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V8 comversion vs hi-po 2.5PI


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Hi there,

 

Been reading the v8 conversion topic with interest. My motor (69 TR6) is probably going to need a rebuild soonish and I was wondering how much power can you get out of the 2.5L PI motor by doing the cam, heads etc?

 

Also, if anyone has really hotted up their original motor, how costly was it (hence making the v8 conversion not seem like such a bad idea cost wise). A bloke in Australia stated you could pull 250bhp out of the original but couldn't exactly explain how, so I was a bit sceptical.

 

cheers

Cam

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Hi there,

 

Been reading the v8 conversion topic with interest. My motor (69 TR6) is probably going to need a rebuild soonish and I was wondering how much power can you get out of the 2.5L PI motor by doing the cam, heads etc?

 

Also, if anyone has really hotted up their original motor, how costly was it (hence making the v8 conversion not seem like such a bad idea cost wise). A bloke in Australia stated you could pull 250bhp out of the original but couldn't exactly explain how, so I was a bit sceptical.

 

cheers

Cam

Cam,

 

Exactly what I was going to ask as my first post!

I think getting 250BHP out of the six would make it pretty un-user friendly, but a nice 4.6 rover lump would make a cracking car!

Lots of US guys have put ford or chevys in, but a nice big capacity all ally rover lump would be hard to beat (IMHO) does anyone know of a TR6 owner who's done this?

Thanks

 

Simon

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I would be interested in seeing a 250 bhp TR6 engine being driven on the street, if one actually exists...!

 

Check this site for two very interesting reasons why it would be unlikely, firstly the section dealing with measurement of engine power output, and secondly the relationship of inlet valve area to the engine's ultimate power potential.

 

http://www.pumaracing.co.uk/pp03.htm

 

By these calcs, a reasonably achievable maximum power is about 210 bhp - beyond that I suspect it would be big bucks for small gains.

 

See also under the heading:

TECHNICAL ARTICLES

Power, Torque And Vehicle Dynamics

 

If you have a genuine, original CP series (1969) PI TR6, you would be crazy to put a V8 in it. The car will be worth far less than it is now. If you want the V8 solution, you would be better off getting a US LHD car and doing the conversion.

Edited by Roger H
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I managed 225Bhp in a TR6 with a out of the 3.5 Rover/Buik easily without trying too hard. Mild cam, Reworked heads, headers (inch and a half) and the 4barrel holley of course. I know there are people out there who went for 25 bhp more with harder cam and more on the heads larger jets and better dizzy in their V8's........

Personaly in the TR6 i had to be aware of the Gbox and diff bieng standard and also the car then become a little difficult to hold down with 250bhp. I will post pictures as requested in the V8 thread but waiting for nicer weather and a little time off work to get it out of the garage.

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Sounds like an interesting TR6 marios did you have to modify the chasis, enginebay etc much? I would have to aggree with Roger H. I'm not sure if I could hack into my 69 without a few pangs of regret.

 

So, has anyone topped 200bhp with the 2.5L motor?

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It'd be a great shape to modify a nice early 150BHP car, but I'll bet there are plenty of later (imported) 6's that'd be quite nice to modify?

I bet the rover lump wouldn't be much heavier than the straight 6 either!

Simon

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Dukey - You are right.... The engine bay mods may be something (as everyone quite rightly says - you will not want to do without thinking what have i done!! But in a nutshell trimm back a little of the inner wheel arches and the corner webbing for the exhaust rack and pinion slightly forward, Strut brace re-made (kept the original steering column re-routed through the exhaust manifold. That was it...But also more importantly it changes the drive of the car. it becomes a long legged drive brute of a drive even with lightening the flywhell there is a difference to the short revvey responsive six engine. My friend has 190bhp (150bhp originally) from a co called racestoration i think and he would be with me 1st 2nd and i would start to pull away in third. I must admit i like his car it is exciting rather than scary.

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Or even a V6 eg the 2.5 or 2.6 Omega which had a great engine even though the depreciation was horrible - I know cause I had one. Good enough for the boys in blue - they must be the easiest and cheapest to buy secondhand.

