Performance Upgrades Questions

[Jackamo]

After moving to NY from Colorado (yes, I'm doing it bass ackwards) I've finally decided to give some love to my '75 TR6; my ten-year old purchase made possible thanks to EBay and Sam Adams. It's in pretty decent shape and I've had some work done on it by a local shop to get it in good driving order. Shop's link below for anyone who cares:

https://www.briarcliffclassic.com

I read the Classic Motorsports article originally from 2007 which upgraded a 1975 TR6, and decided that would be a great path to go down. I'm hoping to gain some knowledge, insights and opinions on carrying out similar mods. I drive the car around our little town with my seven year old, who loves riding in the Sports Car! My goal is to recover some of the horsepower and then some while maintaining a pleasant drivability. While I'm fairly mechanically inclined, the TR6 is shoehorned into a modest two-car garage alongside a couple of Ducatis, seven Razor scooters and a few Treks, so my in-house maintenance capability is fairly limited. I'll be having much of the "heavy" engine work done at my shop.

I'm submitting several questions for your input.

- I'm thinking of switching to SU carburetors available at Moss (recommended by our local shop). The article used Webers, but I've heard that they could be labor intensive as far as maintaining. Thoughts? Sidedraft vs downdraft - what are advantages-disadvantages?

- Any experience with installing a cam? The article mentioned a GP2 cam from Goodparts. Opinions on this?

- Thoughts on porting and shaving the cylinder head? The article stated shaving the head would increase compression. Any ramifications I should consider?

- Ideas/recommendations on headers for the car? Will they provide additional benefit, given the above items I wish to have done?

- Is there a preferred choice for upgrading the distributor to electronic?

I don't want to go crazy with mods, as much of the work will be done in the shop ($$$), but at this point, the above upgrades are where I'd like to go. I would greatly appreciate everyone's input on the above.


Regards,
Jack

[poolboy]

What was the rationale for replacing the ZS carbs with SU carbs ?

[Jackamo]

SU’s were a recommendation from my local guy when I referred to the article which went with Webers. His opinion was SU’s would provide some performance upgrade while being easier to deal with than Webers. Do you think a rebuild of the ZS carbs would suffice and work well with the other upgrade ideas?

[oppositelocksmith]

Jackamo, look up the recent engine builds by myself, Prasnick, and Wolf76TR6. All will give you an idea of some things you can do. Prasnick’s sounds right in line with your plans.

On on another note, I would question working with a shop that has a stock answer of changing to SU’s.

On the Webers- MCCH’s are no longer available, downdrafts are not bad carbs, but the TR6 manifold adapter designed for them is terrible. Triple Webers can give more gains but are more work. The stock ZS’s are likely to support your needs.

[poolboy]

SU’s were a recommendation from my local guy when I referred to the article which went with Webers. His opinion was SU’s would provide some performance upgrade while being easier to deal with than Webers. Do you think a rebuild of the ZS carbs would suffice and work well with the other upgrade ideas?

Of course....People who tell you that a pair of HD or HS 6 SU's are going to provide better performance, more power than a pair of 175 ZS carbs, either don't know what they are talking about, don't know how to properly adjust them, don't recognize the fact they may just need rebuilding... or trying to sell you something they are more familiar with.
And as far as Weber DGV's being any better than either SU or ZS carbs, well that's just plain nonsense.....It's only the "WEBER" name that's made them attractive.
And as far as the Weber MCCH, no difference....both the owner of a TR6 with those carbs and myself experienced no difference during our test drives.

[skootch13]

After moving to NY from Colorado (yes, I'm doing it bass ackwards) I've finally decided to give some love to my '75 TR6; my ten-year old purchase made possible thanks to EBay and Sam Adams. It's in pretty decent shape and I've had some work done on it by a local shop to get it in good driving order. Shop's link below for anyone who cares:

https://www.briarcliffclassic.com



- I'm thinking of switching to SU carburetors available at Moss (recommended by our local shop). The article used Webers, but I've heard that they could be labor intensive as far as maintaining. Thoughts? Sidedraft vs downdraft - what are advantages-disadvantages?

As stated, no need to do this.

- Any experience with installing a cam? The article mentioned a GP2 cam from Goodparts. Opinions on this?

I have the GP2. I like it. Nice idle, good power down around where you need it.

- Thoughts on porting and shaving the cylinder head? The article stated shaving the head would increase compression. Any ramifications I should consider?

yes. Shave the head to at least 9.5:1 or everything else is a waste of money. I hear you can go to10.5: on regular gas.



- Ideas/recommendations on headers for the car? Will they provide additional benefit, given the above items I wish to have done?

got those too. it made a difference to me. Stock answer is headers give 10% more HP. it seems like it builds revs quicker too.


- Is there a preferred choice for upgrading the distributor to electronic?

I'm on points. This question can start a war. lol. At least get the distributor rebuilt.

Don't forget to lighten the flywheel. It will make the car build revs quicker.


Regards,
Jack

Good luck and have fun.

