Getting more juice

[Andy Moltu]

Nigel

I guess really upping the grunt in the GT6 might be limited by what the differential can take reliably?

[simonjrwinter]

I wonder what the OP did 14 years ago?

[Nigel Triumph]

1 hour ago, Andy Moltu said:

Nigel

I guess really upping the grunt in the GT6 might be limited by what the differential can take reliably?

Andy,

You're right but the weakest link is most likely to be the gearbox with D-type overdrive. I've only fully given it the beans in direct top, for fear of what may happen in intermediate gears or in overdrive.

When the transmission shows signs of distress I will have the gearbox rebuilt with the stronger internals from a Dolomite 1850 (which fit into the existing GT6 casing) and a J-type O/D. As for the diff, it's currently running the standard 3.89 ratio, which is too low. In due course I will replace it with a 3.63 ratio from a Spit 1500.

Bringing the thread back on track, the engine specification really works and should produce peak power similar to a CP series TR6, although we know they never made much more than 135bhp in reality.

Nigel

[DRD]

2 hours ago, Nigel Triumph said:

That's exactly the spec I chose when rebuilding a 2500S saloon engine for my GT6 last year, including Chris Witor's excellent CW3021 camshaft. In addition, the engine is balanced and uses a GT6 flywheel, weighing only 8Kg. My starting point 2500S engine was rated at 105bhp by the factory, so very similar to the US-spec TR6.

 I can't yet give a dyno figure, it was going for a rolling road session when lockdown started. Subjectively, the engine feels very strong throughout the rev range now it's run in. Compared to my CP series TR6, the tuned GT6 doesn't have quite the same punch of torque from around 1,500rpm but from 2,500rpm onwards, it's hard to notice any performance difference. In the lighter GT6, it absolutely flies and top gear acceleration is astonishing!

I would not advocate the expense of Webers for road use, SU HS6 carbs are perfectly adequate. I'm sure Webers are fine instruments but if my budget had stretched to the cost of triple Webers, I would have chosen EFi.

Nigel

Hi Nigel, what needles are you using in the SU's?

Cheers Daz

[Nigel Triumph]

47 minutes ago, DRD said:

Hi Nigel, what needles are you using in the SU's?

Cheers Daz

Hi Daz,

Chris Witor recommends BFZ needles for this spec. I used Dolomite Sprint Sprint short dashpot HS6 carbs to clear the low bonnet line of the GT6. For running in, I've kept the Sprint's BDQ needles and yellow springs which seem to work well. There's not much difference between the profiles of these two needle types but once lockdown is over, I'm booking a rolling road session to perfect carbs settings and ignition advance curve.

Nigel

[DRD]

1 hour ago, Nigel Triumph said:

Hi Daz,

Chris Witor recommends BFZ needles for this spec. I used Dolomite Sprint Sprint short dashpot HS6 carbs to clear the low bonnet line of the GT6. For running in, I've kept the Sprint's BDQ needles and yellow springs which seem to work well. There's not much difference between the profiles of these two needle types but once lockdown is over, I'm booking a rolling road session to perfect carbs settings and ignition advance curve.

Nigel

Interesting, I've got BBA which are much richer, especially at the top end. Even with these it does start to lean off above 4500rpm.

Daz

[Andy Moltu]

Is that because of the needles or fuel delivery?

[DRD]

33 minutes ago, Andy Moltu said:

Is that because of the needles or fuel delivery?

It's the needles, as always its a compromise to get something that works right across the rev range.

[Nigel Triumph]

2 hours ago, DRD said:

Interesting, I've got BBA which are much richer, especially at the top end. Even with these it does start to lean off above 4500rpm.

Daz

Hi Daz,

I've not been brave enough to take my new engine past 5k rpm yet, will get the rolling road session done first. I can't tell if it's going weak at the top end at this stage. The plugs are normal light brown colour but I haven't tried a plug chop after a flat out run. Maybe I should.

The BDQ needles I'm using currently are a little richer than Chris Witor's recommendation at the top end but slightly leaner at the 3/4 stage. Rolling road will be very interesting.

Nigel

[DRD]

2 hours ago, Nigel Triumph said:

Hi Daz,

I've not been brave enough to take my new engine past 5k rpm yet, will get the rolling road session done first. I can't tell if it's going weak at the top end at this stage. The plugs are normal light brown colour but I haven't tried a plug chop after a flat out run. Maybe I should.

