Everything You Need To Know To Find The Best GTM Gearbox

Which engine should I fit?  Author Message rssgtmcoupe GTM on order
Joined: Mon Sep 14, 10:09 pm
Posts: 9
Location: Peterborough
GTM: Cox/Coupe  Which engine should I fit? Hi . Following my post ' Problems Selecting Gears ' I removed the engine and had the gearbox "mended"
Once fitted back in the car it jammed again. Failed to get it on the road this summer!
I posted an appeal at work for mini engines and parts. (I work in engine R&D). I now have an embarresment of them. To much so I would like advise which to build and fit.
The existing engine runs well and is 998 with 731 cam, hardened crank and ported head. It is attached to the Duff 3 synchro box. Rubber type driveshafts.
I have been given the following :1.3 MPI engine only, top end minus crank and most sensors. It has the injectors and manifilds, also a Motec programmable UCU. Only 100 hours dyno running but has a score in one bore.
good bores and bearings, Kent fast road cam, but some bits missing.
bored out ex track racing engine. Condition not sure. Has ported lead-free head but 4.33:1 diff.
Box containing a 998 plus other odd bits.
A 998 standard engine complete but has been stood outside for years.
A complete diff. A complete gearbox. 2 sets of twin HS2. 1 x HS4 carb. 1 x Electronic distributor. 2 driveshafts.
All the newer ones have 4 syncyro boxes and pot joints.
Please tell me what would be best suited to the car as I have yet to drive it. Thanks Roger (rssgtmcoupe)

Sat Sep 04, 9:22 pm Andy Ready for SVA
Joined: Thu Nov 15, 10:22 pm
Posts: 363
Location: Ireland  Re: Which engine should I fit? If it were me, I would be going for bigger CC rating, so a or or , I'm running a very worked done by MED on a single 45 weber DCOE. Its on a SCCR box with 4 pin diff and hardy spicer output shafts.

It all depends on what you want from the engine, is a high bhp high rpm engine, the is again high bhp but has increase torque due to the crank stroking.

Sun Sep 05, 10:09 pm rssgtmcoupe GTM on order
Joined: Mon Sep 14, 10:09 pm
Posts: 9
Location: Peterborough
GTM: Cox/Coupe  Re: Which engine should I fit? Hi Andy Thanks for your reply.

I forgot to say what the cars is to be used for, its is only meant for the road although a track day is not out of the question.
I work in electronics and have never built an engine. I am not sure what version of what fits together on the collection of parts that I have. For example I see that there are differences in the newer head to the older ones. Cash is a problem so would want to use the parts I already have.
I mention the Diff ratio as I would not like to be over revving on motorways. If I use one of the injection model diffs around 3:1 will the acceleration be badly affected on such a light car? I found the ratios on the Somerford web site.
I was advised previously that I need a different gear shift mechanism, I plan to buy this when I am sure what direction to go with the engine.
Roger

Mon Sep 06, 4:48 pm Andy Ready for SVA
Joined: Thu Nov 15, 10:22 pm
Posts: 363
Location: Ireland  Re: Which engine should I fit? rssgtmcoupe wrote:Hi . Following my post ' Problems Selecting Gears ' I removed the engine and had the gearbox "mended"
Once fitted back in the car it jammed again. Failed to get it on the road this summer!
I posted an appeal at work for mini engines and parts. (I work in engine R&D). I now have an embarresment of them. To much so I would like advise which to build and fit.
The existing engine runs well and is 998 with 731 cam, hardened crank and ported head. It is attached to the Duff 3 synchro box. Rubber type driveshafts.
I have been given the following :1.3 MPI engine only, top end minus crank and most sensors. It has the injectors and manifilds, also a Motec programmable UCU. Only 100 hours dyno running but has a score in one bore.
good bores and bearings, Kent fast road cam, but some bits missing.
bored out ex track racing engine. Condition not sure. Has ported lead-free head but 4.33:1 diff.
Box containing a 998 plus other odd bits.
A 998 standard engine complete but has been stood outside for years.
A complete diff. A complete gearbox. 2 sets of twin HS2. 1 x HS4 carb. 1 x Electronic distributor. 2 driveshafts.
All the newer ones have 4 syncyro boxes and pot joints.
Please tell me what would be best suited to the car as I have yet to drive it. Thanks Roger (rssgtmcoupe)

