perfomance

I have a '74 TR6. My question is: if the engine is the same as the '69 model, why is there such a great difference in the horse power numbers? The '74 is rated at 104 hp and the '69 was 150 hp. I have removed all of the emmissions stuff, put in an electronic ignition, put on a stainless steel sport exhaust system. What else can I do to increase horsepower without major engine modifications, or adding a third carb? Or am I just out of luck?

Three answers.

First, the 150 hp TR6 was only the UK PI models. They were rated for 125 hp on carbs.

Second, between those two models, all manufacturers changed from quoting gross hp to net hp. Gross hp is done on the dyno under ideal conditions with no ancillaries (water pump, alternator, etc) to sap power. Net hp includes those parasitic losses. 125 gross will be about 110 net.

Third, US models got lower compression, EGR, etc for emissions and lost some power. Simply removing the gear won't restore the power - you'll need to rebuild it to UK specs.

TRs were hit hard by emissions relatively early. I have a road test from '73 or so where an MGB actually outran a TR6, simply because the TR had seen much of its power sapped and the MG hadn't (yet). Of course, in '75 it hit the MG, and then they were both in the same (underpowered) boat.

I'm no expert on LBC's, but I think some basic performance parts are in order. You already have a good start with the ignition and exhaust. I would look into a higher performance camshaft, intake manifold, and carb setup. After that, a rebuild with higher compression pistons and reworked head might be needed. Before you do or add anything, make sure you are getting the most out of what you already have. You would be surprised how much power you could add by a simple tune-up. I'm sure someone will disagree with me. Oh well, that and 75 cents will get you a Coke.

Eric --
thanks for the info on hp. Do you know where I can get the specs for the UK version of the car?

Mailbox, thanks for your comments as well. I would like to try to do this without rebuilding the engine. I could see bolting on the ram air package from goodparts.com, or maybe even the three z-s setup.

Rob,
My 73 TR6 has many of Richard Good's stuff on it from goodparts.com. Although the engine is rebuilt stock (bored, out of necessity) I did put the triple ZS carbs, cold air induction and roller rockers. Does it perform better? heck, I don't know, sure is pretty to look at. The sad truth, unless you really modify the engine (performance head, pistons, cam, flywheel, etc.) you will still get your butt kicked by a newer Miata, or even a hot Civic. Don't get me wrong, I can and have beat all other TR6's in my area, but it will never be a street beast, like the one Richard Good tinkers with, but mine sounds good, looks good and is a great stress reliever.

Bill

Unless a car is hopelessly under carburated from the get go additional carb capacity will not help without additional changes ie: cam, headers, compression. Switching to three Z-S's MAY give you a little more top end but low end acceleration and driveability will suffer.. Bob

Every once in awhile, I run across ads for rocker arms that increase the valve lift and duration, like going from 1:3 to 1:5. Obviously its harder on the cam; does anyone have experience with them, and do you have to suffer the expense of roller rockers to get the increased ratio?

Bob,
I hate to differ, but the triple ZS carb setup is extremely driveable, tuneable and good-natured. Off the line is where I get the best performance. Gas mileage has not changed. Perhaps you are thinking of the triple Weber setup, which is useless in a street TR6.

Bill

IMHO, roller rockers should be at the bottom of your list. If you want more performance without going to the expense of a Stage 2 setup (and reduced reliability), invest in a streetable cam, hardened lifters, and higher compression. The cam you are looking for will give you around 0.400 lift at the valve (with stock 1:1.45 rockers) and have reasonable duration (260 to 270 degrees). The Isky 'Z-19' grind is my personal favorite, but others offered by Schumacher, TSI, Goodparts, and BPNW are good too.

The stock carbureted TR6 head is 3.550 inches thick. (I believe the stock TR6 PI head is 3.330 inches). Milling the head down to about 3.430 inches will get you into the 9.0 to 9.5 CR range which will give you a seat of the pants grin on pump gas. Keep rocker geometry stock by installing pushrods shortened by the same amount the head is milled (Schumacher offers these custom push rods).

