I have a question about internals of a motor. Is there any reason to run a fully forged bottom end on a N/A car, i will be using my car as a weekend/ strip car and i dont know how i should build my bottom end. I don't think i will be doing power adders but if i do it will be a 100-150 shot. What would be the best bottom end for what i plan on doing, running cast everything, forged pistons and rods, or doing fully forged? i want to get about 400-420 hp. what are the benifits on hypers to cast to forged pistons. cast to forged rods, what would be the best decision to go with.

 

My understanding is if you are running nitrous than you need to run forged everything. At least thats the talk I have heard.

 

all rods are forged, except the PM rods and they sort of are. you don't want hypers with a power adder and if you run a power adder you really want a forged crank. the advantage of forged over cast or anything else is strength and a long life. you'd be way ahead to decide what you're going to do and plan and build for it instead of building anf "maybe" running a power adder down the road.

 

Factory rods may be "forged", but I can guarantee you that they don't have the same metallurgy, the flow of the metal into the forge is completely different (and poor) and quality control is not up to the standards of most aftermarket companies. Just because both pieces are forged doesn't mean they're the same. You're comparing apples and oranges.

You say you don't think you'll be doing power adders? You need to make up your mind. Either build an n/a motor or build a nitrous motor. N/A motor around 450hp you'll be safe with a set of stock rods that have been worked. ARP bolts, resizing and shot peening will add some strength. Press on a set of good hypereutectic pistons and you'll have all the strenght you need and the hypereutectics will be quieter and add life to the motor when compared to a forged slug. If you decide to spray it I would go with a set of Eagle H beams at the very least and a set of forged flat tops with rings gapped accordingly.

 

I'm not super experienced in this field, but from what I hear nitrous requires a little more strength in the crank and rods due to the sudden shock of power that it delivers, but for the most part the major concern is melting the top of the pistons. Torque is torque, no matter how you get it, but nitrous creates far hotter combustion chamber temps.

 

Actually, using nitrous increases the oxygen content of the intake charge, which makes the engine want more fuel. Hence the reason you need to jet or change to fuel injectors that are larger. Since the nitrous that is injected is mostly in liquid form, it doesn't take up much room in the intake port, allowing the engine to make most of its n/a power plus the extra power the nitrous and extra fuel allow. The additional power added by nitrous creates more power and more heat, just as joe350 stated. But there are other things to consider during a nitrous build. On a n/a build, we usually go for the best flowing intake port we can get, but a nitrous build won't rely on a good flowing intake port as much. The reason is that the nitrous will give us that extra power in the intake. The trade off is that it creates more exhaust gases. For a nitrous build, the exhaust needs a lot more attention in regards to flow than the intake. Brodix makes a set of heads that have 2.02 intake and 1.80 exhaust valves that work really well for nitrous builds. A little porting on the exhaust will help evacuate the extra gases created by the extra oxygen and fuel induced by nitrous. This will lead to a cooler intake charge because there will be less exhaust gases hanging around to contaminate the incoming intake charge, and less chance of detonation. The other thing to consider is intake port size. A good rule of thumb here is, the more surface area the port has, the more likely that the liquid nitrous will become gaseous and cause a reduction in power output. Anything you can do to reduce the heat in the intake ports and the charge coming through them, will lessen the chances of detonation and increase the power output. Just my

 

If you have the money for a high dollar bottom end Definatly dont get cheap there and go forged.I run a stock bottom lt1 which will handle 100-150 shots without coming apart. If your building on a budget lt1 parts could be the way for you to go. Lt1 rods cheap yet will handle up to 500hp with arp rod bolts. I always say build what you can with what you have to work with. If you have the cash build the bottom rock solid! Theres no price to big for peice of mind when you push that little red button.

 

There was a guy in an issue of HOT ROD that had an 88 Trans Am with the 5.7L TPI engine. The bottom end was completly STOCK, stock crank, rods, and pistons, heck even the rod bolts were stock. Anyway, he was running a 150 shot wet kit on the motor, and after 100 or some odd passes the thing never came apart. Now maybe he was lucky, but I think that if the engine is tuned right for nitrous then you'd be fine. I had thought that spraying a 150 shot on a hypereutectic piston is the MAX you should give it, and for every 50 shot that you spray you need to retard ignition timing by at least 2*. Also, having a nitrous progressive timing controller helps out a bit too so the engine doesn't see all that load at one time. You can gradually increase what gets to the motor. This also helps with traction limited cars.

I agree, to an extent. Usually, any increase in combustion chamber pressure directly results in an increase in combustion chamber temperatures. And nitrous sure does a good job of adding pressure. BUT, you forgot one of the main benefits of a nitrous motor. When nitrous is sprayed it goes from a liquid to a gas. And the intake charge gets really cold. Sometimes when nitrous is sprayed it comes out as cold as -125*F. In my opinion, that's where the intial *hit* comes from. It's also one of the reasons why high compression motors like nitrous, it helps to cool down the intake charge and possibly increase detonation supression. I'm just saying that it would not be wise to spray anything over a 50-75 shot on a stock motor. Even though it might make that power, if any one thing is off serious damage can occur. It won't do anything for longevity of the engine either.

 

I would go with a good set of cast pistons with polished crowns, stock rods with ARP bolts, and a factory nodular iron or a aftermarket cast steel crank. That will hold 500 hp as long as you tune it correctly.