Improved Performance Plan - Opinions Please!

[bravenrace]

I have a TVR 2500M, and would like to improve performance. Since this has a TR6 engine, I thought I'd ask hear.
The engine is in excellent condition, so I don't plan on a full rebuild at this time. I'm new to these engines, but not engines in general. I've done some research, and this is what I'm thinking about:

1. Pull the head, send it out for a reputable Triumph shop for porting, shaving, and a good multi-angle valve job. If I find the right place, I'll probably just follow their recommendations as to what to do with it.

2. Add a performance cam and valvetrain components. I'm think a GP2 cam here, but am open to recommendations.

3. I'm keeping my Stromberg carbs for now at least, but will tune them to provide the proper air-fuel mixture with the new setup.

4. Install either a Crane or Pertronix electronic ignition conversion, as much for ease of maintenance as anything.

5. Re-curve the distributor to optimize the other changes.

6. Improve airflow to the carbs via a fabricated ram air system.

7. Add a fabricated free flowing exhaust system.

How does this sound? Am I on the right track? Anything else I should consider or do different? Would a header help much? From the outside, the stock exhaust manifold looks like it might flow well enough on it's own. There's also the complications of fitting a header to the TVR chassis.
What kind of horsepower should I expect from this combo?
This will be an occasional street and road course car. I may consider vintage racing at some point, so I wouldn't want to do anything to it that would make it illegal for that, but I haven't looked into the rules yet.
Thanks,
Jim

 

[crj7driver]

Sounds like a good start. The TR6 motor develeps very bad harmonics just above redline, to the point of breaking the crankshaft. So if you ever want to increase redline, You will need to go to a custom/high end crankshaft $$$$$. Also the cam spins in the block so when you get around to it most people have bearing races machined into the block.

You will need to determine if you ever plan to run forced induction, moss has a supercharger kit that makes the car quite spirited. Which costs around $4000, and will give you the most bang for the buck (comes with the carb and everything). I think all of your planned options will cost this much and not yield as much HP.

Lastly, if you do go forced induction the current cam and lower compression you are currently running are much better suited to supercharging.

Here is a clip of a supercharged TR6....not my car but one in the forum. Although it may seem, I am not trying to steer you to supercharging, just that it is the most cost effective way of going fast. As for racing, I don't know what is legal and not.

https://www.youtube.com/watch?v=n-sHHm9oR-E


Good luck

 

[Alan_Myers]

Hi,

Regarding the header, yes I think it a very worthwhile improvement considering all the other changes you are making. Any help you can give the engine scavanging exahust gasses will just help it "breathe" better. I'd recommend a true "extractor" design, which is a 6-into-3-into-1 design on the 2.5L TR motor. (If you want dual exhaust, it can be split behind the collector. However a single pipe exhaust system will generally give better performance.)

I'd opt for an ignition that can be upgraded with a multi-strike capacitive discharge box later, if at all possible. I'm not sure if either the Pertronix or Crane you are looking at can be. Probably the Crane can, but I'm not certain. The CD ignition will give higher voltage for stronger spark and the multiple sparks per combustion event will make for a more complete burn of the fuel and air in the cylinder. Both better power and improved economy are often possible with this type ignition.

I strongly second the suggestion to put cam bearings in the block. This change uses Spitfire cam bearings, search for more info. Adding bearings will help the cam run better, correct any existing clearance issues and prevent heavy wear that might result when using a higher/faster lift cam and/or stronger valve springs.

Slim down the valve seat as much as possible to open it up and let as much fuel and air in as possible. I'm not certain exactly what's possible in the 6-cyl., but on the 4-cyl. TR motor's head I know the seat area can be reduced to as little as .020" on the intake side and .030" on the exhaust side. This improves flow by about 5%. Unleaded valve seats might be needed on the exhaust side, as well as stainless steel valves and appropriate valve guides. The valves themselves can often be re-shaped behind the head to improve flow, but only up to a point that doesn't compromise strength. Some replacement valves are already "gas flowed".

There are other valve train components that you can change, depending upon how much you want to spend. Anything to lighten the work of the camshaft is good: i.e. allow spring caps, chromoly pushrods, lightened rockers (ISTR, there are good and bad quality rockers/pushrods in the 6-cyl. motor, too, you might do some research). If you go to alloy spring caps, it might be a good idea to use 10 degree locks as some security against pull through.

