converting 2 bolt to 4 bolt
Thread Starter
Instructor
Joined: May 2013
Posts: 105
Likes: 14
From: Chandler Arizona
converting 2 bolt to 4 bolt
I would like to convert my 2 bolt to a 4 bolt. Is this fairly straight forward? Will it weaken my block? What should I tell the machine shop? Thanks
Thread Starter
Instructor
Joined: May 2013
Posts: 105
Likes: 14
From: Chandler Arizona
Sorry, I should have been more specific. It's a Chevy 350 with a casting date of 1971. The engine is not original to the car. One machine shop I spoke with told me that drilling the extra holes would weaken the block. I had never heard this before. I would like to make the conversion to a 4 bolt if possible.
Le Mans Master
Joined: Oct 2010
Posts: 6,931
Likes: 845
From: melbourne florida
2023 C3 of the Year Finalist - Modified
if i was doing it i would use the splayed caps. but it depends on your power level, if you are using a cast crank don't waste your money. studs will strengthen the 2 bolt up a little. but the weaken the block stuff is ridiculous.
Drifting
Joined: Jan 2012
Posts: 1,908
Likes: 129
From: Fredericksburg Virginia
A few thoughts:
I was faced with the decision of refurbishing my LT-1 Camel Hump Heads for $700 that would limit my cam choices to under 0.500 or purchasing new custom aluminum 200cc heads that would give me fairly unlimited possibilities for $950.
In the same breath, I would also mention that 2-bolt blocks are not junk...they are definitely good up to 600 HP or so safely and can be balanced to a 6,500 or 7,000 RPM engine, just like a 4-bolt. My 500 HP build could just as easily have been based on a 2-bolt block, for example.
So, I would question the need to move forward with throwing money at a conversion. And if you feel so passionately about it, look into the cost of a new or refurbished 4-bolt block first.
I was faced with the decision of refurbishing my LT-1 Camel Hump Heads for $700 that would limit my cam choices to under 0.500 or purchasing new custom aluminum 200cc heads that would give me fairly unlimited possibilities for $950.
In the same breath, I would also mention that 2-bolt blocks are not junk...they are definitely good up to 600 HP or so safely and can be balanced to a 6,500 or 7,000 RPM engine, just like a 4-bolt. My 500 HP build could just as easily have been based on a 2-bolt block, for example.
So, I would question the need to move forward with throwing money at a conversion. And if you feel so passionately about it, look into the cost of a new or refurbished 4-bolt block first.
Burning Brakes
Joined: Sep 2012
Posts: 818
Likes: 0
From: coon rapids mn
whats the block casting number ?like mentioned above splayed caps and bolts should put threads into a beefier part of the block.if you engine is worth money ,bag it and store it .get a better block to build a 383 + ci short block.competition products sells 383 short blocks starting at $2000.
Team Owner
Joined: Sep 2006
Posts: 31,236
Likes: 4,327
From: Westminster Maryland
Hi,
I really don't know very much about building engines but I believe the same block casting was used for 2 or 4 bolt main caps.
So wouldn't it be a matter of doing the machining and then installing the proper parts and fasteners when making the change from 2 to 4?
Regards,
Alan
Or do I know so little I don't even understand the question?
I really don't know very much about building engines but I believe the same block casting was used for 2 or 4 bolt main caps.
So wouldn't it be a matter of doing the machining and then installing the proper parts and fasteners when making the change from 2 to 4?
Regards,
Alan
Or do I know so little I don't even understand the question?
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Racer
Joined: Feb 2013
Posts: 386
Likes: 3
From: Clifton Virginia
Instead going 4 bolt from 2 bolt. Do the ARP stud on the 2 bolt main. It will be stronger than a 4 bolt main and you can have over 500HP easy on a 350.
Last edited by jackwabbit703; May 8, 2013 at 02:43 PM.
Le Mans Master
Joined: May 2007
Posts: 5,021
Likes: 1,120
From: North tonawanda NY
I just bought a 4bolt long block o. Craigslost for 300 bucks with 12,000 miles on it since being rebuilt and stored my 2bolt original block..... even with replacing all the bearings and crank due to a broken ring I still came out way ahead... its a high nickel marked 010-020 block too which are stronger and have a higher wear resistance. I would suggest doing g something like this.
