'69 engine rebuild

[Jeffrey S.]

Hello all! After 43 years and a couple of hundred thousand miles, it's time to rebuild the engine in my '69. It is a small block 300 hp automatic. Among the many concerns I have for this project, I would like your opinion on one issue. It has been recommended by a few friends and a couple of rebuilders that as long as I'm doing the engine I should make it a 383 stroker while keeping everything external all original. This engine has never been out of the car and I do want to keep everything that can be seen as original as it is. The question is would changing internals in this manner have any affect on the value of the car- positively or negatively. I have no intention of ever selling this car but I would still like to factor this into the equation. I would really appreciate and value any input from you all.
Jeff

[Patrick H.]

Re: '69 engine rebuild

Jeff,

If you're going to do that realize that it will have ramifications on the transmission as well. You will probably need to change torque converters and make other modifications.

If it were me I'd buy a different block to go this direction. The last thing you want is an oops.
If you go bigger you'll probably go with different cam, heads, etc and your 450hp motor won't be the docile 300 horse engine you remember.

Then again, knowing your car, I'd do the best factory stock rebuild possible. Ask Duke for a copy of his article(s) and information and go to it.

Patrick

[Duke W.]

Re: '69 engine rebuild

Installing a 3.75" crank in an 870 block requires turning the main bearing Journals down to 2.3", which is not a very elegant solution due to the loss of crankshaft torsional rigidity, and the block will require grinding for clearance.

Consider doing a Special 300 HP configuration with a McCagh Special camshaft. The writeup is in the Fall 2009 Corvette Restorer. Instead of your engine running out of breath at 5000 it will pull strong to 6000+, but normal around town driving and idle behavior will be the same. No one will know, but you and it's not that much more expensive that a stock rebuild.

Duke

[Joe L.]

Re: '69 engine rebuild

Installing a 3.75" crank in an 870 block requires turning the main bearing Journals down to 2.3", which is not a very elegant solution due to the loss of crankshaft torsional rigidity, and the block will require grinding for clearance.

Consider doing a Special 300 HP configuration with a McCagh Special camshaft. The writeup is in the Fall 2009 Corvette Restorer. Instead of your engine running out of breath at 5000 it will pull strong to 6000+, but normal around town driving and idle behavior will be the same. No one will know, but you and it's not that much more expensive that a stock rebuild.

Duke

Duke------


1969 small blocks don't use the '870' block. They use the 3932386 (early) or 3970010 (late). The main journal size was 2.45". There are 3.75" stroke small block, 2 piece seal cranks available in this journal size (although not from GM).

[David L.]

Re: '69 engine rebuild

Duke------


1969 small blocks don't use the '870' block. They use the 3932386 (early) or 3970010 (late). The main journal size was 2.45". There are 3.75" stroke small block, 2 piece seal cranks available in this journal size (although not from GM).

There were actually 3 different casting numbers on 1969 blocks (302 & 350). The mid-production 1969 blocks had a 3956618 casting number. A few casting date examples of the 3956618 block: "L-31-8", "A-2-9", "B-4-9", and "C-17-9".

Dave

[Duke W.]

Re: '69 engine rebuild

Duke------


1969 small blocks don't use the '870' block. They use the 3932386 (early) or 3970010 (late). The main journal size was 2.45". There are 3.75" stroke small block, 2 piece seal cranks available in this journal size (although not from GM).

Yes, I confused the model year.

Installing a 3.75" stroke crank in a 350 block is an option.

A 3.75" crank will increase torque/power across most of the range, but will not generate significantly more top end power (Taylor's similar engine rule).

The only way to achieve significantly more top end power with either stroke length without some big cam that will screw up the idle and low speed torque is to improve head flow.

So, improving head flow is the first priority, and increasing stroke is an option if you want to spend the additional money. Retarding the OE cam or the McCagh Special cam are also options. The McCagh Special cam was designed specifically for the flow characteristics of massaged heads.

Look at this thread post #24.

https://www.forums.ncrs.org/showthre...00+hazed+tires

Here's another one on the same subject, post #2.

https://www.forums.ncrs.org/showthre...ighlight=myers

Any/all of the above changes are internal to the engine and are not detectable in judging, and in fact, engines with some or all of these modifications have passed a PV to earn a Duntov or McClellan award, so there would be no effect on the value of the car - just make it faster and more fun to drive.

Duke

[Jeffrey S.]

Re: '69 engine rebuild

Thanks for your responses. The engine/trans/rear axle is the same combination as in the car referred to in Duke's post #24. I also have full time vacuum advance. I am not interested in increasing top end torque. I want low to mid range punch. The heads were done a few years ago and improvement in flow was a goal. The intake and exhaust passages were cleaned up. The valves were opened up with hardened seats installed. Patrick- why would the torque converter and trans need modifications? The estimates of additional hp from the engine builders would yield about 75-100 additional horsepower and a big improvement in torque in the lower end with a very smooth idle.
Jeff

[Duke W.]

Re: '69 engine rebuild

A 3.75" crank with no other changes will NOT materially increase power, A stroker will not be as rev happy as the 350 because peak power will occur at the same mean piston speed, which would be lower revs. I doubt if your "engine builder" ever read Taylor.

The improvement in torque improvement across most of the rev range will be real and very useable in normal driving.

The McCagh Special camshaft will improve top end power without affecting low end torque or the smooth idle of the OE cam.

Patrick may be saying that the added torque may require transmission upgrades, but I think the TH400 can handle it as it was also used in the same form with big blocks.

Duke