This all assumes your engine's bottom end is in good order to deal with the increased power brought about by the bumped CR and valve lift.

I'm not convinced that the additonal valve lift offered by a higher rocker ratio results in additional noticeable power. Certainly the increased loads on the valve train introduced by higher rocker ratios is something to be concerned about in your decision.

Rick O.
72 TR6

<blockquote><font size="1" face="Verdana, Arial">quote:</font><hr>Originally posted by Bob Claffie:
Unless a car is hopelessly under carburated from the get go additional carb capacity will not help without additional changes ie:<hr></blockquote>

I tend to agree with Bob. Adding more carburetion may subjectively increase performance by giving more throttle open area for the same accelerator pedal setting thus it feels like the car is more powerful & revs faster. An old trick in the used car business was to increase the throttle linkage ratio to give the same effect. The only way to prove it is with some kind of measured performance test. "Seat of the pants" is not a very reliable test. Real drag & circle track racers (big V8's) learned that a single four barrel was as good or better than multiple carbs. Higher port & carb velocities are more beneficial than are huge intake areas.

Side note - Folks who run multiple Webers actually have the huge looking carbs choked down with small venturi tubes which gives the equivalent of fewer or much smaller carbs. It is common for a TR6 with three 40 mm Webers to have 28 mm chokes installed in them.
D

[ 01-14-2004: Message edited by: Dave Russell ]</p>

I'll offer a totally different take on things...

First, some data:
The TR-4 through TR-6 all gave about 65 horsepower at the rear wheels. Most of them ran to 60MPH in around 10-12 seconds. I G-Teched my '60TR3 which has the 2.2L engine and it was rebuilt about 8 years ago. It hit 60 in 10.5 seconds.

The fastest TR6s were the PI cars, which ran 0-60MPH in the 8.8second realm. In comparison, my wife's 1998 Oldsmobile Intrigue grocery getter does the same run in 7.7seconds.

You can spend a lot on upgrading the performance of a TR. You can buy a PI system, or go for a hotter cam, but this essentially makes them ride a little rougher, run a little hotter and generally makes tuning a little more difficult (smaller margins for error.)

If you go back to original reviews of TR6s, you'll find that no motoring press ever found any issue with engine performance...actually quite the opposite. Everyone always loved the torquey performance of the engine. What all the writers griped about was the completely outdated chassis. Usually, the TR6 would romp all over MGBs, but under certain conditions, the chassis would flex horribly, and the rear wheels would hop, limiting traction. Over bumps the frame flexes and groans. So what Road and Track and Car and Driver etc.. always said was "frame is the limiting factor."

So I might suggest that adding 20hp here or there might gain you some marginal performance gains in the real world, but if you're planning on driving the car just on the street, it won't necessarily increase your pleasure.

If you want to go really fast, that's not what your TR6 is all about. For the price of an engine rebuild and hop-up parts you can now buy a '84-'86 Corvette or even cheaper: a '89 Camaro, which are not wonderfully charming cars, but they go extremely fast.

The people here are right about how to go about getting HP gains...but I'm not so sure you'll be as pleased as you think once those gains are realized.

I think if you chose your parts carefully, you could increase your horsepower and still have a very streetable car. I'm not familiar with LBC's, but alot of hi perf companies offer a cam, intake, and carb setup matched for your car. At the very least you can call or write any of these places for info. Talk is cheap. Look how much this advice cost you.

I agree with Rick O regarding where you go for added HP. Milling the TR 6 head to 9 or 9.5 comperssion ratio provides a low cost boost to performance. My son and I completed a rebuild last year on a 74 TR6, shaved the head, added a mild cam (APT performance in California) header, free flow exhaust, and SU carbs. This car now has 9,000 throuble free miles since rebuild. Offers terrific off the line tourqe and can keep up with my AH 3000 (my son thinks the 6 can beat my car. . . Kids!). So my recommendation is determine what expectations you have for your car and design an engine to deliver that level of performance. I will also add that the advise of this group is always highly valued!

