Please help me ID my compression ratio and choose a piston.

Guys,

I'm rebuilding a 1969 440 HP that was last rebuilt in the mid-90's. It's .030 over and has pistons marked TRW L2266F. The heads are stock 88cc 906's. Looking the pistons up, it says today's version are a 8.66:1 compression ratio with stock 88 cc heads. These pistons don't come up to deck height, so they probably are 8.66. Does anyone know if a TRW piston from the mid-90's is the same as today's version from Speedpro? Does that compression sound right?

I'd like to put the 440 back to stock specs including the compression ratio, or at least very close. I could live with anything from 9.8 to 10.2 as the final compression. I don't mind running race gas. What modern day piston would give me that or put me close? 8.66 sounds like a slug.

Thanks!!

You want to use one of these:

Icon IC9953

Keith Black KB237

Sealed Power L2355F

2266’s have always been down the hole about .090” on a stock block.

Yes, there are essentially the same and have the same compression distance of 1.991". Depending on head gasket, actual head cc's, and any decking the CR can be anything from 8.35 to 9.0. The 8.6 is probably close.

If you're truly looking to up your performance, think now about cylinder heads. If budget does not allow for both pistons and heads, I would consider heads before pistons.

Uncut block at 10.725, 88cc heads, .040 gasket....... you’re gonna be in the 8.55:1 vicinity with 2266’s.

Starting with that scenario, swap to the Icon IC 9953 pistons, mill heads to 83cc...... puts you at 9.85:1.

Decking the block to zero brings it up to 10.17:1.

my 2 cents; decide what kind of gas your going to use first.

Along that line of thinking......wanting to run pump gas......

The pistons I mentioned above, along with an 84cc closed chamber head(edelbrock), zero deck, and a .040 gasket puts you right in that 10:1 area.

To run the open chamber iron heads and have decent CR, and live on pump gas....... use KB184’s, and adjust the heads and block for proper quench.
It will usually end up at around 9.6:1.

So, assuming a stock cam, how is the horsepower and torque affected by running 9.6:1 instead of 10:1? 50HP? 10HP?

If the old rule of thumb about 1 point of compression = 10% has any validity, I'd say 10ish.

Kevin

Blue printing the motor including degreeing the cam and getting the best tune up from the motor you may see 100HP + gain
I've built a bunch of Hi Po stock stroke single four barrel pump gas street motors that made over 430 HP easily, the last one had a really goofy solid lifter camshaft in it that was ground on a 101 LSA installed at 99 ILC with around .550 net lift at the valves
That motor had a set of mildly ported 906 heads that had 2.14 intake valves with 1.81 exhaust valves, I made all eight combustion chambers have between 84.0 to 84.5 CC in them. They varied over 4.0 CC before starting to blue print that motor. It ended up with right at 9.5 to 1 compression ratio with a set of SRP pistons and it had a Holley 850 CFM D.P. mounted on a Eddy Performer RPM intake, the owner loved that motor
He said it would pull real hard up to 7000 RPM where he would shift because he was afraid of the stock blueprinted LY rods Probably a good choice
Be careful and have fun
EDITED: All the stock 906 uncut heads I have checked where all above 91.0 CC
I had the set of 906 heads I used on my first pump gas 511 C.I. stroker motor cut to 84.0 CC, that motor had dead on 9.25 to1 compression ratio and ran good It made 612 HP at 5500 RPM and 645 Ft. lbs. torque at 4500 RPM with a low deck six pack set up in a patched up 400 block with four sleeves n it That motor far exceeded my wildest expectations

big horsepower gains from 9.6 to 10 are rubbish. maybe 2% difference at very best. I've been thru this on stock or near stock engines. BB mopar's had awful combustion chambers. if using pump gas your much better off dropping the compression and using more timing than raising compression and backing the timing off. reconfiguring the combustion chamber with a quench dome piston is best. if that can't be done stay around 9:1 and let some head mods more than make up for any power loss.

I think the part you're missing is the Eddy head will make more power even with the same compression ratio. Making your 88 cc heads as good as the Eddy heads will cost more than the Eddys.