Ok, well if thats the limiting factor then I throw my two cents worth into it,

You really want a cc engine minium in the Coupe anything less would just be dissapointing and even more so on a track day so,

(I have been given the following :1.3 MPI engine only, top end minus crank and most sensors. It has the injectors and manifilds, also a Motec programmable UCU. Only 100 hours dyno running but has a score in one bore.) this engine is actually a later model block (A+) this would be a good start so long as the score is not too deep and can be removed with a quick hone, if this is not the case then a simple over bore to or could be done relatively cheaply. You should be able to pick up a crank etc fairly easily, and I would ditch the fuel injection (they were Toffee anyway) and go for a twin SU or single 1 3/4" SU carb.

good bores and bearings, Kent fast road cam, but some bits missing. this could be a runner also with similar systems to the above ( dependent on whether its an A series or A+ block)

As for gearboxes, the casing on all A series will mate up to the larger block, however you can't mix a A series with an A+ block/box. For diff ratios I would go for either a 3:44 or 3:2 ratio, depending on what rpm you want at highway speeds, the first will give a quicker acceleration higher rpm the later will be lower rpm at speed.

Without more information or photo's its hard to give more advise, you could also ring me or skype me if you want more advise or info, pm me if you want.

Andrew

Mon Sep 06, 8:11 pm rssgtmcoupe GTM on order
Joined: Mon Sep 14, 10:09 pm
Posts: 9
Location: Peterborough
GTM: Cox/Coupe  Re: Which engine should I fit? Hi Andy. That is the type of information that I am after. Much appreciated.

While buiding the car I had a thought that the original engine may be a bit small and after all the time and effort did not want to be dissappointed by the performance. I think that the is the way to go so have looked up the serial number 12HC14AA. I found a site that says this is an MG Metro engine and that the diff should be 3.44. I will confirm that when I split it. The head and valve gear will have to come off the MPI as this is missing.
I am relieved that the injection would be more trouble than it is worth.
Would you think leaving in the fast road/rally cam a good idea? I have one from the MPI if not.

Thank you for the offer to advise me. I will take you up on it if I get stuck

Regards Roger

Tue Sep 07, 5:34 pm Andy Ready for SVA
Joined: Thu Nov 15, 10:22 pm
Posts: 363
Location: Ireland  Re: Which engine should I fit? Roger,

Yes leave in the uprated camshaft, you might want to give the head a going over prior to reassembley, not sure what the valve sizes are on a MPI head but I'm sure they won't be too bad for that setup, yeah go with the 3:44 diff, the MG metro blocks were always good and it should be A+ aswell,

Wed Sep 08, 7:42 am

[Brief Description] The GTM-2V Gear Box is a unique combination of GTM-1V gear box and our non-spring clutch V3, this exclusive integrated design not only save the room in your boat, also improve the performance and appearance.

The main components of GTM-2V gear box are precision-engineered and manufactured with up-to-date CNC technology, it has a lustrous external finish whilst careful internal machining of any low-stress areas has removed surplus metal and reduced any unnecessary weight to reach its unmatched performance and provides sufficient room for the lubrication oil.

The creative design of output collet shaft integrates both gear drive shaft and flexible shaft collet, this one piece design shortens total length of the output shafts and enable GTM-2V Gear Box to be installed with smaller hulls, the two output shaft collets will accept any 1/4 inches (6.35mm) diameter flexible shaft.

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The gears inside the box has lighten hollowing out design and manufactured with technology of compacting process of powder metallurgy the same technology used for gears in full size automotive transmissions, the new gears delivers more rigidity and much lighter in weight compare to the gears in GX-1, and these gears were supported by total 8 heavy-duty ball bearings via harden drive shafts, this results in ultra smooth operation and enable to handle any gas or electric motor over 15HP with up to RPM+ without failure.

The GTM-2V gear box kit will work with any gas marine engine available in the market including Arrow Shark, Zenoah, RCMK (single or twin), QD, CY or clone engines in either stock or modified versions, and it can be installed to any mono hull from 55 inches up to 70 inches, please double check the dimension picture above for more detail and make sure it suits your engine or hull application before placing the order.

Please Note: The Gear Box will be shipped to you without pre-filling the lubrication oil, you will need to fill the lubrication oil after you receive it. Any brand of 4 stoke oil or gear oil will work.