Valve size ???

[fordracer]

Is anybody here running 427 valve sizes on a 390 ? I know about notching the bore for clearance but are the larger valves worth the added work ? Again I'm looking for as close to 500 hp as I can get, I would like 450 + at the rear wheels.

[kountzecobra]

I'm not sure, but I don't think you can notch a 390 cyl bore enough to clear 427 size intake valve. I would call George at Gessford and ask him.

[bmalone]

What heads do you plan on using? 390s had 2.04 and 1.57 valves.

I think you can use 428 heads on a 390 without running in to a problem. You will then have 2.09 and 1.65, which is the same as the 427 LR. I do not think the bore is large enough to support the larger 2.19 and 2.25 of later generation 427s.

Like David said, ask George.

[A Snake]

A little insight here and I'm not trying to rain on your parade, just give you something to think about. There are two reasons why 427 sized valves won't work on a 390. First, the medium riser heads have the valves spaced farther apart in addition to the larger diameter. the spacing is BECAUSE of the larger diameter. Second, in spite of what you may hear, you WILL hit water if you try to notch the 390 cylinder bore enough to clear the valves....especially with a high lift cam.

Now, unless you wanted to try for 9,000 rpm, the bigger valves won't do anything but steal your low end torque.

As previously posted, the 428 CJ valves help quite a bit....especially if the heads are ported by a pro OR you by the aluminum Canadian CJ heads which already have the port work done.

Can you make 450 rear wheel hp with a 390? Yes, but you won't want to drive it on the street. That takes at least 11:1 compression or more and a really stout camshaft along with a large (850cfm) carb. Definitely not a daily driver type engine. Racing fuel only and changing spark plugs like you change socks and shorts....because the rich idle needed for the lumpy cam along with low rpm driving fouls the heck out of them. Don't forget, with that wild cam, you'll need some stump pulling gears like at least 4.10:1 or lower.

Just some thoughts. Frankly, if you have a 390 block, go find a 410/428 crank, put the CJ heads on it with a decent manifold with a good half inch lift cam and prepped carb. You'll probably make 400 hp and still be drivable with a nice rumpty rump idle. Frankly you'll love it and a Viper still won't be able to catch you!

Al

[SFfiredog]

Even if you could fit medium riser valve sizes in a 390 bore, the valves would be so shrouded by the cylinder wall that flow would be decreased instead of increased.
Recipe for a 500 hp 390:
.030 390 block
Scat 4.125 stroker crank
431 ci
10.5 to 1 compression
mechanical flat tappet cam with specs around 248 degree duration a .050" with about .590 lift
Erson rocker assy
Edelbrock Performer RPM heads w/ mild port work
" " " Intake
MSD distributor and 6AL ignition
750 to 850 double pumper

Should make an easy 500 hp and still be easily streetable.
--Mike

[fordracer]

Thanks for all the excellent replies. I already kinda figured MR valve sizes would be too big . Not to flame anybody here but I know my power goals seem a little high but I am used to driving a mid 11 second Mustang on the street. My mental picture/ dreams of a Cobra has to be faster than that. My Mustang was 2950 lbs with 400 hp. I figure a Cobra realistically weighs 2700-2800 lbs , so I am going to need 475- 500 hp. I'll probably go with a 428. Again guys thanks a lot for the help.

[FE Specialties]

Fordracer,
What year was your mustang, and what motor??
Tom

[fordracer]

'89 LX. Fuel Injected, Supercharged. Rear wheel HP numbers were 370 @ 5400 rpm and 390 ft/lbs. @ 3600. It was an absolute hoot to drive. 5 speed. It would blow the tires off up through 3rd gear. Put some slicks on it and it averaged a 1.54 60' and a best 11.64 @ 115.8 at Houston Raceway Park. I need a Cobra that will be a scary nasty beast.

[Captain Speed]

I have a 390 bored .060 over with iron heads which have been ported and 2.09/1.66 installed. This comes out to a 401. Intake is the Ford 1964 2/4 with two 600 hollies. Cam is Elgin solid with 245deg. at 50, 324deg adv. and .524 lift. Compression is around 10.2. The engine runs great and is very driveable. My rear gears are 3.07 as most of my driving is on the highway. 70mph is around 2800 rpm. Which is where the power starts to come in. Everyone has a plan of their own, so good luck!!

[ADR]

There's another thing alot of peaple don't realize is that the size of the valve has very little to do with it. A CJ valve doesn't work better because it is .04 or .05 bigger in diameter, it works better because of its shape.