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I still think a fairly standard 4.6 litre rover engine would make it a lovely car. I'm pretty sure the V8 gearbox would have to be used, the only thing that would concern me would be the rest of the drivetrain, ie the diff. Does anyone know what sort of power/torque the standard diff can take? is there an upgraded diff available?

Simon

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Yup I'd want to run the 5 speed rover box (LT77 or 380) or a T5 from a TVR, the standard overdrive box struggles to stay in one piece with the 6 so the rover will make short work of it. The diff probably wouldn't cope so it'd be either BMW diff or Sierra Cossie diff both with their relevant driveshafts.

Would be much cheaper BHP for BHP than tuning the 6 aside from the 6 being such an old design. My 220BHP RV8 cost me £ 1,500 for a complete rebuild.

Edited by Cinnobar
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Greetings,

 

Thought I'd chime in from the States. I went down the road of investigating a V8 swap and just was not happy with moving the steering rack (read "bump-steer") and re-routing the steering shaft via multiple u-joints and fixings. After a little research, I landed on a 1995 BMW M3 Engine and Transmission mated to a Nissan R200 LSD rear.

 

Very little sheet metal work was required (slight trimming of RH foot well corner to accommodate the DOHC cylinder head but no other alterations) and absolutely no changes to the steering rack placement or column/shaft (it fits right under the US spec intake. I did have to make a new cross-member that bolts between the spring perches and notched out the bottom cross-member about 1/2 inch. The engine mounts were fairly straight forward utilizing the factory mount on the left and a simple angle mount made of 3/16 in steel for the right. I then welded square tubing to the frame just in front of the rear wishbone mounts to use as the engine mount stands and pancake style poly mounts. The transmission mount was also a simple piece of angle iron bent and welded between the two frame members. BMW uses a remote shifter for their transmissions so simple modifications of the components put the shifter right where the factory TR6 was. I found that the E36 radiator mounted right into the area as well and added an electric fan on the inside. I removed the a/c and did have to source out different pulleys to clear the steering rack and found that a Suzuke Samarai Alternator was just the right size to squeeze in. The 1995 M3 was the only year BMW produced this engine for the US with OBD1 software so electronics was no problem. The US spec is 240hp but with Exhaust, Conforti Chip, Cold Air Intake, Larger Injectors and an Aluminum Flywheel I have about 300hp.

 

I really wanted to do something different than the typical Rover or Ford V8 and have a passion for the BMW engines. Currently, the frame/driveline is completed and awaiting the body to come back from paint. During the mock-up stages of this project it was amazing how tight and proper the BMW engine looked in the bay. It truly looks as if Triumph and BMW planned for this type of merger. Lucky you, the Euro Spec M3 engine has a lot more HP stock than what I can get over here.

 

Also, I did add a lot of reinforcement to the chassis and diff mounts as well as a 6pt roll cage to help cure the twisting of the frame. All the typical suspension mods have also been performed/installed as well.

 

Anyway, hope this wasn't too long of a dissertation but thought I'd chime in.

 

Dave

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All,

Kas Kastner claimed 218bhp from his 2 litre sixes, by going well into 8000+ revs.

He wouldn't consider trying anything like that for a 2.5. Crankshaft "was a piece of rubber".

John

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As a general rule in race spec. You can expect to get 100bhp per litre from the triumph ohv. With a bored out 2.5 your looking at almost 2.8 so think 280bhp tops. I think the quickest TRs are getting something like that. But obviously at a considerable expense! I've heard of 200-225 in some fast road goers. What with mapped ignition and EFI it should be more town friendly.

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Guest andythompson

I really don't think there are very many genuine 200bhp+ 2.5 engines on the road. On the track maybe but their life must be fairly short. I wonder how many horses of those claiming +200bhp get to the rear wheels?

 

Few people use engine dynos to determine their bhp and you lose a lot less than you think in the driveline..maybe 12-15% absolute tops so rolling road figures for many reasons can be a bit dodgy if "factored" incorrectly.

 

It has been said here before that the inlet valve sizes (say 38mm) limit horsepower to around 210bhp notwithstanding bottom end frailties.

