Holley only makes 58mm TB's now. They discontinued their 52mm. What harm would a 58mm TB do on a mostly stock LB9, with cat-back ?
I have 21lb accel injectors, and a cat back. That is about it on my 305. The oem TB is worn out. I don't like the BBK logo on their 52. I'd rather get the holly and install my own top plate.

Any for seeable problems running a 58TB on a mostly stock motor? The MAF measures the air, the o2 measures the mixture. If any thing I feel the ECM will adjust.

 

You'll probably lose a little throttle response due to having such a large opening. 58 is really WAYYYY too big. Honestly, 52mm is way too big. Keep in mind GM put the 48mm on their ramjet 502 and it made some ridiculous amount of power. I had a 48mm on my 383 for the longest time and didn't gain anything with a 52. I had some minor IAC tuning tweaks to make and it never felt as smooth. Ultimately went back to the 48mm.

 

Not trying to be a jerk but seen the 48mm on ramjet reference a ton of times and GM has been know to do things because it saved them $$$ LS engines proves that they will use larger TB's on lower displacements.

BBK still makes the 52mm TB looks like. Picked up a lightly used BBK 52mm for my 86 C4 not long ago, guy said it whistled and annoyed him so he took it off. Also read posts that said similar but I don't care and I'm gonna polish it up some(not port) before install so that may quiet it down?

https://www.bbkperformance.com/gm-30...-88-recon.html

https://www.bbkperformance.com/gm-30...ody-89-92.html

 

The point isn't WHY GM put it on there. It may in fact have been financial. The point is that it made 500 hp. I'm not even saying that maybe it woulda made more with a bigger TB, but it still made 500hp through the 48. The vast majority of us 305 and 350 TPI guys are SO FAR from needing a 52mm, let alone a 58mm. ...and that's not even talking about a loss of throttle response and potentially low end torque. If it were me....going on my experience...I'd look for a decent condition used OEM 48mm throttle body. Just my 2 cents.

 

But if I were the OP....and did NOT want to go back to stock, ya might check out this 52 over purchasing a 58.
https://www.thirdgen.org/forums/engi...ttle-body.html

 

"The point isn't WHY GM put it on there. It may in fact have been financial. The point is that it made 500 hp. I'm not even saying that maybe it woulda made more with a bigger TB, but it still made 500hp through the 48. The vast majority of us 305 and 350 TPI guys are SO FAR from needing a 52mm, let alone a 58mm. ...and that's not even talking about a loss of throttle response and potentially low end torque. If it were me....going on my experience...I'd look for a decent condition used OEM 48mm throttle body. Just my 2 cents."

Couldn't agree more with Abubaca. Mine doesn't even need the Summit/BBK 52mm that's on it and it's, uh, a little more than stock. And I saw that Holley in the classifieds.That's a deal at that price. I'd buy it for no other reason than to put it on a shelf but I've got too much of that already. Besides, it's a much nicer piece than the BBK.

 

No reason to run a 58mm. Way too big for a stock LB9.

You only need a larger throttle body when the engines airflow requirement at MAX RPM exceeds what the existing TB can flow.

 

That's like saying NASCAR makes big HP thru a restrictor plate, so we should all use restrictor plates and have million dollar engine programs LOL

Bolting on a larger TB won't increase the HP unless the current one is undersized and often OEM TB's are sized for low RPM driving. Still it's an easy mod most can do and makes part CO's $$$ A stock LT1 made 10hp on the chassis dyno with a 52mm TB, so I'd imagine the 502 ramjet would be happier with a larger TB but a stock TPI is no stock LT1 or Ramjet, now a TPI with some mods.....

There is more than enough proof early EFI was wrong in may ways and TPI should be more than enough of an example!

All Hail GM!

 

The Analogy of a restrictor plate is poor. NASCAR specifically implements them to reduce power on some tracks.

 

I actually like that analogy. ....and go put that restrictor plate on your carbed 305. It won't restrict a darn thing. Because it flow plenty for a 305. Just not a 10k RPM Nascar motor. Same as the 502. The 48mm may in fact restrict the 502, but it still supported 500 horsepower. -which means it can support 500 hp on a 305, assuming the rest of the engine can make that. It's not exactly apples to apples, but I promise you.....the 48 is holding you back...AT ALL. There are COUNTLESS dyno test proving an increase....as well as a decrease in power on stock displacement engines, with 48, 52, and 58mm TBs. Which only goes to prove there really isn't any difference until you start really pushing the power up high in the powerband. Which of course....some engines do. But none that we're discussing here.

....and even IF tests proved a consistent 10hp increase at max RPM....we still have to address the loss of low end torque and throttle response. The loss of torque is sound in theory, but I'll admit there aren't tons of test showing this, however the loss of throttle response is widely known to be a negative side effect.

