GT big block experiance : New GT crank info added
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Spanish Fly
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Eden has proven the durability of the GT kit, a fine piece of British engineering.
I can't help but think Richard is missing a trick offering it with 66mm bore rather than 70mm.
How many rebores do you need?!
SF
I can't help but think Richard is missing a trick offering it with 66mm bore rather than 70mm.
How many rebores do you need?!
SF
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rosscla
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He gives his engineering and design reasons for that Scootering article a few months backSpanish Fly wrote:Eden has proven the durability of the GT kit, a fine piece of British engineering.
I can't help but think Richard is missing a trick offering it with 66mm bore rather than 70mm.
How many rebores do you need?!
SF
"Our dilemma is that we hate change and love it at the same time; what we really want is for things to remain the same but get better."
I have just ordered the big block myself. I'm no tuner. This thread and the article convinced me I can install and setup this up myself. Looking forward to riding it!
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Lambretta LiS150 1965 - MBGM RT195 w/MBGM Clubman & Keihin PWK28
Lambretta TV175 1962 - GranTurismo 200 w/MBGM Clubman & Dellorto PHBH 28
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Spanish Fly
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Yeah, I know. Richard's reasons are totally sound from an engineering stand point.rosscla wrote:He gives his engineering and design reasons for that Scootering article a few months backSpanish Fly wrote:Eden has proven the durability of the GT kit, a fine piece of British engineering.
I can't help but think Richard is missing a trick offering it with 66mm bore rather than 70mm.
How many rebores do you need?!
SF
Market perception is a different issue.
If it was 225cc out of the box, I believe, it would be even more popular.
TS1 was 200 when it came to market but not for long. As FastFrog would say........size matters.
SF
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Rich_T
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200cc is not just engineering, there is a difference between market perception and market reality.
The problem is that at 70mm the tips of the open petals would touch the piston skirt. To get around this you make the reed sit higher but when you do this the 30mm manifold for the L/H side does not clear the frame. OK, you say, offer only R/H manifolds like the RB and TS1. Well, there is a large manifold and the R/H side which is available for the GT kit and guess how many have been sold? Zero. No 34mm R/H carbs have been sold at all (I'm still on the first test castings). I think out of nearly 70 kits this year maybe 2 have gone out with a 30mm R/H manifold but that is it everything else is 30mm L/H side.
This underlines the point that the Big Block GT kit is filling a market that the RB and TS1 can not. This market is the flexible, sporty, stock looking ,stock sounding, battery tray retaining, rally going, tourer.
So to go to a 70mm production bore would hamper the possibility to have a carb on the left and this is THE key feature of the GT kits which gives it such flexibility.
The largest production bore I can safely achieve and have the carb on the left is 66mm (350LC piston options between 68-70 are non-existent). Once we are at 66mm bore we run into another problem which is to gas flow the skirt. This is done on the CNC because the skirt is much thicker, if it were a 70mm bore then the skirt would snap during this machining operation. Could it be left and done by hand? One off yes; production no, it is too big a job to do by hand on every barrel.
So can the GT kits go to 70 bore? Yes they can but you need a laser cut packer for the reed valve (I made Eden's by hand). To date there has been no enquiries at all for a reed packer. Again this indicates that the majority market is 30mm carb L/H side, 66mm bore. BTW, once you're at 70mm bore you are R/H side carbs only, you can't go back unless you start using off set cones etc (I don't know for sure that they'd totally clear).
The reality is that all kits have to work as a business model (because of the costs involved), and this means you have to successfully identify and provide for a volume market.
To assume that because TS1 benefited from a change to 225, therefore a GT200 would also benefit would be a case of perception, not reality.
The fact of the matter is that the change for TS1 did not impact their target market (because the battery tray is already off and the frame clear). For TS1 it was a straight dash for power/capacity, a no brainer.
In the case of GT kits this change (to 225cc) would be weighing up the difference in sales potential between carbs on the L/H side or carbs on the R/H side. Or to put it another way, direct competition with TS1 and RB's in a competitive market (no battery trays) or have the option to double the potential markets with carbs on both sides (where TS1 and RB can't go). I think most will agree, after reviewing the above, that 70mm out of the box would seriously restrict the market potential. So, although size matters to some people, quantity sales matter much more.