John

Hello Rob,

one difference I believe is that the pitch of the US spec engine inlet ports is different. Why is a mystery, and I do not know what benefit if any the UK spec head has on performance. One thing that seems to be effective is a 6-3-1 exhaust manifold, that and a good cam.

Alec

Or you could just buy a TR8 and blow the doors off of lots of cars.

Well....I guess I had better watch out for Oldsmobile Intrigues the next time I am out in my '8. Actually, I realize that TR8's arn't all that fast in detuned stock form (it just feels that way compared to my '7). But they were pretty quick for their time. Not much of anything went fast that was buit in 1980. But there is great hot-rodding potential with that motor. There is one in my area that has been taken out to 5 liters with appropriate other mods that can run with the big boys. You can make anything run with a unlimited budget.

I didn't mean to get into an arguement with anyone about who has the fastest toy. To me going fast is not what LBC's are all about anyway. I personally would rather cruise the Texas Hill Country, have a good time, and enjoy the camaraderie of other LBC owners.

That's all I got to say on this subject...happy motorin' y'all.

[ 01-15-2004: Message edited by: REK ]</p>

I agree with much of what has been said and would like to share my experience with my TR4a.
Since my car is a 1965 emissions changes do not enter the picture, but I did previously own a 75 TR6.

First, on emissions controlled TR6s, the compression is very low, milling the head to get 9 or 9.5:1 is very worthwhile.Secondly, they had a very mild cam, again for emissions reasons, so if you want to go past bolt-ons that would be a benefit. A header is probably worth a small gain, all of these things tend to have a synergistic effect, but do not expect to build a rocket with a couple of hundred bucks. As far as I know the rest of the exhaust is the same as used for the higher output injected cars, so should flow fine for a "fast road" car. I cannot comment on the triple carb setup from personal experience, but since each cykinder is only (2498cc divided by 6) 416cc and you only have to fill one at a time, this is like having a 4 cylinder engine of 1665cc with 2 carbs. Sounds like plenty to me.

My TR4 dynoed 91 hp at the wheels with a cam, header, 9.75 compression, 2 inch free flow exhaust and a bit of combustion chamber work. I believe a stock car would do about 70rwhp. in good tune.

It tends to be a slippery slope once you start; I now have bigger valves, chromemoly shortened pushrods, 2.25 inch exhaust and a different cam All this made different needles and electric fuel pump with larger diameter fuel hose necessary, and I'm still trying to get it tuned properly!
Good Luck, Simon!

What an incredible wealth of knowledge!
It's not that I want the car to be a go fast machine. I would just like to get where I am going with a little bit more authority. I will be doing a suspension upgrade before the springtime, with new urethane bushings and new uprated springs at all four corners. The ride may be a bit stiffer, but the handling should be better.
Thanks for all of the feedback. It certainly seems to be a topic that gets people talking.

There's plenty of potential in the old 6 motors.

Have a look at the link to my 2500 saloon (below).

I've done huge amounts of work to that and it hauls ass compared to plenty of new cars. The handling is incredible too. But I guess compared to a TR6 I've got a really rigid monocoque body.

I only recently got pipped at the line - two days ago - by a brand new Audi TT coupe. Not by much either - and I think it gave the owner a bit of a surprise.

I've got loads of photos of the stuff I've done. The motor is still street-able and has plenty more power to come yet.

Admittedly any new japanese family car will be very close to its 0-100km time but who cares. It's the 0-60km time that kills people - I've got so much torque down low (even with a 3.45:1 dif) that it's neck snapping through first and second gears.

I love the sound of my car too.....

Oh boy...

Go warm it up a bit. You'll enjoy yourself. Just don't ever expect to always be the fastest car at the lights.