 

I'm 100% speaking from a stock engine standpoint. Not involving other mods that would increase engine airflow potential (heads, RPM..etc)

By all means, buy a 58mm TB if your plans eventually include a larger engine, more RPM, better heads...etc.

But just buying the 58mm TB when you don't plan on doing anything else doesn't work out. At that point a 52 would be better.

Most of the TB shoot-outs were done on L98's or 383s with other mods.

 

Correct. I'm 100% agreeing with you. ...i just thought his analogy of restrictor plates actually helped make that argument!

 

Reading it again, I'm guessing I missed the implied sarcasm.

 

Maybe I didn't word it right.

I was telling YOU, Thirdgen89GTA that I liked his analogy.

The rest of my post was directed towards Boot77.
...just like a 48mm flows plenty for a 305.

 

....and we haven't even begun to discuss the screens on the MAF and K&N filters....

 

A hole X size can support XXX power if you try hard enough. The end goal is to make X hole support XXX power with the least losses top or bottom range, unless you want to target a certain area.

 

It did exactly what gm designed it to do, and did it very well. Was not a failure in any way. Maybe you are too young to remember, but at the time the tpi corvettes we're right up there with many exotic European cars in power, acceleration, even fuel economy. Curious, how gm was "wrong" not trying to insult, but rather find out how it was a failure? The truth is it was revolutionary, and one need only look at the modern ls, ford mod, even Mopar V8 intakes to see they took intake harmonic wave tuning to the next level.. but it started with the tpi/Ford 5.0 intakes. Computational fluid dynamics simulations and years of testing have refined it from what it started out as. But gm most definitely didn't get it "wrong" with the tpi their goal was respectable power, increased fuel economy, and emissions compliance. And coming out of the late 70's gas crunch it was the first real performance Detroit had offered in over 15 years, the fact it did it with a warranty, good mileage, and quieter operation with big block torque off idle was f*#kin amazing. The world stood up and took notice! And it was literally the most powerful small block V8 Detroit had produced in over 15 years. The fact it did it on 87 octane was no small feat. Kids today have never experienced an underpowered lackluster 2bbl V8 that was a bitch to start in winter and at best would go 75-90,000 miles before needing a valve job, and having substantial bore taper etc. 🤣

 

Spend the money on headers, high flow catalytic converter and high flow exhaust, you'll gain more power with no loss of drivability or throttle response.

 

TPI was designed for a 305 and put on a 350, another example of GM using what it had to save money. The problem with a lot of designs is by the time they are production ready, better ones make them obsolete but since they put LOTS of money into that research and development.

I like TPI it's a novel intake but you can't make it do what it doesn't want to, you can only enhance it. And the C4 Corvette itself is a greatly underestimated car, still when all CO's are using the self imposed production power limits.

In my opinion power went away and is now back in cars not because of emissions or GAS but because of SAFETY. I could point to a million youtube examples of kids doing stupid stuff in a modern car and walking away from it, cars are A LOT more idiot proof now. Back then people were starting to have lots of disposable income and wrapping themselves around trees in high powered factory cars left & right. Much of Hot-Rod tech/mods are based on WW2 fighter plane research, it's not like they didn't know how to make power or make it emission friendly. I still rem all the old guys peddling camelbacks and saying they lost/banned the tech to make those heads or some other BS!

Anyways since we are getting further & further off topic I'm out!

 

You are linking a for sale ad 5 years old !!

 

Putting aside all the too big or not debate, What's worn out on the old TB? Worn bushings or a handful of broken off screws in the aluminum? You can rebush them fairly easily, same as a qjet base/tb. The screws are a bit harder to deal with but they can be dealt with too with the right expertise.

 

....yeah....I saw that you bumped it, didn't check the date. Oops.

 

4 broken screws. Not easily removable.

 

To play devil's advocate, any half *** machine shop can get the screw out threads intact, if they can't they can do a plunge cut with a mill taking the broken bolt out, helicoil it, or weld it up and redrill. Probably 1 hour labor. As an industrial maintenance tech I can guarantee you broken bolts in aluminum that's been heat cycled thousands of times is not much of a challenge, 90% of the time a hand drill, steady hands, and easy outs can get them out. Rambunctious, bull in a china shop mentality is what usually causes broken bolts, and the same rambunctious fool then takes a drill to it, f#$ks it up then says it's impossible to fix.not saying you are "that" guy, just that they are in fact almost always very easy to extract with minimal damage to the threads.

 

Why spend money on a machine shop, when a new TB is cheaper. The problem is, I don't want BBK engraved under my hood. I'd rather buy the BBK, and have their BBK milled off it.

 

That's ridiculous to say that. These little black iron screws sit in an antifreeze passage, and are 1/2 rotted away by the time a tool touch them. And they snap at the lighted touch of a 1/4" drive rachet.