I thought I would start a new thread for this.
It occurred to me that quite a few of us have fitted "go faster" bits to our Stags over the years without ever really knowing whether we were doing any good, and I have heard enough accounts of various modifications that have not worked over the years to know that a lot of time and cash has been squandered.
I have had the good fortune to approach Stag engine tuning from a completely different direction for the simple reason my 1st Stag engine was not fitted to a Stag but a TR250 (although it is badged as a TR5)
As a result of the engine not being in a Stag, I had to develop most of my own parts and therefore did not get sucked into the easy option of handing over a big wedge of cash in the hope that the items purchased would give the engine the desired get up and go!
Why did I chose a Stag engine in the first place?
Firstly because I love V8 engines
Secondly because the 3.9 Rover I already had was just a bit too big in all directions to fit in the TR without cutting big lumps out of the engine bay.
Thirdly it used virtually the same gearbox as the TR and that made fitting a whole lot easier.
Fourthly because it was the largest capacity engine made by Triumph and also the most powerful (don't believe the 150bhp TR engines ever made anything near 150bhp, nearer 125 in reality)
And finally because when I looked at one in bits at the Stoneleigh Triumph autojumble I was amazed it made as much power as it did such was the poor design of inlet and exhaust manifolds.
Having made the decision to fit a Stag engine to my TR, I wanted it to be as efficient and economical as possible because I was doing about 12,000 miles per year in my TR. This was part of the reason for not tuning the straight six to a higher level, good power can be made but at a cost of low teens fuel consumption. I was getting high twenties mpg out of my 2.5PI.
I wanted more power but good economy, and the easiest way to do this is start with a bigger capacity and a lower level of tune.
The greatest obstacle to fitting the Stag engine in the TR was the exhaust manifolds. I had a good cheap supply of inch and a half stainless steel Renault downpipes sold by a guy at the autojumbles, straight bits and bends with useful flanges on the end.
The design I used was a blatant copy of the standard Rover SD1 manifolds that had been used to great effect with my 3.9 Rover V8 engine Toledo. I simply copied the pipe lengths and diameters, though I had upped the diameter to one and three quarter inches on the Rover V8.
The exhaust system was most simply done by using the ubiquitous twin TR system with straight though 2 inch silencers.
This set up combined with a Holley 390cfm 4 barrel carb was the base set up for all future attempts at extracting more power from the Stag engine.
My very first run on a rolling road was at the TR international at Malvern. I asked the operator what could be expected from a 150bhp TR engine, he replied that a good one might do 125bhp.
I spent most of that day at the rolling road, and the best figure for a standard car was 122bhp, most of the "tuned" ones significantly less!
The Stag engine produced 165bhp and averaged 27mpg. As far as I was concerned it was mission accomplished for several years.
Then I started to feel the need for more power and many hours were spent in the garage trying different things, the annual TR international being the test of my latest attempt so development was slow and with losses as often as gains.
However, practice makes perfect, and I now have a good idea of what works and what doesn't.
Over the years I have accumulated many results sheets from rolling road sessions, and one thing I began to notice having such a wide range of exhaust manifold designs, was the differences in engine torque figure at different rev ranges. All my cars use the twin TR silencers, so this factor is a constant.
Some of these results have really surprised me. Often the headline BHP figure is similar, but the way the torque is delivered makes a huge difference to the way the car drives. This is the first time I have put all the torque figures on one graph, and on some of them I have had to back calculate the torque from the power figures as no torque curve was given.
IF YOU THINK ALL EXHAUST MANIFOLDS ARE EQUAL, THINK AGAIN!!!!!!
Stag torque curves.jpg
Sometimes little things make a huge difference, the thick green line and the thin green line are the same exhaust system, just with a balance pipe fitted between the left and right pipe. The torque increase was easily felt, and fuel consumption improved by 10%. I hadn't fitted one to begin with as I didn't realise Stags had one.
You will notice a dot on each line with a number of BHP, this is the peak power revs for each particular engine set up. Notice the set up without a balance pipe actually produces a higher power figure at a higher rpm, but this "improvement" was only over 5300rpm and it was worse everywhere else.
The thin black line is the regular Stag tubular manifold. The engine these are fitted to is the same engine that produced the two green lines, now in a different car and fuelled by the standard Stromberg carburettors. This run may be down in numbers over 4000rpm as it turned out the needles and jets were badly worn to the point where over fuelling was likely to reduce power. The carbs have since been fixed, but no re run has been done.
If anyone has a dyno plot for torque that they would be prepared to post on a car that has tubular manifolds fitted, it would be interesting to compare results.
If anyone does post results could they also mention if the fueling was correct (if known), and whether the car is still using the regular Stag exhaust system, and whether the fueling is by efi, Holley, Weber or Strombergs.
I hope to put together another graph showing just what a Stag owner can get at the first level of tuning for power.
