Rebuilding a Number Matching Big Block

[Ricochett]

Im in the process of rebuilding my 427/390 motor, It is a number matching motor
i would like to bore it out 030 over and raise the compression ratio up some maybe
11.0 to 11.5 somewhere in that area! My question is? Will this hurt the value of the
motor/car by doing this ???????

 

[bill81vette]

As far as I know,no...
you are keeping the engine with its original vette...

 

[6880 Mike]

I agree: no real harm done. Do not have the block decked and do not allow yourself to be talked into it.

 

[Vettehead Mikey]

If you bump up the compression so that it's no longer driveable on straight pump gas, this might hurt the value.

 

[lars]

Raising the compression to over 11:1 will definitely hurt the value. Pump gas won't support 11:1 compression with iron heads and the stock cam, so anyone interested in your car will need to un-do whatever you did to get the compression back down in the 10:1 range, unless you use octane boosters or race fuel. You can also retard the timing to run that comp ratio, which will be a bigger power loss than if you kept the stock comp and ran a good aggressive timing curve.


If you're going to run this car on the street using pump gas, 11.5:1 is a really bad idea.

Lars

 

[Hib Halverson]

Listen to Lars or...buy lots of 100-oct. unleaded racing gasoline.

 

[JohnZ]

Your engine was built originally at 10.25:1 - leave it there. If someone has suggested raising it, they've given you really BAD advice. :eyerole

 

[Tom Bryant]

Think of what a pain in the butt it would be to have to worry if you could buy gas every time you ventured away from the house very far. Most stations that sell race gas won't let you pump it directly into your car unless it's a race car on a trailer. You will be far better off maximizing the tune on the stock CR.

My '67 390 horse had the Hooker side pipe headers, a cam and carb upgrade and would really get with it. It also would still start and drive nicely and was pleasant around town on pump gas.

Tom

 

[Ricochett]

Number matching motor

Thanxs guy's

im just trying to figure out the best to get some power out of
this 427/390 what i have decided so far is to go with a
Roller cam Hyd. RPM range 1500-6500
Port & polish the heads
Competition valve job ( on stock valves )
Change the carb around a 850 dble-pumper

And for the bottom end not sure yet if i should bore the block out .030
and increase the piston ration to get more power

What do ya'll think??????

 

[lars]

Just a couple of comments based on personal experience and a lot of dyno testing:

• A hydraulic roller cam with an operating range up to 6500 is a complete waste: Hydraulic roller lifters aren't good for rpm over 6,000, so select a cam better matched to the limits of the lifters.
• Porting and polishing those heads will likely do more to hurt flow than to improve it. In addition, it will destroy all value of the original heads. If you really want to do some grinding, do a simple port-match to the intake, and blend the match into the port about 1/2". In addition, a simple casting flash removal process is about all you need. This will help flow without screwing up the heads and the value of your castings.
• If you want to increase head flow a little, do a good 3-angle valve job and install a set of tuliped, swirl polished, necked valves. Manley has them for about $20/ea, and SI is selling them for about $12/ea.
• Boring the block won't do much for power - you should bore the block and replace the pistons if your piston-to-wall clearance is out of spec. I've never heard of a "piston ration," so I can't comment on its effectiveness.
• One of the most effective things you can do, if you're wanting to screw around with that engine, is to install a set of headers in place of the stock exhaust manifolds. The stock manifolds are pretty restrictive, and the headers will gain you over 20 hp. They will, however, limit your ground clearance.
• You can also make huge gains by simply correctly curving your ignition and properly setting up your original carb. I've seen gains of 20 - 70 hp with these tuning setups alone, whereas swapping a poorly tuned carb for another poorly tuned carb will gain you nothing.

Lars

 

[Crimson Thunder]

You may want to take your numbers matching motor and stick it in a corner of your garage and build/buy a new one to have fun with.

 

[Ricochett]

Just a couple of comments based on personal experience and a lot of dyno testing:

• A hydraulic roller cam with an operating range up to 6500 is a complete waste: Hydraulic roller lifters aren't good for rpm over 6,000, so select a cam better matched to the limits of the lifters.
• Porting and polishing those heads will likely do more to hurt flow than to improve it. In addition, it will destroy all value of the original heads. If you really want to do some grinding, do a simple port-match to the intake, and blend the match into the port about 1/2". In addition, a simple casting flash removal process is about all you need. This will help flow without screwing up the heads and the value of your castings.
• If you want to increase head flow a little, do a good 3-angle valve job and install a set of tuliped, swirl polished, necked valves. Manley has them for about $20/ea, and SI is selling them for about $12/ea.
• Boring the block won't do much for power - you should bore the block and replace the pistons if your piston-to-wall clearance is out of spec. I've never heard of a "piston ration," so I can't comment on its effectiveness.
• One of the most effective things you can do, if you're wanting to screw around with that engine, is to install a set of headers in place of the stock exhaust manifolds. The stock manifolds are pretty restrictive, and the headers will gain you over 20 hp. They will, however, limit your ground clearance.
• You can also make huge gains by simply correctly curving your ignition and properly setting up your original carb. I've seen gains of 20 - 70 hp with these tuning setups alone, whereas swapping a poorly tuned carb for another poorly tuned carb will gain you nothing.

Lars

Lars
Thanxs for your input! you have made me really think about a few things, i think i may take you up on your ideas thanxs again

 

[Ricochett]

You may want to take your numbers matching motor and stick it in a corner of your garage and build/buy a new one to have fun with.

Sharkcar after thinking about a few things after getting some very great advice from a lot of members here You are so right im just going to put it back to stock except
the cam im going up a little on the cam
thanxs again

 

[Hib Halverson]

The earlier advice on camshaft profile is spot on. Look for a hyd. roller profile which, in a 427, makes peak power at around 5500-5750 and set your rev limit at 6000. I wouldn't rev higher than that with 2-bolt mains and a cast crank.

As for the heads, in my experience, the Corvette oval port heads really work well with a mild port/polish and multi-angle faces and seats. However, as said earlier, doing the heads on that engine will destroy their value.

Also, the previously mentioned headers, optimized ignition curve and carburator calibrations are all wise advice.

 

[Ricochett]

The earlier advice on camshaft profile is spot on. Look for a hyd. roller profile which, in a 427, makes peak power at around 5500-5750 and set your rev limit at 6000. I wouldn't rev higher than that with 2-bolt mains and a cast crank.

As for the heads, in my experience, the Corvette oval port heads really work well with a mild port/polish and multi-angle faces and seats. However, as said earlier, doing the heads on that engine will destroy their value.

Also, the previously mentioned headers, optimized ignition curve and carburator calibrations are all wise advice.

Hib
Thanxs for your advice