D4TE Build
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Joined: Nov 2003
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D4TE Build
I have a D4TE I am rebuilding it is bored .040 over.
-Sterling 381p pistons
-Stock heads
-Edelbrock performer intake
-Holley 600CFM
I think the compression is going to be in the low 8's. Should I get new pistons?
What cam should I use to get the most torque low to mid range?
I would like a nice and flat torque curve over the longest range.
-Sterling 381p pistons
-Stock heads
-Edelbrock performer intake
-Holley 600CFM
I think the compression is going to be in the low 8's. Should I get new pistons?
What cam should I use to get the most torque low to mid range?
I would like a nice and flat torque curve over the longest range.
Hotshot
Joined: May 2003
Posts: 11,141
Likes: 25
From: south louisiana
Why go so low on the compression ? Can't tell you anything with those pistons, don't know their specs. As for a cam with that low a comp ratio, a Comp Cams 268H is about the largest you'd want. Maybe a smaller grind with a wider lobe separation angle ( less overlap) to improve the dynamic compression . If you haven't bought pistons, I'd recommend some with a better comp ratio, like flat tops for a 67-70 car 390. These will raise the static ratio up to 9.5 to 10.0 to 1. With your heads, it'll still run on 87-89 octane pump gas, with the right cam.
Cargo Master
Joined: Aug 2000
Posts: 2,931
Likes: 12
From: SW Michigan
pistons
Pc, I wouldn't use the 381ps. I don't have my spec sheets handy, but memory says the 381p is a copy of the 410 style piston most of the later 390 pickup truck engines came with. If you are using the D2 heads and choose the felpro gaskets ( .041 thick ), you'll get something like 7.78 to 1. Not enough. There are better choices out there. I'll try to hunt up my piston numbers.....most FE trucks have no trouble with 9-91/2 to 1, and that is easily available with the right pistons. DF
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Post Fiend
Joined: Feb 2001
Posts: 6,624
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From: Missouri
TRW L2291F pistons are cheap, forged and will work great. With a felpro 1020 gasket they will give you a little over 9.5:1 with the c8 heads. Take a dremel and polish the combustion chamber until it is just smooth and you will be fine. There are some flat top cast pistons out there that will give you about 9:1 but I can't remember the number. Dinosaurfan posted a bunch of part numbers and specs a while back and I was supposed to make a website with them but I got busy and just remembered them. I think I will try to find time for that this weekend.
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Hotshot
Joined: May 2003
Posts: 11,141
Likes: 25
From: south louisiana
Silvolite also makes flat tops for the 390. Part # 1131 has a comp height of 1.76 and with a 70 cc chamber, 10cc head gasket, 5 cc forthe reliefs and area above the rings, 4.3 cc for the deck clearance ( .020 after milling the block and heads .005 each for cleanup) will give a 10.0 to 1 ratio. With the C8 heads and a Crane 272 degree Energizer cam, your motor will run on 87-89 octane gas with 12 degrees initial timing. It'll also have excellant bottom end and pull all the way to 5500 rpms. This is basically the combo I'm running in my 68 Merc with a 428PI intake, 750 Holley, FPA headers with the exception being that my pistons are still the std bore stock cast flat tops. For a little more bottom and less top end, just substitute a smaller cam, and possibly use the Silvolite part #1130 for 9.5 to 1 ratio or 1116 for a 9.7 to 1 ratio, to compensate for a smaller cam's tendencies to increase the dynamic comp ratio.
Hotshot
Joined: May 2003
Posts: 11,141
Likes: 25
From: south louisiana
If it's already 40 over, then you'll need to go to 60 if the block will handle that size, many 390 blocks won't. May be best to find another block in that case or go with the TRW forged pistons, they'll need more piston to bore clearance than the Silvolites will, so may work better in your case. Where are you located ?
Hotshot
Joined: May 2003
Posts: 11,141
Likes: 25
From: south louisiana
Oh, well. I've got a good low miles 390 short block for sale here in Louisiana, just wondered how close you were. It's 60 over too, with cast dished pistons, C7ME-A block, crank's 10/10. Like I said, if you're going to go with 60 over , have the block's cylinder walls checked to see if they'll stand it first or get a set of TRW forged one's to fit your 40 over block. Before doing that, though, have a machinst check the bores to see if the TRW's will fit them.