1970 lt1 deuce pistons
 

hi

can some one tell me if the the original pistons for my deuce should be LT1 350 "std" or .030 over pistons.........and they should be press fit correct?

also are the 69 302 pistons the same .030 over dia pistons except they are floating pin?

thank you so much

regards
chris

Original "LT-1" pistons for your Deuce would be standard size with press fit pins. 69 Z-28 pistons had floating pins. I think the pin height of the 350 pistons versus 302 pistons is different as well in addition to the press pin versus floating pin. Pin heights vary due to crankshaft stroke being different on the two engines.

I'm sure one of the engine gurus will chime in, but that's what I recall.

To the best of my knowledge the LT1 was a standard bore 11:1 high dome piston....these pics are from my 70 Z28 engine rebuild. Note part number stamped on the top of each piston...

LT1 pistons and 302 pistons look similar, but as noted, because they use the same length rod, the pin height is different.

The dome on the 302 is slightly higher, but barely noticeable.

69 L46 used the same piston as the 70 LT1. Both are press fit as noted, although the pistons have provisions for spirolox, so would be easy to convert to floating. No performance gain.

Wiseco Pistons will work fine and pink rods are really not necessary.

so that i am clear

for my LT1 deuce

1) the pins will be press

2) the pistons have to be for LT1 sbc NOT 302 sbc

3) pistons i need are GM#3959456 or GM TRW L2304 replacement?

i also read here on the site that they should be .030 over??
is this correct or not??
should they be 4.000 dia OR 4.030 dia?

im reading different things?

thanks so much
regards
chris

The LT1 came from the factory with a 4.000 inch bore. If the block has not been bored oversize then you need pistons for a 4.000 inch bore. If the block has been bored oversize then you need to know how much it has been bored and get pistons to fit your bore size. If your block is worn and needs to be bored then you will need to talk with your machinest and figure out how much it needs to be bored and get pistons to fit after it has been bored.

i understand boring a block as i have several drag cars that i built engines for

my issue was i did not know if the LT1 came with 4.00 inch bore OR 4.030 bore due to the fact i had read some many different things on this site and others

i felt that it could have been very possible for don yenko to bore the yenko engines out for several reasons

thanks everyone for the answers

i will continue looking now for LT1 4.00" OD forged GM TRW pistons

thanks again
regards
chris

FYI All of your pistons are in backwards. Im guessing including the Thrust side of the rods...

hi

kenmaisano post comment

this is not my deuces engine pictured here.......picture was posted by another site member to show piston part numbers

thx
chris

You are very observant Ken...this was the first time I ever tore an engine down and rebuilt one and when we reassembled we put the pistons in backwards....fortunately after we bolted one of the heads back on and tried to rotate the crank and the pistons were hitting the valves, we realized our mistake and took all the pistons out and rotated them all 180 degrees. Boy, you can't get anything past the knowledgeable people on this site :-)

Great looking cars , I would think the bore is 4.00”
Maybe your confused with the 396 in 70 was 4.030 bore if I’m not mistaken..
What are wrong with the original pistons ? If your going to replace them I would measure the bore for roundness before ordering pistons , so if it’s out of round it could be fixed & have the block machined for the new pistons..

If bore is in good shape, a simple hone and new rings could be the ticket and you can re-use the original pistons. Any competent machine shop can point you in the right direction. I wouldn't purchase any parts until after tear down and inspection by the machine shop.

X2 COPO. Good advice!

Factory LT1 pistons have a .100 dome hite and were forged pressed pin, 302 has .200 dome hite and were forged as well with floating pins.

As noted 302 pistons have a different pin hite location in piston due to only 3” stroke, LT1 has a 3.48 stroke crankshaft, rods are the same length at 5.7”

Original LT1 was a 4.00” bore as noted, it makes sense to measure your bores for wear and if needed bore to .030.

Aftermarket L2304 are available in .030 & .060 only, some company’s make a cast type LT1 piston in .020/.030/.040/.060

If your motor did not have forged pistons originally you should have it rebalanced as piston weights are very different between cast and forged.

I do have a set of std & .030 I’m thinking, pm me if interested.

Hope this helps.

Mike.

There was a Speed-pro (TRW forged) piston available at one time in 40 over:

https://www.summitracing.com/parts/slp-lw2304f40

It was a lightweight forging, hence the LW.

I looked for them but could never find any available.

I can't imagine any 48 yr old block having absolutely perfect 4.000" bores without taper, etc. If you really want to do it right, I would suggest going 0.030" over and using any aftermarket LT1-style piston.

I guess you could get away with stock pistons and standard bore if you have a really great block, only want to idle onto a show field, and don't mind loose piston-to-bore clearance. These cars were driven hard when new, and it's pretty likely that they will ALL have some bore wear.

Here's the PDF showing all the pistons from Speed Pro including the L2304F at .040. Not sure they still make them but they are still listed.

I ordered the .430 domes last year and had them milled down for 11:1 compression in my 302.

I agree completly, I have also gotten away with coating the piston skirts to tighten up the bore clearance somewhat if a budget is a concern? The L2304 can be run up to .005 ( IMO ) without skirt clatter when cold, let’s face it lots of these collector cars don’t see a lot of mileage every year, especially if you live in climate that has snow for up to 6 months like we do, or have your stuff in indefinite storage , LOL like me.

FWIW - the new version of the L2304 with coated skirts is no where near as nice as the older versions, not only is the pin 18 grams heavier, they are usually all over the place on pin fit, I just used a set of .060 and they were anywhere from .0001 tenth to .0006 tenths clearance. Plus the domes are almost a cast type rough finish. They L2304 domes are .200 give or take, the current L2210 - 302 piston comes with a .430 dome and must be machined to around .200 ( depending on chamber cc and head gasket parameters ) to achieve the original 11 to 1 compression ratio.

Hope this helps.

rszmjt

hi mike

i sent you a pm regarding the pistons

thx
chris

I have a used set of these GM#3959456 pulled them out in 1986 or 87