 

I believe Kastner claimed 247bhp at 7600rpm from his ultimate TR6 engine but it was only good for a few hours if it didn't go pop in the meantime. He was quoted as saying something to effect of don't try to emulate his kind of power nowadays as the life expectancy of such a beasty is very short and they were doing it to beat factory Porsches, Toyotas and Datsuns... not club racing.

Edited by andythompson
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In the '60s and earlyl '70s it was very respectable for a performance car to get 1 HP / cubic inch displacement ( i.e. 150 BHP for the 2.5 litre ). Exotics like Ferrari etc. would exceed that but little else. The E-type Jaguar sets a fair standard for that, and did it with the help of DOHC and other features lots more advanced than the TR employed. On a smaller scale, consider the Lotus 1600; again in the same ballpark. Neither of these can boast better reliability than a 2.5 litre TR ( particularly if it's on triple Webers :D ).

 

So I'm content to stay in the 150-170 BHP range with the prospect of doing 100,000 miles on it - pretty good power-to-weight ratio too. If I want 300 HP I can buy a BMW M-series convertible for what it costs to build a world-class concouse winning TR ( to today's standards <_< ) - but that would weigh about 3000 lbs.

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Guest GeoffWalker

I think the best conversion for a TR6 would be bmw 535 or 635 engine. I have seen two German Tr6's on Ebay and Pistonheads a few months back with this running gear. The six cylinder sound will cloak the extra power available under the bonnet. An old rotten M6 would be the Ideal donor car with 286 bhp, providing you were mad and not short of the pennies.

I'm happy with my 150 bhp tr6 with tripple K & N's.

 

Restoration is almost finished . I'll post the first photos of the completed car in 3-4 weeks.

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Guest harry dent

Dave,

I echo what Alec has mentioned.I would love to see and read what you have done on your TR in TRaction

or by any other means as I and a lot of TR nutters would be VERY interested.

Regards Harry. :):)

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I would be interested in seeing a 250 bhp TR6 engine being driven on the street, if one actually exists...!
You can get 250bhp (possibly 260 but that IS Really pushing it!) - there are around 5 - 10 of these spec cars around. But at this level you are talk BIG MONEY. Most if not all will be race cars. We will have one to add to this in the next month or so.

 

They need to be all steel (can get maybe 225 on a no steel but cannot rev high enough for the ultimate power), triple webber 45, 11.5 CR, 2.6 or 2.7litre. I know a green one racing has made 230bhp at the wheels at hi-tech roller near birmingham!

 

A 4 can make around 240bhp as well! (but or greater similar spec!).

 

Ours will be being run in on the street in next month or two then raced - but WILL be driven occasionally onthe road (it is may father ex-road car!). Fit a short Crown wheel and pinion say 3.9 or 4.1 with OD and this type of car will sort out most things on the road.

 

NOT Cheap though - far from it - but you could build a 200 - 220 bhp one for alot less and still be great fun with a low diff and OD. I'd do that not bugger about with a V8 (having said that I have put a 400bhp 5.7 all alloy corvette engine in my TVR 5.0 litre cos it was er slow! - but I am MAD!) :D

Edited by jellison
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My favourite subject this, making the 6 cylinder go faster.

 

I managed just about 220bhp with excellent torque figures (the bit that matters!) on cambridge motorsports rolling road . Easy to drive on the road and revved to 8k.

 

Really good soundtrack as well. But it would cost about 10-12k in todays money. I was thinking of building another steeler but i thought why bother i could put in a fairly bog standard ford duratec 4 cylinder and get 200bhp out of the box. I could then mate it with a ford type9 5 speed box with close ratios or a quaife sequential box and there you have it another "ultimate" tr for half or less of the cost of a steel engine, plus with less weight the available power can do more.

 

Think about it it makes sense.

 

Or you could put an mgb 4 cylinder engine in a 5, not.

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I think the best conversion for a TR6 would be bmw 535 or 635 engine.

 

The only problem with the "Big Sixes" from BMW is the length. I measured these as well and found them to rerquire cutting more sheet metal and steering rack relocation. The BMW S50/M50 engines are just the right size. Plus, the M3 variant is loaded with HP and easily tapped for a little more. Reliability is also exceptional.

