4 bolt main cap ?

**JaycenK** · 11-30-2008, 11:30 PM

Can anyone tell me what the advantage of 4 bolt mains in the LT1 blocks are?
I know the corvette LT1's & LT4 had 4 bolt mains but all the F-bodys had 2 bolt mains except a few specialty cars.
Why was this the case? Can you have a 2 bolt main block drilled for 4 bolt main caps?

**Sleeper101** · 12-01-2008, 08:31 AM

yes you can have a 2 bolt block drilled to accept 4 bolt caps. from what i have been told the 2 bolt blocks drilled to a 4 bolt cap is suppose to be stronger than a factory 4 bolt main block. im currently looking into this also as im fixing to put my stroker motor back together. anyone else got any input?

**aeromachine** · 12-01-2008, 09:46 AM

Originally Posted by Sleeper101

yes you can have a 2 bolt block drilled to accept 4 bolt caps. from what i have been told the 2 bolt blocks drilled to a 4 bolt cap is suppose to be stronger than a factory 4 bolt main block. im currently looking into this also as im fixing to put my stroker motor back together. anyone else got any input?

Use the aftermarket "Splayed" caps on the 3 center mains. The bolts go in at an angle under the water jacket where there is more iron to grab. Also, they pull in the original cap registers tight and help reduce the caps "walking" in the registers.

The block must be align-bored / honed after the caps are installed; I usually get around $350 for labor for the whole job. Multiple folks make caps; I suggest Milodon.

**5.0THIS** · 12-01-2008, 11:00 PM

There actually has been some debate as to wether a factory four bolt main block as strong or stronger than a 2 bolt block that has been adapted to aftermarket splayed mains.

Nonetheless, a 4 bolt main simply provides a stronger bottom end. That being said, most people who say they need a 4 bolt main really dont... And you RARELY see an engine fail because one of the main caps broke. Cheap insurance anyway, and the four bolt block is the preferred block to start a build with.

**JaycenK** · 12-02-2008, 07:44 AM

Cool thanks guys!! I guess it would be worth it to do it now and have the add protection incase I decied to go wild down the road.

**Sleeper101** · 12-08-2008, 03:50 PM

Well I found out there is alot cheaper option, My machinist says he uses a Solid 1/4 inch plate he drills 2 holes in and machines 1 side flat to go against the main cap and Bolts it to the main cap using ARP Studs.

**Firebirdjones** · 12-08-2008, 06:24 PM

That would be interesting to see. Does it still allow room for a windage tray???

**Firebirdjones** · 12-08-2008, 06:26 PM

Originally Posted by 5.0THIS

There actually has been some debate as to wether a factory four bolt main block as strong or stronger than a 2 bolt block that has been adapted to aftermarket splayed mains.

Nonetheless, a 4 bolt main simply provides a stronger bottom end. That being said, most people who say they need a 4 bolt main really dont... And you RARELY see an engine fail because one of the main caps broke. Cheap insurance anyway, and the four bolt block is the preferred block to start a build with.

What happens more times than not with 2 bolt mains is not so much cap breakage but simply just bearing failure. Just as Aeromachine aluded to,,,those caps really squirm around at high rpms,,,all that movement is hard on the bearings. The 4 bolt mains eliminated some of this. The splayed mains pretty much stop it.

**5.0THIS** · 12-09-2008, 12:03 AM

Originally Posted by Firebirdjones

What happens more times than not with 2 bolt mains is not so much cap breakage but simply just bearing failure. Just as Aeromachine aluded to,,,those caps really squirm around at high rpms,,,all that movement is hard on the bearings. The 4 bolt mains eliminated some of this. The splayed mains pretty much stop it.

Just going off of what I have seen. I have built several circle track engines with both two and four bolt mains. These are engines that live between 5000 and 7500 rpm most of the time. With a 50 pound crank rule, and I beam rods, I really havent seen a difference in bearing wear between the two cap setups.

**bigrondownhiller** · 12-09-2008, 12:59 PM

Originally Posted by Sleeper101

Well I found out there is alot cheaper option, My machinist says he uses a Solid 1/4 inch plate he drills 2 holes in and machines 1 side flat to go against the main cap and Bolts it to the main cap using ARP Studs.

Main stud girdle. It will help keeping everything a little stiffer. What kind of power and rpm are you planning for your engine?

**Sleeper101** · 12-09-2008, 05:00 PM

well the one im building for a friend we plan on making little over 450 n/a at the crank and he wants to add a 150 posssibly a 200shot to it.

**bigrondownhiller** · 12-10-2008, 09:09 AM

Then I would do a splayed cap. Without the nitrous it might be fine but with it I wouldn't do without.

**5.0THIS** · 12-10-2008, 09:59 AM

Originally Posted by Sleeper101

well the one im building for a friend we plan on making little over 450 n/a at the crank and he wants to add a 150 posssibly a 200shot to it.

any four bolt main will be fine, just use ARP hardware.

**Sleeper101** · 12-10-2008, 02:31 PM

were going to use the 2 bolt caps with the plate my machinist makes. he has built MANY MANY sprayed motors and have never split a cap using those along with arp hardware. its the cheapest n seems to be the best bang for the buck. ill get some pics tom when im at the shop to show exactly what were building.