Hey fellas I have a question about some mechine work I need to get done. I have a 454 destroked to a 427 that has 12.5:1 compression ratio. Forged TRW L-2300 .030 over Pistons with a .140 dome. Question is if I have the dome shaved off of the pistions will that reduce the CR enough to run on pump gas or pump gas + octane boost? Thanks in advance.
We need to know the chamber CC, deck height, and the head gasket you plan to use in order to accurately calculate it. I can say that those pistons have a fairly thin deck (at least the examples I've seen) and it may be difficult to completely remove the dome. However, with some effort it may be possible to get the CR down to what you need. Have you given any thought yet to a choice of camshaft?
Machinist - Wikipedia, the free encyclopedia <BUTTON class=vspib type=submit></BUTTON>I HAD MY PISTONS MILLED AT THE TOP I DO NOT SEE A PROBLEM BUT YOU DO NEED TO NOW THE THICKNESS OF THE TOP IF AND WHEN THE PISTONS GET MILLED, JUST TO KNOW OR FEEL CONFIDENT THAT YOU HAVE MATERIAL TO TAKE THE COMBUSTION BLOW OR HEAT. I WAS TOLD AS LONG AS YOU HAVE LOWER THAN 10 TO 1 C.R. YOU SHOULD BE OK FOR PUMP FUEL CORRECT? Knuck From Indiana.
The TRW BBC pistons (most of them) are a bit deceptive. Though some, (not all,) are capable of being milled to the point of complete dome removal while still keeping sufficient deck thickness....because of the valve angles and the corresponding notches, they can fail at the notch under moderate to heavy loads, or at the radius where the notch meets the (now) flat piston deck. This is exaggerated when using the larger diameter valves like the 2.25 or 2.30...and, of course, depending on the cam lobe lift. Some of the TRW/Speed-Pro designs are worse about this than others, but it's always something that needs to be considered when using any of this brand of forgings, and milling the dome, IMHO. For a mild pump gas street engine, it may never be an issue. For something that gets beat on, it can. There also is a tendency for them to have "thin spots" in the piston deck, so you have to be thorough when checking the deck thickness. I'm not trying to scare the OP- chances are that for a mild-to-moderate street engine, they will be just fine, even completely milled- but stuff like this should always be considered, as in, "Measure twice, cut once".
That flatlander site says they're about 10-1 with 100cc closed chamber heads, and can be machined flat ("with dome removed") to yield 8.5 to 1. I think open chamber heads are usually around 120 cc, so if OC is what your are using you start off around 8.3 leaving the domes alone. OC heads are a compression ratio reducer on a CC motor.
If it's de-stroked is the pin hole in the correct location on your pistons or do you have longer rods to compensate for the loss? Have you checked deck height? You have some homework to do. A 427 has a 3.75 inch stroke and a 454 has a 4 inch stroke. Your piston is gonna be .250 down the hole and you'll have REALLY low compression.
Uh, no, 4.0 dn to 3.75 is .125 in hole. There is another way to determine CR, find a whistler CR tester and check. Most if not all racing clubs and organizations have them. It is not perfect, but will give the current ratio and then you can calculate removal.
First off thanks everyone for there input and information. I bought this engine from a drag race buddy of mine and figured it would push my 34 around nicely. He was going to put this engine in his 69 Camaro drag car, but then sold the car. I wanted to see what kind of shape it was in (guess he's not that close of a buddy.) So I tore it down. It was all that he had advertised all new parts just rebuilt. The heads have been decked and gasket matched ported and polished. They are open chamber and originaly 113cc (6272292). I will get more info and get back, thanks again to all that replyed so fast.
I would be more inclined to open your CC up a bit and unshroud the valves than take a bunch o meat off the piston....a big cam will bleed combustion pressure as well.. Hans
Ok. Making some assumptions, as follows... 1) The heads, despite the decking, are likely close to 113cc as they sit. Those heads are generally larger, like 115-116cc, as cast. It's also possible that there's been chamber work, as well as a valve job, or two, and we don't yet know if they've had larger valves installed, which would tend to "raise" the valve back up as the new seat is on fresh metal. The head porter, may, or may not, have equalized the chambers. The only way to know is to cc them. 2) Using the Fel-Pro Q1037 gasket, which is a nice compromise for iron head/block combos, is relatively thin, and is a "small-bore" gasket. 3) Assuming a deck height of 0, which may not be accurate.... Moshing all that together, I get a static ratio of about 9.38:1. Keep in mind that you have a closed chamber dome design, being used with open chamber heads. That's fine and causes no particular problems, but explains why the actual compression is so far off from what you thought you really had.
Mechinist is a newly defined job field . The term was coined by a member of the HAMB . Machinists + Mechanics = mechinist think i might just start a wiki on that one if you guys like it
I once machined a set of TRW super high compression pistons for a friend building a Mopar 340. I was concerned about the amount of material left on the top and the only thing I could find on the matter was to leave all piston tops no less than .250" thick. Once I did some measuring, his pistons had something along the lines of .550" thick at the start. When I was finished it still was .300 or so, can't remember exactly. It just seems to me that all the forged pistons are extremely thick on top, just for such occasions were individuals need a custom set up. Best thing to do is when in doubt, call the manufacturer if you can, and get their opinion.
The old style TRW/SpeedPro pistons are thick on top.....and heavy. I ball end milled 200 grams out of each of a set of TRW flat tops for a 440. The guy ran a small shot of the funny gas and ran low 11's with a 3900 lb car. They held up much to my amazement.
Not really sure what the 340 or 440 Mopar pistons have to do with a very specific BBC piston design...and the statement that "all the forged pistons are extremely thick on top" is, with due respect, just silly. In addition, even if the piston top is a uniform thickness after milling (which it won't be), that will have little relevance to the thickness at various points around the valve notches. That's why we try to ascertain the state of things before we start removing metal. It appears that the poster won't need to worry about milling his pistons, anyway....and since he hasn't posted again, he has possibly resolved the situation one way or another.
The Jalopy Journal
