58mm Naysayers.
Thread Starter
Le Mans Master
Joined: Aug 2000
Posts: 8,838
Likes: 31
From: Australia
58mm Naysayers.
Having been here for 6 years are very familiar with opinions as to 58 TB usage on 350.Loss of drivability , bottom end torque , car will rust , etc.
Had track day and decided to test 58mm BBK intended for my race 383.
'87 with 95K 350 TPI / ZZ4 cam /siamized base / headers /3.07 /MT ETs
18+ runs with stock TB
Change to 58mmTB , no changes to engine ,TPS preset.
12 runs with 58mm
Exactly the same times both ET and 60 ft.No flat spot , SOTP felt better off the line with 58mm.
2 13.2s with each , balance 13.3. all 1.86 -1.87 60ft on ET streets.(Has gone 13.103 in cooler temps/ low humidity)
While this is obviously not a recommendation to run a 58mm on a 350, it shows that the negative effects of such are not as bad as claimed.
Even got same fuel economy (indicated ) on drive home with 58mm.
Only side effect is loss of very low part throttle reponse such as creeping foward in traffic from a stop.1/4 or more throttle and no difference.
Update.
As of 5-31-06 ,same 58mm combo as above (hood had not been opened between race meetings)
in cooler air ran 13.0XX all day with three 12.98X -1.78 60fts.
None of the claimed LOSS of bottom end torque here.
Had track day and decided to test 58mm BBK intended for my race 383.
'87 with 95K 350 TPI / ZZ4 cam /siamized base / headers /3.07 /MT ETs
18+ runs with stock TB
Change to 58mmTB , no changes to engine ,TPS preset.
12 runs with 58mm
Exactly the same times both ET and 60 ft.No flat spot , SOTP felt better off the line with 58mm.
2 13.2s with each , balance 13.3. all 1.86 -1.87 60ft on ET streets.(Has gone 13.103 in cooler temps/ low humidity)
While this is obviously not a recommendation to run a 58mm on a 350, it shows that the negative effects of such are not as bad as claimed.
Even got same fuel economy (indicated ) on drive home with 58mm.
Only side effect is loss of very low part throttle reponse such as creeping foward in traffic from a stop.1/4 or more throttle and no difference.
Update.
As of 5-31-06 ,same 58mm combo as above (hood had not been opened between race meetings)
in cooler air ran 13.0XX all day with three 12.98X -1.78 60fts.
None of the claimed LOSS of bottom end torque here.
Last edited by rodj; Jun 23, 2006 at 02:06 AM.
Melting Slicks
Joined: Oct 2002
Posts: 3,193
Likes: 1
From: Cincinnati Oh
I wonder if a larger displacement (383ci and up) with a larger demand for air would show modest gains with the larger TB?
Good test though!
Do you know if you leaned out at all under WOT with the larger TB?
Good test though!
Do you know if you leaned out at all under WOT with the larger TB?
Thread Starter
Le Mans Master
Joined: Aug 2000
Posts: 8,838
Likes: 31
From: Australia
I tried different fuel pressures on both setups (have AFPR) but can not say any was spot on given range of times ran.
Did run highest mph ,103 ( 101 -102 usually) with 58mm so would indicate top end working right.
Did run highest mph ,103 ( 101 -102 usually) with 58mm so would indicate top end working right.
Drifting
Joined: May 2003
Posts: 1,730
Likes: 1
From: Charlotte NC
St. Jude Donor '05
A 58mm won't hurt you by any means. They are just not a good HP/$$ in most cases thats why i don't reccomend them often.
THe only thing to worry about is the TV cable will not be porportioned right with the new TB.. So with a small pedal movement, your getting the slack shift poing and the weak line pressure as opposed to the 48.
I perosnally have a monoblade on my 355 and that is one snappy biiiaaatch!! I don't even feel like I move the pedal, I just apply more pressure to it and it goes.
THe only thing to worry about is the TV cable will not be porportioned right with the new TB.. So with a small pedal movement, your getting the slack shift poing and the weak line pressure as opposed to the 48.
I perosnally have a monoblade on my 355 and that is one snappy biiiaaatch!! I don't even feel like I move the pedal, I just apply more pressure to it and it goes.
Melting Slicks
Joined: Dec 2001
Posts: 2,437
Likes: 1
From: Gainesville Fl
Originally Posted by Morley
One limiting factor is that unless your plenum has been bored to 58mm, you effectively turned that 58mm TB into a 52MM, since the bores in the plenum are only 52mm from the factory.
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Thread Starter
Le Mans Master
Joined: Aug 2000
Posts: 8,838
Likes: 31
From: Australia
Originally Posted by Morley
One limiting factor is that unless your plenum has been bored to 58mm, you effectively turned that 58mm TB into a 52MM, since the bores in the plenum are only 52mm from the factory.
Plenum has been taken out to 58mm and area behind TB cleaned up .Are unsure of effects on 48mm setup (doubt it would be negative) as changed as same time as cam .
Test above was done only to prove / disprove claims of overly negative effects of 58mm on small stock type engines.
Last edited by rodj; Mar 26, 2006 at 06:26 AM.
Melting Slicks
Joined: Dec 2001
Posts: 2,437
Likes: 1
From: Gainesville Fl
Originally Posted by rodj
FORGOT.
Plenum has been taken out to 58mm and area behind TB cleaned up .Are unsure of effects on 48mm setup (doubt it would be negative) as changed as same time as cam .
Test above was done only to prove / disprove claims of overly negative effects of 58mm on small stock type engines.
Plenum has been taken out to 58mm and area behind TB cleaned up .Are unsure of effects on 48mm setup (doubt it would be negative) as changed as same time as cam .
Test above was done only to prove / disprove claims of overly negative effects of 58mm on small stock type engines.
I agree with ur findings. I had a thought however that if you had an LTx type setup you might even see some benefit from the 58mm TB because those motors breath a bit better. just a thought.
Melting Slicks
Joined: Nov 2002
Posts: 2,471
Likes: 2
From: 1993 Quasar Blue 'vert Scottsdale AZ
Like said, it depends on what your intake is ported to. It may also have something to do with the fact that you are in the southern hemishere where toilets flush backwards.
Le Mans Master
Joined: Jul 2000
Posts: 5,012
Likes: 5
From: OKC OK
Originally Posted by Alvin
A 58mm won't hurt you by any means. They are just not a good HP/$$ in most cases thats why i don't reccomend them often.
Originally Posted by Alvin
I perosnally have a monoblade on my 355 and that is one snappy biiiaaatch!! I don't even feel like I move the pedal, I just apply more pressure to it and it goes.
I'm getting an Al flywheel installed tomorrow, so I'm a little worried about tip in driveability issues
Originally Posted by pipe
Hmmmm wonder how a Monoblade would work on my 383? Really wild solid roller and BIG ports on Brodix track 1s
Team Owner
Joined: Aug 2000
Posts: 24,125
Likes: 3
St. Jude Donor '14
Originally Posted by TA
I wouldn't have thought there would be much difference, but unless you have the 383+ why spend $400 for NO gain. 
