De-americanising an engine

[Tim D.]

Hi all,

I'm in the process of looking for a TR6 to replace my Lotus Elan +2.

There seem to be a number of american re-import TR6s out there, many with conversions to the correct hand drive.

However I am aware that the US engines had lower compression ratio and power outputs and generally ran on Strombergs.

So, my questions are:

1) what sort of work needs to be done to bring the engine itself up to UK spec (is the drop in CR just different pistons or something more fundamental)

2) If I left the Strombergs is this going to be an issue with the increased Enthanol in fuel (those rubber diaphragms look iffy). If not, can SUs be used and would they be any more resistant?

3) If I wanted to convert to PI, I notice that refurbed kits are available, is it a "bolt on" mod?

(I am pretty reasonable at spannering, rebuilt a spitfire, elan and almost finished a sebring sprite replica)

 

thanks for any help!!

Cheers

Tim

[foster461]

Hi all,

I'm in the process of looking for a TR6 to replace my Lotus Elan +2.

There seem to be a number of american re-import TR6s out there, many with conversions to the correct hand drive.

However I am aware that the US engines had lower compression ratio and power outputs and generally ran on Strombergs.

So, my questions are:

1) what sort of work needs to be done to bring the engine itself up to UK spec (is the drop in CR just different pistons or something more fundamental)

2) If I left the Strombergs is this going to be an issue with the increased Enthanol in fuel (those rubber diaphragms look iffy). If not, can SUs be used and would they be any more resistant?

3) If I wanted to convert to PI, I notice that refurbed kits are available, is it a "bolt on" mod?

(I am pretty reasonable at spannering, rebuilt a spitfire, elan and almost finished a sebring sprite replica)

 

thanks for any help!!

Cheers

Tim

 

 

Tim, welcome to the forum.

 

1) what sort of work needs to be done to bring the engine itself up to UK spec (is the drop in CR just different pistons or something more fundamental)

 

Head needs to be milled up to .25 inch to get the CR back to around 9.5:1. Needs a PI cam or equivalent. Those are the main changes but any individual engine may need more work if it has a lot of miles on it.

 

2) If I left the Strombergs is this going to be an issue with the increased Enthanol in fuel (those rubber diaphragms look iffy). If not, can SUs be used and would they be any more resistant?

 

I dont think the two Strombergs alone will get you to 150HP but there are options for adding a third Stromberg or going to Weber dcoe's. We have a lot of TR6's with Strombergs in the US and I'm not hearing of issues with ethanol in the gas (we have 10% ethanol)

 

3) If I wanted to convert to PI, I notice that refurbed kits are available, is it a "bolt on" mod?

 

People have done it. You would need to do the engine mods in item 1, source all of the parts and modify the fuel tank for the fuel return. TBI and EFI are other options for injection or there's the dcoe's that I mentioned earlier..

 

Stan

[Tim D.]

Great info.

So from this I take it that the heads are standard uk/us.

Anyone have any idea how much decking the block will cost? Had a lotus 4 cylinder decked rebored crank ground and balanced ad it was about £800

Cheers

Tim

[Tony Millward]

From what I remember reading Tim, the cylinder heads are also different...mainly the position of the ports?, perhaps someone more knowledgeable can jump in here.

 

Cheers

 

Tony

[Tim D.]

I'm sure you guys have discussed this to death, but how does power output differ between:

PI

Twin strombergs

Twin Su

Triple SU

On a uk spec engine

I am not interested in webbers/dellortos as have spent 10 years playing with them on a spit and elan and want a change!

I am also most interested in torque, the elan was all hp at high revs, which is fun for short times, and now want low rev grunt

Tim

[250]

Posted Today, 04:13 PM

From what I remember reading Tim, the cylinder heads are also different...mainly the position of the ports?, perhaps someone more knowledgeable can jump in here.

 

Cheers

 

Tony

 

The inlet ports are definately diferent on the 250 closer together if I remember right so suspect the USA 6 could be the same. I changed the inlet manifold to a TC one to allow me to fit different head.

 

Mark.

[rpurchon]

Hi all,

I'm in the process of looking for a TR6 to replace my Lotus Elan +2.

There seem to be a number of american re-import TR6s out there, many with conversions to the correct hand drive.

However I am aware that the US engines had lower compression ratio and power outputs and generally ran on Strombergs.

So, my questions are:

1) what sort of work needs to be done to bring the engine itself up to UK spec (is the drop in CR just different pistons or something more fundamental)

2) If I left the Strombergs is this going to be an issue with the increased Enthanol in fuel (those rubber diaphragms look iffy). If not, can SUs be used and would they be any more resistant?

3) If I wanted to convert to PI, I notice that refurbed kits are available, is it a "bolt on" mod?

