You do not want to use larger than a 52mm tb on 350(or less) cubic inches.

02-28-2010, 09:05 PM
ASM 58mm vs Stock Bored 52mm Throttle body
Article by Leon Hartsock (ZDriver96)
February 20, 2010
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When I set out on this project I really didn’t know what to expect. On one side individuals were stating that the 58mm throttle body was not needed for an engine putting down around 400 rwhp. On the other side proponents stated that they felt the 58mm throttle body gained them power. But nowhere was I able to find back to back tests comparing the two. GM High Tech ran an article on this years ago called, "LT1 Aluminum Rocker Arms and 58mm Throttle Body Upgrade". This article included a 52mm vs 58mm throttle body test but compared them against each other with different intake manifolds. So I figured it was time to settle this age old question once in for all. I was not interested in hearsay, not interested in track results done on different days in different weather, not interested in what a mathematical formula stated, and not interested in whether your girlfriend was on Team Jacob or Team Edward. Why am I not interested in these? Because none of these definitively show if power is gained with a throttle body modification. In my comparison the only variables will be the Throttle body’s themselves and the slight change in outside temperature as the day warmed. This would ensure consistency and a true measurement of just how much, if any, power is gained through the addition of a 58mm over a 52mm throttle body.

The ASM 58mm Throttle body:
There are many different companies that design and sell throttle bodies. I wanted the best of the 58mm throttle body’s out there. I did not have to look far. I gave Jim Shofner a call at Arizona Speed & Marine and spoke with him about his throttle bodies for my built LT1 application. I could tell he was very knowledgeable on his products and he took the time to answer all my questions. Upon receiving the 58mm ASM it was clear that this was a quality piece. But would it install easily? More importantly would it perform as good as it looks?
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The 58mm ASM came with all hardware and gaskets to replace the OEM. Both the IAC and the TPS sensor fit in smooth. The throttle cables snapped in nicely. The install was seamless.

The competition:
Sitting to the left is the OEM throttle body, which was ported to 52mm and an added airfoil. Sitting on the right is the 58mm ASM throttle body.
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The ASM 58mm is weighs less than the stock throttle body. The ASM also eliminated the TB coolant connections found on the stock throttle body. The throttle cable connection is made out of a hard plastic vs the metal construction on the stocker. The IAC also seems to respond differently to the ASM as it likes to hold the idle a couple hundred rpm’s higher while your car is neutral but still moving. This might be a tuning issue but when the 52mm is installed it idles lower while the car is moving. But when the car comes to a complete stop the idle returns to the 900 rpm range which is what the computer is tuned for.

STRESS RELIEF:
Vital to any modification or parts installation is the speed bag. If only I had this piece of equipment the first time I saw that GM engineers, in all there wisdom, deemed it necessary to have the water pump weep hole directly over a non-water resistant, o-ring cover lacking, sensitive electronic optispark. Notice the big screwdriver and duct tape also vital to f-body maintenance
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Preceding the Testing Process:
Prior to this throttle body project ever starting, my 1996 Z28 Camaro underwent an extensive make over. This Camaro has a 11.1:1 355 engine with LE2 heads and matching LE2.3 camshaft. Every single mechanical piece in the Long block is new. The T56 six-speed transmission has less than 15,000 thousand miles and the clutch has less than 5 thousand. Jeremy Formato from Faster Proms performed dyno tuning. Jeremy spent a couple hours dialing the timing and air/fuel ratio with the 52mm. He kept the fuel purposely slightly on the rich side to leave room for a 58mm, which did not affect power gains when using the 52mm throttle body. I’ve known Jeremy for a long time and knows he does great tuning.

Getting a feel for the 58mm Throttle Body:
I drove the car a good 100 miles prior to brining the Camaro to the dyno. As expected the throttle response had increased. I was not subjected to the throttle ever sticking. I could not feel any power difference in WOT runs but then again the gains could be small and not really noticeable. Only thing I did notice was the rpm’s staying up a little higher while putting the car in neutral and coasting. When the car stopped the revs would drop to idle. Datamaster logs also showed everything operating normally with left and right fuel banks fluctuating between 126 and 138.

58mm vs 52mm Show down Results!:
The guys over at Proven Performance let use their dyno for my comparison project. Not only were very professional and knowledgeable but they had inexpensive costs on labor and dynometer usage. Unfortunately the car was run to 5700rpms (red line) for the first couple runs without me catching it. I only had a limited amount of time on the dyno and wanted to keep things consistent so we just measured the power gain up to 5700 rpms. The runs afterward to 6500 rpms showed the power continue to increase into the 6200 rpm range just like 52mm. But these subsequent runs had slightly lower power results because the engine was running hotter. Fan settings set at 180 degrees with a 160 degree thermostat. Temperature gauge stays at about 170 degrees. When the 52mm was tested the engine had 15 minutes to cool down.
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At certain rpms the torque gain of the 58mm was up to 20 ft lbs higher than the 52mm. Horsepower gains are most noticeable in the upper rpms where the engine is utilizing the additional airflow.
Its important to remember that this test is simply comparing the 58 vs the 52.mm throttle body. This is not an accurate reflection of an LE2 setup because I have a plate covering 70% of my right exhaust causing the car to lose a fair amount of horsepower in an effort to lower the exhaust noise level.

This graph shows the wide band O2 reading. You can see that 58mm provided more air thereby leaning out the air to fuel ratio. If it leaned out the mixture its telling me that the engine did make use of the additional cfm.
http://i712.photobucket.com/albums/w...rfuelgraph.jpg

This graph shows the temperature and humidity difference between the 58mm and 52mm runs. It was 6 degrees cooler and 9% more humid when the 58mm was run.
http://i712.photobucket.com/albums/w...conditions.jpg

Conclusion:
Well the graphs speak for themselves. It can be argued that the temperature change and tuning could have resulted in the gains. But I doubt a 6 degree temperature change will net you peak 7rwhp and mid range 20ft lbs of torque. The tune was actually meant for the 52mm. We richened up the tune and got the same horsepower and torque as when it was leaner to accommodate the future 58mm. When dyno tuning the 52mm weeks prior to this comparison the Camaro put down 389rwhp. The 9rwhp increase was due to temperatures being in the mid-upper 50’s. At 76 degrees the 52mm put down 380rwhp. 9rwhp difference needs approximately 20 degrees.
I would think this test is applicable to anyone considering a 58mm throttle body for a vehicle putting down close to or over 400rwhp