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Author Topic:   Advice on a 390 build up

Posts: 107
From: Ardmore, ok
Registered: May 2000

posted 11-01-2001 09:47 PM     Click Here to See the Profile for Okiehog   Click Here to Email Okiehog     Edit/Delete Message   Reply w/Quote
I just bought a fresh 390 shortblock from a guy, 40 over, and 10/10 on the crank, (CJ rod bolts, interestingly enough). Truck block. I got it for next to nothing.
Here is my question. Would I be well served to put my 428 CJ heads, some roller rockers, good intake, etc. on this shortblock? A local machine shop guy says from the look of the piston cuts, I could run premium pump gas and be okay.
I am wanting to build to around 425+HP. I am not going to put the car (68 GT Fastback, 4spd) on the strip. Just a strong street car. Will the bottom end of this shortblock be strong enough for this application?
I would really appreciate some input here.

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Posts: 33988
From: Saco, Maine
Registered: May 99

posted 11-02-2001 07:16 PM     Click Here to See the Profile for SteveLaRiviere   Click Here to Email SteveLaRiviere     Edit/Delete Message   Reply w/Quote
Sounds like a good plan. Do you know what the pistons are?

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Posts: 6602
From: Sonoma,CA,USA
Registered: Mar 2000

posted 11-02-2001 10:14 PM     Click Here to See the Profile for steve'66   Click Here to Email steve'66     Edit/Delete Message   Reply w/Quote

Edelbrock's performer rpm package makes 410+ h.p. with a 390, so you'll be close with the cj heads and a performer rpm manifold/cam etc. It made over 400 ft lbs of torque too, and had a nice flat torque curve. You'll have to check the combustion chamber size of the heads though. You (or your machinist) can calculate the compression ratio of the combo once you know that and which pistons are in the short block. Try to get as close to 10-1 as you can with pump gas. Sounds like a healthy street motor to me.


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Posts: 107
From: Ardmore, ok
Registered: May 2000

posted 11-02-2001 10:18 PM     Click Here to See the Profile for Okiehog   Click Here to Email Okiehog     Edit/Delete Message   Reply w/Quote
Originally posted by SteveLaRiviere:
Sounds like a good plan. Do you know what the pistons are?

Not sure if they are forged or cast. However, upon closer examination, it is clear that some work has gone into the shortblock. They chamferred the oil filter opening, as well as the oil drains in the oil valley. May be some other stuff I have not found, but this became apparent real quickly.

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Posts: 132
From: Seattle
Registered: Oct 2001

posted 11-03-2001 08:06 PM     Click Here to See the Profile for badazzcougar   Click Here to Email badazzcougar     Edit/Delete Message   Reply w/Quote
Ive built up several high performance FE motors and it is entirely realistic to expect 400 HP out of a 390. Dont expect a lot more than that though. Sounds like youve got the necessary oil mods. I had run quite a few cams and had greatest success with the Lunati 00043 cam and 10:1 compression using CJ heads and a Performer RPM manifold and a edelbrock carter clone. In that one I used flattop cast pistons due mainly to the fact it was a lower RPM ( under 6300 ) motor that would never see nitrous. The are available through Napa for $100 a set for the flat top 10:1 pistons. screamin deal! make sure you restrict the oil to the rocker assy's . Either the rollers or the factory CJ rockers will work well but you'll need the restrictors to prevent filling up the valve covers with oil. Holley 65 jets work well for this.

[This message has been edited by badazzcougar (edited 11-03-2001).]

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Rory McNeil

Posts: 1235
From: Surrey, B.C. Canada
Registered: Nov 2000

posted 11-04-2001 04:12 AM     Click Here to See the Profile for Rory McNeil   Click Here to Email Rory McNeil     Edit/Delete Message   Reply w/Quote
As long as this 390 doesn`t have the 75-6 truck low compression pistons, or a large dish, the CJ heads should work out well for you. The easiest way to check for the low compression deal, is to measure the pistons deck clearance. Normally, FE`s are less than .020" below the deck @ TDC, while the low comp. pistons are down over .100" (they are actually 410 pistons, & without the longer stroke of the 410-428 crank, the piston sits way down in the hole) I races 3 different cars with 390`s with the C8OE-N CJ haeds, all ran well.

78 Fairmont 428 4 speed 10.20@130mph
80 Fairmont 302 5 speed 12.8@105mph
85 Mustang NHRA Stocker under construction, 302 5 speed

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