The problem is that at 70mm the tips of the open petals would touch the piston skirt. To get around this you make the reed sit higher but when you do this the 30mm manifold for the L/H side does not clear the frame. OK, you say, offer only R/H manifolds like the RB and TS1. Well, there is a large manifold and the R/H side which is available for the GT kit and guess how many have been sold? Zero. No 34mm R/H carbs have been sold at all (I'm still on the first test castings). I think out of nearly 70 kits this year maybe 2 have gone out with a 30mm R/H manifold but that is it everything else is 30mm L/H side.
This underlines the point that the Big Block GT kit is filling a market that the RB and TS1 can not. This market is the flexible, sporty, stock looking ,stock sounding, battery tray retaining, rally going, tourer.
So to go to a 70mm production bore would hamper the possibility to have a carb on the left and this is THE key feature of the GT kits which gives it such flexibility.
The largest production bore I can safely achieve and have the carb on the left is 66mm (350LC piston options between 68-70 are non-existent). Once we are at 66mm bore we run into another problem which is to gas flow the skirt. This is done on the CNC because the skirt is much thicker, if it were a 70mm bore then the skirt would snap during this machining operation. Could it be left and done by hand? One off yes; production no, it is too big a job to do by hand on every barrel.
So can the GT kits go to 70 bore? Yes they can but you need a laser cut packer for the reed valve (I made Eden's by hand). To date there has been no enquiries at all for a reed packer. Again this indicates that the majority market is 30mm carb L/H side, 66mm bore. BTW, once you're at 70mm bore you are R/H side carbs only, you can't go back unless you start using off set cones etc (I don't know for sure that they'd totally clear).
The reality is that all kits have to work as a business model (because of the costs involved), and this means you have to successfully identify and provide for a volume market.
To assume that because TS1 benefited from a change to 225, therefore a GT200 would also benefit would be a case of perception, not reality.
The fact of the matter is that the change for TS1 did not impact their target market (because the battery tray is already off and the frame clear). For TS1 it was a straight dash for power/capacity, a no brainer.
In the case of GT kits this change (to 225cc) would be weighing up the difference in sales potential between carbs on the L/H side or carbs on the R/H side. Or to put it another way, direct competition with TS1 and RB's in a competitive market (no battery trays) or have the option to double the potential markets with carbs on both sides (where TS1 and RB can't go). I think most will agree, after reviewing the above, that 70mm out of the box would seriously restrict the market potential. So, although size matters to some people, quantity sales matter much more.
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paulnobodyimportant
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Good reply there Rich. It all makes sense now from both a user's and the commercial point of view.
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Spanish Fly
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I'll get me coat. 
SF
SF
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Rich_T
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My post above is not meant as a bashing. I'm trying to be informative as possible with minimal text to stop everyone nodding off so please don't take offence.
When manufacturing products in production quantities there is a massive amount of technical and strategical thinking required. A lot of it is to do with independently validating market perceptions or hunches into qualified information. You also have to study the competitive products very closely, improve on and incorporate novel beneficial features. There are a lot of market perceptions that are way off track and it is both easy and understandable to follow the same tack.
Much as it interests me it would bore the pants of most and others will doubtless have their opinions so probably best to leave it, one for the pub.
On another note, there are a couple of GT big block owners out there who are going for 70mm bore and I'm very interested (and probably a few others too) to see how you get on. Eden has set the bar for a road going 230cc @ 27bhp with various bits of cannibalised parts languishing in and around his garage. All held together with duck tape and assorted cable ties.
I'd be staggered if he has hit on the magical combinations first time out so it will be very interesting to see how others get on and if a reliable 30bhp is on the cards, we'll have to see what the tuners can do.
When manufacturing products in production quantities there is a massive amount of technical and strategical thinking required. A lot of it is to do with independently validating market perceptions or hunches into qualified information. You also have to study the competitive products very closely, improve on and incorporate novel beneficial features. There are a lot of market perceptions that are way off track and it is both easy and understandable to follow the same tack.
Much as it interests me it would bore the pants of most and others will doubtless have their opinions so probably best to leave it, one for the pub.
On another note, there are a couple of GT big block owners out there who are going for 70mm bore and I'm very interested (and probably a few others too) to see how you get on. Eden has set the bar for a road going 230cc @ 27bhp with various bits of cannibalised parts languishing in and around his garage. All held together with duck tape and assorted cable ties.
I'd be staggered if he has hit on the magical combinations first time out so it will be very interesting to see how others get on and if a reliable 30bhp is on the cards, we'll have to see what the tuners can do.
