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View Full Version : how to convert pre-CB to common block



tvanlant
03-15-2006, 09:21 PM
I've passed the recommended hp level for the pre-common block in my 87 GLHS and I want to switch to common block. I would like to use my rotating assembly, if possible, cam, accessories, and as much else as I can from my current engine.

If you could please list ALL of the things I will need to change.
Thanks, Tyler

turbovanmanČ
03-15-2006, 10:09 PM
Everything external bolts on.

Whats different is the cranks, oil pans and timing related items. CB uses round tooth, you have square tooth so you need to get 2 round tooth pulleys-one for you cam, one for you aux shaft.

tvanlant
03-15-2006, 11:19 PM
Can I not use my square timing sprockets off my pre-CB on the common block? Also, if I put a round tooth sprocket on my cam, wont that throw the timing off?

86Shelby
03-16-2006, 12:45 AM
Can I not use my square timing sprockets off my pre-CB on the common block? Also, if I put a round tooth sprocket on my cam, wont that throw the timing off?

The square tooth sprocket won't fit on the common block crank. Your cam timing will be off a few degrees. An adjustable cam sprocket or keyways will alow you get it back where you want it.

tvanlant
03-16-2006, 12:58 AM
Excellent. So if I get a complete common block short block, all that I will need to change is the sprocket on my cam, correct? All the accessories from my old engine will bolt to it, correct?

GLHSKEN
03-16-2006, 07:52 AM
Ues, Accessories bolt on

tvanlant
03-16-2006, 12:31 PM
Are you running a CB in your GLHS, ken?

GLHSKEN
03-16-2006, 12:40 PM
Mine has been off the road for a bit. I was running an 87 block with tII rods and laid down 291/341 on the dyno. I was not worried about it in the least at that level.

A +40 went bad and toasted that engine. So I built a cb forged engine with a CB 2.2L cast crank. This time the cal did not provide enough fuel and torched a piston... (swapped to a menegon head... what a difference)

turbovanmanČ
03-16-2006, 12:56 PM
Excellent. So if I get a complete common block short block, all that I will need to change is the sprocket on my cam, correct? All the accessories from my old engine will bolt to it, correct?


Yep, :nod:



Bummer Ken, you have luck like me, :(

Turbodave
03-16-2006, 01:53 PM
Common block uses a different water pump and pulley. I've never tried to swap one over, but I remember hearing that the non-common block w/p hits the block when bolted onto a common block engine. Can anyone confirm this?

BadAssPerformance
03-16-2006, 02:09 PM
Common block uses a different water pump and pulley. I've never tried to swap one over, but I remember hearing that the non-common block w/p hits the block when bolted onto a common block engine. Can anyone confirm this?

I have the '87 water pump on my '89 CB and it fits ok w/o touching the block. Only issue is that the water pump needs to be removed to remove the oil pan or the oil pan needs to be notched to be able to remove the pan with the pump attached.

So, the subject of the thread makes me ask much HP is the non-common block good for?

cordes
03-16-2006, 02:27 PM
I have seen many guys state that they get weary of the pre-cb at over 300HP. If it is a TII short block a little more. There have obviously been several guys who have put some good power through them though.

GLHSKEN
03-16-2006, 02:57 PM
I have the '87 water pump on my '89 CB and it fits ok w/o touching the block. Only issue is that the water pump needs to be removed to remove the oil pan or the oil pan needs to be notched to be able to remove the pan with the pump attached.

So, the subject of the thread makes me ask much HP is the non-common block good for?

The notching works great... no leaks after I did it.

Turbodave
03-16-2006, 03:12 PM
I have the '87 water pump on my '89 CB and it fits ok w/o touching the block. Only issue is that the water pump needs to be removed to remove the oil pan or the oil pan needs to be notched to be able to remove the pan with the pump attached.

So, the subject of the thread makes me ask much HP is the non-common block good for?


I knew I heard of some clearance issue, but that's no big deal if it only comes into play when removing the oil pan. Hopefully that's not something you have to do that often.

8valves
03-16-2006, 03:43 PM
So, the subject of the thread makes me ask much HP is the non-common block good for?

Joe O'Connor has dyno'd 370 or in the neighborhood on a pre-common block engine. As far as I know that's been running like that for a long time now. Ken would probably know how long it has been, or at least a guess. I think it's over a couple years.

