Sv29/ilmor 725/indy
10-02-2012, 12:14 AM
#41
PF Marine
Platinum Member
Peter, comparing your lower to Nascats, your skeg looks longer (deeper). Did you cut yours down or is that how it came from Ilmor?
10-02-2012, 07:27 AM
#42
Registered
I had my lowers done at the same time the drives were apart to have the gear ratio changed as well as swapped the prop rotation so there wasn't any way to really A / B the lowers & isolate the gain to just the blueprinting of the lowers. I also had just added a tunnel tab. All changes made yielded a positive result but to this day actual top speed potential is unknown b/c I'm out of prop & couldn't put my hands on a set of 39's when I needed them.
The laws of physics alone will tell you having a true & symmetrical lower bullet & skeg over one w/ a rougher cast finish & maybe even a slight bow in it. Unless you did all your A / B testing the same day in the same conditions & temperatures & continued to refill the fuel to the same level I don't think one can really pin point where the measurable gain came from. I don't know too many people that do thjat when they are prop testing etc.
My skegs are stock length to my knowledge.
The laws of physics alone will tell you having a true & symmetrical lower bullet & skeg over one w/ a rougher cast finish & maybe even a slight bow in it. Unless you did all your A / B testing the same day in the same conditions & temperatures & continued to refill the fuel to the same level I don't think one can really pin point where the measurable gain came from. I don't know too many people that do thjat when they are prop testing etc.
My skegs are stock length to my knowledge.
10-02-2012, 07:32 AM
#43
Registered
Thread Starter
Your observations are correct... the skeg has been cut down to reduce drag and be more suited to the smaller diameter propellers we will be using, it is still 1" lower than the bottom of the blade.
Peter
10-02-2012, 08:32 AM
#45
Registered
Join Date: Jun 2006
Location: Seneca Lake
Posts: 253
Likes: 0
Received 0 Likes
on
0 Posts
Peter
Not to change the subject , but I see in your avatar that there is a race car , and the track looks a lot like watkins glen where I live . Have you ever been up here for vintage racing or anything else. We have a lot of speed boats on the lake , if you ever bring that 29OL up we would love to show you a great time Racing/Boating.
Regards
Wellcrafted
Not to change the subject , but I see in your avatar that there is a race car , and the track looks a lot like watkins glen where I live . Have you ever been up here for vintage racing or anything else. We have a lot of speed boats on the lake , if you ever bring that 29OL up we would love to show you a great time Racing/Boating.
Regards
Wellcrafted
Last edited by wellcrafted; 10-02-2012 at 08:38 AM.
10-06-2012, 03:21 AM
#47
Registered
Thread Starter
Peter
Not to change the subject , but I see in your avatar that there is a race car , and the track looks a lot like watkins glen where I live . Have you ever been up here for vintage racing or anything else. We have a lot of speed boats on the lake , if you ever bring that 29OL up we would love to show you a great time Racing/Boating.
Regards
Wellcrafted
Not to change the subject , but I see in your avatar that there is a race car , and the track looks a lot like watkins glen where I live . Have you ever been up here for vintage racing or anything else. We have a lot of speed boats on the lake , if you ever bring that 29OL up we would love to show you a great time Racing/Boating.
Regards
Wellcrafted
The picture is at Spa in Belgium enjoying one of my other hobbies, would love to drive Watkins Glen and Laguna Seca one day.....
Peter
10-06-2012, 10:32 AM
#48
Registered
iTrader: (2)
I had my lowers done at the same time the drives were apart to have the gear ratio changed as well as swapped the prop rotation so there wasn't any way to really A / B the lowers & isolate the gain to just the blueprinting of the lowers. I also had just added a tunnel tab. All changes made yielded a positive result but to this day actual top speed potential is unknown b/c I'm out of prop & couldn't put my hands on a set of 39's when I needed them.
The laws of physics alone will tell you having a true & symmetrical lower bullet & skeg over one w/ a rougher cast finish & maybe even a slight bow in it. Unless you did all your A / B testing the same day in the same conditions & temperatures & continued to refill the fuel to the same level I don't think one can really pin point where the measurable gain came from. I don't know too many people that do thjat when they are prop testing etc.
My skegs are stock length to my knowledge.
The laws of physics alone will tell you having a true & symmetrical lower bullet & skeg over one w/ a rougher cast finish & maybe even a slight bow in it. Unless you did all your A / B testing the same day in the same conditions & temperatures & continued to refill the fuel to the same level I don't think one can really pin point where the measurable gain came from. I don't know too many people that do thjat when they are prop testing etc.
My skegs are stock length to my knowledge.
If your boat tops out at 80 and you run it often and frequently hit top speed which is not problem in an 80mph boat then you have a better idea of how conditions, temp, wind, load affect top end. When your boat goes 150 how often can you really go that speed?
I guess a better test would be at a known rpm say 4000 has the speed changed after any improvements.
10-06-2012, 12:35 PM
#49
Diamond Member #001
Charter Member
iTrader: (2)
Join Date: Oct 2000
Location: Coastal North Carolina
Posts: 4,808
Likes: 0
Received 5 Likes
on
4 Posts
The problem is that all manufacturers have to work with cast lower units, which are subject to warpage during the casting, machining, and heat-treatment processes. The issue is important enough that the old APBA LLC insisted on CNC-blueprinted lowers from Mercury for the initial SuperCat class many years ago. This adds a significant cost to the production of these drives, and may not yield results that Joe Boater would recognize, but racers probably will. Besides that, there are plenty of theories on lower unit hydrodynamics. A quick look at the various manufacturers' products will demonstrate that.
As far as back-to back tests go, I can state from personal experience that Ilmor lower units can be swapped in less than five minutes. Heck - Depending on what gear ratio Peter uses, I may loan him mine for a test!
__________________
Retired! Boating full-time now.
Retired! Boating full-time now.
10-07-2012, 07:40 AM
#50
Registered
VIP MemberJoin Date: Jun 2008
Location: long island ny
Posts: 240
Likes: 0
Received 0 Likes
on
0 Posts
I had my lowers done at the same time the drives were apart to have the gear ratio changed as well as swapped the prop rotation so there wasn't any way to really A / B the lowers & isolate the gain to just the blueprinting of the lowers. I also had just added a tunnel tab. All changes made yielded a positive result but to this day actual top speed potential is unknown b/c I'm out of prop & couldn't put my hands on a set of 39's when I needed them.
The laws of physics alone will tell you having a true & symmetrical lower bullet & skeg over one w/ a rougher cast finish & maybe even a slight bow in it. Unless you did all your A / B testing the same day in the same conditions & temperatures & continued to refill the fuel to the same level I don't think one can really pin point where the measurable gain came from. I don't know too many people that do thjat when they are prop testing etc.
My skegs are stock length to my knowledge.
The laws of physics alone will tell you having a true & symmetrical lower bullet & skeg over one w/ a rougher cast finish & maybe even a slight bow in it. Unless you did all your A / B testing the same day in the same conditions & temperatures & continued to refill the fuel to the same level I don't think one can really pin point where the measurable gain came from. I don't know too many people that do thjat when they are prop testing etc.
My skegs are stock length to my knowledge.
