New Big Block Gran Turismo Kit 200-245cc

[Rich_T]

The Big Block GT is prototyped from this tooling but this is only to enable the jigs and programs to be constructed. Everything else on the barrel has been proven over the last 10 years with the small block. Sure a few widths and angles are changed but these take advantage of the larger stud spacing and will be advantagous changes. Two port profiles were tested, a bridged design and a trapazoidal design. For reliability the trapazoidal design profile came through however the tooling is designed to run with both if required.

The LC barrel is 272cc on a 60 stroke. This is done for a couple of reasons, firstly to keep the cylinder length down (for foot print and packaging reasons), secondly to keep the piston velocity down and the crank webs small by comparison to CR250 cranks for example. The wide flange releases all the porting constraints. The increase in piston surface area should improve BMEP, the reduction in cylinder wall area is compensated for by very wide ports (no stud problems). It's a work in progress and will be some time away.

The Big Block GT is a matter of single digit weeks away, the LC double digit months at least. If, however, anyone is thinking about a big LC motor I'd be interested to hear from you.

[cezeta]

when i had my ts1 re done by mbd i asked for a 240 cc gt186 kit. what i meant by this was a lower smoother state of tune with any power lost by de tuning made up by cc s. it worked well apart from the open carb which remains a pain in the ass.

so im hoping the new gt kit is still "stage 4 with reeds" like before as you dont want to improve a great kit into a crap one.

bgm make a fast flow standard style filter, coupled with a mbgm clubman if they are as good as claimed then this could be the promised land for many (or the work of the devil for the open carb ripspeed exhaust brigade )

great work richard, im having one.

[joespeed]

still cat iron then, thats a shame

You have to remember that the Small Block GT186 kit put a lot of TS1 225 kits to shame even though it was a full 40cc smaller. It managed to achieve this in cast iron too which kind of turned conventional wisdom of plated barrels on it's head. It is considerably harder to produce a barrel in iron than it is to produce it in aluminium (I've cast barrels in both) yet I still elected to go cast iron. This is not done out of shear belligerence, it is done for a series of very carefully considered reasons.

Now the GT kits have gone up to the 200 casing it will be interesting to see how a cast iron barrel compares in this arena; remember that Eden's barrel puts out 27 odd BHP without any ill effects. This cylinder has the capability to match it.

The new manifold options are 30mm on the L/H side for PHBH30 carbs and 34mm carbs on the R/H side for Mukuni or similar (not VHSB 34 as the bore is bigger than 34mm).[/quote

rich,what are your carefully considered reasons? did you consider the new 200 case any further?

[Rich_T]

rich,what are your carefully considered reasons? did you consider the new 200 case any further?

The Misano case is not in my control and as such I would not and could not design around it. If it will take a 200cc cylinder on 200 stud spacing then it would work but basing investment and tooling decisions around someone elses product is not sensible. Flexibility in application and simple robust service life is key to a wide market appeal.

There are three main areas where I believe cast iron wins over plated cylinders. Firstly, the aysemetric thermal distortion of the cylinder when fan cooled. Secondly, the elastic limits of the plating compared to the parent cylinder metal. These are physical properties and these problems are either reduced by a factor of ten (at least) or simpley do not exist with an iron cylinder. Thirdly, honing, rebores and oversizes are far easier and cost effective to achieve.

The bad reputation of iron cylinders was gained by very poor quality Indian components being mis-matched with equally poor quality pistons from multiple sources. Consistance of bore and pistons was the great success of the TS1 when the same logic is applied to iron barrels they are just as reliable, in some ways even more so.

[Spanish Fly]

Rich.
A great looking product is interesting to see it evolving through the manufacturing process.
Were you able to get the casting patterns made up directly from the 3D CAD data or did your supplier need dimensioned drawings?

SF

[Adam_Winstone]

"when the same logic is applied to iron barrels they are just as reliable, in some ways even more so"

Agreed, iron barrels are still a great option. The biggest feature of alloy barrels is that they shed heat so much better than iron ones, making them much more forgiving that iron barrels. What this actually means it that just about anyone can bolt on an alloy kit and have some chance of it still being reasonably reliable, just because alloy is that much more forgiving. However, in the hands of someone who knows how to set up a motor then iron can be just as reliable and does, as you have already identified, give some benefits that the alloy does not (e.g. cheap rebores). Only when you get to the top end of performance, and set up, does the alloy barrel's heat loss factor become worthwhile... even then 9 times out of 10 you could do the same with iron, although it would be set up differently.

Rich is simply making an informed decision on which benefits to promote in this big-bore addition to an already proven reliable kit range.

Adam

PS - If you ever needed an example of this, I was asked to look at a mate's unreliable GT186, which had holed 3 pistons within a couple of hundred miles!!!!!!!! Sure enough, the compression was way too high and the timing was a mile out! With these elements corrected the bike has gone from local chatter about 'unreliable GT kits' to being 'the best thing since sliced bread'. An alloy kit might have only gone through a couple of pistons in the same distance but it wouldn't have lasted to that much longer.

[Rich_T]

Rich.
A great looking product is interesting to see it evolving through the manufacturing process.
Were you able to get the casting patterns made up directly from the 3D CAD data or did your supplier need dimensioned drawings?

The positional accuracy and shape of 2 stroke sand patterns is absolutely critical to the manufacturing process and repeatable quality. Therefore all patterns and cores are cut directly from CAD data, this is much faster, consistant and accurate than "old school" pattern making. Dimensional drawings do exist but this is for technical reference and planning CNC machining operations/checks. Consequently a full set of drawings would serve no practical purpose.

[Spanish Fly]

The positional accuracy and shape of 2 stroke sand patterns is absolutely critical to the manufacturing process and repeatable quality. Therefore all patterns and cores are cut directly from CAD data, this is much faster, consistant and accurate than "old school" pattern making. Dimensional drawings do exist but this is for technical reference and planning CNC machining operations/checks. Consequently a full set of drawings would serve no practical purpose.

Thanks for that Rich. An interesting insight as to how you are utilising the power of the 3D CAD.
As an design engineer from a manufacturing background I'm really impressed with the way your product is engineered from concept to manufacture. Few of your rivals, perhaps with the exception of Ron Moss, can have the in depth knowledge of their 'own' product that you do. I feel that can only be a massive benefit to anyone who chooses to buy a GT kit in the future. Great stuff.

SF

[Rich_T]

Pictures of the internal ports on the new GT Big Block. Stock timing work out at 127 transfer and 177 exhaust (1 degree more on transfer and 5 degree more on exhaust than the small block). This bore is machined to 66mm, the plan is for a range of pistons to take it up to 70 (or perhaps 71) bore.

[Mr G in NYC]

I like the look and sound of this 200 Kit.
Definite interest when you are ready to
sell them. Put me down for one.
I need a new project for 2013 G.