Aaron Miller

turbovanmanČ
03-16-2006, 03:59 PM
I would believe that if your racing and running max HP all the time, then a CB makes sense. If you keeping the boost reasonable on the street with the occasional strip blast, the non-CB should be just fine, :thumb:

GLHSKEN
03-16-2006, 04:10 PM
Joe O'Connor has dyno'd 370 or in the neighborhood on a pre-common block engine. As far as I know that's been running like that for a long time now. Ken would probably know how long it has been, or at least a guess. I think it's over a couple years.

Aaron Miller

1st time I saw Jope at the track was 2001. still has the same engine. Runs 125mph consistantly

GLHSKEN
03-16-2006, 04:12 PM
LOL... You start making over 300whp, you can ONLY run hard for 12-13 seconds at a time seconds at a time... That's a full 1/4 at 105+mph. Not many chances to really stretch the legs.

8valves
03-16-2006, 04:27 PM
1st time I saw Jope at the track was 2001. still has the same engine. Runs 125mph consistantly

There ya have it folks, straight from the archives...!!! :p :lol:

Just kidding Ken- you know I'm a respectful young'n.

Aaron Miller

GLHSKEN
03-16-2006, 05:08 PM
Lol...

tvanlant
03-16-2006, 05:42 PM
Well, I need an new water pump anyway, so should I just get one for a CB?

I'm going by what thedodgegarage says for hp to the pre-CB, which is 250 hp. My car is a daily driver and gets run hard every day.

turbovanmanČ
03-16-2006, 06:13 PM
Get a CB waterpump, will make it alot easier. You might have to run the CB wp housing though.

cordes
03-16-2006, 06:21 PM
Get a CB waterpump, will make it alot easier. You might have to run the CB wp housing though.

I did not notice a difference between the two housings this last summer when I did the swap on my omni. Perhaps I was not looking hard enough?

turbovanmanČ
03-16-2006, 06:31 PM
I did not notice a difference between the two housings this last summer when I did the swap on my omni. Perhaps I was not looking hard enough?

When I cracked my housing, they listed pre CB under a different part number. Also, if memory serves, the pump the way it mounts is different between the 2. Now, again, I could be wrong but this is what sticks out in my head, :thumb:

GLHSKEN
03-16-2006, 06:48 PM
I did not notice a difference between the two housings this last summer when I did the swap on my omni. Perhaps I was not looking hard enough?


The pre cb housing will interfere with the pan.... been there had to grind.

cordes
03-16-2006, 06:59 PM
The pre cb housing will interfere with the pan.... been there had to grind.

OK, that certainly makes sense. I put the newer housing on the older block and not the other way a round. Good to know.

tvanlant
03-21-2006, 12:42 AM
Hey, I just seen on TU that there is a different oil pump for the common block too. So I need to buy another pump for $120? This conversion is getting expensive.

The new question:

Do I really need to switch to a common block in fear of making too much power for it? I will at max be making 300 hp at the crank. I was just going by what gary donovan said on his site about the pre-common blocks twisting and breaking cranks around 250 hp. Is it reallly necessary that I do the switch? Or could I get away with the pre-common block?

tvanlant
03-21-2006, 12:50 AM
I think I'll start a new thread for this question.

turbo xtc
05-09-2006, 08:06 AM
Common block uses a different water pump and pulley. I've never tried to swap one over, but I remember hearing that the non-common block w/p hits the block when bolted onto a common block engine. Can anyone confirm this?
no the pulley won't hit but the belt rubs on the backside of they pulley therefore the pump housing has to be changed for two reasons(1)water pump spins backwards (2)there are only two belts for the water pump one is shorter then the other your brackets will have to be changed and i never got to mis-match them the transmission is different if you have a auto tranny common blocks have a 8 bolt pattern non-common has 6 and your flex plate has 4 bolts for the converter non-common has 3 and you can't just change the torque converter because the oil pump in the tranny has a different type of slot.I had to use the water pump and i used the alternator off a 1989 daytona but i had to change the pulley on it it is smaller and every time i started it up it squealed.I used the cam spocket to change to rounded they are more quiter then the square-toothed spockets

Subliminal
05-09-2006, 08:22 AM
My advice:

Run whatcha got until it breaks. In the meantime, start building a common block in your garage. When you get done, or when it breaks, just swap it over. These accessories you're talking about (water pump, etc) can be had for peanuts in the fs section.