Piston possibilities
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More Turbo
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Piston possibilities
Anyone ever think about a piston with 1.660 comp height, 0.975 pin, 4.05 bore? In other words a low compression 390 piston. Valve reliefs are of course far off and the top would need to be modified, but they are prety cheap and you don't have to screw with the pin. Anyone?
R.
R.
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From: Delaware
A compression height of 1.66 is only 0.010 more than a stock 400 piston. Of course most 400 replacement pistons are 1.64 or worse, but 0.020 isn't much help.
As far as boring a 400 +0.050, that is not out of the question from what I have read.
It is a good idea, maybe there is a 390 replacement piston somewhere with 1.67 or better.
As far as boring a 400 +0.050, that is not out of the question from what I have read.
It is a good idea, maybe there is a 390 replacement piston somewhere with 1.67 or better.
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1.660 comp height?
Could someone verify the 390's CH. The dimensions sound like a 410 piston and they aren't as common.
http://www.racerwalsh.com/engine_spec_sheet.htm
http://www.racerwalsh.com/engine_spec_sheet.htm
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From: Delaware
It is a Silvolite 1139. It has a 9.5cc dish. At 1.66 CH it is no better for compression than a 400 flattop at 1.64 CH.
http://www.beckracing.com/slvpg51.htm
http://www.beckracing.com/slvpg51.htm
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More Turbo
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That's the low compression piston, also known as sealed power 381P Higher compression 390 pistons have heights at 1.739, 1.759 and 1.776 with a huge recess in the piston head. I'll have to look further. My point is that the 300-6 pistons aren't the only ones to look at.
R.
R.
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A CH of 1.739 is worth looking into. There are other 300 I6 pistons with CH of 1.74 and some Ford 391? pistons with CH of 1.74. A dish is no problem with an Aussie 2v head or 351C-4V head with 63cc or less combustion chamber, if you can get zero deck height.
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From: Mooresville
THE PISTONS YOU NEED
If anyone knows the 400 engine then let them tell me worng. The deck hight is 10.297 or real close (i'd have my machinest check after the line bore) The stock piston stops before zero deck. Just call je and tell them your deck height and piston size and pin size and they will make you a piston with a 1.71 CH and with a 0.40 gasket should be 0.007 below deck. Now get a closed chamber head and still have the dished piston and you will have the quech that you need to keep the motor from pinging and have the compression that you need. If you think that JE pistons are to expensive the call BSR 704-662-0901 and talk to emory. He works beside me at the speed shop and we have talked about doing this for my motor. If I remember righ the price wasn't to high. Email me if there is any questions on this.
Also you can check out http://www.projectbronco.com/
matthew@midgettmotorsports.com
Also you can check out http://www.projectbronco.com/
matthew@midgettmotorsports.com
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From: Delaware
I have priced custom pistons at $750.00/set. Price is not the only concern however. Custom pistons are Forged Pistons. While forged pistons are the strongest, they also expand the most. Therefore the clearance is highest, and they can slap when cold. This is not a problem in a race car, but some people might not want a motor like that.
What we are seeking here is an acceptable alternative to expensive pistons that slap.
What we are seeking here is an acceptable alternative to expensive pistons that slap.
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When do you need forged pistons?
Rarely on a street engine. The piston manufacturers are up front with this information. Are you running nitrous, forced induction, over 11:1 compression, or sustained speed over 7000rpm? At about $250 a set, hypereutectics are a bargain. They're stronger than cast. They're lighter and seal better than forged.
Except for the stroke, I'm doing an engine very similar to Danlee. There are no off the shelf pistons available for the CHI 3V heads that have a dish shape to match the combustion chamber. It's more like a figure 8 than a "D" shape. I've seen professional engine builders remove a lot of material from piston tops, .060-.075" is not uncommon. The trick is not to remove material in the quench area.
That still leaves 75-80% were you can remove material.So I'm going to make a template that matches the chamber shape, put them on the mill and route out my own reverse dome to whatever depth will give me the optimum compression ratio. I'm estimating about .050" on a set of flat tops.
Except for the stroke, I'm doing an engine very similar to Danlee. There are no off the shelf pistons available for the CHI 3V heads that have a dish shape to match the combustion chamber. It's more like a figure 8 than a "D" shape. I've seen professional engine builders remove a lot of material from piston tops, .060-.075" is not uncommon. The trick is not to remove material in the quench area.
That still leaves 75-80% were you can remove material.So I'm going to make a template that matches the chamber shape, put them on the mill and route out my own reverse dome to whatever depth will give me the optimum compression ratio. I'm estimating about .050" on a set of flat tops.
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From: Delaware
I am not going to change pistons, at least for the present. With the flattops and the CHI 3V heads, I get plenty of compression. The roller cam that I plan to use gives me over 500 HP and torque and reduces the dynamic compression low enough that with Aluminum heads, I don't need quench.
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I knew you were working on it but I didn't remember what the final compression came out to. I have a litle more stroke to contend with so a zero deck works out to 13:1 with flat tops. One of these days I need to have you run a couple cam profiles so I can make sure the compression is low enough to run on pump gas.
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From: Delaware
My compression with 1.64 Ohio flattops and 64cc heads is about 10.5:1. That considers that there is 0.0665 deck height with those pistons. That is something that I will try to measure. I am also +0.030.
With 68 degrees ABDC IVC, the DCR comes out to about 8.0:1. That should be fine with 93 Octane and aluminum heads.
You will need one hell of a cam to run 13:1 on pump gas even with quench. You should get some dish in that piston.
Whenever you are ready, feed me the cam, compression and head flow specs and I'll run the numbers.
I know that 8.5:1 is the maximum DCR for pump gas, but I don't know if that considers quench or aluminum heads.
I did find out that head flow is worth more than compression.
With 68 degrees ABDC IVC, the DCR comes out to about 8.0:1. That should be fine with 93 Octane and aluminum heads.
You will need one hell of a cam to run 13:1 on pump gas even with quench. You should get some dish in that piston.
Whenever you are ready, feed me the cam, compression and head flow specs and I'll run the numbers.
I know that 8.5:1 is the maximum DCR for pump gas, but I don't know if that considers quench or aluminum heads.
I did find out that head flow is worth more than compression.
Senior User
Joined: May 2002
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From: Mooresville
I was wrong
It wasnt JE pistons that I had priced it was Ross pistons. I think that they were not over $550. I have built many race motors and a few street motors and used high quality parts. I have never had piston slap. Remember we are not running 1970's forged technology. There is many ways that a piston manufacture can control thermal expansion.