Roller rockers are nice, can help prevent wear and tear on the valves and guides, particularly if valve geometry is off a little after shaving the head to increase compression and installing a reground cam. But, realistically, rollers won't really add much power, by themselves.

You might want to consider a triple carb setup. www.goodparts.com offers a triple manifold, and you only need to add a third Zenith Stromberg to match the two you already have. These could be changed out to SUs, too, if you find them easier to work on. Both carbs can be set up to run quite well, are flexible for all around driving and give reasonable economy.

I'd suggest getting copies of Kas Kastner's tuning books. There are small books very specific to TR250-6 and the 2.5L engine that can be bought from The Roadster Factory, etc., or his three more recent books compiling all the old tricks and tweaks and adding lots of recent news and stories, available directly from www.kaskastner.com or from The Roadster Factory (www.the-roadster-factory.com).

Much of Kas' performance work was done within very restrictive SCCA Production class rules, and should be widely acceptable under vintage rules. Besides that, it would be wise to get specifics from any local rule book before making any major mods.

If I recall correctly, Kas got around 160 HP out of the carbureted 6-cyl. 2.5L and up around 190 HP out of the P.I. version with the original Lucas fuel injection.

Yes, the crankshaft is a limitation on this engine. With some work it can be made to rev reasonably well, but a billet replacement is the ideal solution.

/ubbthreads/images/graemlins/cheers.gif

 

[Brosky]

How many miles are on the engine?

If you are doing all of this to the top, what are the plans for the bottom? Once you pull the head and start modifying you can count on getting into the bottom. Maybe not by choice, but if it isn't very low mileage, you soon will.

 

[swift6]

As you are well aware of, your more space limited in the TVR engine bay than the TR6 is. I've seen 2500M's with triple webers. Not sure if the front carb of a triple ZS or SU set up would encounter interference with the bonnet or not. The twin ZS's can get you to the 150hp range with different needles.

The headers I have on my TR6 came from a 2500M owner because they wouldn't fit into the TVR chassis. There are a few different header designs out there though and mine are of the variety that need a lot of extra room. The stock manifold is good for 150hp or so. After that, a header is needed. Some of the other designs might fit.

It's not hard to build a TR6 engine to 150hp spec. No more difficult or expensive really than a stock rebuild. The Moss supercharger kit will take a stock engine to the 150hp mark with no internal mods to the engine. Since you keep the low compression its a bit nicer at the gas pumps that way.

Roller rockers give the opprotunity to change the rocker ratio and can free up a few horses but are not noticeable by themselves. If you go with rollers than the external oil line is suggested but its not necessarry with standard rockers. The cam bearing issue is a good suggestion but not required if your not using a monster cam and changing the rocker ratio. Finding a machine shop that will line bore the block for cam bearings can be difficult and expensive. The block is longer than a V8's and most machine shops are not set up for inline engines with more than four cylinders.

I have heard nothing but wonderful things about the GP2 camshaft. I have the GP3 in my TR6 and its a little obnoxious. /ubbthreads/images/graemlins/grin.gif


Don't worry about the crank. It sounds as if your intentions are not all out race. If they were then you would want to build a 'race' engine and thats when you would need to worry about the crank. From the sounds of it, street and occasional track days, then 'fast road' spec is what your looking for. The TR6 engine is a long stroke torque engine. Plenty of fun can be had without revving past the 6,000 rpm mark. Shortly after 6Krpm is where the first set of destructive harmonics begin. As long as your crank is in good shape, it will be fine below 6Krpm.

An aluminum flywheel frees up some revs and lets the power be applied quicker. There originally was some thinking that the extremely light flywheel would cause idle problems and low speed driveability problems. It seems that in practice, this is untrue as every review I have heard of the aluminum flywheel on TR6 engines have been favorable. Seriously considering this change myself. Though if I get my engine to rev much faster I will seriously need a rev limiter as an insurance device.

