64 conversion from 300 HP to 340 HP car

[John S.]

Someone in my area is converting a NCRS top flight 300HP roadster to a 340 HP one. Is this something that can be done and have it be 'numbers' matching and be judged as original? Is there a way to tell is this has been done on a car?

Seems a bit illegal to pass it off as stock. What is the opinion of this and can you tell so one does not buy one of these?

[Paul Y.]

Re: 64 conversion from 300 HP to 340 HP car

You can hear the solid lifter cam. The pad will say RD for a 300hp and RE for a 340hp. Tach has different red line. Lot's of other differences.

[John S.]

Re: 64 conversion from 300 HP to 340 HP car

You can hear the solid lifter cam. The pad will say RD for a 300hp and RE for a 340hp. Tach has different red line. Lot's of other differences.

If they change the tach and restamp the block, change heads, cam/lifters, intake, carb, etc., does it pass for original? Seems like they can't restamp and make it all correct to me, but?

[Dan D.]

Re: 64 conversion from 300 HP to 340 HP car

340 needs the 8" harmonic balancer. Without it you will get a bad engine vibration at about 3,000RPM. You do not want this.

Tell your friend to leave it alone. It is fine the way it is. -Dan-

[Paul Y.]

Re: 64 conversion from 300 HP to 340 HP car

I'm sure it has been done, but is it worth it? I doubt it. Like Dan sayes, there are quite a few details that need to be addressed. It will never be stock or original if it is changed. You can build the motor anyway you want but it won't be original and/or stock. Put an LS2 in it if you can, now that may be fun.

[Michael H.]

Re: 64 conversion from 300 HP to 340 HP car

340 needs the 8" harmonic balancer. Without it you will get a bad engine vibration at about 3,000RPM. You do not want this.
-

Dan,

That isn't exactly correct. The "balancer" has nothing to do with balancing the engines components, other than it's own balance. (and other than an externally balanced engine, such as a 400 inch small block or 454 inch big block)

[Duke W.]

Re: 64 conversion from 300 HP to 340 HP car

...dumb thing to do nothwithstanding the fact that the 340 HP engine was not a 1964 configuration, and most guys don't know enough of the details to convert a 300 HP to a 1964 365 HP without missing a lot, and getting it right would be very expensive.

If he wants "more power" in a package that will pass NCRS Flight Judging and a PV look at the Special 300 HP configuration written up in the most recent issue of The Corvette Restorer.

Duke

[Mike M.]

Re: 64 conversion from 300 HP to 340 HP car

agree with duke: removing the 300 HP suffix destroys FOREVER the factory broach marks. its a loosing venture if taken to completion. as duke mentioned, the original engine, keeping its 300 hp suffix, cast intake, steel valeve covers, etc etc, can be made , internally, to outrun a bone stock 340 HP engine. mike

[John S.]

Re: 64 conversion from 300 HP to 340 HP car

Bad news is I think maybe he will convert it and then try to pass it off as the bigger HP motor as stock to an unknowing buyer. Just seems like a bad attempt to try that conversion, but if honest about it no problem. Like others have said, if he wants performance one can stay stock exterior and get it.

[Dan D.]

Re: 64 conversion from 300 HP to 340 HP car

Dan,

That isn't exactly correct. The "balancer" has nothing to do with balancing the engines components, other than it's own balance. (and other than an externally balanced engine, such as a 400 inch small block or 454 inch big block)

I did that Mike, on a 1962 300HP. When I changed to the Duntov cam the engine went through a very pronounced resonance between 2500 and 3000. Bad enough that I was afraid I might break the crank. Changing to the 8" balancer completely eliminated it. I never did understand it, except I know the Duntov cam has some very harsh dynamics. And why else would they put that balancer only on solid lifter 327 engines.
I know it does not change the balance of the engine, but apparently that particular engine configuration generates some crankshaft harmonics that need a heavier balancer to swamp it out. -Dan-

[Michael H.]

