Another big block conversion question

[Rookie Vette owner]

I'm still working on converting my 73 to a 427 and trying to find all the obstacles that are out there. The latest that I heard yesterday, was that there is a difference in the front frame crossmember where the harmonic balancer will hit if you are working with a "small block" frame. I had already heard that I could not use generic big block pulleys, but this is the first about a difference in the frames. I thought all the frames were basically the same except for improvements made through the years 68-82.;help

 

[fine69]

I'm still working on converting my 73 to a 427 and trying to find all the obstacles that are out there. The latest that I heard yesterday, was that there is a difference in the front frame crossmember where the harmonic balancer will hit if you are working with a "small block" frame. I had already heard that I could not use generic big block pulleys, but this is the first about a difference in the frames. I thought all the frames were basically the same except for improvements made through the years 68-82.;help

There is not a difference in the frames between big and small block Vettes. I am swapping my SBC for a 427 that I've been rebuilding - at a slow pace that my wallet can handle! May I ask why you're going with a 427 instead of 454 -- which would be correct for your car.

 

[wallyknoch]

There is not a difference in the frames between big and small block Vettes.

Im not sure this statement is correct. Two reasons,

#1 it`s hearsay....

#2, The balancer may hit the front cross member because a BB is slightly longer than a SB. And the BB frames DO have a special indentation to accomodate this issue. I could possibly see that it would be a no issue with frames up to 74, the last year BB were offered. But after 74, ie 75`s it might be present and become a minor issue.

Easy fix though. Heat the area red hot and cosmedically drive some clearance in the frames front cross member.

 

[Rookie Vette owner]

The reason for the 427 vs 454 is pretty much the same as your's $$$
I was given an unbored/turned engine. It makes a pretty good starting point, but the $$$ still ring up fast. I intend to go with the aluminum heads to reduce the weight (back to SB range) hydralic roller cam, no turbo or nitrous, etc... Just to have to drive around town or to the mountains.

 

[Rookie Vette owner]

Im not sure this statement is correct. Two reasons,

#1 it`s hearsay....

#2, The balancer may hit the front cross member because a BB is slightly longer than a SB. And the BB frames DO have a special indentation to accomodate this issue. I could possibly see that it would be a no issue with frames up to 74, the last year BB were offered. But after 74, ie 75`s it might be present and become a minor issue.

Easy fix though. Heat the area red hot and cosmedically drive some clearance in the frames front cross member.

Is the indentation easily recognizable and if I do have to make it, will I still need to use the "corvette" pulleys or will regular BB pulleys be acceptable?

 

[6880 Mike]

...There is not a difference in the frames between big and small block Vettes....

I agree. Your stock frame will accept a big block. To make the swap as pleasant as possible, my advice is to purchase the assembly instruction manual for '73 and take a look at the factory big block installation. The AIM will list the pullies, balancer, brackets, radiator, shroud, fan, etc. you will need. Stick with stock parts and you should be okay.

 

[Crimson Thunder]

1965 was the year they had to modify the front crossmember to make room for the balancer on the big blocks.Your car should have no problem accepting a big block.

 

[fine69]

Im not sure this statement is correct. Two reasons,

#1 it`s hearsay....

#2, The balancer may hit the front cross member because a BB is slightly longer than a SB. And the BB frames DO have a special indentation to accomodate this issue. I could possibly see that it would be a no issue with frames up to 74, the last year BB were offered. But after 74, ie 75`s it might be present and become a minor issue.

Easy fix though. Heat the area red hot and cosmedically drive some clearance in the frames front cross member.

Years ago, I helped someone install a 454 in his 1972 Vette. It originally had a base 350. It fit without mods as I recall.

I just measured the big block, it's just shy of 2 ft long... a couple inches longer than the 350. The front cross member in my Vette has the indentation that you described. I never noticed that before. Cool. It should fit without problems.

 

[Rookie Vette owner]

Question for Fine69 big block swap

I'm looking for a set of aluminum heads for my 427 and before I go to far, I wanted to know if you had your transplant completed or if you know of any problems with clearance problems between valve covers and the power brake booster. I have read where special low profile V/C were available and I assumed that was the reason. I also figure that the added height of roller rockers will necessitate the use of tall covers, so I'm trying to see what my options are.

 

[LVMYVT76]

I just read in my new CORVETTE FEVER mag, that the clearance problem was usually due to the locking nut used. Comp cams has a nut that can be used to delete the problem. You might check into this.

 

[Rookie Vette owner]

Thanks, I had just picked up that issue over the weekend, just got around to looking at it last night. They refer to the lock nuts as being the issue with using low profile covers. Do you or anyone know if there is any other issue with aftermarket aluminum heads and taller valve covers running into clearance issues with the brake booster? Are the aluminum heads themselves taller than the original, I know they have more build up in some areas that require longer than stock bolts to mount them?

Thanks again!

 

[corvette66]

I recently used the GMPP BBC aluminum heads 12363391 they are the ones with the 2.25 intake valves. They seem to be the same hight as a stock head, but the front row of head bolts (longest ones) are about 1" longer than stock bolts. So that being said, hmmmm they could be taller or the bolt boss is machined higher in the head.

I have no power brakes on my 69 so hard to say about the booster.

I had a 73 vette that i put a 454 in and used the tall moroso valve covers with a brake booster and it fit just fine, but they are an in-between size valve cover, they make shorter and taller covers than the stamped steel moroso ones.

As far as the balancer goes, on my 73, i used a 6 1/4" balancer with a flat lower pulley and a short water pump, had no problems.

 

[Rookie Vette owner]

I had a 73 vette that i put a 454 in and used the tall moroso valve covers with a brake booster and it fit just fine, but they are an in-between size valve cover, they make shorter and taller covers than the stamped steel moroso ones.

As far as the balancer goes, on my 73, i used a 6 1/4" balancer with a flat lower pulley and a short water pump, had no problems.

With the conversion in the 73, what other parts of the drive train did you upgrade on? As far as the 6 1/4" balancer was this a custom piece or just a regular part that happened to fit? Same for the "flat pulley"?

Thanks, Tom