Help me design a 390!

[tpiini]

Whoa guys! Let's be nice here. please! My main reasons for going with the 390 are that I have a friend with a boat load of them and he's wanting to give them to me and I just like the "look" of the FE in the Cobra.

I have seriously thought about a stroked Windsor, but I've had stroked engines before and just like the idea of bigger bores/shorter strokes for the cubic-inch recipe. Especially in such a light car. Now if I were moving a heavier car, I'd go the stroke/torque route.

But like I said, my Cobra is an entertainment machine for me. Due to physical limitations, I can't ride motorcycles any more, so the car is my "outlet." Melting a set of tires now & then is just part of the fun for me. I don't mind the thought of changing rear gears, but I find the 4.57's entertaining as hell with the 289 and figure that as long as the 390 will hold up to steady 2850 RPM cruising, why not keep them for starters? If it turns out that I can't get any traction at all, I'll knock them down to something more reasonable.

Thanks again for helping me out. Any and all suggestions are appreciated. Even the ones that tell me I'm making mistakes here. Actually, I especially appreciate those comments. I learn more from them.
Tom

[Clois Harlan]

Hey guys just looked at my post and I didn't intend to put in the word "ALUM" in front of those H-Beam Rods. And yes they do make Alum H-Beam Rods but they are usually used for drag racing, I am told.

Clois

[SFfiredog]

A 390 and a 427 FE have the same stroke so building a 390 to physically rev to 7000 to 7500 is no problem, and not that expensive either. A stock 390 crank can handle 7500 rpm if neccessary so all you would need is a good set of aftermarket rods and light pistons.
The question is, do you want to make any power at those rpm levels.
You stated that you want to cruise on the freeway at 2500 to 2850 rpm steady. The cam needs to be sized to be make cylinder pressure and flow to be smooth and not "jerky" or "cammy" at those rpm levels. It is not practical to expect a cam to work well at that rpm and also be able to pull hard to 7000 rpm.
Most street cams have a 3000 to 3500 rpm "sweet spot" (2500 to 5500 rpm or say 3000 to 6000 rpm)
Above and below those rpm levels a different cam would make more power.
For example, if you cam an engine to cruise well at 2700 rpm,
it will most likely make it's max hp by 5500 to 5800, let's say 425 hp. That's not to say if won't rev to 6500 rpm, but at that level it may only make 375 hp, with the power dropping every 100 rpm above the max hp number. It makes no sense revving an engine where it doesn't make power (road racing is the exception, where you may need extra rpm to allow for gear spacing in turns)
The small 4.050 also hurts high rpm performance of a 390.
High rpms and big power generally require larger valves, and large valves get shrouded in the small 390 bore.
HTH,
--Mike

[steelcomp]

Quote: "Whoa guys! Let's be nice here. please!"

Sorry...that was meant in fun. Not meant to offend. Seemed funny at the time.

[Dwight]

WITH A HOT 390 YOU NEED TO THINK ABOUT TIRES!! BIG WIDE TIRES! SOFT AND STICKY TIRES! AND GEARS 3.00 TO 3.23. 3.50 AND 3.73 WILL MELT THE TIRES.

[Jack21]

Sorry. Didn't mean to come across as "Preaching". It's your car, your money...

Just trying to help the guy avoid an end result that he might be unhappy with. I've been there, you've been there. Expensive and frustrating when what you thought you wanted, is not what you got.

[steelcomp]

Originally posted by Jack21


Sorry. Didn't mean to come across as "Preaching". It's your car, your money...

Just trying to help the guy avoid an end result that he might be unhappy with. I've been there, you've been there. Expensive and frustrating when what you thought you wanted, is not what you got.

Sure can't argue with that!!!
It's all good.

[bulletbrown]

Tpiini, I have a Shell Valley Cobra with a hot 390 4sp. and 9" with 350 gear, I agree with DWIGHT 100% , I have 15.5 wide tires and smoking them is know problem. High rev. is NOT NEEDED, shift early and often . 20 to 80 mph is a blast. The sound is great and the torgue is fun.
Bob

[tpiini]

You know, I think I just need three Cobras. Keep my little screaming 289. Build one with a torque-monster big block. And lastly, one with a little 4-banger to trip around in for some fuel mileage. Yesterday I took the 454 Corvette out for a spin. Today, the Cobra. Although the Cobra will spank the Corvette in a drag race, there's just something about stomping into that 454 that makes me smile.

I don't know why I consider this such a hurdle, but with the high-winding 289 I now have, the car runs great with the 4.57 gears. Why am I willing to toss the perfectly good engine to build a high-buck 390, but am balking at swapping out a stupid cheap set of rear gears to make it run right?

Maybe I need a therapist instead of a 390. (?)

[Enginetime]

See if you can bore out one of your 390's to 428 std bore! A sonic check will tell you. About one in three willk pass or if you have a truck 390 with a (105 number on the casting) this will bore to 428 std. no problem. Then you can run a 428 crank, 4.13 ross pistons, ect. Can be done on a budget but put the bucks into head work or edlebrock AL heads. Comp cams makes a great extreme energy cam for FE's, choppy idle, 2,000-6,000 rpm. Nice package and have done several with good results.
Mark