what is the size of a stock 305 Throttlebody? I was think about getting a 52mm. If i went up in size would i have to change anything else? Would i suffer in gas milage? What kind of performance gain can i expect if any? Thanks in advance!

 

I beleive it came with 48mm. As for changing anything else...yeah I think you have to. More air coming in, so you'll need more to go out, maybe headers. ANd I think you'll need to play with the Prom too?? Anyone else????

 

I don't think it will have any detectable effect whatsoever, unless your old one is defective. IMHO it would be a total waste of lots of money. It is in the typical category of unbolting easy-to-get-to, highly-visible parts and replacing them with the latest buzzword, without any clear plan or understanding of what the motor's limits to its performance are at the moment.

 

RB83L69:


It wouldn't be a total waste of money if i can get better performance out of a new one. Plus it looks better and will handel more. a 52mm throttlebody can flow up to 950cfm. a 58mm will flow up to 1050cfm. Im thinking about going with a 58mm. So i have to get headers? I dont really want headers. I thought about just getting a bigger Y-Pipe. anymore info would be appreciated!

 

if you still have stock runners, base and heads then belive us when we say that you do not need 950CFM from your throttle body if the rest of your intake isnt capable of supporting it. if the bigest restriction in your intake system hasnt changed (heads, base) then a bigger TB in front of it isnt going to help any.

once you get into some more serious intake mods then you MIGHT need a bigger TB

 

ok thanks!

 

Think of your motor as a pump. That's what it is, of course; it draws air in, and expels it. A little else happens along the way, but as far as things that flow (like TBs) are concerned, the rest doesn't matter.

Now imagine that you hook up your pump up with a number of pieces of garden hose. Imagine you've got 50' of 5/8", 25' of 3/4", 50' of 1/2", and then 100' of 5/8", all strung together in a string.

OK? Now what happens to the total flow of the system if you take the 25' of 3/4" out and put in 25' of 1"? What happens if you put in 25' of 2"? The same thing, right? Nothing. Because that's not the part that's controlling the flow of the system.

Changing the throttle body on a stock 305 TPI is just like that. It isn't the limit, so it has no effect on the total system flow. It's money down the drain. Unless it's really, really important to you how your throttle body "looks", keep your money in your pocket, and use it to replace the 50' of 1/2" hose with 3/4" or something, once you identify what it is. I can already tell you what it is: it's your exhaust manifolds. Keep those, there's no need in doing anything to anything else, because they are the limit, not the other thing whatever it might be.

 

i forgot to mention that i have a 350 with my old 305 TPI setup on it. I have 21lb injectors, mild cam, magnaflow muffler (2.5"), high flow converter and a custom chip. Thats all i have on her now but i plan on getting a SLP Cold Air Induction kit, turbo, and a bunch of other things.

 

That is one of those, "Oh by the way" things.

 

Exactly what is a "mild" cam?

As RB was trying to explain, the throttle body probably isn't your major restriction. A 502CID Ramjet uses a 48mm TB to make loads of HP and torque all the way up to 5,500 RPM. That engine might make better use of a larger TB, but a 350 with stock heads probably doesn't need it. That money could be better spent on heads, valves, exhaust, a porting kit - whatever means you want to make your "air pump" more efficient.

 

The guy told me it is a 268* cam. When it was at the shop this other guy says that the RPM range for it was 2000-5500. I dont really have the specs on.

 

i hate to be the one to **** in your cheerios, but you dunno anything about your car, you don't know anything about your engine, you just flat out don't know anything...go read up on engines, get a basic understanding, look up every little thing you don't understand, and eventually, you'll figure out what your talking about...i'm not trying to insult you, i'm not trying to make you feel bad, all i'm trying to say is that until you understand what's going on, you should leave your engine alone, otherwise your gonna figure it out one day and realized how much money, time, and parts you've wasted...let it come together slowly, don't dive in blindfolded.

 

Stock TB is 48mm...

you are gaining 4mm on each side with a 52, and for what your engine is, you don't need it. You won't notice a performance gain with one on a stock setup or even a 58 for that matter. You can make your existing TB look sharp just by cleaning it up nicely. You are better off doing the port work, putting some headers on it, and a bigger exhaust. You can do all that for the price of a bigger TB (roughly) Take these people's advice, they know what they are talking about. You can be a lot happier with these other mods than a bigger TB, and you will notice a difference.