Re: 64 conversion from 300 HP to 340 HP car

I did that Mike, on a 1962 300HP. When I changed to the Duntov cam the engine went through a very pronounced resonance between 2500 and 3000. Bad enough that I was afraid I might break the crank. Changing to the 8" balancer completely eliminated it. I never did understand it, except I know the Duntov cam has some very harsh dynamics. And why else would they put that balancer only on solid lifter 327 engines.
I know it does not change the balance of the engine, but apparently that particular engine configuration generates some crankshaft harmonics that need a heavier balancer to swamp it out. -Dan-

I would have to guess that if a new 8" balancer corrected a vibration issue, the issue must have been with the replaced 6" unit.
The balancer doesn't balance anything. It's a damper. It's function has nothing to do with balance. It has to do with the twisting that a crankshaft sees during each power stroke of the engine.
The movement/rotation of the inirtia ring on the damper balances, or dampens the effect of the crankshaft twist.
The twist is minute and you would probably never feel it, especially at the RPM range that you mentioned. The most aggressive twist is usually near/at the engines maximum torque peak RPM.

A higher HP engine produces more crankshaft twist so a larger/heavier damper is used.
The 8" unit was originallly designed and used on engines that may/could see extended full throttle operation at or near the torque peak, such as road racing or other high speed operaton. It wasn't as critical for engines used for steet/drag racing as the engine passes through the critical flex RPM quickly as the car accelerates.

It's the CW/CCW rotation of the inertia ring on the hub that dampens the CW/CCW flexing of the crankshaft.

Most people don't understand the function of a torsional damper.

[Domenic T.]

Re: 64 conversion from 300 HP to 340 HP car

I agree with what the 8" (HARMONIC BALANCER) does. I have always viewed it as a MINI flywheel that stabilizes the crank on HP engines.

DOM

[Gary C.]

Re: 64 conversion from 300 HP to 340 HP car

If the 300 HP car has been NCRS Judged previously, the engine HP rating is in the car database. The change of engine suffix should be caught during subsequent Judging. Gary....

[Michael W.]

Re: 64 conversion from 300 HP to 340 HP car

If the 300 HP car has been NCRS Judged previously, the engine HP rating is in the car database. The change of engine suffix should be caught during subsequent Judging. Gary....

How would that work Gary- that information would not be available to the second set of judges, nor are judges to use 'prior knowledge'.

To address John's question, obviously the engine would not be 'original' in the context of being the one the factory installed, but this factor of authenticity is not evaluated in Flight Judging. I won't touch the phrase 'numbers matching'.

It is not illegal or immoral to modify an engine or even restamp it in most places, but it is counterfeiting if it's being done with the goal of deceiving others.

[Dan D.]

Re: 64 conversion from 300 HP to 340 HP car

I would have to guess that if a new 8" balancer corrected a vibration issue, the issue must have been with the replaced 6" unit.
The balancer doesn't balance anything. It's a damper. It's function has nothing to do with balance. It has to do with the twisting that a crankshaft sees during each power stroke of the engine.
The movement/rotation of the inirtia ring on the damper balances, or dampens the effect of the crankshaft twist.
The twist is minute and you would probably never feel it, especially at the RPM range that you mentioned. The most aggressive twist is usually near/at the engines maximum torque peak RPM.

A higher HP engine produces more crankshaft twist so a larger/heavier damper is used.
The 8" unit was originallly designed and used on engines that may/could see extended full throttle operation at or near the torque peak, such as road racing or other high speed operaton. It wasn't as critical for engines used for steet/drag racing as the engine passes through the critical flex RPM quickly as the car accelerates.

It's the CW/CCW rotation of the inertia ring on the hub that dampens the CW/CCW flexing of the crankshaft.

Most people don't understand the function of a torsional damper.

I understand it is the twisting of the crank Mike. This has been discussed on previous threads.
It only occurred under WOT conditions, so maybe it was the higher down force from the increased HP that was enough to wind up the crank.
There was nothing wrong with the original balancer, it was only a couple of years old and few k miles.
But we (I) have high jacked this thread, and we have milked it enough, so over and out. -Dan-