Piston Deck Hight

[Marvin S]

Can some one help me figgure this out.I just removed my engine today to go through it as it was rebuilt before I got and the guy dint know what was in it.Its a 67 440 with 915 heads That ran well but dint have much power.So I figgured that it has low comp pistons and a lazy cam.So heres what I found. Plain flattops that are .150 below deck surface and the cam was measured at actual valve opening with a dail indicator. It was around .340 for EX and IN.That sounds pretty poor.I was trying ti figgure the compression ratio of this rig with not much luck.So I guess that what Im asking in the way of a question. .150 below deck 79cc heads and a .040 overbore.Anyone have an idea. Many Thanks.

[DEMON SIZZLER]

Marvin, if your head gasket "compressed" thickness is at .039", then your compression should be about 8.3:1 and if you used a steel shim head gasket, the compression would be about 8.6:1, DAVID.

[Marvin S]

Thats one thing I forgot the head gasket it was the blue felpro and it compressed at .039/.040.

[ehostler]

Demon Sizzler hit that one. There is a good calc http://www.kb-silvolite.com/calc.phtml

[340duster1]

For your valve lift did you measure the valve or the pushrod movement? If you measured the push rod you would have to mutiply that by the rocker arm ratio (1.5)

[dirty dan]

You have .150thou below deck!
Man no wounder you have no power.
What you need is more squezzzzz.
Find a piston that will give you about .20 - .50 thou deck hieght.
And a cam simular to the 484 purple shaft .
This combo will give you a good dependable street engine.
The rest of the engine can remaine the same,unless your looking for more.

[Marvin S]

I measured the valve lift at the top of the rocker just above the valve stem. One other thing I noticed is that there was no intake manifold gaskets other than the valley tin. Is there not supposed to be a thin paper gasket on both sides of the valley tin.It looked like it had some vacume leaks as some exhaust ports where white and some black.Thanks guys.

[451Mopar]

With a piston 0.150" down, flat top with no valve reliefs, 440 (0.040") over, 0.039" compressed head gasket, and 84cc heads compression is 8.03:1.

You mentioned 79cc heads, which brings the compression up to 8.31:1 compression.

A 0.020: head gasket would increase the compression to 8.60:1 compression.

Normally the valley pan intake gasket is used without any other gaskets.

It sounds like the hydraulic plunger compressed when you measured the valve lift. You need to measure the cam lobe lift and multiply by 1.5, or you can measure at the valve, but you will need to use light weight "checking" valve springs, or a lifter that does not compress under the valve spring pressure.

[Marvin S]

Okay I went over and measured the actual cam lobe lift and came up with 300 and 305 so this puts it at about .450 that sounds a little better. Good point.

[451Mopar]

The stock 375 HP 440 cam has the same lift.
Specs for the stock HP cam are 268/284 duration,, 46 degrees overlap, 0.450"/0.458" valve lift.

[biggerhammer]

I would recommend decking the block some, and if you can afford it change pistons to a better one with the pin location lower in the piston

[Marvin S]

I was looking at getting Either the TRW L2266F piston which is forged and is supposed to give 9.1.1 with 906 heads guessing that this would get me about 10.1.1 or so with my 915 heads.Or was also looking at the KB silvo-lite pistons in a rated 9.0 to1 for a 88cc head.Also looking at the MP 280 .474 lift cam HD rockers and springs and the TCI breakaway converter with a new eldebrock 800cfm carb.

[ehostler]

A 440 bored 40 over with the 2266 pistons and 915 heads will give you 9.37:1 CR. you have to remember the 2266 piston are low compression pistons and sit .089 below the deck. The 906 heads (at 88cc) had you at about 8.67:1 CR.

Use the compression calculator at http://www.kb-silvolite.com/calc.phtml to get your numbers.

[Marvin S]

I think I finially got this compression calculator to work. I compared a figure out of one of my books and it came out the same for a TRW L2310F 022 deck 80cc head .035 gasket 10.6to1. Man this piston selection buiness is tough work. One more question.I see alot of pistons advertised with compression dist say 2.065 what does this mean to me.Thanks for all the help

[deadhorse66]

I think that is another term for compression height. It is the distance from the center of the wrist pin bore to the crown of the piston. You can use this to figure on paper how much below the deck your piston will be after assy. Add 1/2 of stroke to rod length to compression height and subtract that from the deck height of the engine and it will tell you where the piston will sit in the cylinder @ tdc.

[Marvin S]

Kind of figgured it was something like that.Everybody has a new term something. These companys could sure make this alot more friendly to use. Okay now what would be the hight in the bore of the wrist pin center on a stock 440block so I can add the comp dist to this to get an idea what im looking at. Again THANKS

[deadhorse66]

1/2 of stroke (1.875) + rod length (6.768) - deck height of RB engine (can't remember..10 something)=compression height of piston which reaches zero deck with otherwise unmolested parts. Just subtract where you want your pistons to deck from that (ex.--.080 below) and you will have your desired compression height.