TVR 2500M's in stock form so outperform stock TR6's that its not even funny. 150 hp in a TR6 is fun, in a 2500M it would be a blast and a rocket! Which is why I would love to add one to my stable some day. Especially with the engine that is already in my TR6! /ubbthreads/images/graemlins/thumbsup.gif

 

[bravenrace]

The engine and car only have 9400 miles on them, which is why I don't plan on pulling the engine and getting into the block. If it is absolutely necessary to add cam bearings or shave the fire deck, then I'll likely buy another engine and build it instead of tearing into my engine that otherwise doesn't need anything.

 

[bravenrace]

[ QUOTE ]
Sounds like a good start. The TR6 motor develeps very bad harmonics just above redline, to the point of breaking the crankshaft. So if you ever want to increase redline, You will need to go to a custom/high end crankshaft $$$$$. Also the cam spins in the block so when you get around to it most people have bearing races machined into the block.

You will need to determine if you ever plan to run forced induction, moss has a supercharger kit that makes the car quite spirited. Which costs around $4000, and will give you the most bang for the buck (comes with the carb and everything). I think all of your planned options will cost this much and not yield as much HP.

Lastly, if you do go forced induction the current cam and lower compression you are currently running are much better suited to supercharging.

Here is a clip of a supercharged TR6....not my car but one in the forum. Although it may seem, I am not trying to steer you to supercharging, just that it is the most cost effective way of going fast. As for racing, I don't know what is legal and not.

https://www.youtube.com/watch?v=n-sHHm9oR-E


Good luck

[/ QUOTE ]

Thanks, although I'm not sure how my intended plans add up to the same cost as a supercharger. I'm looking at adding a cam, having about 1k of head work done. Everything else I need to do anyway, so I'm thinking I could spend about $2k or less to end up with about 150hp. What am I missing?

 

[bravenrace]

Thanks Shawn. You are right that my goal is to build a nice street and track car. I want spirited performance, but not to the point that I start breaking a lot of parts.

 

[Brosky]

With that low mileage and what you're planning to do, you should be fine.

 

[gjh2007]

you have a PM

 

[Guest]

[ QUOTE ]
The Moss supercharger kit will take a stock engine to the 150hp mark with no internal mods to the engine.

[/ QUOTE ]


Shawn, I think that might be a little bit of an exaggeration on Moss's part. I spoke to Moss extensively and they felt that you really need to make the mods that you and I both have, coupled with their supercharger, to reach the 150bhp mark. I considered converting to the supercharger, but didn't have a spare $4000 lying around.

 

[Guest]

ps, I ordered the aluminum flywheel for my car for Christmas. I will let you know how it feels in a few weeks.

 

[roofman]

I just picked up this months issue of Clasic Motorsports magazine and it has an in depth article on getting more horsepower from a tr6 engine . It includes dyno results and exact parts used. Check it out.

 

[swift6]

It covers most of what has been said. Increase compression, flow the head a bit, different cam etc... but seemed to mostly be an add for the new weber single bbl side draft. A carb originally designed for Harley Davidsons.

Not a bad article, does cover the basics pretty well. I was hoping for more. Maybe comparing triple ZS, triple webers, SU conversion etc...

 

[trboost]

I've been on both sides of this conversation many times before & have had cars with both conventional & forced induction. The simple answer is a blower is the best bang for the buck. The not so simple answer is what exactly do I want the car to do. If your looking for low cost reliable HP, basic enhancments like ignition, exhaust & minor compression increases are all the most popular approach. We increase HP/Torque by increasing the amount of air/fuel into the engine. A naturally aspirated engine draws air/fuel in by vacuum created by the downward motion of the piston & exiting exhaust. This has it's limits for a reliable street motor. A modifed TR6 street motor capable of over 150hp or better would have to have compresion of over 12.1 & many other expensive components & engine work. Even at that, it would never be as streetable as a forced induction engine using 7.75:1 compression. Check this site out https://www.bgsoflex.com/crchange.html . Your peak HP would also be generated at high rpm's , not generaly usefull on the street.

A highly developed , multiple carb, lumpy cam, high compression engine will be idling, accelorating & criusing every running moment under the stressfull conditions needed to create that HP. A properly designed modern boosted engine runs on stock compression & only under momentary conditions does it change it's characteristics.