[poolboy]

Since the 75 was one of the years that came from the factory with the "125 HP" cam (311399) I think you should keep it...I did.
I would have the head shaved to increase the compression ratio to mid 9.
Here's a reference:
https://www.goodparts.com/tr6-compression-ratio/
And do a little experimenting with the ignition timing ....then see how you like all that..

[Cygan]

You wrote; "My goal is to recover some of the horsepower and then some while maintaining a pleasant drivability " and "I don't want to go crazy with mods, as much of the work will be done in the shop ($$$)...." This is good because it is easy to go crazy with mods. You seem to have an objective in mind. Let's talk about recovering HP. How much HP is enough?

Bolt on equipment may not give you the boost you may be expecting. A tired engine will not respond as well as it might. So an engine rebuild might be a good place to start. "Power is made in the head" so most folks start with a head rebuild. you have choices here. certainly they will square up the head. Most folks will opt for a 3 angel valve job and install new guides and stem seals. The next thing folks may want to do is deck (shave) the head. Raising the compression on a TR is done by making the head thinner, making the volume smaller and keeping the stroke the same. This is opposed to using high compression pistons. PB mentioned a compression ratio of 9.5:1, because you will still be able to use pump gas. Then you can have the head ported. There isn't a lot of meat there and if too much is taken off then you will break into the water jacket. So you really want somebody who has done this operation before successfully. Smoothing down the flash inside the head and matching the intake ports, the manifold gaskets and the ports on the intake manifold will help the flow.

You can square up the block and then check the bores for roundness and scratches. If they aren't round or are scratches, you will want to bore the block out to the next oversize piston. Speaking of pistons, you will want to decide if you want Forged or Alloy pistons. Forged pistons are very nice, but they cost a fortune for the TR. If you have decided to go "all-in" and want to put a supercharger on the car, then I would go with forged pistons. I mean after the cost of the blower and everything else, the cost of the pistons are a mosquito bite. You will want to blueprint your old oil pump of buy a new one. The crankshaft should be checked for cracks and the journals tested for roundness. If necessary you can have the cranked turned to the next smaller size bearings. And fresh bearings on a newly turned crankshaft are a must.

Then you will want to consider the cam. You should do your homework because the cam really influences the behavior of your car. There are lost of racing cams out there that put you powerband up into the high rpm range. The are great for racing, but not so great for the street. You idle may sound like a "box of rocks". Having modeled a few of these cams, almost everything you do will move your power band high in the RPM range. Sticking with the 125 hp cam is a good choice + you won't need to re-curve your distributor. You may find that a fresh engine will give you all the HP that you need.

Cygan

[BWA]

That classic motor sports article is in my opinion is the go to for modest upgrades for the TR6 engine.
One thing they did not talk about is the extra boost you will get from going with an electric fan.
So concentrate on the fundamentals:
Make sure the internal parts are not worn out.
Increase compression
Get the head to breath better
Go with a mild cam that will take advantage of a better breathing head.
Free up the drive train from parasitic loss (the air pump and fan)
Get the engine properly tuned as the original settings were designed to reduce emissions and they ended up reducing the efficiency of the engine.
Stick with the stock TR6 carbs as they are good as long as they are not worn out.

I had a 1991Honda Civic SI that had a true 108 hp at the flywheel and the car weighed a bit over a ton.
By today's standards that does not seem like much but it had lots of zip.
That little car had ample power to go 200 km/hour (125 mph).
How do I know this, I put the pedal to the floor on an open highway and it easily did it.
Jay Leno constantly tells us that most of the legal fun occurs in driving between 40 mph and a 100 mph.
If you can get the TR6 engine to put out something comparable to 108 hp at the flywheel then you will have a car that has ample zip for some fun driving.

Cheers
Byron

[L.O. Guvna]

The hardest lesson any TR6 steward learns is.....there is a ceiling to what we can get out of these motors. The second hardest lesson is learning that the best bang is freeing up the motor. And drive train.

When you blue print this block, shave this head, move to GP2, flow that head, and all the sexy stuff you can throw at it.....you have maybe....190 at the flywheel. I mean, call it 200 if you want to round up. But stop and think about that number. We all get distracted with a 2018 8 speed camaro with a blower and small spinner, and 600 at the rear wheel. That aint us.

to lock's point - there is plenty of examples of what you can do. And lock, wolf and everyone else borrowed from Craig Kenyon, Kai at Wishbone, Richard at goodparts....etc. There are good recipe's for improving this motor, but it aint' gonna magically go to 300 or something that puts us in the hot rod category. Mild rod. At best.

and Pool is your source for fuel delivery. the 175's are great, particularly his that he offers in his program.

Good luck with your project.