 

Did I mention lighter as well!

 

Dave

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Quote from 'PUMA RACE ENGINES' :

 

''What we are going to calculate is the potential peak power of a fully modified engine in race tune with excellent port work and "perfect" induction and exhaust system design. This analysis applies mainly to engines designed originally for normal road use but we will also consider briefly how a custom designed race engine like an F1 engine might fit into this scenario. Copyright David Baker and Puma Race Engines "

 

This quote from PUMA RACE ENGINES and knowing that the BMW M3 4 cyl 2302cc made 215 bhp and the M3 6 cyl 3 liter made 286 bph

make me thinking that the bph in the postings above are very optimistic.

 

I've done the PUMA calculation with the characteristics of my TR3 racer : 2186cc, OHV, 41mm inlet valves, pushrods, 2 valves per cylinder... Fully race modified my engine would make 160.25 bph at the flywheel, with the ancillaries in place, according to PUMA RACE ENGINES. I've put my car on 2 rolling roads and one

engine dyno : the first rolling road result : 198 bhp at the flywheel. The second rolling road : 195 bph at the wheels and estimated 183 bhp at the flywheel (this rolling road is a new one, with a very modern concept, and used by BMW and Porsche race cars, but sadly the owner is selling power chips). The transmission loss may be estimated too low, but everything is done to achieve an as low loss as possible, i.e. a dog box with straight cutted gears is fitted , the engine/gearbox/differential pinion are in one straight line and the steel crankshaft has 8 counter weights (a smooth running crankshaft is helping to prevent vibrations of the flywheel and in the rest of the drive line).

On the engine dyno, my engine made 161 bhp, exactly what PUMA RACE ENGINE is predicting for the TR four cylinder type of engine. When I could believe the rolling roads, I could call myself an engine wizzard,

instead I rather believe the 161 bhp of the engine dyno. Quoted bhp are rather meaningless, measured bhp even so. I don't go to a rolling road to know the power anymore, only to check if a modification is an improvement or not.

 

Correction : the figures of the second rolling road are 195 bph at the flywheel and 183 bhp at the wheels of course, not vice versa.

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It may be a case of semantics here, but at what point does a race prepared engine cease to be a TR6 engine?

 

Let's use a custom made billet crankshaft, carrillo con-rods, forged pistons and balance the lot on a knife edge. Change to an alumium flywheel, ally waterpump etc. Substitute a full race cam, tubular pushrods and roller rockers. Improve the valve specs and work the ports, shave and 'up' the CR so that racing fuel is required. A competition oil pump will be required and a baffled sump (preferably alloy and finned would be nice).

 

It seems to me that the only Triumph component is the block (and that appears to be under pressure to be bored out to be +8%.....maybe even 'stroked' a bit...and if Andy Thompson's recent post is an indicator, the head will also be alloy.

 

Electronic ignition and ditch the Lucas PI for triple webbers or six mikuni's. High flow fuel pump (not Lucas of course)...custom tuned 6 into 1 exhaust manifold with 2.5" single pipe out the rear (no muffler....or is that required for the spectators?)

 

Shame about the the CP TR6 one lap behind.... it really does look soooo pedestrian...nice car though...

 

As a footnote...poor ol' Darryl Uprichard (owner of Racetorations) must be somewhat dissapointed with only getting 200bhp out of his rally TR3... it appears that he has to find 20% more power if he is going to be competitive.... but there again, power is not what wins the race, it's the total package (don't mention driver skill!)

Edited by Roger H
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In "race prepping" and engine it is still a 6 engine. All that has been changed are the consumable items, even the block is consumable. Come to think of it so is the car!

 

If Triumph were making the car today they would have had to upgrade most of the components,(product development) we are just carrying on that development in their memory.

 

I did a track day many years ago with my freshly restored but very standard 5, that is when i realised a standard car is not suitable for sustained spirited driving.

 

The brakes faded the fluid boiled it had body roll, understeer and when i saw a picture of it whizzing down the straight, back end squatting and nose up ready to take off, looking like Kenneth Williams in a hurry, i knew i had to do somthing about it and did.

 

I rest my case.

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