Why 52mm over 58mm TB?
Thread Starter
Racer
Joined: Sep 2004
Posts: 400
Likes: 4
From: Phoenix AZ
Why 52mm over 58mm TB?
As I look over alot of the members mods I see that most guys are running 52mm Throttle Body's instead of 58mm. Can someone explain why most go with 52mm?If I am running all the freebie mods, heads and gm hot cam, full exhaust and LT's what would benefit me most on my 94LT1? Thanks.
Race Director
Joined: May 2001
Posts: 14,165
Likes: 9
Honestly you don't need a bigger throttle body at all on a 350 cubic inch motor. It might give you some benefit on a blower motor, but not normally aspirated.
I got my throttle body because it's very pretty and I got it for a good price, and I didn't know any better. I have the dyno charts to prove that it's useless.
On that though, the reason why people go with 52 over a 58? On the LT1 at least the intake is already perfectly matched to a 52. A 58 requires you to do some work on the intake.
If you put too much throttle body on your machine you'll basically screw up the tune and you'll decrease your throttle resolution. This example is exaggerated but you'll get the point.
Imagine a throttle body that can flow 100% more air than the stocker, but the stocker is perfectly sized to the engine. If you put on the bigger TB you will be flowing all the air that engine can possibly use at 50% throttle. Your tune will be messed up because you are flowing more air than it is expecting at 50% throttle so it'll be running lean and having to try and correct for it. Furthermore the upper 50% of your throttle will basically be dead because despite the fact that it opens further, no more air is actually sucked in.
Save the money and spend it somewhere else, you'll be better off in the long run.
I got my throttle body because it's very pretty and I got it for a good price, and I didn't know any better. I have the dyno charts to prove that it's useless.
On that though, the reason why people go with 52 over a 58? On the LT1 at least the intake is already perfectly matched to a 52. A 58 requires you to do some work on the intake.
If you put too much throttle body on your machine you'll basically screw up the tune and you'll decrease your throttle resolution. This example is exaggerated but you'll get the point.
Imagine a throttle body that can flow 100% more air than the stocker, but the stocker is perfectly sized to the engine. If you put on the bigger TB you will be flowing all the air that engine can possibly use at 50% throttle. Your tune will be messed up because you are flowing more air than it is expecting at 50% throttle so it'll be running lean and having to try and correct for it. Furthermore the upper 50% of your throttle will basically be dead because despite the fact that it opens further, no more air is actually sucked in.
Save the money and spend it somewhere else, you'll be better off in the long run.
Team Owner
Joined: Sep 2002
Posts: 22,209
Likes: 12
From: OBAMA IS HITLER
I'm running a 52mm because it was part of a heckuva deal I got on my intake. With my mods and 350cid - and going to full Superram next month - I'm sticking with the 52mm.
58mm with full mods would apply more to 383cid and larger.
58mm with full mods would apply more to 383cid and larger.
Drifting
Joined: May 2004
Posts: 1,280
Likes: 0
From: Gretna NE
St. Jude Donor '09
Many people will choose the 52mm due to cost, due to the fact the intake modding is not required, or due to 58mm TBs require computer tuning/chipping.
But the real arguement out there is that if a 58mm is to big or a 52mm is suffice for your engine that the 58mm TB is going to cause a velocity decrease in your airflow. If a 52mm can flow enough air (max allowed by heads, intake etc.) for your motor then putting in a 58mm is only going to allow your motor more area to pull the air in, thus it can do it slower as it has more area. So now you have the same amount of air in the intake and its moving at a slower speed. Whereas with the 52mm it is flowing the same volume faster.
Determining if a 52mm is too small is another question. Correct me if im wrong but I believe that if you hook up a vaccuum gauge to the intake and if it makes a significant change in the direction of Zero at WOT with the 58mm than the 52mm, then it shows you that the 52mm was not sufficient for your combo. Then again you would need access to both TBs in order to test this.
All IMO of course, open to correction or comments,
Dan
But the real arguement out there is that if a 58mm is to big or a 52mm is suffice for your engine that the 58mm TB is going to cause a velocity decrease in your airflow. If a 52mm can flow enough air (max allowed by heads, intake etc.) for your motor then putting in a 58mm is only going to allow your motor more area to pull the air in, thus it can do it slower as it has more area. So now you have the same amount of air in the intake and its moving at a slower speed. Whereas with the 52mm it is flowing the same volume faster.
Determining if a 52mm is too small is another question. Correct me if im wrong but I believe that if you hook up a vaccuum gauge to the intake and if it makes a significant change in the direction of Zero at WOT with the 58mm than the 52mm, then it shows you that the 52mm was not sufficient for your combo. Then again you would need access to both TBs in order to test this.
All IMO of course, open to correction or comments,
Dan
Last edited by ddr698; Nov 17, 2004 at 03:57 PM.
