I bought a set of heads on Ebay cheap. They are the 3986133 heads. They are the semi closed chamber. Just wondering what compresion that will give me in a .030" over 396 with TRW L2240NF pistons, with a stock head gasket, and the block decked.(Not sure how surface was taken off) They have to be better than the 781's I took off it. Just wanting a ball park figure.

What are the specs on the 2240's?

it wont be much, the 2240 pistons are advertised at 9.59 to 1 with 100.9 cc heads per there listing. and those '133 heads are shown as open chambered heads more then likely 112 cc or better and the 781 spec out at 118 cc's

at the best you might be looking at 8.4 to 8.5 to 1 compression giving a rough est. since we are lacking more details about your motor specs.

your best bet would to find some actual closed chambered heads in the 90cc range to get the compression up to a respectable range for a performance engine.

if your heart is set on the heads you have just bought the best things you can do to them is to put in new larger valves 2.19/1.88 to help lower the chamber size and to use steel shim gaskets from mr gasket since they actually measure .018 compressed ( this is the measurements i get on my mr gasket steel shims that have measured many times) most say they are .022 but really they are thinner then that.

this might get you close to 9.0 or so going this route. still this is only a rough guess until we have deck height and better cc information on the 133 heads and the domes.

no matter what i doubt you would ever see anything over 9.0 to 1 using the '133 heads as they are.chambers are just to big.

more then likely the current heads you have 781 are around the 8.0 to 1 mark or less.

2240 pistons are direct replacement for the 325/350hp 396 motors. even tho they spec out at 10.25 in the books for these motors most often they was less then this. but they also ran around 96 cc chambered heads on these motors.

This is the info from the Speed pro version

396ci Closed Chamber Head Stock-Type Piston, .030'' Overbore
Piston Dia.: 4.124''
Piston Top: 21cc Dome
Pressed Pin
Comp Ratio: 8.05:1 w/100.9cc Heads, 7.10:1 w/119cc Heads
Ring Grooves: 5/64'', 5/64'', 3/16''

Mortec doesn't list the bowl size for your 133's, any idea how big they are?

BTW, the 781's are listed as 118cc

Originally posted by rthlc:
This is the info from the Speed pro version

396ci Closed Chamber Head Stock-Type Piston, .030'' Overbore
Piston Dia.: 4.124''
Piston Top: 21cc Dome
Pressed Pin
Comp Ratio: 8.05:1 w/100.9cc Heads, 7.10:1 w/119cc Heads
Ring Grooves: 5/64'', 5/64'', 3/16''



BTW, the 781's are listed as 118cc I believe those pistons are with the domes removed. I have .182" domes on my pistons. smile.gif

These heads would be good with a Comp HE268H wouldn't they? Also a high rise cast iron dual plane? Can I run the 268H with stock valve springs? I have on small blocks alot. Just wondering if the stock springs would be strong enough?

The 8.05:1 w/100.9cc Heads is with the domes removed for sure.
As ddeennis mentioned,go with the bigger valves and the steel shim head gasket.I'd get the heads milled too.

Originally posted by mr 4 speed:
The 8.05:1 w/100.9cc Heads is with the domes removed for sure.
As ddeennis mentioned,go with the bigger valves and the steel shim head gasket.I'd get the heads milled too. I would, but I am just putting it together to sell it.(probably) I have a new roller cam 468, so I don't really need/want it. It would make an excellent motor for someone! smile.gif