Qusetion about FLYCUTTING pistons

[TeamHawaiin]

I'm getting a headache trying to make a decision on what to do with these pistons I have. They are SBC TRW forged pistons that are for 400 chevy and 5.7 rods. I already have good 5.7rods and a 400 block that is standard bore but needs to be cleaned up. I really want to build this motor since I bought these pistons from EBAY for $250.00. They were assembled on an engine but never ran. They are new, just a few scratches where they dug out the keepers in the sides. They have floating pins.
Here's the problem, they are 12.5:1 compression I believe with a 72cc head from what I last read up on them. Part # is L2477. They are listed in the older JEGS magazines but not the new ones. I originally bought these pistons for my S-10 drag truck but I sold that truck to buy my ZZ4 350 powered Hawaiian jet. I want to pull that ZZ4 out to put in the 400 with big cam and tunnel ram, but I need to run this thing on pump gas. I was thinking about having a machine shop flycut a good portion of the dome off to lower the compression. The heads I presently have are camel humps ported heavily with fresh 2.02 valve job. The heads are only 58cc though. I was at least thinking of selling the heads to get at least halfway to buy some Dart heads or some good flowing heads with big chambers. Sorry this is turning out so wordy but I'm trying to lay all the info out on my first post. Any advice from you guys would be aprreciated. My main goal is to use the pistons I have but get the compression down enough to use pump gas.

[Moneypitt]

According to TRW, 7cc dome, 5.7 rod= -.020 deck, 64cc=12.55/ 68cc=11.95/76cc=10.9......Hope that helps..........I don't think there is anyway to run those pisons with those heads and pump gas, unless you machined a dish in them.......11cc dish would get you to the 10.8-11.0 range, BUT, how thick are the tops?....MP

[TeamHawaiin]

I will measure the tops tomm. You are wanting me to measure from the top or center of the pin to the flat surface of the piston?
I do have some 76cc heads from a 350 with 1.94 valves. Will I still need to drill steamholes if I use these heads?
I suppose I can really save a ton of cash by using these and hogging them out myself. I can use money saved on the tunnel and cam.
That # for the -.020 deck. This is if my block has been decked? I know for sure this block is virgin and has never been machined except from the factory.

[Moneypitt]

I will measure the tops tomm. You are wanting me to measure from the top or center of the pin to the flat surface of the piston?
I do have some 76cc heads from a 350 with 1.94 valves. Will I still need to drill steamholes if I use these heads?
I suppose I can really save a ton of cash by using these and hogging them out myself. I can use money saved on the tunnel and cam.
That # for the -.020 deck. This is if my block has been decked? I know for sure this block is virgin and has never been machined except from the factory.
The minus .020 in the hole is figured with the comp distance and the rod length. I assume the steam holes are to match the 350 heads to the 400 block?....Something I'm not familure with, but I seem to recall something about it.... The piston thickness is about the actual thickness of the material in the top. Could you machine a 11cc dish out and still have enough thickness. (7cc dome off, plus 11 cc dish= 18cc.........58 cc+18cc=76cc/10.9:1.......)
What stroke are you using? You didn't mention a crank, 400? I hope so, because those pistons are for a 400 stroke......There are several combinations of 350/400 parts to wind up with the 383 type engine, but, I would perfer the 350 stroke and 400 bore, quicker grabbing the Rs, and higher winding. The 400 is kind of a torque monster, but slow to rev up.....And your pistons won't work with the 350 crank and 5.7 rods....There are people here that are up on all this SBC stuff, maybe there are more ideas to choose from.........MP

[ol guy]

If you flip those pistons over and look past the wrist pin area you see that, do to keeping a weight that will spin rpm, there is no way you can fly-cut that piston to work with the heads you have, or any other head on pump gas. Now a light at the end of the tunnel!!! Back in the 80s One cam manufacturer built a 12.5 motor that would run on pump gas and I believe it was crane but the idea plopped. I would call chet or donny at herbert cams, they have played with the same idea and have more time on dynos and cam design than most people have been alive. They are now in chino ca. and I have used nothing other than what they recomend and have never been let down for thirty years. The numbers on the cam may not look right to you because so many people over cam boats but the proof lies in the performance of the product and trust the guys that have been doing it a while. JUST TELL THEM WHAT YOU GOT AND WHAT WANT and let expierence talk THen do-it M