Race Director
Joined: May 2001
Posts: 14,165
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Originally Posted by TankerVette
Nathan,
Can you clarify? The stock is 48mm, I think. Are you saying that we don't need to go bigger then 48mm? (I got ported heads, 224/230 cam, will have long tubes...)
Can you clarify? The stock is 48mm, I think. Are you saying that we don't need to go bigger then 48mm? (I got ported heads, 224/230 cam, will have long tubes...)
This topic has been beat to death, do a search and you'll find that the common belief is that you really don't need one. GM uses a very small TB on one of their big blocks as well.
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Safety Car
Joined: Sep 2000
Posts: 3,524
Likes: 4
From: Hinckley Ohio
Originally Posted by Nathan Plemons
This topic has been beat to death, do a search and you'll find that the common belief is that you really don't need one. G.
Trying to remember who did dyno with 58mm tb on 52 mm openings and saw little gain, then opened the intake to 58 mm and saw big change .
Until I see controlled dyno testing disputing this, I am convinced max overall power comes with 58mm throttle body on intake with matched 58mm openings. That is what I did....haven't seen any evidence to dispute my decision , then I do have cam, ported heads.......
I tend to believe the 58mm tb got its bum rap from people who just bolted them on without matching the intake to them...
Le Mans Master
Joined: Dec 2003
Posts: 5,867
Likes: 17
From: Phoenix Arizona
I have used both on my 92 LT1 w/ heads, cam, ported intake, exhaust, chip, injectors, etc etc. I prefer the 52 MM because it feels stronger and more responsive on the bottom end. At WOT and high RPMs I believe the 58MM makes more horses but didn't feel as good during normal driving.
Obviously this is "seat of the pants" and not scientific . BTW, my intake was ExtrudeHoned then hand port-matched to the 58MM.
Obviously this is "seat of the pants" and not scientific . BTW, my intake was ExtrudeHoned then hand port-matched to the 58MM.
Last edited by Digital Disaster; Nov 17, 2004 at 05:02 PM.
Melting Slicks
Joined: Jan 2000
Posts: 3,418
Likes: 1
From: NW Chicago Suburbs
I know guys that installed a 58mm TB on and LT1/4L60e on a b-body. within a few weeks the trans was shot. Turns out it's important to reprogram the trans pressure on a 'e' version of the A4 trans. The bigger TB makes more HP for a given TPS voltage because for a given opening, the 58mm moves more air than a 48mm. At WOT there's no difference, the restriction isn't the TB. But at partial throttle, more air is more HP and the trans' line pressure needs to reflect that.
This is also why many people report better low end with the 52/58mm TB, it's at partial throttle. Nathan proved it makes no difference at WOT.
This is also why many people report better low end with the 52/58mm TB, it's at partial throttle. Nathan proved it makes no difference at WOT.
Drifting
Joined: May 2004
Posts: 1,280
Likes: 0
From: Gretna NE
St. Jude Donor '09
Originally Posted by silver & red CE
This is also why many people report better low end with the 52/58mm TB, it's at partial throttle. Nathan proved it makes no difference at WOT.
Safety Car
Joined: Sep 2000
Posts: 3,524
Likes: 4
From: Hinckley Ohio
Originally Posted by silver & red CE
Nathan proved it makes no difference at WOT.
This thread seems to show about 25hp gain from a 58mm throttle body on a modded engine.
http://forums.corvetteforum.com/show...ight=dyno+58mm
What seems to be fallacy in my opinion is that a 58mm throttle body might hurt performance....Near as I can tell this is either speculation or at best sop.....and again perhaps when mismatched to 52mm intake...
I don't think the high air velocity at the throttle body on a LT1/4 is needed, in fact slower is probably better.....velocity is more important thru the individual ports going to the cylinders...
Racer
Joined: Jan 2002
Posts: 419
Likes: 0
From: Tampa FL
I did back to back dynos on my modded LT4 with the 48mm and 58mm and saw a good gain w/ the 58mm. Once I port matched the intake to 58mm the gain was even better. With all the mods to increase airflow, why not here? I have the dyno numbers somewhere I will try to dig them up.
Racer
Joined: Jan 2002
Posts: 419
Likes: 0
From: Tampa FL
This is from my old threads....
"1st:344hp and 377torque w/48mm TB and 52 mm intake (no tuning)
2nd:344 to 353, picked up 9 horsepower just w/ switching to the Holley 58mm (intake is stock 52mm) no tuning.
After tuning hit a max of 387. A few weeks later after hand porting the intake to 58mm went from 387 to 406 rwhp.
I should add that the engine was using Mobil 1 today and regular penzoil on the older run. "
"1st:344hp and 377torque w/48mm TB and 52 mm intake (no tuning)
2nd:344 to 353, picked up 9 horsepower just w/ switching to the Holley 58mm (intake is stock 52mm) no tuning.
After tuning hit a max of 387. A few weeks later after hand porting the intake to 58mm went from 387 to 406 rwhp.
I should add that the engine was using Mobil 1 today and regular penzoil on the older run. "