The CJ intake valve is flat a hell on its back side and it unclogs the port at low lift and work really well with the 30 degree valve seat.
Makes for really nice low lift flow numbers. In a high horsepower 390 I would still use the CJ valves but I would switch to a 45 degree seat for a higher lift cam. With a bigger camshaft, you actually want to kill a little bit of low lift flow and the 45 degree seat will do that and will shift the flow numbers more to the high end.

Its way more important to have a properly shaped valve than it is to have the very largest valve you can get. I wouldn't give you a squirt of pee for a stock medium riser valve, they have almost a tulip shape and they wont flow as well as a nail head shape (flat) valve.

The exhaust port is another matter ( at least on my edelbrocks) they love a tulip shape valve with as much as a 30 degree angle on the back side.
Just a thought
Dale

[M & M]

I have 390 heads (C4AE-8090-G) on my 427. This is a high performance low riser head. I was told my valve size had been increased on those heads to 2.09 and 1.65. Is this possible? If so would this setup work for him? Or are you still faced with too small of a cylinder for clearance?

Thanks,
Mike

[jdean]

ADR....i agree the "bigger" recipe does not always deliver when it comes to intake or exhaust flow. With both valves, ports and runners, it is the shape and the coordination of all components that make power.

An example is the Vortec SBC head. It has smaller valves and runners than about any other performance SBC head, but it performs better than bigger ones costing twice as much - it's all about shape!

[SCOBRAC]

I have a really nice 428 you can have cheap.. W/ 390 GT heads.. 2.09/1.65

[427 S/O]

World record holders Hawk&Bailey Racing, run 390Gt heads in their 1967 Shelby mustang 428.
1.57 Eg/2.04 Int...D/SA national Record
with a 10.53 ET@124.74Mph.
They hold the eighth mile record as well.

Torque monster!!!!!!!

[FE Specialties]

FordRacer,

SF Firedog is right on the money!! Only thing I would change is the possibility of running either a hydraulic roller or mild solid roller cam!!!
With a CJ crank-422 ci, .060 over, Edelbrock heads-mild porting, 10.5 to 1 compression, Performer RPM intake-port matched, 800 cfm carb, and a hyd roller cam at 236 duration at .050, you will make about 509 hp at 5500 rpm. 553 ft/lbs of torque at 3500 rpm, and 516 ft/lbs of torque at 2000 rpm.
The age of flat tappet cams is over. There is no reason not to take advantage of todays technology in camshaft design!!!!

With the aluminum heads and 10.5 to 1 compression, you can run pump gas with about 38 degrees total advance. And as you can see there is gobbs of low end torque with this set-up. The engine will idle around 900 rpm and definetly be very streetable in a Cobra!!
Call me if you have any more questions!!!
Tom.

[decooney]

Hi Tom,

if what Pathenry says above is true about that guys Mustang being a "World Record Holder" at that time, what does that make your 10 second 1967 Mustang I saw run last weekend?

are we saying that you are within World Record contention on your first time out? Just goofing around? Your little project shop car is already running 10s... I don't get it, am I missing something here?

Duane

[FE Specialties]

HEY Duane;

Thanks much for the pics and support last weekend!! The car is running exceptionally well for its first time out. Especially considering that I was at 1/3 throttle for the first 30 feet or so. Didn't want to get to crazy on a brand new car that hadn't been tested yet!!!
I didn't even intend to run a full past all day to tell you the truth, but the car ran so good, felt solid and straight that I went with it anyways.
127.3 mph with a 1.60 60ft is fantastic. With a full holeshot, we should get 128.5-129.5 on the speed, making this car capable of possible high 9s!!! Did I say NINES!!!

Not bad for a single carbed, less than 12 to 1 motor, without any juice!!!!!! Besides, bottles are for babies!!!!

P.S. Its all in the heads!!!!

Tom.

[PJS50]

That's impressive Tom...
I had a '67 Stang but it wasn't that fast... That's really getting the bacon delivered!!!
I went to a Super Ford event at Milan Dragway (Milan Michigan) about 18 years ago and watched a guy in a kit AC with I think a 428 pull a 10.80 quarter mile... From that point on, I knew I had to have one... I am finally getting the ball rolling...
All of this go-fast talk is getting me so worked up that I am thinking of selling some of my other hobby items (shooting/gun collecting) to get into a Cobra quicker...
Maybe I can sell my wife, keep the guns AND have the car TOO...!

[Clois Harlan]

Definately loose the guns before you get the Cobra. After a few deliveries by the Big Brown Truck your wife will go looking for the guns and then you.



Just kidding!

Clois

[M & M]

Tom,

Do you ever get up or have plans to make it to Woodburn Dragstrip here in Oregon?

Mike