2 bolt vs 4 bolt is 4 worth it?
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From: Mobile, AL
Car: GTA
Engine: 383 HSR
Transmission: TH-700R4
Axle/Gears: 3.42
2 bolt vs 4 bolt is 4 worth it?
I have a two bolt block and I was looking to get a four bolt block. A buddy of mine says there really is no huge gain of having a 4 bolt other than it is stronger at high rpms vs a 2 bolt is better for low end... any insight in this?
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From: Yellowknife, NWT, Canada
Car: 84 Z28
Engine: 357
Transmission: TH-350C
Axle/Gears: 3.43
not much better. definately not worth it if its going to cost alot more over a 2bolt block.
If you need strength keep the 2bolt and get it machined for a 4bolt splayed cap. its stronger than a production 4bolt and will most likely cost the same if not less.
If you need strength keep the 2bolt and get it machined for a 4bolt splayed cap. its stronger than a production 4bolt and will most likely cost the same if not less.
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From: RIO RANCHO, NEW MEXICO
Car: 1985 TRANS AM
Engine: 383 SBC
Transmission: T-5
i have heard that there is really no huge advantage and i even watched a build up (mabe horsepower tv???) where they took a 2 bolt block and bought aftermarked main caps and they stated that this would be stronger than a 4 bolt by a long shot. those main caps are really going to come into play if you are making gobs of horsepower and are turning 7500+.
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From: Elk City OK
Car: 92 25th anv z28
Engine: 346 TC78 Turbo
Transmission: 4L80E
Axle/Gears: 3.25 9"Nodular, Strange axles
Well.. I'm running a 2 bolt main in my car and at time have spooled the thing up to 8500 rpm (woops) After that i decided to run a rev limiter. Everything held together. Never had car dynoed but people running my set um are making around 600 hp at the wheels
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From: Littleton, CO USA
Car: 82 Berlinetta/57 Bel Air
Engine: L92/LQ4 (both w/4" stroke)
Transmission: 4L80E/4L80E
Axle/Gears: 12B-3.73/9"-3.89
The factory came up with the 4-bolt main concept primarily for truck engines. They weren't interested in making the cap "stronger", but rather to clamp it more securely to the block so the cap wouldn't "walk". A thumper motor pulling hard at 4000 RPMs is just as likely to damage a bearing from cap walk as is a high-winder turning 7000 RPMs. Note that they continued 4-bolt mains in trucks even after 1992, but no 3rd gen "performance" engine got them. In fact, very few passenger car engines got them after 1977 (Vettes excepted).
You should also know that the outer bolt holes of a factory 4-bolt main block actually weaken the main web in the block. The strongest combo is to take a 2-bolt main block and have aftermarket splayed 4-bolt caps installed. The angle of the outer bolts doesn't have the web weakening effect.
You should also know that the outer bolt holes of a factory 4-bolt main block actually weaken the main web in the block. The strongest combo is to take a 2-bolt main block and have aftermarket splayed 4-bolt caps installed. The angle of the outer bolts doesn't have the web weakening effect.
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From: Cypress, California
Car: 1989 GTA
Engine: 369 TPI
Transmission: 4L60E
Axle/Gears: 3.70 Nine Bolt
The only reason I went with a 4 bolt for my build up is because I was able to get a "core" 4 bolt block for the same price as the two bolt.
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From: Yellowknife, NWT, Canada
Car: 84 Z28
Engine: 357
Transmission: TH-350C
Axle/Gears: 3.43
Originally Posted by 1989GTATransAm
The only reason I went with a 4 bolt for my build up is because I was able to get a "core" 4 bolt block for the same price as the two bolt.
When i bought my new block they only had a 4bolt in stock and it was only about $60 more than the 2bolt. For that kind of price diff i didnt care, it wont be making eough power or be spinning high enough to warrant getting a 2bolt block splayed to 4.
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From: Mobile, AL
Car: GTA
Engine: 383 HSR
Transmission: TH-700R4
Axle/Gears: 3.42
So a 2 bolt converted to a 4 bolt is the best route? How much does this stuff go for? in the ball park?
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From: Springfield,Mo
Car: 87 Berlinetta,work in progress
Engine: 468 BB,still in the build process
Transmission: TH350,3500 stall
Axle/Gears: 9" Ford,learning how to live under
Yes,a 2 bolt converted w/ splayed caps is about as good as it gets from a stock block.How much power are you looking to make?I really doubt you need to do anything to your 2 bolt block.If it needs align honed,put studs in it.Otherwise,if your looking at 500HP or less,I'd say run it and spend your $$$$ elsewhere.Just my
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From: Mercedes Norte, Heredia, Costa Rica
Car: 1984 Z28 Hardtop
Engine: 383 Carb
Transmission: 4L60
Axle/Gears: 3.54 Dana 44
Originally Posted by nelapse
So a 2 bolt converted to a 4 bolt is the best route? How much does this stuff go for? in the ball park?
If you've got a 2 bolt block, build a 2 bolt engine. If you've got a 4 bolt block, build a 4 bolt engine.
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From: Mobile, AL
Car: GTA
Engine: 383 HSR
Transmission: TH-700R4
Axle/Gears: 3.42
I am looking for about 450-500 hp I have driven a 600 hp mustang and I think there is such a thing as too much hp, at least for street fun... the reason why i brought all of this up is because i have a problem... I have a 2 bolt motor that is a little rough and requires a complete rebuild... and I wasnt sure if i should spend that kind of money on a 2 bolt or 4 bolt. I will stick with the 2 and start my rebuild
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From: Madison, WI
Car: 1986 Camaro Z28
Engine: 400
Transmission: T5
Axle/Gears: 10 bolt Posi 3.73
Originally Posted by five7kid
... making the cap "stronger", but rather to clamp it more securely to the block so the cap wouldn't "walk". A thumper motor pulling hard at 4000 RPMs is just as likely to damage a bearing from cap walk as is a high-winder turning 7000 RPMs. ...
