The Gran Turismo big block conundrum

[Rich_T]

After much chewing the fat this afternoon discussing the sensible order of new product development; the decision is made that the big block GT kit will be next. Good news for some but there is a slight divergence of opinions in the ranks and perhaps something we can sort out here.

All the GT kits are based on 350LC pistons and for part of the common parts philosophy, the Big block version would also use all the common parts to the original, manifold, reed block etc (some changes to port configurations, which are currently being tested out on a prototype).

Here is the problem, discussion, divergence or whatever. Plan A would be to start the kit bore size at 66mm (200cc) with a Mitaka 350LC piston. This would give the potential of 21 over-sizes! Plan B would be to start at 70mm (225cc) with a custom piston from Omega (UK manufacture). This would give about 7 over-sizes, pegs and recesses in exactly the right place.

The problem is, as always, the balance with price. Plan A is going to be around £395 retail (inc VAT) but excluding head whereas Plan B would be more like £540 (inc VAT) excluding head, the special piston is a big cost.

The question is this: Would you spend an extra £145 to get 25cc straight away or would you prefer to start at 200cc at a lower price and make your way to 225cc under your own steam and piston supply (Worsner etc)?

As background information. The Mataka pistons currently used run out at 66.5mm bore with over-sizes at every 0.25mm. This size range covers small block perfectly but not all the potential in a big block casting. When the castings are machined it will be one size only, not half 200 and half 225.

Personally, I see it going down the 200cc route but my technical “sounding board” says, “Can’t see a demand for anything smaller than 225cc, price won’t matter”. Max bore on the new barrel will be 71.5mm (233cc on 58 stroke or 240cc on 60 stroke). Production eta would be first quarter 2013, spec will be in line with current GT kits with bigger ports, 30mm manifold on L/H side or 34mm manifold for R/H side.

So which way to go, what do you think, please discuss.

[Muttley McLadd]

Personally, I'd go with a 200. If only because it'd be less vibey than a 225+.

What about selling the barrels without pistons?

[byron]

I'd be happy with a 200cc kit, Mitaka pistons are a good known brand, the range of oversizes is a bonus.
And does the extra cc's really make that much difference...? so one could also say that it's not worth a 2mm increase in bore from the current small block kit...
And I'd say most would want the 225 version, "ain't no subsitute..." etc
which would also be more of a jump from the GT190 version.

So, in summary, go big
I'd say, from a potential business view, you should opt for 225

[Rich_T]

Reliable kits are about control of quality and variables.

The most critical variable is the piston / bore. The last iron barrels to be sold seperately to pistons were SIL, dark days, enough said really.

[joespeed]

you cant beat cubes,so big would be better with long stroke/rod combination.

[Muttley McLadd]

Is the big block one a big torque kit for tall gearing?

[Rich_T]

personally I would also go for the 225, but having said that if you made the 200 people could always bore that to 70mm and use their own piston choice, if they choose a s**t piston thats their problem not yours.

This is pretty much my opinion too, at 66 bore you have options and a 66 bore in a big block will be better than a 66 bore in a small block as the ports will be considerably bigger, especially the exhaust.

The comitment to Omega pistons will soak up a very large amount of funds as they will have to be ordered and paid for in one go, not cheap at all.

The GT kit design is based around a 58 stroke (which are usually stronger cranks) however conversion to 60 stroke without a packng plate is very easy. 62mm stroke throws the port timings out a bit far form my liking and you end up needlessly spending money in modifications to correct it. Rod conversions such as 110mm would require a laser cut packer but are relatively easy to do but remember that all adds cost and essentially the question of this thread is what is the general opinion of cost V specification.

[Rich_T]

Is the big block one a big torque kit for tall gearing?

Ho yes.

[corrado]

I'd look at offering a bespoke package including crank, exhaust and carb, similar to what's happening with the Super Monza, and have a specific aim for it's performance. For me that would be a frugal touring set up, 200cc, TV rodded crank, 24 / 25mm carb, clubman type exhaust, 20 bhp and 20 ft / lbs torque at 6,000 rpm, 4.5 ish final drive giving a genuine 70mph and genuine 60 mpg. A set price so people know what the total outlay is from the off, £1200 to £1500. Maybe no more initial outlay on your part over and above 'x' numbers of cylinders and pistons if working closely with an exhaust manufacturer. Carbs and cranks only needing to be purchased once a kit is ordered. Keeping costs down with say SIL crank, machined for Yam rod and bearing and tig welded. The "bigger is better" and higher BHP market is already covered for those that want it.
I envision unwrapping my parcel on christmas morning with all the essential parts neatly stored encased in polystyrene blocks.
Dream on I hear you cry.

[YAMLAM]

200cc all the way. if people want a grunty 225 they will probably buy one of Rons kits.