I have a vortech supercharger setup on a very modified lt4. I was looking at the tb and noticed it was only a 48mm. Would going to a 58mm tb make any difference? the motor is seeing around 12lbs of boost. with no belt slipage. Would i see a drop in boost? Thanks for any input.

 

It really depends on how much air you are pushing into the engine.

At 100% efficiency on a 350ci and 12 psi at 6k rpm you should be pushing about 1100cfm. Arizona speed and marine rates their 58mm TB at 1050cfm, which would be a much closer match than the 48mm TB that you are currently running.

My guess is that you'll add one or more psi to the system by making the switch.

Just remember that you'll have to port the inlet to your intake manifold. It is 52 or 54mm currently and will obviously have to be opened up to atleast 58mm for the new TB.

http://www.azspeed-marine.com/58mmltthbo.html

The Holley unit is a bit cheaper I believe.

 

am i going to have to get it retuned with the upgrade? For the price difference the mono blade looks like the best deal for upgrading boost later. Any pros or cons for the mono blade? does it effect tuning?

 

the monoblade does look killer!

 

Brian, would that CFM number not change with a blower motor? In my mind, it would seem since air compresses, that the flow would be much higher then 1050cfm on a motor with boost.

 

That is with the air compressed. At 0psi or NA the 5.7L engine moves about 600 cfm at 6000rpm. The 1100 cfm is how much ambient air flows into the blower. But this is assuming 100% efficiency and no heating by the compressor.

Actually now that I think about it. The cubic feet per minute unit for ANY boosted 5.7L engine should be 600cfm at 6k. Its a volumetric measurment. This is at the inlet to the motor. The inlet of the blower, however, gets a much higher cfm because the air is getting compressed.

Now the drag would definately go up because of the increased density of the 600cfm of air that is flowing into the TB.

Does that make sense? Its like saying I have a 5 gallon bucket filled with water or with lead. The bucket(engine) can only hold so much volume. But the mass(hp) of what gets moved through depends on the density(boost) of the stuff inside(air).

The BEST way to find out if the new TB will help is to place a boost gauge on each side of the TB and see if you are getting a pressure drop across it at WOT. Just make sure that the boost gauges are calibrated closely. Perhaps try it, then switch the gauges and try it again to make sure the readings are the same. When you are talking a 0.5-1psi drop making 20hp then its important to get it done accurately.

 

I believe he was asking about the TB being rated using no boost. The TB will flow considerably more air when boost is applied. So the factory 48mm TB which flows ~750CFM @ 14.7 psig (0 psi or atmospheric) will flow considerably more with boost added.

If you were to test on a dyno (back to back) between the 48mm and the 58mm TB, I suspect you will find no gain. I did just that but with the 58mm and the MB when I was @ 11 psi, and there was <2WHP difference (<0.2%), which could be easily attributed to testing variances. I would avoid the MB for other reasons...
Aaron

 

what other issues would there be with the MB tb? should i just keep the 48mm tb or go to the 58mm tb and avoid the MB? Looking for the quick input. I have a possible deal on a MB tb. Thanks

 

If you go the MB route, do the dyno test. I bet you will be disappointed with the results.

Issues with the MB? There have been numerous examples of FI where the boost holds the large blade (airfoil) open once the gas is released. Do a search on this topic, you should find plenty of results, all FI though.
Aaron

 

when the car is under no boost.....would the 58mm tb help with fuel economy? lol