peyano

Hi All,

What are the best modification to do to an original 427/390hp engine, just to give it that bit of extra punch, without going to crazy? im pulling the engine out to give it a good clean up and thought i may trick it a little while i am at it.

i appreciate any comments/opinions

Thanks

Nowhere Man

What do you want? The 427/390 is a great street BB engine with good mid range power. If your engine is original to your car anything you do to radical will devalue the car

DansYellow66

A recent thread noted that the 427/390 responds well to the 427/425 cam. However that's a fairly involved upgrade as the valve springs would also need replacing. And it's a mechanical lifter cam so adjustments would be necessary once in a while. There are probably some good hydraulic cams available that are close to the 427/425 cam.

And the BB is known to be responsive to opening up the exhaust system and lowering restriction. So headers or a low restriction exhaust system should help.

But, I would not overlook a careful tuning and blueprinting of what you have. That's assuming the motor is in good condition internally. Sometimes restoring the carb and distributor and blueprinting their settings and adjustments can make for a much more responsive motor. Some minor changes, such as the distributor advance curve and changing to manifold vacuum for vacuum advance can pick up a little more power and the improved smoothness and responsiveness of the engine will make it seem even more powerful.

Forgot to add that if your motor has reproduction shielded wires I would give them a good inspection as some of those reproductions were barely good for a few months. Taking a Taylor wire kit and installing them in the repro braided wire shields on my car was a significant improvement.

63split63

Would you have a link to the braided wire shields mentioned ?
Bill

Bluestripe67

It's YOUR car, enjoy it as YOU see fit. A full blueprint of the ignition system provides seat of the pants results and can be removed in the future if necessary. A CDI ignition system will make a difference an it is easy too remove. If you are taking the manifold and heads off you can use the manifold gasket too match the intake runners to each other. Yes, it's work, but it will result in a smooth path and better combustion=more power. Dennis

DansYellow66

Here are a couple. You can do a search under "427 shielded wires"

https://www.corvetteforum.com/forums...lug-wires.html

https://www.corvetteforum.com/forums....html:leaving:

I used a black Taylor wire kit but the better solution appears to be to use Pertronix 7mm black wires.

capevettes

There is some hidden horsepower in the heads. Look into "pocket porting". Without getting into radical cams and all, you can unleash some horsepower and make it breath a little better. If your motor builder is savvy he will know how to do this properly.

ILBMF

Got a '66 390 hp car here. It has the 425hp cam, carb and valve springs. Always made good power on stock cast intake manifold. I'm rebuilding the engine right now and verified the parts were indeed 425hp.

63Corvette

I ran a 427/400 (with air) for years, so i feel qualified to add my response. I used the stock 427/425hp cam, lifters and springs on my street car, which saw "some" track usage (autocross and HPDE).
In my opinion, the solid lifter cam works very well at high rpm, and the smaller "oval" ports in the heads and manifold give an increase (over the 427/425) in torque at lower rpms, so the net is positive. I had no trouble witht oiling or rods (on tires of that day), but I did have reliability problems with both the air conditioner (blew it up at 7000rpm) and eventually after a year, I lost a piston. My stock (non-hypereutetic) cast piston broke and disintegrated on the street at 7000rpm, and the still connected con rod then took out the block. SO...........in my opinion, IF you are going to use the rev range above 5500rpm, your modifications should include cam and valve train, but also forged (or at least new hypereutetic cast) pistons for reliability....and no high rpm A/C use.

Vet65te

Peyano - Is the 390 horse 427 in there now in good running shape? Curious if it' a bit 'long in the tooth' and maybe not up to where it should be. As Keith already mentioned, a 390 horse Bigblock should provide plenty of pulling power in it's original configuration. If yours is a bit tired maybe a stock rebuild is worthwhile. If it is in good shape and you're still looking for 'more power' (que Tim the Toolman grunt here ;-), a cam upgrade might help a bit but your lower horse bigblock typically came with milder rear gears like 3:36 or 3:08 while the higher revving 425 horse setup came with 3:55's, 3:70's or 4:11's.
Mike T - Prescott AZ

uxojerry

Contact Mark Jones at VORTECPRO. He's done a lot of vintage rebuilds for more power.

SWCDuke

The 427/390 is an excellent, broad torque bandwidth engine for a high performance road car. If you want "more power" without screwing up the idle, low end torque, and fuel consumption, simply massaged the heads.

Otherwise use all GM OE replacement parts from Federal Mogul. Don't buy into any advice to fill it up with aftermarket hot rod parts. You'll just screw up a great engine.

All Corvette big blocks from '65 to '68 except L-88 used the same, prone to break, single spring/damper first design valve spring. GM didn't release the second design dual spring with integral retainer and valve seal until 1969. It is no longer available from any known sources, however, a search should reveal some recent recommendations.

The conn. rods are sort of okay, but should be disassembled and Magnaflux inspected, which will require "resizing" them and new bolts, but for not much more you can buy a set of new aftermarket rods that are more durable.

Beyond that fix the lazy centrifugal advance, but don't lower the CR. If the pistons are OE and it doesn't detonate, you don't need to lower the CR and take the loss in torque, power, and fuel economy.

It's best to fix the spark advance map before you pull the engine. Get the centrifugal as aggressive as possible without detonation. Then on disassembly make all the measurements to compute the true CR, and put it together with the same CR. Search for a recent thread started by me on how to "manage" your CR for all the details.

Duke

mashinter

Good advice. I worked in the dyno lab at Chevy in 1969. I saw broken pistons on the hydraulic cam engines. I wouldn't go high rpm (425 cam) with your pistons.

ILBMF

This motor I have here has TRW pop ups. What came in the 390 hp?

Mr D.

TRW .125 domes

jdk971

save the 390 and drop a 454 in. dress the 454 like the 390. jmho jim

Crunch527

Shelve the original engine and get a crate and go have fun!

dugsgms74

Speaking from experience, long tube headers really wake these engines up. As Duke said, a nice bowl port and some chamber work to unshroud the valves is a worthwhile mod.

427Hotrod

A 390 HP engine had cast pistons originally. If it's got forged it's been reworked already...which would be a good thing.

You've got the "bones" to make a great engine. As mentioned, forged pistons are always a good thing...and hopefully lighter ones because 427 pistons are heavy. Going lighter makes it easy to balance and easier on the rods. 3/8" rods will handle a lot if in good shape with good bolts. Your choice on whether to rebuild them or just install a set of aftermarket ones that are stronger and will allow you to use a longer rod while you're at it (allows an even lighter piston).

I've used the 427/425 solid cam in a lot of 396/427/454's and it does well. It's actually a very mild cam and can be improved upon easily with stuff available today. Hyd Roller cams are reliable, rev well into the 6500 range and will make much more power while retaining low speed manners.

A nice bowl cleanup and valvejob on your heads by someone who knows what they are doing will do wonders.

Headers are a good thing....


A very mild/basic 427 is an EASY 11 sec engine in a Vette. That's getting into the fun category!

JIM

peyano

Thanks for all the responses guys. Awesome info. I appreciate it