Drifting
Joined: Jan 2012
Posts: 1,908
Likes: 129
From: Fredericksburg Virginia
Totally agree with Mr. Jackwabbit703 that putting KNOWN premium parts in, like ARP studs, would make a 2-bolt block even more suitable for a solid build.
Of course, if you have a 2-bolt block, you probably have a cast crank and rods.
If you want to bump horsepower to the level of even REMOTELY being concerned about 2-bolt vs. 4-bolt lower ends, you're going to end up with a new crank, rods, pistons, and probably heads.
Doing that, you're probably doing cam, lifters, rockers, etc. If done right, you may end up with the ONLY part you're left with is the block itself, including new fasteners. Maybe you'll keep the oil pan, but will probably want more capacity.
Then you'll need a carb and ignition to keep up. And maybe make it a little prettier along the way. Then you'll be tearing into the engine bay.
Don't ask me how I know this...I'll have to explain my past 9 months and $5,000 of Corvette ownership.
Of course, if you have a 2-bolt block, you probably have a cast crank and rods.
If you want to bump horsepower to the level of even REMOTELY being concerned about 2-bolt vs. 4-bolt lower ends, you're going to end up with a new crank, rods, pistons, and probably heads.
Doing that, you're probably doing cam, lifters, rockers, etc. If done right, you may end up with the ONLY part you're left with is the block itself, including new fasteners. Maybe you'll keep the oil pan, but will probably want more capacity.
Then you'll need a carb and ignition to keep up. And maybe make it a little prettier along the way. Then you'll be tearing into the engine bay.
Don't ask me how I know this...I'll have to explain my past 9 months and $5,000 of Corvette ownership.
Last edited by keithinspace; May 8, 2013 at 03:20 PM.
Instructor
Joined: Mar 2013
Posts: 215
Likes: 0
From: Sunshine Coast Qld
Sorry, I should have been more specific. It's a Chevy 350 with a casting date of 1971. The engine is not original to the car. One machine shop I spoke with told me that drilling the extra holes would weaken the block. I had never heard this before. I would like to make the conversion to a 4 bolt if possible.
Race Director
Joined: Jul 2001
Posts: 15,892
Likes: 42
Hi,
I really don't know very much about building engines but I believe the same block casting was used for 2 or 4 bolt main caps.
So wouldn't it be a matter of doing the machining and then installing the proper parts and fasteners when making the change from 2 to 4?
Regards,
Alan
Or do I know so little I don't even understand the question?
I really don't know very much about building engines but I believe the same block casting was used for 2 or 4 bolt main caps.
So wouldn't it be a matter of doing the machining and then installing the proper parts and fasteners when making the change from 2 to 4?
Regards,
Alan
Or do I know so little I don't even understand the question?
Whether it's worth the trouble or not just for bragging rights is another story.
Safety Car
Joined: Mar 2007
Posts: 3,652
Likes: 49
From: Bridgewater nj
That's a lot of machine work for not much gain. Many have said it makes the block weaker especially in the small block 400 but you can find a 4 bolt 350 easily! Almost every Chevy truck bigger than a CK1500 will have a 4 bolt.
Many of us have seen very strong 400+ HP 6800rpm ,ARP 2 bolt main 350 with no problems so IMHO build what you got and use that money on a nice set of heads instead of machine work
Many of us have seen very strong 400+ HP 6800rpm ,ARP 2 bolt main 350 with no problems so IMHO build what you got and use that money on a nice set of heads instead of machine work
Team Owner
Joined: Oct 2004
Posts: 81,241
Likes: 3,063
From: altered state
St. Jude Donor '05
ts a high nickel marked 010-020 block too which are stronger and have a higher wear resistance.
OP ditto on getting another machinist
A studded 4 bolt will take enough power to equal the blocks failing point which most here will never find. Dont worry about all the horror stories.
Im using a late GM mexican made block 3.75 stroke no splayed mains and run it up to 7k without worry nothing has exploded yet.
Race Director
Joined: Jul 2001
Posts: 15,892
Likes: 42
I just bought a 4bolt long block o. Craigslost for 300 bucks with 12,000 miles on it since being rebuilt and stored my 2bolt original block..... even with replacing all the bearings and crank due to a broken ring I still came out way ahead... its a high nickel marked 010-020 block too which are stronger and have a higher wear resistance. I would suggest doing g something like this.
