L2388 Pistons replacement weight diference.

[COKE]

Good day to all,

I have a 440 block with the Discontinued L2388 piston on it.
I have read posts from other people wich used to have the same pistons on their 440 blocks and they sat 0.10 or even  0.12 down in the hole(It seems that they were the lowest comp pistons in the market ).
Well ,mine are between 0.068 and 0.070 down in the hole at TDC,so i can start to assume that some "Genius" put these ultra low cr pistons  and  milled  the block 0.04 - 0.05.

I would need to bring up the comp. cause i have the MP 84cc alu heads.and with these pistons i would get a 9.3 CR using a 0.040 gasket.
I have found  a set of Icon pistons wich would  be ideal,cause they have a 1.991 comp distance and valve reliefs.
The 2388 have a 1.926 comp distance so :

1.991-1.926=0.065

0.070-0.065=0.005 deck


As you can see,these pistons will give a 0 to 0.005 deck with the  reliefs for the valve clearance,wich would get a 10.2 CR.

The trouble is that  even being forged they weight only 686g while the old 2388 weight is 827g.And off course , the crankshaft was  balanced for  these junk.

  827-686=141g difference

I suppouse that i can,t mount them without balancing,and there is nobody around here able to balance a V engine,cause they require the bobweight system,
There is  nobody who has the machine,cause almost all the competiton balance jobs here are over 4-5-6 in line engines wich are easier to balance.

So, i,m looking for a 1.991 comp distance ,flat top& 2 valve reliefs on the 800g range.
If somebody knows any reference would be aprecciated.

Thanks a lot for any input

[John_Kunkel]

The KB-146 (1.992" CH) weighs 775 grams but I don't know how much of that you lose by machining the dome; it also comes with a 191 gram pin instead of the 225 gram pin supplied with the L2388.

[COKE]

Thanks John,but they are listed as 2.060(At least at Summit) and they aren,t easily available.

However,how much weight difference can be between two pistons whitout the need to rebalance the crankshaft again?

Thanks.

[John_Kunkel]

OOPS!! KB-184 is the 1.992" CH piston.

[redgum78]

Hey Coke just thinking out loud here. Could you make up the weight difference or at least get closer to what you need using heavier pins alone?

[BSB67]

Are you sure they are 2388's?, or what ever the 1.926 piston is?  Was the block cut 0.060"? you need to understand why the compression distance is only 0.070"

TRW/Speed Pro 2266 might be a replacement that has the same weight.

[COKE]

Hey Coke just thinking out loud here. Could you make up the weight difference or at least get closer to what you need using heavier pins alone?  


Hey redgum,
No,the icon pistons are 141g lighter,the pins wouldn,t make very much.
Besides,the 2388 have the heaviest pins ever.

Are you sure they are 2388's?, or what ever the 1.926 piston is?  Was the block cut 0.060"? you need to understand why the compression distance is only 0.070"

TRW/Speed Pro 2266 might be a replacement that has the same weight.

Yes they are.The part number is stamped on the piston head.
0.070 is the deck. the Comp distance is 1.926 for these pistons.

The block height is 10.6299" so isuppouse that it has been cut,this is a trouble, cause almost all the Flat&V.relief pistons are 2.060 comp height,and they would seat over the block surface(negative deck).
The solution would be a 1.991 comp height piston.This would get a zero deck and 10.1:1 CR on this block,six pack style.

[BSB67]

the 2266 are stock replacement 1.99s

[COKE]

Yes,but they don,t have valve reliefs.
They would sit at 0 deck in the block i have,but i would have valve clearance troubles.

[BSB67]

How do you know you will have clearance problems? What was your clearance with the 2388s?, how big is your cam?, and where was it installed at?

The original block was probably 10.720"+.  If you are at 10.630", that suggests that the block has been cut more like 0.090", unless I've missed something here.

If this is the case, you will have other fitment problems with the intake, unless you cut either the head intake surfaces, or the intake at least 0.090".

[COKE]

That is what i belive.The block has been cut 0.090" or so.

No idea about the valve clearance between the 2388 and the 906 heads i had before, or the MP alu 84 cc i have now,but a flat top piston 0 deck without valve relief is more like it is going to be in contact with the valves.I have read in some article that you need at least 0.030 deck if you are using no reliefs flat tops.
Look the six pack pistons,they sat a 0 deck and had valve reliefs.

I still didn,t buy a camshaft but i was considering a.518 or maybe  .525 lift one.

[BSB67]

Look the six pack pistons,they sat a 0 deck and had valve reliefs.

Not because they needed them from the factory.