If you compare the cost of machining a head & block, triple 2V Webers or triple Z's and a cam , in my eyes the money is a wash but the end result is very differant. The Moss kit is very expensive & I have not seen one in the flesh . I have seen pictures of the kit and the installation instructions & think they over complicated it. The Front engine mounting hardware is over engineered. I do like the serpinteen belt & new intake. The kit covered by Sal Vespertino is way less & much easier to install.

I have nothing against conventional methods but when SC'ing is discounted as "too expensive" compared to simply milling a head & slapping on headers it's not comparing apples & oranges. To get the same end results , you would have to spend much more with out supercharging.

 

[swift6]

Mitch has some excellent points and is very much a proponent of supercharging. Just look at his posting name. Pretty much says it all. /ubbthreads/images/graemlins/grin.gif

Sal Vespertino's kit is definitely the biggest bang for the buck since its cheaper than the Moss kit. Moss would probably argue less complete as well since their kit IS pretty much a complete kit, Sal's isn't.

I do have to disagree with the 12:1CR comment though. I have more than 160hp with about 9.25:1CR. The lumpy idle, the poor low rpm performance etc... is fairly accurate. TR6 engines with 10:1CR, GP3 cams and triple ZS's often produce 175-180 hp. Just to be clear, I am talking about horsepower at the flywheel here. Richard Good has dyno sheets and time slips from some of his TR6's that can verify those numbers. Kai Radke at Wishbone Classics has some as well.

For all around drive ability and power, it is very difficult to beat the basic supercharger set up. I actually like my lopey idle, though I would much prefer the low speed flexibility of the supercharger when having to drive in heavy traffic, an occurrence far more common now than when I built my engine. Maybe the V8 in my TR8 has spoiled me with its off idle torque capabilities.

With 9.5-10:1CR, a GP2 cam, maybe some better ratio roller rockers, some nice flow work on the head, the TriumphTune short primary header, and different needles in the 175ZS's etc... 150hp should be very 'do able'.

Either way that is chosen, 150hp in a TVR 2500M will be an absolute thrill ride. /ubbthreads/images/graemlins/thumbsup.gif

 

[trboost]

Hi Shawn,

Your TR8 is the best example that there is "no replacement for displacement". The V8 in your car has all that usable torque at low rpm's.Torque is what you feel when you mash the pedal, it's the most noticable part of a performance upgrade.
I have seen Kai & Good stats on their engines making 180hp at the flywheel but I think the driving expieriance would be completly differant. It would be an interesting road test comparison. I have never dyno'd my car but I'd be thrilled to have 180 flywheel hp.

Please understand, I am not preaching that SC'ing or turbo charging is the only answer. I am a huge Truimph/sports car enthousiast and I'm always intrigued and amazed at how we all improve our cars. I'm no supercharging Guru, but have learned through friends, reading & practical experience. I also have no fears of the entire Triumph world converting to forced induction /ubbthreads/images/graemlins/smile.gif
but I'm always willing to share anything I've learned as the friends on various lists have with me.
Years ago my 240Z had triple 2V Mikuni's & all the goodies. I even had some fun at BridgeHampton race track. I loved the induction sound they made !!

 

[swift6]

[ QUOTE ]
I have seen Kai & Good stats on their engines making 180hp at the flywheel but I think the driving expieriance would be completly differant.

[/ QUOTE ]

/ubbthreads/images/graemlins/iagree.gif No doubt about that. The torque curves are very different with the two different approaches. Therefore the driving experience would be very different as well.

/ubbthreads/images/graemlins/cheers.gif

 

[bravenrace]

Thanks guys. This is all good information and I appreciate it! I'm not new to forced induction. I've had cars with Roots type blowers, centrifigal blowers and turbochargers. I turbo'd a Honda CRX way back in 1990 when nobody was doing it, and it made big power. But at this point I have no plans to use forced induction on my TVR, mainly because its not in the budget and I want to leave my options open for vintage racing in the future. So I'm going to do what I can with this engine and that's what I'll have, whatever power it makes. Besides, I have a Mustang that's soon going to be getting a 408 ci sroker motor making over 475hp, so I don't need the TVR to be a rocket ship, just powerful enough to have fun on a road course with.
Thanks again for all the suggestions, and please let me know if I'm off my rocker with this!

 

[trboost]

Hmmm, I wonder what would happen if the 408 happen to fall in to the TVR /ubbthreads/images/graemlins/cool.gif