thru bolts vs. cap screws
 

I am in the process of rebuilding my motor and i am trying to decide which rods to use. i did some research on the cap screws vs thru bolts and found that the cap screw is considerably stronger. so my question is, should i run a 3/8 cap screw or a 7/16 thru bolt on the rods. my setup is a solid roller top end kit with llyod heads, stock bore ross forged pistons, stock crank, and well, im trying to figure the rods out.

the only reason that i am asking this question and not just going with the cap screws is because of the cost difference. The cap screw design is 100 bucks more and i dont think that i will need something that is that strong.

thanks
Bobby

I posted this in the LT1 tech and only got one response so i thought i would try it here.

Re: thru bolts vs. cap screws
 

How about what are your rod choices? That would be a better discussion since then we can take into account all the properties of the rods and not just the rod bolts.

Bret

Re: thru bolts vs. cap screws
 

i am wanting to get some scat 4340 i beam rods. as you know they come in through bolt and cap screw design. I was going to reuse the stockers but once you get new arp bolts and then get your rods resized, you are looking at almost the price of the scats. i know alot of people are saying that the stock rods are good for ~550 hp (with some good bolts) and i know that they have the thru bolt design.

arent the stock rod bolts 3/8? if so i am thinking that a set of the scat rods with 3/8 cap screws will work with my setup.

rod prices:
3/8 cap screw: 189
7/16 cap screw: 288
3/8 thru bolt: 189

i know that eagle also has some cheap rods but i think that they are 5140 not 4340, and i think that i would rather have the 4340 because they are stronger, correct?


Thanks
Bobby

Re: thru bolts vs. cap screws
 

Maybe you should be looking at the complete rotating assembly based upon the power and rpm level you are building for. It doesn't make too much sense to put "800 hp rods" in a 500 hp engine or with a 500 hp crank. Parts need to be matched for the job they need to do.

Ask you engine builder, or if you are him, give all the details of your goals, car, and other engine parts. IMO, the issue isn't "thru bolts or cap screws" it's more overall part strength and durability. SStrokerAce was saying about the same thing (I just talk more. :) )

Re: thru bolts vs. cap screws
 

i am wanting to turn the motor to about 7000 rpm and make in the neighborhood of 420 rwhp. i want to stay with the stock crank if it all possible. the car is an m6 and i have the top end to support the power, just trying to figure out the bottom end. :)

Thanks
Bobby

Re: thru bolts vs. cap screws
 

Any of the Scat I beams will work then. The cap screw is always the setup I would pick with the 7/16 bolts being the strongest ones. For 500-550hp the regular 3/8 cap screw rods will be fine, but the 7/16 versions have polished beams and have a stronger bolt. They also have more mass but it's in the part that counts.

Bret

Re: thru bolts vs. cap screws
 

Thanks for your help, much appreciated! ;)

Bobby