons for street use as nothing good will come of it. 9.5:1 max and 175 PSI for a pump gas street engine IMO.

Why do you say nothing good will come of it? With my 98cc heads the CR will be about 10:1....

 

[jenkins71]

The L2295F pistons have a minimum clearance of 0.005", and do not look coated (according to Summit website pic), and can be measured directly at the specified point.

Thanks man, where do you find info like this?

 

[IQ52]

Why do you say nothing good will come of it? With my 98cc heads the CR will be about 10:1....

Meep-Meep is trying to be gentle I think. I keep watching this and other threads trying to stay out. You are "good compressioning" yourself right into detonation. And for what? One point of compression in a 400HP engine is worth maybe, if you're lucky, 16HP. And for that you are willing to go through the crap of dealing with an engine that sounds like a diesel or idles like a top fueler. With factory iron heads on a street cammed, pump gas engine, I wouldn't run more than 9.5:1 like Meep-Meep says.

But you do what you want 'cause yer gunna anyway.

 

[jenkins71]

Meep-Meep is trying to be gentle I think. I keep watching this and other threads trying to stay out. You are "good compressioning" yourself right into detonation. And for what? One point of compression in a 400HP engine is worth maybe, if you're lucky, 16HP. And for that you are willing to go through the crap of dealing with an engine that sounds like a diesel or idles like a top fueler. With factory iron heads on a street cammed, pump gas engine, I wouldn't run more than 9.5:1 like Meep-Meep says.

But you do what you want 'cause yer gunna anyway.

Listen man, I don't know ****. I'm just trying to wrap my head around this stuff! I'm 26 years old. Never in my lifetime were these engines still in production. I'm learning the best I can, through asking questions. I get some people telling me that 10.5:1 is good on pump gas, and other people telling me 9:1 is better. I wish more people would weigh in, and I always appreciate the free advice! Thanks for the input.
I don't have my heart set on using the domed pistons if that's not the best thing to do. I'm doing tons and tons of research, asking questions that you might think are stupid because I really don't know anything here.

 

[IQ52]

We all sincerely want to help, but sometimes the more people wade in, the more muddy the water gets.

Okay, Okay. First engines we don't take to even the supposedly 'safe' compression limit. The engine package has to be considered.

I have built pump gas engines for awhile now. I don't design engines for the forums but I have posted test engines we have run on the dyno and driven on the street. We've done 500in iron headed 91 octane engines running 11.9:1 compression, 38 degrees advance locked, making 750 HP, 451ci aluminum headed motors at 11.7:1 compression making 780 HP on pump gas and they don't detonate. Those are not what you need to build at first, even if you want one.

Low compression will work for a first build and it doesn't mean you are a wimp if you run one. Here is a 400ci example.

http://www.forabodiesonly.com/mopar/showthread.php?t=293381

Saw the owner leave the gas station the other day in a big cloud of 2bbl tire smoke.

Do the exact same thing with a 440 and you are at 400 HP. 400HP on the street can be a handful.

Then there is always Pop's 440. This will walk you through a 404HP 440 starting w/ 9.5:1 compression, backing it down to 8.9:1 and then going from 495HP to 650HP using the same short block the whole way. It detonated at first the way Pop built it on the 9.5:1 404HP runs because of the compression ratio/camshaft/ignition timing. Every run thereafter had no detonation.

http://www.forbbodiesonly.com/moparforum/showthread.php?64775-Pop-s-440-is-near-ready-to-dyno&highlight=pop%27s+440

 

[69Bee]

Thanks man, where do you find info like this?

I am a machine shop, and have catalogs with the specs in it. Also, if you had the original box, it is printed on the front. Last case, you can call Sealed Power directly, and ask their tech line the same.

 

[jenkins71]

We all sincerely want to help, but sometimes the more people wade in, the more muddy the water gets.

Okay, Okay. First engines we don't take to even the supposedly 'safe' compression limit. The engine package has to be considered.

I have built pump gas engines for awhile now. I don't design engines for the forums but I have posted test engines we have run on the dyno and driven on the street. We've done 500in iron headed 91 octane engines running 11.9:1 compression, 38 degrees advance locked, making 750 HP, 451ci aluminum headed motors at 11.7:1 compression making 780 HP on pump gas and they don't detonate. Those are not what you need to build at first, even if you want one.

Low compression will work for a first build and it doesn't mean you are a wimp if you run one. Here is a 400ci example.

http://www.forabodiesonly.com/mopar/showthread.php?t=293381

Saw the owner leave the gas station the other day in a big cloud of 2bbl tire smoke.

Do the exact same thing with a 440 and you are at 400 HP. 400HP on the street can be a handful.