The BDQ needles I'm using currently are a little richer than Chris Witor's recommendation at the top end but slightly leaner at the 3/4 stage. Rolling road will be very interesting.

Nigel

Hi Nigel, if you compare the needles on mintylamb there's quite a big difference between BDQ and BBA.

Cheers 

Daz

[astontr6]

On 4/22/2006 at 11:09 AM, scellis said:

I have a original US spec TR6 with about 106bhp. What is the best/easiest way to get some more juice out of the engine, to say 140-150bhp?

Hi Scellis!

There is a BL ST booklet 'Triumph Competition preparation manual TR250,TR5.TR6'. ISBN978-1-78318-001-1 This was printed for the USA market and answers most of your questions if not all. I believe that reprints are still available from Brooklands Books ltd here in the UK. It fully covers tuning up Carb. TR6's and others.

Bruce.

[Patrick Boxall]

Hi Everyone, interesting string. I have a 72 TR6 running SU's and am having a real problem with the engine running on. The needles I have are the std BAG, but want to try the next size up. Burlen weren't able to help, said it was a 'dark art' which surprised me seeing as they are the experts.

I have seen other comments on the site suggesting BCH, BDA and BAM. 

My car is running too lean. I am not an expert by any chalk so the car is at a local garage.

Any suggestions would be really welcome. I guess the real solution would be the rolling road, but just trying some options first.

Thanks

Paddy

[DRD]

58 minutes ago, Patrick Boxall said:

Hi Everyone, interesting string. I have a 72 TR6 running SU's and am having a real problem with the engine running on. The needles I have are the std BAG, but want to try the next size up. Burlen weren't able to help, said it was a 'dark art' which surprised me seeing as they are the experts.

I have seen other comments on the site suggesting BCH, BDA and BAM. 

My car is running too lean. I am not an expert by any chalk so the car is at a local garage.

Any suggestions would be really welcome. I guess the real solution would be the rolling road, but just trying some options first.

Thanks

Paddy

Hi Paddy, is the engine standard or modified?

I would recommend finding a good rolling road and someone  who knows  how to tune SU carbs properly.

I had running on problems but this is caused by the high compression ratio. I fixed it with an anti run-on valve.

Daz

[Patrick Boxall]

Thanks Daz, it’s standard. I think you’re right about the rolling road. 
cheers

Paddy

[Motorsport Mickey]

2 hours ago, Patrick Boxall said:

Hi Everyone, interesting string. I have a 72 TR6 running SU's and am having a real problem with the engine running on. The needles I have are the std BAG, but want to try the next size up. Burlen weren't able to help, said it was a 'dark art' which surprised me seeing as they are the experts.

I have seen other comments on the site suggesting BCH, BDA and BAM. 

My car is running too lean. I am not an expert by any chalk so the car is at a local garage.

Any suggestions would be really welcome. I guess the real solution would be the rolling road, but just trying some options first.

Thanks

Paddy

Patrick,

I soon found out that SU support was lacking back in 1986. I was buying SU parts from our local Burlen agent Who laughed at me when I asked if they had a flow bench.

However  to get me out of his hair, he did me a service by recommending Peter Burgess near Alfreton of J 28 on the M1 . Peter is in my opinion one of the top SU tuners in the UK... and maybe beyond. Enough of the TR specialists have since used and continue to use Peter To convince me I wasn’t mistaken. These days he has a state of the art rolling road and a dynamometer now being installed in a cell, and is often busy with cylinder head work not only for the TR specialists but also Moss. The guy is straightforward and honest... sometimes painfully so, if there is something wrong with your setup he will find it and advise in an unvarnished fashion. 
When I raced Peter developed my heads which I used to my benefit, 6 X TR Championship wins, 3 with a TR4  ( on SUs) and 3 with TR7 V8, he’s adept at all heads and develops them on his own flowbench. He is a large supplier to the MG crowd also and you often see genuine other exotica on his rolling road. Other than as a highly delighted customer I have no connection with Peter.
I’m afraid you’ve not given the information on your profile for me to tell where in the country you are ( just the county would do) so whether you could try him conveniently I can’t tell.

Mick Richards.

Edited May 16, 2020 by Motorsport Mickey

[DRD]

5 hours ago, Patrick Boxall said:

Thanks Daz, it’s standard. I think you’re right about the rolling road. 
cheers

Paddy

Then BAG needles should be ok or pretty close.