Technical Low compression 390 FE, cam thoughts?

My friend is using a mid ‘70’s 390. I think he feels it’s a ‘74, had it written on the exhaust manifold

So, he has headers, performer RPM and a Holley 4 bbl, I think a 650 vacuum
Secondary to install and want to put a cam in it.
Right now it’s an engine for a future project, he’s looking for a F1 truck, etc. He has access to a C6 transmission, and will probably scoop it up.
He’d like to get in the 350hp range, roughly.
Cam recommendations would be helpful.
I should mention he’s going to use a roller cam as well.

Thanks.

 

For a mild engine with a dual plane intake, low RPM torque is more important than horsepower. I can't say specifically which cam, but I would suggest a mild camshaft with short duration.

Of course, you don't get that choppy idle everybody likes. But you also don't get the low RPM stumble on acceleration. And actually, probably more torque and better throttle response with the mild camshaft.

I've actually grown tired of the choppy idle. I like a smooth idle for a change.

Good luck with the 390.

 

He’s looking at a Howard’s cam, .525 lift, 110 LSA. Don’t recall the duration, but I think the 110lsa helps a low CR engine.

 

You'll need all the horsepower you can get if you run a C6

 

WHY.....don't you/your friend...say...call Howard Cams ???????
Why ask a bunch of folks that IF...they have knowledge, it's second hand knowledge at the best !
Talk to the "experts", seems the most intelligent thing to do...right ?
Howard or any other cam...talk to the people that actually design and make the cams !!!

Mike

 

If it's a '74, that's a truck motor and the best thing he can do is put higher-compression pistons in it.

 

Have him call Brent Lykins at Lykins Motorsports. Brent is a FE specialist and custom cams for FE's are his bread and butter.
(502) 759-1431
brent@lykinsmotorsports.com

 

When I hear low compression
I immediately think of a blower

 

C4 will work better if he can scoop one of those up. Less rotating weight.

 

^^^^^^^^These guyz are right....he should call Howard Cam OR Delta Cams for their recommendation.
[I REALLY like Delta Cams..GREAT prices and they custom grind. Good customer service too!)
Tight LSA does help low compression engines so 110*LSA should work out pretty good with the A/T.
(that also gives the rumpity-rump idle too !)
Delta ground me a roller on a 108* LSA for my 5.0 engine with 230/236 @050 duration which works out great...for me.. but I have a M/T.
Duration figures are weird... 230 in a 5.0 will act totally different in a 390. That's where a good customer service guy can steer you in the best direction. They will want to know the intended use for the vehicle..weight...transmission.. maybe even the gear ratio..so it's important to have all this info when talking to them.
As far as Lift goes....you do know you'll need good valve springs to make this all work ! I guess the good news is...the stock pistons are so far down in the cylinders piston-to-valve clearance shouldn't be an issue!
If you're gonna get new springs you may as well have the valves ground and the heads milled some to get a little more compression.
Just REPLACING those big old boat anchor heads and that 100 lb intake alone with Aluminum will make a noticeable difference in performance because you have reduced the front end weight by a couple hundred pounds (or more!)
Cost-wise... fully assembled Aluminum heads will prolly run you about the same money as re-built heads and the milling/machine work involved. (ASS-uming all the valves are good enough to get them re-ground..then it will cost you MORE than Al heads)
The performance "snowball" just gets bigger and bigger.
Tell you buddy to start working ALL the over-time he can !
6sally6

 

He filled out the sheet on the site, but will have to wait for them to reply

 

It's really difficult to make up for lack of mechanical compression. I'm guessing cost is a large factor here.

 

Here is the formula I used to rebuild the 390 in my '76 F250 about 10 years ago after it burned a head gasket. This was a factory 4 bbl motor, but the same rules apply to the OP's friend's 390.

• Bored 0.030" over (drank enough coolant to score a few cylinders...)
• 9.5:1 Flat top Silv-O-Lite pistons - this is the single best upgrade you can preform on these low compression truck motors.
• Howard's Dual Pattern Cam - (P/N 250031-12, if I remember correctly....)
• Long Tube Truck Headers and 2.75" exhaust through a pair of glasspack mufflers.
• Factory cast iron heads and intake, no porting other then simple cleanup and gasket match and a quickie valve job (guides and valves) on the heads.
• Holly 600 cfm carb
• Stock Duraspark II distributor and ignition module.

This engine dynoed at right around 355 hp and 485 ft-lbs of torque, and had one big fat torque curve. A bigger carb would have upped the peak horsepower numbers, but at the expense of the fat torque curve. Ran that truck for a bit with the C6 (it would pull a 10,000 lb enclosed trailer effortlessly) before trying an AOD conversion, but ran into torque convertor issues.

 

It really is the best bang-for-the-buck thing you can do. Yeah, it won't like running on cheap farmer Co-op gas anymore, but will run much better. Should even get a significant mileage bump. And don't assume a bore job is needed. I rebuilt a much-abused '68 360 years ago and at 250K+ miles the cylinder taper was just barely over the maximum allowable. I know of more than a few that got a ridge ream/hone with new stock-bore pistons and rings and ran great...