Russ: 3/31/2000 - 6:58:09 PM
Pop Up Pistons
Has anyone out there ever used Ford pistons with a 4 1/8 stroke Merc crank? I realize the norm would be a Merc Piston, but how about cutting the combustion chambers in the heads to accomodate the 'poped up piston'. Some of the piston dome could be turned down as well. I am thinking of a street machine application. How much can be cut from a stock head if any? How about the speed equip aluminum heads, how much can you safely cut from them? Were only talking about 3/16' needed from the head, without trimming the pistons. Am I way out on this, or is this a viable approach for some more horsepower?

Sonny Ayers: 3/31/2000 - 7:31:32 PM
RE: Pop Up Pistons
Hi Russ, I'm new to this forum, and haven't worked on a flathead in years. That said, I still have some ideas about your questions. If you use ford pistons the pistons will pop up almost out of the block. :-) Pistons accomodate the the different strokes by having the wrist pin higher or lower. The Merc pistons would jump out of the block 1/8 inch and even if you cut them down and milled out the head you wouldn't gain anything. Best to go with the after market 'racing' pistons. Sonny

Sonny Ayers: 4/1/2000 - 4:57:03 PM
RE: Pop Up Pistons
Duhh .....Oh well if you were to use 3-3/4 inch pistons in with a 4 inch crank they would pop up 1/8 inch. Maybe I have been away from this stuff too long. ....Sonny

rodnut: 3/31/2000 - 7:44:00 PM
RE: Pop Up Pistons
Unless you have a lathe and mill to do the work, the cost of having it done would likely exceed the cost of new 4 1/8'' stroke pistons. Flathead pistons don't leave much to machine from the crown without seriously weakening the crown. You could get away with removing SOME material above the piston on most aluminum heads, but certainly not 3/16''. I would not recommend it. The stock heads probably wouldn't tolerate much at all. Plus, the thinner you make the casting, the hotter it will run. Why do you ask? Do you have a 4 1/8'' crank? I ask because you really aren't going to gain much in the way of useable torque here to justify the work/cost involved.

JWL: 3/31/2000 - 8:19:26 PM
RE: Pop Up Pistons
First, no, I have never used Ford pistons with a 4 1/8 crank. There have been heads designed for pop-up pistons but I think only Navarro has them today. The stock heads won't take a 3/16 cut, but most aluminum heads probably could. There is a potential horsepower improvement available because more extensive work could be done to the transfer area of the head for better flow without compromising compression as much as a standard configuration does. I don't think this would be an inexpensive venture. Also, the major area of improvement would seem to be available in the upper RPM ranges which don't get much exercise in a street machine.

Jim Marlett: 3/31/2000 - 9:00:09 PM
RE: Pop Up Pistons
Making pop up pistons by using ford pistons on a Merc crank has been done for years by those who choose that route. As the folks above have noted, the important part of this is to make sure the rings stay below the block surface. The Baron race heads use this principle, but I don't know which combinations they are designed for. These were the best flowing heads in Mike Davidson's tests. According to Barney Navarro, since the head crawls around a little bit it is hard to get a tight fit on the side of the pop up and that results in end gasses. That is why he uses an extended dome with the edges at the block surface. Iron heads might be a better choice for a pop up piston since they would theoretically expand at the same rate as the block, making closer tolerances possible. I don't know if stock heads can be machined that far. Some racers recommend that a 45 degree cut be made on the piston where it sticks up above the relief and I assume one could infer the same could be recommended for the part that sticks up into the transfer area. The object is to reduce the rocking motion of the piston when the fire is lit. One nitro racer told me he could actually hear the pistons knock as they rocked until he started cutting them. I can't imagine how he could hear that over nitro, but he says he could.

Russ: 3/31/2000 - 11:37:20 PM
RE: Pop Up Pistons
It's clear to me the pistons would be above the block half of the increased stroke. The idea to improve flow by moving the combustion chamber up in better relation to the valve plane, and as JWL stated without compromising compression. Some pistons are meatier at the crown than others, so that can be taken into consideration. I am inclined to agree that the stock iron heads are going to be a great gamble and that aluminum heads although meatier than iron heads are a gamble also. The project is theory at this point, with a friend to be the brave one. A new engine for a 34 coupe, authentic mcculloch supercharger included. Any recommendation as to cam duration for best drivability? This project is going to move on. I'll keep you all posted. Maybe get some pictures to share.

Jim Marlett: 4/2/2000 - 12:21:47 AM
RE: Pop Up Pistons
Unless you just want to do it yourself, go buy some Baron heads for pop-up pistons. As far as I know they are still in business. The phone number listed in Frank Oddo's book is (818) 702-0043.

Harlan: 4/1/2000 - 10:06:40 PM
RE: To Sopp
If you call Offy there tech can tell you how thick there head is for machining. I called to ask for I wanted to open up a set of late modle heads to drop compression to a lower #8.5. As for cam ,M.C.F. recommends a very mild cam. If you call they are very helpful.

trader: 4/2/2000 - 5:16:24 PM
RE: Pop Up Pistons
I have run the ford pistons on a 4 inch crank in a (relieved) 59A, block with good results. However, there is the top ring, right at the relief. Jim Martlett, was right on the money, when he said, to make sure the rings stay below the block surface.. If your block is relieved, then you have a new area of concern. I do not know what type of piston you are talking about, but you better check to see what the distance of the top ring land is!!! A piston with a .250- .280 inch top ring land is necessary for most relieved blocks. Raise the piston .187 inch beyond it's design limit, and you may loose the tops of the pistons, if the ring snaps out, or is burned out. Are you talking about(factory)dome pistons, or popups?? Barney Navarro made pistons, which were similar to a (Chrysler)hemi-dome, to fit some of his cylinder heads. At first it sounds as if you are trying to build compression? Next you mention you want to add a McCulloch supercharger? You want to help him from here,WALT Dupont???

Walt Dupont: : 4/3/2000 - 4:18:58 PM
RE: Pop Up Pistons
Russ. If your going to run a supercharger get this pop up piston buisness out of your head. It's hard enough to keep the compression down as it is with a bored and strocked engine. As for a cam i'd save my money and run stock cam. You don't want much overlap on a street engine with a blower. Did i tell him Trader? Walt

Russ: 4/3/2000 - 9:56:17 PM
RE: Pop Up Pistons
Thanks all for the input. I will share your comments with my buddy and see what decision comes out of all this. I think he is feeling brave. This is whats in store at this point. Edelbrock heads ( one early 24 stud and one 8ba due to clearence problem with the hoses ) milled to accommodate stock ford pistons with a 4 1/8 crank. Pistons trimmed, 280 degree cam - think it's an isky grind. The Mccullogh is running on his current 21 stud. He's gonna do it! He is a old time hydroplane racer, was on an Indy team once also. He is doing all his own machine work, except for the crank grind. Should be interesting Will keep you posted.

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