LOG

[Anthony]

I was lucky to have a friend who was a professional drag racer and engine builder. He has always told me that the head and cam are the choke points on any engine. Performance carbs flow rates are wasted on stock heads and cams. The Strombergs are already supplying more fuel than the stock head can make use of according to him. My head was skimmed to make it true, probably only a minimal compression increase. I did the valve job myself using his equipment. New points distributor. Mikuni carbs for their reliability ( love them). EBAY cam maybe from a GT6 with a slightly hotter profile. Electric fan. AAW wiring. I built my engine with his assistance and our modest touches have made the drive a lot of fun. I was aiming for a more reliable car than the original and the extra pop is a welcome by product. Money is always an issue and I did things that were affordable. I think these cars have a perceived level of performance that is what makes them so much fun not the actual performance numbers. Just remember that all of that new power is delivered through one of the weakest links in the car, the diff mounts. Enjoy the journey!

[TRick6]

I was lucky to have a friend who was a professional drag racer (71 Vega photo below) and engine builder. He has always told me that the head and cam are the choke points on any engine. Performance carbs flow rates are wasted on stock heads and cams. The Strombergs are already supplying more fuel than the stock head can make use of according to him. My head was skimmed to make it true, probably only a minimal compression increase. I did the valve job myself using his equipment. New points distributor. Mikuni carbs for their reliability ( love them). EBAY cam maybe from a GT6 with a slightly hotter profile. Electric fan. AAW wiring. I built my engine with his assistance and our modest touches have made the drive a lot of fun. I was aiming for a more reliable car than the original and the extra pop is a welcome by product. Money is always an issue and I did things that were affordable. I think these cars have a perceived level of performance that is what makes them so much fun not the actual performance numbers. Just remember that all of that new power is delivered through one of the weakest links in the car, the diff mounts. Enjoy the journey!

Wow Anthony, you knocked it out of the park. Having been an old drag racer and small block Chevy engine builder myself (my little 305 ci 71 Vega pictured), your friend is correct that the head and the cam is where the action is to the engine; controlling the breathing. I would add one very important thing, these little TR6 engines possess one-sided heads, meaning the intake and exhaust ports are on the same side. This design limits, or better still restricts the HP production. Cross flow heads, intake and exhaust ports on opposite sides, are far more receptive to producing HP. Stubbornly I went the route of all out building this little engine the way I learned to extract HP from the little Chevy V8. My results were disappointing yielding me about 125 HP at the rear wheels. This was with a blue-printed big end, a popular cam, extensive head work, a fancy exhaust header and MIkuni carbs (which are amazing), the Toyota 5 speed, and the 4.08 Nissan differential upgrade. I could have gotten more engine HP but the car would have become less and less street friendly the more power I produced. The car was fun to drive but, then I drove Rick Patton's supercharged TR6 and knew I had to have more power. So I sold that TR6 engine and Toyota transmission and performed an engine swap to acquire the performance I wanted. You can click on the signature link to British V8 for a tour.

So I would recommend that you drive a few different modified cars to determine the level of performance you desire and build your modifications on paper first with real costs for a bottom line. Then double it.

[HuhReally]

How do you drive? Do you routinely upshift near redline? Or routinely cruise near 5000 RPM? I ask because HP is a linear relationship of torque x RPM divided by 5252. Which means that the driving experience below 5200 RPM is really dictated by the torque being produced. Maximum Brake Torque is directly related to the Volumetric Efficiency of the engine As Long As the ignition timing is optimized at that operating point. This is the where I believe you can have a better driving experience by controlling timing more precisely for your specific engine. Read up on spark hook tests and general theory of engine operation at less than wide open throttle.

[old6er]

SU’s were a recommendation from my local guy when I referred to the article which went with Webers. His opinion was SU’s would provide some performance upgrade while being easier to deal with than Webers. Do you think a rebuild of the ZS carbs would suffice and work well with the other upgrade ideas?

I bought a nonruning car that had a set of brand new SU's on it when put away. They are on the shelf and I am running a rebuilt set of ZS's. What does that tell you ? Want to buy the SU's ?

[TRick6]

How do you drive? Do you routinely upshift near redline? Or routinely cruise near 5000 RPM? I ask because HP is a linear relationship of torque x RPM divided by 5252. Which means that the driving experience below 5200 RPM is really dictated by the torque being produced. Maximum Brake Torque is directly related to the Volumetric Efficiency of the engine As Long As the ignition timing is optimized at that operating point. This is the where I believe you can have a better driving experience by controlling timing more precisely for your specific engine. Read up on spark hook tests and general theory of engine operation at less than wide open throttle.

Very real condition questions. I don't generally up shift near redline, but I do on occasion. I never cruise near 5000 RPM; my 5th gear is a 059 to 1 which could push me over 200 MPH with my tire size. I leave that cruise/RPM to NASCAR. I am not the 1st to enjoy a "muscle car;" the auto industry targeting those that do for many years. I am a spirited driver possessing the need for speed as those 1st motorists loving driving and wishing for more power. Very few automobiles utilize the available engine power at all times. What I enjoy is the knowledge of the existence of the horse power and when I crack the whip (wide open throttle), those horses come to life and pulled the wagon at the speed desired. I have also concluded that 10 lbs per developed 1HP is adequate for a narrow short wheel base 2100 lb car as the TR6. Much more without serious chassis modifications could be hazardous to your health.