If something like a Comp Cam XE275HL is what you are planning,  it might have enough clearance, might not.

You could buy the cam you want, assemble what you have, and check the clearances and determine from that if the 1.99 flat tops will clear.  If not, determine what amount of fly cutting that you need, and have that done.   I don't think that the piston you want is a shelf item, and therefore, to achieve your desired outcome does not appear simple

[firefighter3931]

There are a couple of options here :

(1) install new pistons and rebalance ; the pistons will have to be custom made most likely and the whole deal will be expensive.

(2) Mill the cylinder head deck surface .050 to reduce the chamber volume if you want to keep the existing shortblock intact. This would be the more economical way to go.



Ron

[BSB67]

There are a couple of options here :

(1) install new pistons and rebalance ; the pistons will have to be custom made most likely and the whole deal will be expensive.

(2) Mill the cylinder head deck surface .050 to reduce the chamber volume if you want to keep the existing shortblock intact. This would be the more economical way to go.



Ron

You realize that will be a total of like 0.140" off the block, as it has already been cut 0.090".

[firefighter3931]

There are a couple of options here :

(1) install new pistons and rebalance ; the pistons will have to be custom made most likely and the whole deal will be expensive.

(2) Mill the cylinder head deck surface .050 to reduce the chamber volume if you want to keep the existing shortblock intact. This would be the more economical way to go.



Ron

You realize that will be a total of like 0.140" off the block, as it has already been cut 0.090".

Ya, not ideal but it should work out to ~ .100 with a .039 Felpro 1009 head gasket and a nice bump in compression. There will also be some manifold surfacing required. Not the best way to go for sure but the OP lives in Spain and has few resources/options available. 

The other option would be to leave it as is and cam accordingly for the low static compression and live with the outcome.

If it were mine ; I'd just get another block and start from scratch with new pistons and rods. 


Ron

[firefighter3931]

quote author=BSB67 link=topic=88861.msg1006245#msg1006245 date=1329354524]
Are you sure they are 2388's?, or what ever the 1.926 piston is?  Was the block cut 0.060"? you need to understand why the compression distance is only 0.070"

TRW/Speed Pro 2266 might be a replacement that has the same weight.

Yes they are.The part number is stamped on the piston head.
0.070 is the deck. the Comp distance is 1.926 for these pistons.

The block height is 10.6299" so isuppouse that it has been cut,this is a trouble, cause almost all the Flat&V.relief pistons are 2.060 comp height,and they would seat over the block surface(negative deck).
The solution would be a 1.991 comp height piston.This would get a zero deck and 10.1:1 CR on this block,six pack style.
[/quote]


If the 2266 pistons bring you to zero deck then use them.....there will be no need to rebalance. 

Don't worry about valve clearance....you'll have plenty unless you go with a big duration cam. The Edelbrock heads don't have the valves in the stock location anyway so a stock replacement piston like the 2355 with reliefs doesn't help with piston to valve clearance. I had a large solid lifter cam ; 264@.050 & .580 lift with a zero deck 2355 6-pack piston and we ended up with .080 intake/.100 exhaust piston to valve. I doubt you'll be running anything like that.

This seems like the most reasonable path to incresed compression without hacking the new heads 


Ron

[COKE]

There are a couple of options here :

(1) install new pistons and rebalance ; the pistons will have to be custom made most likely and the whole deal will be expensive.




Ron

Not  necessarily.
Like i said before, KBs Icon have a set wich has a 1.991 CH Flat top and valve reliefs.
This would sit at zero deck in this block,and the CR will go to 10.1:1

The trouble is that i don,t find nobodody around here who has the bobweight machine for V engines balancing.

[COKE]

You realize that will be a total of like 0.140" off the block, as it has already been cut 0.090".
[/quote]

Ya, not ideal but it should work out to ~ .100 with a .039 Felpro 1009 head gasket and a nice bump in compression. There will also be some manifold surfacing required. Not the best way to go for sure but the OP lives in Spain and has few resources/options available.  

The other option would be to leave it as is and cam accordingly for the low static compression and live with the outcome.

If it were mine ; I'd just get another block and start from scratch with new pistons and rods.  


Ron
[/quote]

Ron,

We were writting at the same time and i missed you last input.
I also would like to get another block,but here you wouldn,t have too much luck looking for cheap junky yard 440 out of a Motorhome.
So i have to defense myself using what i have.

I don,t want to shave the block more than it is ,it would limit it to the usage of the pistons that it has now.(However somebody from othe forum said me that you will get more CR shaving 0.010 from the block than0.010 from the head,due they are closed chamber heads.)

