I have a couple of questions? First which rods are better H or I, given they are made out of the same grade steel. Second as for eagle rods are their highest I beam stronger then eagles mid grade H. Third what grade steel should I use??41-- or 54--??
This will be going into a 355 with 6in rods, Iron eagle heads and 150hp shot of NOS.
John

 

For an N02 motor I would go with the h beams. they are heavy but somewhat stronger than most I beams.

 

look at H and I.....H is a rotated I.... they could have made a bifferent name...

 

I'm currently building a block, its in the machinists hands right now and after carefull consideration I opted for the I-beams. the reason being is they're deffinatly good for around 550hp, even the GM "pink" rods which are nothing but glorified stock rods are ran on stroked bigger cubed engines with good power. The Hbeams are deffinatly stronger, but whats over kill? On a street engine I think those qualify as just that. When you get closer to finishing and you realize that you're spending about $2,300 on a SHORT block, then you start to back up again and think (well maybe i beams will do) and you'll scratch those forged pistons you wanted etc

Dont buy what you dont HAVE to. But dont cut corners either.

I beams are plenty strong, the Ibeams I'm running are the eagles.

 

It kinda depends on the size of the web and flange area of the 'H' or 'I' of the rod, but in general the I beam rod would make more sense in the type of application its used in. Theres essentially no bending forces on the front and rear sides of the rod (as if viewed from the front of the engine) but there are some in the other direction. When they design buildings and put up beams, you dont see the beams with the flanges to the sides do you? They are installed as an I, because beams resist bending more in that orientation. Notice the factories dont use the H beam either.

 

The factories don't use Nitrous either.

 

Ok, I still am not sure which is better. This will be mostly a race only motor. Very limited street use. As for the NOS 150 will most likely be the lowest amount it will see 250 isn't out of the question. Madmax I see the point of the bending forces on the side of the rod. Is that still relavent with the bigger NOS shot. I will spend the extra cash for which ever is better. I just am not in the mood to see rods hanging out the bottom of the block.
John

 

Well like I said, its sorta dependant upon the thickness of the flange and web areas, and how wide they are. The cross-section and where its at is everything in the bending resistance of the rod. If you had a square shaped box in which to fit an I or an H of the same material, thickness, and size with a load from the top (like top of the I or H just like it looks on the screen) the I would resist bending more than the H would every single time. Off the top of my head I cant remember how much the factor is exactly but its fairly considerable. The only advantage the H style rod might have is the width of the flange area can vary from the top of the rod to the bottom without much hassle, but with an I shape it would be best if it didnt vary too much. That would allow the H style to have more area, but the thing is you have to consider the area of the weakest spot, which is where the area is the smallest. Large, strong flanges tend to overburden web areas anyway, the web area will have a tendency to buckle past a certain point. Ideally and hopefully, side bending will not be an issue and it wont matter which you choose, you just pick the one that has the largest cross-sectional area. That will resist the forces transmitted from the combustion and also from the piston changing directions at TDC on the exhaust stroke. If side bending becomes an issue (and its likely there will be some but probably not alot) the I rod will probably resist it much more than the H rod even taking into consideration the designs I have seen. And thats how much confidence I have that theres not enough area in the H rod to make up for the weakness of putting it on its weak side in relation to the load. I could spend time doing calcs to give you an exact number, but I'd need more info than you have or probably can even get. I'll check on a general factor when I get home.

tpi_roc... Yea, youre right, no nitrous from the factory. So whats your point?

 

That H-beams not coming from the factory isn't relivant

 

like madmax said, youd hafta figure out the moment of inertia of the cross section and how far each of the flanges is from the neutral axis of bending... even though the H beam may have wider flanges, if they're closer the neutral axis, they may not be as strong b/c of the increased stresses in the flange

 

Yes, it is relevant. If the H rod was a better design for resisting bending, compression, and tension with the same weight, the factory would use them exclusively. The engineers are not that stupid to ignore a better design with no added cost.

 

Now thats touchy ground

There are probably plenty of people to argue both sides of that one.

However I do agree that I-beams are the wiser choice, that is why I bought them.

 

and a lot of them use the Lentz rods.. but.. i imagine you can't find an I beam that has been conclusively built to those standards for less than 2K.

That is why most people tend to use h beams for the extra material (as in mass) that they provide. Its not that an I beam is not strong but.. with soo many of them made as light as possible.. how much has strength been reduced?

Since h beams don't even attempt to reduce weight (in most cases), strength is much less likely to be compromised. I guess thats the logic involved.

 

The heavier the rod, the harder it is for the engine to rev, less horsepower, and worse throttle response.

 

I disagree that the factory uses what is best. The factory uses what will work with no problems. If they used the best stuff a Firebird would be 100,000.00 Look at the mods. done to a Firehawk and how much it added to the price. As soon as you add the juice it better be strong.

 

so if I'm going to do 100hp shot of NOS use H beams? if not use I? or should I just stick with I not matter waht? also I'm gonna get 4340 rods, those are the strongest aren't they? also anybody kow what kinda rpms I could rev with new cast crank,4340rods and forged piston?

 

The H-beams aren't that much more expensive than the I beams. I picked up a new set of the 2-piece forging H-beam rods for $330 shipped.