[ol guy]

After thought. If your'e racing a class that requires pump gas, read above post, If it is a feul cost problem I have one last word. ALCOHOL!!!!!! not to drink but for the motor, Its a perfect combo for that. M

[Moneypitt]

After thought. If your'e racing a class that requires pump gas, read above post, If it is a feul cost problem I have one last word. ALCOHOL!!!!!! not to drink but for the motor, Its a perfect combo for that. M
I'll drink to that...........Old schoolers taught new schoolers, but not quite all of it....MP

[TeamHawaiin]

After thought. If your'e racing a class that requires pump gas, read above post, If it is a feul cost problem I have one last word. ALCOHOL!!!!!! not to drink but for the motor, Its a perfect combo for that. M
OL GUY
No racing as far as proffesionally goes. I just want to build this motor with existing parts I got. If I have to, I will sell them (pistons). I just want to use pump gas for the availability. My main problem seems to be too much piston and too small a head..:D . Anyway, back to the flycutting, you make a good point about the weight of the piston. It looks I might have to take too much off to make this happen, plus it won't work anyway unless I use the cam you were talking about. Thanks for the tip on this. Looks like some drag racer might be getting these and use the money to buy some Kieth Blacks that make 10:1 on the 58 cc heads I have. I have heard good things about them, even though the ones I want are not forged. I will check out this cam you were talking about
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MP
I'm using a 400 crank for this whole setup. I use the head gasket for the 400 to use as a template to drill some 1/8" steamholes in 350 heads. Supposedly you have to do this if your not running stock 400 heads. I can't remember the reason why either, I read it in CARCRAFT Mag. a few years ago. I have a 300 HP rated marine ZZ4 motor in there now with roller cam. I wonder if I plopped on those 58 cc 2.02 camel humps and a very healthy roller cam, what kind of jump in horsepower I'll get. I'll keep the R's but will lose out on 50 cc's.
One thing about working on jetboats, there's no hood to bang your head on or straining over a fender, or radiators to pull for cam swaps, headers are upside down. I wished I would have done this a long time ago. Shoehorning that 350 in the S-10 was not fun. :mad: :mad:

[Ryan00TJ]

The steamholes are needed as the 400 block is a siamesed design with no water jackets between the cylinders. Hence the steam holes. Drill them in your heads or you will never keep a head gasket alive. It's essential.
Your not going to want to hear it but the iron camel humps are really going to choke the 400 regardless of the porting. Their runners are too small even with porting to feed a 400ci engine. With the compression those domed TRW's are going to give with a 58cc chamber combined with iron heads is going to need race fuel no way around it. Your best bet is to sell the heads and pistons you have now and plan again. It sounds as if alot of parts were thrown together hoping everything would work together.
I would opt for a set of the AFR 210cc Eliminators with the 74cc chambers along with a flat top TRW piston. Should keep the compression in the low 10 range depending on other factors... deck height etc.... You'll be able to run 87-9 octane all day with the aliuminum heads. Add a small dome piston for more power but you'll need at least 93 as the compression will be approaching 11-1.
You simply have too much dome and too small of CC right now to meet your goals.
As to the 400. With a 4.125" bore and 3.750" stroke they are awesome motors when built right. Common are 406ci which is a 400 bored .30" over. Using a 5.7 or 6" rods make them awesome power makers. Rergardless of rumors when built right they are awesome high revving motors. It's the stock Chevy 400 with the short rods that are not rev friendly. Their rod to stroke ratio is way off.

