What is a good guideline for when 2 bolts are adequate and when 4 bolts should be installed?

 

I would call your question seemingly simple but with no simple answer other than to look at it practically. If you are rebuilding the bottom end anyway with a new rotating assy., then it only makes sense to upgrade the main caps. While not cheap, the upgrade isn't terribly costly either. But I would never even think of it until upgrading the rest of the bottom end anywya.

As far as the mystique of splayed billet 4-bolt center caps, that is primarily mystique. There is legitimate debate among engine builders about splayed caps on stock blocks. And FWIW, my previous motor did fine with straight 4-bolt nodular iron caps. This round I am using straight steel caps, mostly because the nodular iron caps have been discontinued. If not, I might just have used them again since they did such a good job for me last time. But all in all, the steel caps are probably stronger.

Rich Krause

 

Depends on RPM and power. The higher you want to twist it and the more power the more they are needed.

At around 500hp it's probably a good idea to put them on there.

Bret

 

Well I guess I'm starting to consider the possibility of putting together a mildly tuned 383, so I'm wondering if 4 bolt mains are necessary. At the power levels that are typical with a mild (1 5/8" shorties and something similar to GM 845 or hotcam) 383, would it be a bad idea to stay with the stock main caps? I'm not trying to cut corners, just trying to find out what is actually needed.

 

The stock caps would probably be fine with what you have in mind. Bret knows more about this than I do though.

Rich Krause

 

Here's another view from the peanut gallery...

I'm currently building what your describing. I've planned out a mild 383 (albeit with high compression). I'm using a CC305 cam, when combined with the increased displacement, "should" seem almost like a stocker with more torque. I have a complete forged bottom end (crank/rods (billet rods actually)/pistons). I opted to use steel 4-bolt caps (splayed, but I can't come up with a reasonable explaination as to why splayed would be better than straight - Thats for someone who knows a hella lot more than I do about shear planes and metallurgy ) . I have an entirely different reason for going all forged and steel caps though. I'm planning on spraying 300 horse worth of N2O through this thing, and spinning it to 7000, so I needed the extra strength. I probably should have hard blocked the bottom 1/3 of my block as well, but I didn't (hope I don't regret it later). I suppose my rambling point is that unless your going to do something over and above the mild 383 (blower/turbo/nitrous) then I really can't see a reason to go with a 4 bolt conversion, unless you just like saying you have a 4-bolt block. But then again I could be wrong. It's just my opinion/expsrience..

Dave C.

 

CCCCCYA: This is a little off topic, but I have a 383 with a CC305 and the dyno shows peak horsepower at 5700 and falling off dramatically at 6200. This was before my supercharger and with mildly ported heads and a 112 lsa. I would think that even with a wider lsa and great heads you would have a tough time making power all the way to 7000 with that cam. Just a thought.

 

Very good point, and the cam may indeed end up too small for this motor. I'm going to try and run the 305 just to see what happens (mostly since I already have it), and then see what it does with 300 HP worth of spray behind it. I have a feeling that it's going to want to rev a little more with that kind of juice flowing, but I'll have to experiment to see. Can't hurt, and I can always go bigger on the cam later on down the road (not that big of a deal to swap later when I have a lift available). I like the idea of running as small a cam as necessary to retain some of the "stock feel" of the car.

Time will tell (and a couple bottles )

Dave C.

 

*shrug* theres one guy running a stock crank with 2 bolt mains spraying 300shot of juice. its that picture floating around wiith him popping a wheelie with the bumper on the ground.

 

Assuming it's really is a stock crank/2-bolt/300 shot, the front wheels are up to clear the crank as it falls out one of these days.

If I wanted to psych out the competition, I'd lie thru my teeth about how weak my bottom end was.

This guy probably doesn't lie at all. Ask him what his cam specs are. I'm certain he'll give you chapter and verse.

 

well, all I can say to that is I sure hope he's the one I'm up against at the track, cause chaces are he wont make it to the final round and I will. Spraying 300 on a stock bottom end is just plain old stupid. Yeah, it "might" hold for a while, but it's doubtful. Something like that sounds more like someone talking than doing to me...

Believe me, I wouldn't have spent what I just did for the bottom on this motor if I didn't have to. I DO like to eat you know..

Dave C.

 

Why you have the motor apart why not do 4-bolt splayed caps, An extra $400 for piece of mind is worth it in my opinion.

 

$400 for peace of mind is still $400 wasted if it isn't necessary. I'm guessing there are a lot of guys making 400 hp with 2 bolt mains without problems, which is why I posted.

 

Hi, I am in the area of about 400 maybe a little more with stock rods,crank and main caps (upgrades are as follows arp rod bolts forged pistons) I beat the snot out of my stuff with no failures (6300 rpm shifts etc)

I did toast a couple of pistons but that was not do to a part failure but my stupidly with the tune etc…


So my 2cents is it is not worth the splayed upgrade unless you have the money or running serious HP (I mean over 700 hp)



In my opinion 4 bolt caps aren’t really necessary until about the 600 + hp level or for some serious high rpm high load abuse (such as oval track races) simple upgrades like arp studs are plenty strong for the average Joe.

 

Did I say stock bottom end? no. Stock crank and 2 bolt caps. His name is jason warren. Check out the drag racing section. I do believe he is running bolts not studs, not sure about that though.