Thanks for the info guys. This engine will run stock 906 heads. I don't mind using race gas and setting the timing where it should be. It gets driven so rarely, the extra cost doesn't really make an impact.

Hmmmm. Let me see if I understand. You want less power, and use race gas. Put a domed piston in if you're buying race gas.

setting the timing where it should be

The correct timing for the completely stock engine?

No. The question is, how to keep compression at or around 10:1 using stock 1969 906 heads and 1969 440 block. This is not a how do I make horsepower question. Using today's selection of pistons, which is best to meet the requirement stated?

Yes, as in, I'm not retarding it to prevent spark knock.

The question has been answered.

One of the 3 flat top pistons I listed, deck block/mill heads/gasket thickness to arrive at 10:1...... done.

If you don’t want to mill anything....... you’ll need to have custom pistons made.

Somebody has to have a shelf stock piston with a CH that gets him close to zero deck.

The Ross reverse domes in my 493 needed .007 to zero it with a 76 440 block. It was a 440Source kit and the only thing custom that I recall was the dish volume. The CH was whatever the kit came with for a 4.15 stroke 440 based 493.

Kevin

Wiseco Pro TrueStreet forged flattops will also yield close to10:1 w/ stock dimensions. Todd Marsh sells them for about $450 for a set of 8 and that's WITH rings.
I built a '71 HP 440 engine last year w/ those pistons and they will sit about .025" down in an undecked block. They were .018" down in mine, so w/ a .039" head gasket I got 10.1:1 w/ a set of 346 casting heads that had 82 cc chambers. The heads had only been cut .025".

In theory, the stock uncut block is 10.725”.

With correct stock length rods(6.768”), and a crank that’s an actual 3.750” stroke, a piston with a ch of 2.067” would be down the hole .015”.
I haven’t seen any stock stroke shelf pistons any taller than that.
The Pro Tru piston is shown as having a 2.050” CH.

.030 over 440, uncut block, 88cc Head, cometic .027” gasket, Icon 9953’s......9.7:1.

The “correct” 68/69 440HP piston is a flat top without any valve pockets, with a 2.031” ch....... which would sit down the hole .051”.
This piston provides the same CR as the factory 6bbl piston.
The added CH of the 6bbl piston is to offset the loss of CR from the 4 valve pockets.

I have the 2.05 pro tru pistons and only ended up at 9.7 to 1 with a 80cc head.
The speed pro 2295 hasn’t been mentioned. If it were my engine I’d leave the short block and run the 75cc budget Edelbrock Head.

I don’t believe they’re available any longer.

Besides, there are plenty of better options nowadays.

I would have to completely disagree with this. You are not going to get a 10% increase in power with a one point increase in compression. More like 3 to 4 percent maybe, with the gains being greatest on really low compression engines. The difference between 9.6 and 10.0 on a stock 440? Wild azz guess,5 hp. Maybe. Or less. You will never know the difference.

You could see just about a 3% increase in power going from 9:1 up to 10:1.

So, on a 350hp motor....... about 10hp.

Yes, thank you! I am looking at those now.

I appreciate everyone trying to help and was answering clarifying questions by others.

Whichever I choose, I will get the block decked to make up any difference.

a simple solution if all the OP wants is a 10:1 factory type 440. just mill .030" off the heads and use a .020" steel shim gasket and your there. keeping in mind the only difference between a factory 10:1 engine and what's there is the location of the top of the piston. the top of the piston is the floor of the combustion chamber but it's expensive to move the "floor". just simply move the "roof" of the chamber down and the relationship between the two will be near identical to a factory 10:1 engine. if the 10:1 thing is what I wanted; then this is the easy way there. of course we need to keep in mind that the10:1 engines were never a true 10:1 compression and these engines are not pump gas friendly.

as far as timing goes the service manual gives specs. 5 degrees BTDC for initial with an automatic trans an zero for manual and 35 degrees total (staged with a light spring and heavy spring). duplicating a factory curve will depend on having the correct springs and plate.