[HALLETT BOY]

If you flip those pistons over and look past the wrist pin area you see that, do to keeping a weight that will spin rpm, there is no way you can fly-cut that piston to work with the heads you have, or any other head on pump gas. Now a light at the end of the tunnel!!! Back in the 80s One cam manufacturer built a 12.5 motor that would run on pump gas and I believe it was crane but the idea plopped. I would call chet or donny at herbert cams, they have played with the same idea and have more time on dynos and cam design than most people have been alive. They are now in chino ca. and I have used nothing other than what they recomend and have never been let down for thirty years. The numbers on the cam may not look right to you because so many people over cam boats but the proof lies in the performance of the product and trust the guys that have been doing it a while. JUST TELL THEM WHAT YOU GOT AND WHAT WANT and let expierence talk THen do-it M
I used to build a lot of VW engines in my younger days, I used a lot of Norris cams..anyway, whenever I would deviate from what the guys at Norris recommended, I would always be changing the cams ! They knew their stuff !

[ol guy]

Yeah its a real bitch when the guys that have more dyno time and experience are right!!!!!!

[TeamHawaiin]

Thanks Ryan, it now makes since on why the steamholes must be drilled. On another note. If the holes are drilled for the 400, can those heads still be used for another chevy motor like a 350?
I'll take your advice and others on the board to sell the 400 pistons and more than likely the heads. I have a 350 with stock 8:1 I might same them for because I have a trail truck I would like to build. Those 2.02 valves have got to be better than stock.
Let me get this quote correct.
Rergardless of rumors when built right they are awesome high revving motors. It's the stock Chevy 400 with the short rods that are not rev friendly. Their rod to stroke ratio is way off.
I thought that's what most guys were doing for the revs....using the 5.7 rods on the 400. Can you clear me up on this? I already have 5.7 GM pink rods that was going to the machine shop to be checked for straightness and resized if needed. Thanks
The steamholes are needed as the 400 block is a siamesed design with no water jackets between the cylinders. Hence the steam holes. Drill them in your heads or you will never keep a head gasket alive. It's essential.
Your not going to want to hear it but the iron camel humps are really going to choke the 400 regardless of the porting. Their runners are too small even with porting to feed a 400ci engine. With the compression those domed TRW's are going to give with a 58cc chamber combined with iron heads is going to need race fuel no way around it. Your best bet is to sell the heads and pistons you have now and plan again. It sounds as if alot of parts were thrown together hoping everything would work together.
I would opt for a set of the AFR 210cc Eliminators with the 74cc chambers along with a flat top TRW piston. Should keep the compression in the low 10 range depending on other factors... deck height etc.... You'll be able to run 87-9 octane all day with the aliuminum heads. Add a small dome piston for more power but you'll need at least 93 as the compression will be approaching 11-1.
You simply have too much dome and too small of CC right now to meet your goals.
As to the 400. With a 4.125" bore and 3.750" stroke they are awesome motors when built right. Common are 406ci which is a 400 bored .30" over. Using a 5.7 or 6" rods make them awesome power makers. Rergardless of rumors when built right they are awesome high revving motors. It's the stock Chevy 400 with the short rods that are not rev friendly. Their rod to stroke ratio is way off.

[Ryan00TJ]

Thanks Ryan, it now makes since on why the steamholes must be drilled. On another note. If the holes are drilled for the 400, can those heads still be used for another chevy motor like a 350?
I'll take your advice and others on the board to sell the 400 pistons and more than likely the heads. I have a 350 with stock 8:1 I might same them for because I have a trail truck I would like to build. Those 2.02 valves have got to be better than stock.
Let me get this quote correct.
Rergardless of rumors when built right they are awesome high revving motors. It's the stock Chevy 400 with the short rods that are not rev friendly. Their rod to stroke ratio is way off.
I thought that's what most guys were doing for the revs....using the 5.7 rods on the 400. Can you clear me up on this? I already have 5.7 GM pink rods that was going to the machine shop to be checked for straightness and resized if needed. Thanks
With the heads drilled I don't see a problem using them on a 350 block. Maybe someone else will know the answer for sure. The stock SB 400 came with short 5.56" rods. Don't quote me on the length but they were shorter than 350 5.7" rods. This gave the 400 a bad rod to stroke ratio. Building one with 5.7" rods is better than the short stock rods. However a 6" rod 400 is better than a 5.7" rod.
I think your doing the right thing selling the pistons and heads and going with something tailored to your application.