It also happens too is that not all the cyls have the same deck clearance.
These are the meassures:

Cyl #1: 0.070"
Cyl #3: 0.070"
CYl #5: 0.070"
Cyl# 7: 0.066"


Cyl #2 :0.062"
Cyl# 4 :0.062"
Cyl #6 :0.062"
Cyl #8: 0.062"

So i will need to take the engine for equating all of them to 0.062"
Also yesterday i tried to mount the intake and i couldn,t,at least using the valley pan facing pieces.

Jorge

[BSB67]

It also happens too is that not all the cyls have the same deck clearance.
These are the meassures:

Cyl #1: 0.070"
Cyl #3: 0.070"
CYl #5: 0.070"
Cyl# 7: 0.066"


Cyl #2 :0.062"
Cyl# 4 :0.062"
Cyl #6 :0.062"
Cyl #8: 0.062"

So i will need to take the engine for equating all of them to 0.062"
Also yesterday i tried to mount the intake and i couldn,t,at least using the valley pan facing pieces.

Jorge

It would be nice to make them all even, but you really don't have too. They have come from the factory far worse than that.

[firefighter3931]

It also happens too is that not all the cyls have the same deck clearance.
These are the meassures:

Cyl #1: 0.070"
Cyl #3: 0.070"
CYl #5: 0.070"
Cyl# 7: 0.066"


Cyl #2 :0.062"
Cyl# 4 :0.062"
Cyl #6 :0.062"
Cyl #8: 0.062"

So i will need to take the engine for equating all of them to 0.062"
Also yesterday i tried to mount the intake and i couldn,t,at least using the valley pan facing pieces.

Jorge

It would be nice to make them all even, but you really don't have too. They have come from the factory far worse than that.

I tend to agree with Russ ; it's not that important for a street type build.  It won't be perfect but it'll be good enough and still make lots of power. 

The 2266 speedpro's are the way to go ; least amount of work for the return on effort. No machining heads, no machining block.....just install the pistons and go. You will probably have to do some intake manifold milling to get the ports to line up based on your comments. If the block is indeed .090 below spec then that will be the case. I'd rather surface a $200 intake instead of a set of $1600 heads. 



Ron

[COKE]

Really?
Is 0.010" deck difference between cyl admissible?
The cr varies 0.16!

About the pistons,my intention was to mount an hydraulic cam,for street use,looking for good low rpm torque,nothing for the track.Around 518 or 525 lift  and  226 to 232 int  and 234 to 245 Ex. duration.
Somebody has suggested to me a lunati 494/513 lift and 286/276 duration(Maybe too much duration).
I,m confused about this i don,t know what i could use with 0 deck and 10.5:1CR.

Thanks again for you invaluable help.

[firefighter3931]

Really?
Is 0.010" deck difference between cyl admissible?
The cr varies 0.16!

About the pistons,my intention was to mount an hydraulic cam,for street use,looking for good low rpm torque,nothing for the track.Around 518 or 525 lift  and  226 to 232 int  and 234 to 245 Ex. duration.
Somebody has suggested to me a lunati 494/513 lift and 286/276 duration(Maybe too much duration).
I,m confused about this i don,t know what i could use with 0 deck and 10.5:1CR.

Thanks again for you invaluable help.

The difference between the left/right sides of the engine is not significant ; if you had a full point of compression difference that would be worth fixing. This is just a street motor....not a blueprinted race build 

The 303 Lunati cam would be an excellent choice for this build....lots of low end power and torque, good street manners and descent top end charge. This type of build should make ~ 475hp/520tq 



Ron

[COKE]

Thanks Ron

I hate being so boring so these are my last questions:

-I have used the CR calculator with the L2266 pistons specs  and the CR jumps  to 10.8-10.9  wich i think that is tooo much .This would be using the 0.039 gasket.

Using the 0.050 gasket the cr would be around 10.5:1.
My doubt is about the quench.With 10.5 and that distance between the piston and the head, will it not cause detonation issues?

-About the usage of the 2266s:
The 2388 i have now weight 827g + the pin 224g = 1051 g
The 2266  weight 875 so i would need a 190g for compensating
875+190=1065g

Is a 14 g heavier admissible or will it need to rebalance?

Thanks again.
Jorge

[firefighter3931]

Are there other pin options available ? Personally i'd like to see a 5gram difference (or less) allthough stock factory built engines were all over the map 



Ron

[BSB67]

Are there other pin options available ? Personally i'd like to see a 5gram difference (or less) allthough stock factory built engines were all over the map 



Ron

How much do you think he could reasonably take out of the piston,  maybe 5 grams?