Smokin' 390

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Mar 14, 2000 | 09:54 AM

bigblue

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Senior User

Joined: Sep 1999

Posts: 176

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From: Minneapolis

Smokin' 390

I have a 66 390 that is burning a lot of oil. It burns one quart every 35 miles. The engine has a fresh rebuild on it. The smoke problem started after I put some 428cj heads on it. The engine is balanced with cj heads, file fit rings, big split profile cam 107 & 111 centerline, 1.73 adjustable rockers, custom headers, and Edelbrock intake with 750 double pumper. The cj heads make it smoke a lot! Both valve covers have a breather, but no PCV valve. I have adjusted my rockers until the shafts are just snug and then an additional 1/2 turn. I have good compression. A leak down test while cold shows it can hold 110 out of 120 psi. When I pull the intake I can not see any oil path into the runners. I am not using the intake gasket at front and back, just a big bead of sealant. I do have low vacuume, but that may be from the big cam. When I bought the heads, they were supposed to be a fresh rebuild. I had my shop look at them before I installed them and they said they looked good. Why are these heads causing my engine to act like a mosquito sprayer. I am missing something. This is my summer fun, not a daily driver. Summer is coming. All you engine guys, HELP!

Mar 14, 2000 | 07:32 PM

390fe

Fleet Mechanic

Joined: Jul 1999

Posts: 1,360

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From: Iowa

Smokin' 390

You should have a pcv system. It helps evacuate the crankcase of oil vapor and acidic gasses. Did you file the rings? What was your cold ring gap? It should be .010-.031 on the top ring, .010 to .020 for the second rings, and .015 to .066 on thr oil rings. I'm not a professional engine builder, but these figures are from Steve Christ's book, "how to rebuild big block Fords". If your ring gap is wider than these specs, excessive oil burning will result.
What do your plugs look like? How many miles on the engine scince the rebuild?

Mar 14, 2000 | 10:19 PM

Jman

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Joined: Dec 1999

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Smokin' 390

Do have any particular cylinder that is taking on oil pull your plugs and look at them. If it is 5 or 3 you may have installed the rocker shaft and may have punched through the casting and into the intake passage and oil pressure gally of one of these cylinders. I did it on a 360 that had been welded up at this point the fact that it was welded tells me that it also happens in the first place. could be from over tightening or a stretched bolt.If not oily on any particular cylinder I would say that the rings did not stand up to the compression ratio difference of the CJ heads does some one know how much higher the comp ratio is?

Mar 15, 2000 | 09:19 AM

Post Fiend

Joined: Feb 2000

Posts: 5,130

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From: Brea CA

Smokin' 390

Putting CJ heads on a stock 390 will actually lower the compression ratio because of the CJ’s larger combustion chamber volume. In this case it’s hard to calculate the final compression ratio without knowing what kind of pistons were installed in the rebuilt shortblock.

Barry

Mar 15, 2000 | 10:53 AM

bigblue

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Senior User

Joined: Sep 1999

Posts: 176

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From: Minneapolis

Smokin' 390

Thanks for the replys. All of the plugs have oil on them when I pull them. Ring gaps were done correctly, although I am now suspicious of the oil rings. The engine has about four hours on it since the rebuild. BBB said my compression will be lowered because of bigger chambers. My cylinders are bored .040 and I have the original pistons. With cobra jet heads, how much will my compression drop from the original 10.5:1? Even with my current engine problems, the engine likes 4000+ rpms. My "390 cobra jet" engine is in a 66Tbird. I know this is a truck site, but I have learned alot about all fords here.

66 Tbird 390cj
78 F150 4x4 400
86 F150 4x2 300 Rusty, but trusty.

Mar 16, 2000 | 12:28 AM

Superdave

Posting Guru

Joined: Sep 1999

Posts: 2,297

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From: Indiana

Smokin' 390

Are you saying that you have the original pistons from your original engine re-installed in your .040 overbored cylinders? Or am I missunderstanding your post?

Superdave

94 Ford Aerostar XL 3.0L
82 Ford F250 4x4 XLT,400 CID,C-6 A/T,8700lb GVWR. Black & Silver

Mar 16, 2000 | 09:31 AM

Post Fiend

Joined: Feb 2000

Posts: 5,130

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From: Brea CA

Smokin' 390

Assuming you have .040 over dished and double eyebrowed pistons, your compression ratio dropped to approximately 9.7:1. This is probably as high as you would want to go considering current octane ratings. The .040 overbore is as large as I would go but it does make a definite improvement in midrange power from 4000 rpm and up.

Barry