Neil
It occurred to me that quite a few of us have fitted "go faster" bits to our Stags over the years without ever really knowing whether we were doing any good, and I have heard enough accounts of various modifications that have not worked over the years to know that a lot of time and cash has been squandered.
I have had the good fortune to approach Stag engine tuning from a completely different direction for the simple reason my 1st Stag engine was not fitted to a Stag but a TR250 (although it is badged as a TR5)
As a result of the engine not being in a Stag, I had to develop most of my own parts and therefore did not get sucked into the easy option of handing over a big wedge of cash in the hope that the items purchased would give the engine the desired get up and go!
Why did I chose a Stag engine in the first place?
Firstly because I love V8 engines
Secondly because the 3.9 Rover I already had was just a bit too big in all directions to fit in the TR without cutting big lumps out of the engine bay.
Thirdly it used virtually the same gearbox as the TR and that made fitting a whole lot easier.
Fourthly because it was the largest capacity engine made by Triumph and also the most powerful (don't believe the 150bhp TR engines ever made anything near 150bhp, nearer 125 in reality)
And finally because when I looked at one in bits at the Stoneleigh Triumph autojumble I was amazed it made as much power as it did such was the poor design of inlet and exhaust manifolds.
Having made the decision to fit a Stag engine to my TR, I wanted it to be as efficient and economical as possible because I was doing about 12,000 miles per year in my TR. This was part of the reason for not tuning the straight six to a higher level, good power can be made but at a cost of low teens fuel consumption. I was getting high twenties mpg out of my 2.5PI.
I wanted more power but good economy, and the easiest way to do this is start with a bigger capacity and a lower level of tune.
The greatest obstacle to fitting the Stag engine in the TR was the exhaust manifolds. I had a good cheap supply of inch and a half stainless steel Renault downpipes sold by a guy at the autojumbles, straight bits and bends with useful flanges on the end.
The design I used was a blatant copy of the standard Rover SD1 manifolds that had been used to great effect with my 3.9 Rover V8 engine Toledo. I simply copied the pipe lengths and diameters, though I had upped the diameter to one and three quarter inches on the Rover V8.
The exhaust system was most simply done by using the ubiquitous twin TR system with straight though 2 inch silencers.
This set up combined with a Holley 390cfm 4 barrel carb was the base set up for all future attempts at extracting more power from the Stag engine.
My very first run on a rolling road was at the TR international at Malvern. I asked the operator what could be expected from a 150bhp TR engine, he replied that a good one might do 125bhp.
I spent most of that day at the rolling road, and the best figure for a standard car was 122bhp, most of the "tuned" ones significantly less!
The Stag engine produced 165bhp and averaged 27mpg. As far as I was concerned it was mission accomplished for several years.
Then I started to feel the need for more power and many hours were spent in the garage trying different things, the annual TR international being the test of my latest attempt so development was slow and with losses as often as gains.
However, practice makes perfect, and I now have a good idea of what works and what doesn't.
Over the years I have accumulated many results sheets from rolling road sessions, and one thing I began to notice having such a wide range of exhaust manifold designs, was the differences in engine torque figure at different rev ranges. All my cars use the twin TR silencers, so this factor is a constant.
Some of these results have really surprised me. Often the headline BHP figure is similar, but the way the torque is delivered makes a huge difference to the way the car drives. This is the first time I have put all the torque figures on one graph, and on some of them I have had to back calculate the torque from the power figures as no torque curve was given.
IF YOU THINK ALL EXHAUST MANIFOLDS ARE EQUAL, THINK AGAIN!!!!!!
Stag torque curves.jpg
Sometimes little things make a huge difference, the thick green line and the thin green line are the same exhaust system, just with a balance pipe fitted between the left and right pipe. The torque increase was easily felt, and fuel consumption improved by 10%. I hadn't fitted one to begin with as I didn't realise Stags had one.
You will notice a dot on each line with a number of BHP, this is the peak power revs for each particular engine set up. Notice the set up without a balance pipe actually produces a higher power figure at a higher rpm, but this "improvement" was only over 5300rpm and it was worse everywhere else.
The thin black line is the regular Stag tubular manifold. The engine these are fitted to is the same engine that produced the two green lines, now in a different car and fuelled by the standard Stromberg carburettors. This run may be down in numbers over 4000rpm as it turned out the needles and jets were badly worn to the point where over fuelling was likely to reduce power. The carbs have since been fixed, but no re run has been done.
If anyone has a dyno plot for torque that they would be prepared to post on a car that has tubular manifolds fitted, it would be interesting to compare results.
If anyone does post results could they also mention if the fueling was correct (if known), and whether the car is still using the regular Stag exhaust system, and whether the fueling is by efi, Holley, Weber or Strombergs.
I hope to put together another graph showing just what a Stag owner can get at the first level of tuning for power.
Neil
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