Then there is always Pop's 440. This will walk you through a 404HP 440 starting w/ 9.5:1 compression, backing it down to 8.9:1 and then going from 495HP to 650HP using the same short block the whole way. It detonated at first the way Pop built it on the 9.5:1 404HP runs because of the compression ratio/camshaft/ignition timing. Every run thereafter had no detonation.

http://www.forbbodiesonly.com/moparforum/showthread.php?64775-Pop-s-440-is-near-ready-to-dyno&highlight=pop%27s+440

Thanks man. Those links were really cool. Read em both--very inspiring. I was wondering why you backed Pop's 440 down to 8.9:1 compression? Was it detonating at 9.5:1?

 

[Meep-Meep]

Why do you say nothing good will come of it? With my 98cc heads the CR will be about 10:1....

Because you don't want to build yourself into a corner. Even 10:1 is on the ragged edge depending on what intake you are running; carb set up; jetting; hot day vs. cold day and so on. I have found on my own 10.1:1 440 that the intake and carb combo makes a difference regarding pinging and having an engine that is that finicky is not fun. I also have a 426 hemi with what seems to be running a stock cam, 225 PSI of cranking pressure and God knows what static compression ratio. It's the most miserable POS I have ever driven.

 

[IQ52]

Thanks man. Those links were really cool. Read em both--very inspiring. I was wondering why you backed Pop's 440 down to 8.9:1 compression? Was it detonating at 9.5:1?

I explained it in the post but it wasn't so much a deliberate thing. The engine was detonating as Pop built it. Our cylinder head tests were not going to be with Pop's 452 heads but with our 346 heads and they had larger combustion chambers. So when we switched to the 346 heads it just naturally dropped the static compression. The distributor had to be recurved from how Pop had it, as it had some 40 degrees mechanical advance. Top that off with the small cam and how far he had it advanced and we couldn't get it to stop detonating.

My point is how much horsepower you can make without going to the ragged edge of safe compression ratios while on the street. We did it with 8.9:1. Build it easy on compression, learn what you are doing and go from there.

 

[jenkins71]

Thanks guys. I guess I'm coming from just having read that high CR=power, without ever thinking of the real consequences of running it on the street.

 

[moper]

Thanks guys. I guess I'm coming from just having read that high CR=power, without ever thinking of the real consequences of running it on the street.

Reading is fundamental - so keep doing it. But read books, not the interweb. Compression is a part of the system that makes an engine. It's one that can be played with, but if you're new at it the safe compromise is "lower is better". So for newbies - if you run iron heads - lower is better. If you run open chamber heads - lower is better.

 

[Cranky]

What about quench? Chrysler ran 8-1 on their engines starting in the early 70's and all they ended up with was pinging, dieseling and overheated engines. You can run low compression and you can run high compression if you know what you're doing. Yeah, you are usually safer running lower compression but even that can cause trouble if you do it wrong.....

 

[383man]

Listen man, I don't know ****. I'm just trying to wrap my head around this stuff! I'm 26 years old. Never in my lifetime were these engines still in production. I'm learning the best I can, through asking questions. I get some people telling me that 10.5:1 is good on pump gas, and other people telling me 9:1 is better. I wish more people would weigh in, and I always appreciate the free advice! Thanks for the input.
I don't have my heart set on using the domed pistons if that's not the best thing to do. I'm doing tons and tons of research, asking questions that you might think are stupid because I really don't know anything here.

I know it can be frustrating and confusing. And when 5 different people tell you different things you dont know who to listen too. When I was younger (Am 58 now) I was in the same boat as a teenager and I decided to be a tech for life and learn all I can to build my own engines and not have to ask anyone as I made myself learn all I could to be the best I could. But you can listen to these guys as they are only here to help as thats the great thing about this hobby and that 99% of us want to help each other.
You are right it can get so confusing today with what comp ratio you can run on pump gas and if you dont understand alot of it its even more confusing. One other thing is the pump gas is not as good as it used to be as alot of cars in the hot summer have trouble with the pump gas fuel boiling in the carb bowls because of the ethanal in it and winter grades are the worse.
But your comp will depend on alot and a good eng builder will know that like aluminum heads can get away about 1 comp point higher then iron heads and a good build is to use a flattop piston with a closed chamber head and build good quench in the eng. The cam also makes a difference as it has alot to do with how much cyl pressure the eng builds.

Just to let you know what I run on 92 pump as my eng is a 440/493 stroker with 10.6 real comp and I use Indy EZ aluminum heads. I run flattop pistons that are .006 below the deck and with the .039 heads gasket and my closed chamber heads I have .045 quench. I use a solid flat tappet cam thats 264 & 270 @ .050 and .585 and .592 lift with a 110 LSA. And I have it on a 106 installed centerline. I use about 36 to 37 total timing all in by 1800 rpm and it runs great and never pings on 92 pump. I race it on 92 pump also as I actually have never had racing gas in my car. But I dont want to confuse you as these guys are already helping you out alot. Also on the pistons many forged racing type pistons will exspand more then cast factory pistons as thats why some pistons call for .007 piston to wall clearence and many stock type run .001 to .0025. Course the more clearence pistons may make some noise when cold which is normal. Good luck with it and feel free to ask me anything about my car or if you thing I could help you any. Ron