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From: Armpit state
Car: 71 Nova
Engine: Superramed 383, Topline heads
Transmission: 700r4
Axle/Gears: 8.2 posi 3.08
Yes i have seen some pictures of circle track engines producing around 400-500hp and they showed what happens to a two bolt after a season. You start to see the flex in the main area and all the bearings start wearing in an uneven manner and denotes the flex in the main area and the caps walking. Of course these are engines in 7000+ rpm ranges running a grueling season till they break it down at the end for inspection. A 1/4 mile car or even a daily driver would never be under this kind of rpm for as long of a length of time.
Ive heard this is mainly only true with 400 blocks because the webbing is thinner in those areas because of the journal size. I hope your not confusing the two. This is attributed to the 400 main journal of 2.65. You can retain the 2.45 main journal of a 350 block with an aftermarket crank and even the 4 bolt will be plenty strong to a certain degree. But the splayed is by far the strongest of all. Just wanted to put in perspective.
You should also know that the outer bolt holes of a factory 4-bolt main block actually weaken the main web in the block. The strongest combo is to take a 2-bolt main block and have aftermarket splayed 4-bolt caps installed. The angle of the outer bolts doesn't have the web weakening effect.
Last edited by shaggy56; May 26, 2006 at 04:24 PM.
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From: Smokey Mountains, NC
Car: 91 Camaro RS
Engine: 305 TBI
Transmission: Auto
Axle/Gears: Stock
Here's a quote from montecarloss.com:
If you need a little insurance, you can do what the SBF guys have been doin' for a while, get one of these: Main Girdle WITH fasteners. That should keep your main cap flex in line, just make sure your windage tray (if used) clears.
This is according to several sources, none which completely agree, so I used the lower values from several sources and rounded down to be safe...
2-bolt blocks with OEM main bolts are good to 400hp
2-bolt blocks with ARP main studs are good to 550hp ++High Nickel Blocks to 700hp
4-bolt blocks with OEM main bolts are good to 475hp
4-bolt blocks with ARP main studs are good to 700hp
OEM Blocks with Splayed 4-bolt main studs are good to over 950hp
Bowtie blocks with splayed 4-bolts main studs should handle over 1500+hp!
So essentially, a 2-bolt block w/ studs should handle anything a normally aspirated small block can produce. (assuming everything is in good shape and proper tolerances are closely followed)
Engine RPM plays even a larger factor in determining safe power limits for various block/cap combos.
OEM 2-bolt blocks are good to 6000 rpm.
2-bolts with ARP studs are good to 7000 rpm.
OEM 4-bolt blocks are good to 7200 rpm.
4-bolts with ARP studs are good up to 8500 rpm.
Bowtie or OEM 4-bolt Splayed Studs and cap are good for well over 8500 rpm.
-These figures were aquired from a Super Chevy magazine, Popular Hot Rodding,
and a couple local machine shops
In the Article, it stated that a 250hp engine that was spinning at 7500rpm exerted more loading force
on the Main-caps than a 550hp engine spinning at only 5500 rpm. This means power and RPM must be considered
when selecting how much beef you need in your bottom end.
The HP figures are good references, but the RPM limit of the motor is a better way to choose your block
according to the authors of the article.
2-bolt blocks with OEM main bolts are good to 400hp
2-bolt blocks with ARP main studs are good to 550hp ++High Nickel Blocks to 700hp
4-bolt blocks with OEM main bolts are good to 475hp
4-bolt blocks with ARP main studs are good to 700hp
OEM Blocks with Splayed 4-bolt main studs are good to over 950hp
Bowtie blocks with splayed 4-bolts main studs should handle over 1500+hp!
So essentially, a 2-bolt block w/ studs should handle anything a normally aspirated small block can produce. (assuming everything is in good shape and proper tolerances are closely followed)
Engine RPM plays even a larger factor in determining safe power limits for various block/cap combos.
OEM 2-bolt blocks are good to 6000 rpm.
2-bolts with ARP studs are good to 7000 rpm.
OEM 4-bolt blocks are good to 7200 rpm.
4-bolts with ARP studs are good up to 8500 rpm.
Bowtie or OEM 4-bolt Splayed Studs and cap are good for well over 8500 rpm.
-These figures were aquired from a Super Chevy magazine, Popular Hot Rodding,
and a couple local machine shops
In the Article, it stated that a 250hp engine that was spinning at 7500rpm exerted more loading force
on the Main-caps than a 550hp engine spinning at only 5500 rpm. This means power and RPM must be considered
when selecting how much beef you need in your bottom end.
The HP figures are good references, but the RPM limit of the motor is a better way to choose your block
according to the authors of the article.
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From: Elk City OK
Car: 92 25th anv z28
Engine: 346 TC78 Turbo
Transmission: 4L80E
Axle/Gears: 3.25 9"Nodular, Strange axles
Well once again.. I'm running approx 600+ hp and blow up tranny s and rearends before m
y two bolt.. Now rev limited to 7500.. everything killer.
y two bolt.. Now rev limited to 7500.. everything killer. 
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From: In the corner of my mind!
Car: 1989 TTA #1240
Engine: 3.8 SFI turbo
Transmission: 2004r
Axle/Gears: 3.27
I'll have a 2bolt on the stand with a girdle going on it, should be fine for most peoples planned power level..
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