does running turbos on a sbc require a forged crank and rods or not.  i know that high dosses of nos require a forged system but i was wondering at what point does boost need one?  

I don't expect you to think too much, but just bear with me and try it for a second...

How does nitrous add horsepower? By drastically increasing the amount of oxygen available to the cylinders to burn. How does a supercharger/turbocharger increase power? By drastically increasing the amount of oxygen available to the cylinders to burn...

So, of course a turbo would require a strong (components should be forged or a billet) rotating assembly unless you want to scatter your engine on the road on your way downtown.

A boosted engine in general should have all forged and upgraded aftermarket rotating components. I'm sure there are some that have ran 5-8 lbs of boost on hypereutectic pistons but turbos make a lot of boost (at least ones meant to push an engine to 700-800 horsepower, like you expect), and heavily 'cutting them back' with a wastegate is just as the name would suggest, wasteful.  

yeah i knew that was going to be my answer but i was reading an old issue of chp that was bassed on superchargers an i didn't notice anything about then upgrading the rotating assemblies in any of their cars. it sounded like to me that they were just slamming 10 pounds of boost into stock assemblies and/or gmpp long blocks.  i was just hoping somebody would have convincing facts as to why it wuold not be neccessary and i could save some money.  no such luck.  you can't be cheap when you are doing things like this.  thanks for your help.  

i know that 10 psi is  alot in a supercharger and a little with a turbo but i was just hoping i could save some money  

A supercharged engine is no place to save money! They can make a lot power very easily compared to a naturally aspirated engine. Most people building warmed-over N/A street cars are estimating their horsepower to be up to 75-100 more than what their setup actually produces, this gives them leeway in choosing their components and the component life. A supercharged engine on the other hand, the power is much more legitimate and if you're making more power it's more difficult to control.

Where exactly are looking to save money? The factory cast pistons just have to go, there's no doubt at it, it would hardly take a mishap for those to relieve a lot of cylinder pressure into the crankcase. An iron crank? Also a no, no for any high performance engine. The factory connecting rods? Well maybe in good condition with upgraded bolts they could support 450 horsepower, but even that may be pushing it a little.

Were the engines you looking at actually turbocharged? There's a difference between putting a 177, 256, or 6-71 roots supercharger on a small block and completely re-designing the exhaust system for a turbocharger. Those relatively small roots blowers will not make a lot of boost and they are going to be more user-friendly than a turbocharger unless, like I said, the turbo is really cut back by re-routing the exhaust with a wastegate. And if you're going to wastegating all of the boost out of that turbo you should be considering if you should even use a turbo or not...

How are you planning to feed this thing? I'm afraid your stock TBI won't be up to the task.  

yeah i think most of whatthey were testing in that mag was roots blowers,  they might have had one centrifugal supercharger but i think the most boost they put into any of those motors was 10 psi.  i am planning to run 15 (plans don't always go the way we want - but this is my plan)  noo ia am not going to save any money anywhere i was just hoping.  i have already picked out all the parts for my rotating assembly forged 3.775 crank, h - beam rods and forged pistons.  i am getting the overbored tbi from turbo city and the vaccum controlled adjustabled fuel pressure regulator.  I am in the process of finding some 350 injectors.  but i was just wishful thinking on my part that i would be able to run a $200.00 crank rather than a $700.00 one.  every penny counts but like we already said i can cheap out if i wna to and then i can blow up my motor too.  so i will be spending about $1500.00 on the rotating assembly alone.  its already on my wishlist at summit.  

Umm...

There are no 305 stroker kits on Summit's website that I could find, would you send me the link? By the way, aren't you going to need custom pistons for a 3.775" stroke crank? That is a very uncommon stroke, or is that a typo? What connecting rod length are you planning to use?

How are you planning on using a vacuum controlled fuel pressure regulator when you won't have any vacuum?

Factory injectors still won't suffice, even big block injectors will only support about 300 horsepower under boost. Actually, a TBI unit will probably never work out for you under fifteen pounds of boost, it's only two injectors and they're airflow wise very restrictive even if they're bored out a little bigger. You will most likely need a multi-point fuel injection setup if you want to get enough fuel and air to the engine to support 15 pounds of boost well. Not only is the distribution an issue with TBI (it's not much better than a carb) but you better be using a dedicated turbo hat (if  such a thing exists for a TBI) because otherwise I'm afraid that unit will leak.  

not a kit.  i found my own parts.  the stroke was a typo, i can't type.  no i won't need custom pistons.  

you might be telling me something i didn't know.  Why won't i have any vacuum?

i don't have the money fo rthe turbo yet i am just looking for the 350 injectors fo rmy current set up.  turbo city has a lot of tbi stuff that they specificlal ycalibrate fo rturbos. i will paobably ahve to fabricate a custom hat for my tbi unless i can find one between now and then.

15 psi is my goal.  

5.7 inch rods.  

You may want to consider 6" rods, as with the lower compression associated with blower engines the cylinder  pressure stays higher longer in the power stroke/cycle. This creates more friction since there is more cylinder pressure when the rod is at a larger angle from the crank, and longer rods counteract friction by decreasing the rod angularity overall.

I find it interesting that you are building a turbo engine but you really don't know what boost is. I want you to find out this dilemma of yours on your own rather than having me just tell it you, because I'm afraid this project is going to a very large learning experience in itself you might as well start now...  

i didn't think the 6 inch rods would work with a 305 all the stroker kits i see come with 5.7's.  
What is it that i don't know?  atleast point me in the right direction.  i have been reading tons of stuff about forced induction. magazines, and internet websights dedicated to educating others about turbo charging your car.  i have read nothing about having zero vacuum.  

also i am a begginer i ahve been doing oe maintenance my whoel life but as far as high performance i have been doing this for about 2 years,  my whole family is machanics and high performance guys but they are all old school.  like big carbs ,  dual 4-barrels and roots blowers stuff like that.  they might know a little about nos but zero about turbos so yeah i am learning as i go in more than one way.  i fit breaks i'll just have to fix it.  

How can there be vacuum in the manifold if the entire purpose of a turbocharger is to PRESSURIZE the induction system. Maybe you could look at it as negative vacuum in the manifold rather than vacuum.

Back to the connecting rod length, do you know the stroke length of a 383 or a 400 small block Chevy? Don't they use 6.0" rods? The deck heights between a OE 305, 350, and 400 blocks are all the same.  

so you are saying that because a turobo will force air into the motor that the motor  will not suck any more?  Am i understanding acccurately





but with the 1/4 inch smaller bore wouldn't the longer rod put more load on the side wall of the cylinder?  

The manifold, runners, and intake ports are pressurized at all engine speeds with a turbocharger, what do you think boost pressure is? It's positive pressure measured within the manifold.

In a naturally aspirated engine with the throttle bores shut the engine produces vacuum because of the depression the piston creates is being restricted. If the depression the piston creates is being communicated to a larger opening there is less of a restriction and thus less vacuum in the manifold decreases. It even decreases to the point where at wide-open throttle in some situations it is near zero.

What in the world does the piston diameter have to do with this? Please look at the geometry and explain to me how you think the bore changes anything when the wristpin always stays in the same location.