(I am pretty reasonable at spannering, rebuilt a spitfire, elan and almost finished a sebring sprite replica)

 

thanks for any help!!

Cheers

Tim

 

early usa 6s up to about 71 had the narrow inlet ports spacing.they have a square inlet manifolds for the strombergs.later inlet manifold look like a bunch of bannas!and will be later type head. late usa cylinder heads have lower compression heads.any cylinder head will fit though,even from 2.5 saloons .and you dont need the block skimming just the head.no point fitting a early pi cam if you havent got pi either.

i have su on my car with a diy head porting job .cr and late usa camshaft, and got 185lb torque.145 bhp guestimated figure at the flywheel on the rolling road.car does 30 mpg on a run.

however forget what the engine is like, concentrate on the body, you dont want any rust to sort out.

richard

Edited December 16, 2011 by rpurchon

[Tim D.]

Hi

thanks for the details. So are you saying that the us heads have larger combustion chambers to give lower CR ?

The reason to ask about US engines is that I have seen US reimport cars with good bodies but needed to know about whether the engine could be upgraded.

[RonA]

Hi Tim

My car was originally a late ['75] US car which I bought about 11 years ago as a resto project. Basically when I rebuilt the engine I did the following;

Removed all the anti-polution gear and dumped it.

Replaced the original very low compression head with an early PI head converted to unleaded, the US head had smaller inlet valves and a compression ratio so low it would probably have run on paraffin.

Replaced the Strombergs with HS SUs, I know some people like Strombergs, I don't, never saw the point of them when SUs are simpler and better, you can get SUs cheaply off of various cars [mine were ex TR7] and they bolt straight onto the Stromberg inlet manifold and use the Stromberg filter box, I think I used BDM needles.

I was lucky enough to get a NOS early PI distributor off Ebay at the time, I run that with the vac advance connected.

The car is fast enough for me and I can get 30mpg touring. There are other subtle differences in the engines but nothing that causes any great problems.

The only thing I don't like about the US cars is the diff ratio, they are 3.77 and the UK ones are 3.45, I wish I had changed it when I restored the car, it tends to sound too busy for whatever speed I'm doing.

It's an easy car to change from LHD to RHD mainly just chequebook and spanner work, just one bracket needs welding on.

A lot of ex US cars haven't got overdrive, having once had to drive home 100 miles with a broken OD switch I wouldn't have a TR6 without it, especially with the US diff ratio.

If you haven't already done so, take a test drive in a TR6 to see if you like it after being used to the Plus2!!

If you decide to go ahead and want any further info PM me.

RonA

[Tim D.]

Hi

Have been driven in a TR4A by my uncle every year to the goodwood revival and have always liked it

The Elan is nice but not a softtop and quite a challenge to get running just right.

Cheers

Tim

[Dave McDonald]

Tim

The spacing between the inlet ports on the head is approx 17mm on early carburettor heads and 22mm for PI heads.

Inlet manifolds are available to fit either head for SUs/Strombergs or Webers/Dellortos but if you want to fit Lucas PI it has to go on a 22mm spacing head.

Dave McD

[foster461]

....no point fitting a early pi cam if you havent got pi either.

 

 

I'm pretty sure Tom Fremont has a PI cam in his dcoe'd TR250 and I dont recall that there is a lot of difference between the PI cam and the many options for performance cams for the TR6. In general any US spec TR6 engine can be easily upgraded to 180hp without resorting to exotic bottom end parts and 150hp can be got with simple machining and the corresponding cam/ignition/induction mods without getting deep into the head. Well worth doing in my opinion, it totally transforms the federated TR6.

 

Stan

Edited December 17, 2011 by foster461

[johnny250]

Yes all quite straightforward Tim, my preference: locate the later TR5/6 head (make sure it isn't cracked between cylinders) get it converted to unleaded whilst its off, fit a fast road cam and twin S.U's on a saloon manifold.....extractor exhaust manifold too if you want.

Or alternatively keep your original low compression head and fit a supercharger......

 

john

[Peter Cobbold]

Yes all quite straightforward Tim, my preference: locate the later TR5/6 head (make sure it isn't cracked between cylinders) get it converted to unleaded whilst its off, fit a fast road cam and twin S.U's on a saloon manifold.....extractor exhaust manifold too if you want.

Or alternatively keep your original low compression head and fit a supercharger......

 

john

 

Yes for low-rpm grunt a blower's unbeatable.

[Tom Fremont]

Guilty as charged; I've got the P.I. cam with 40DCOEs and have done 60K miles with it. My case and plenty of others attest to their compatibility. The Webers will increase performance over other normally aspirated options employing fewer than (6) throttles but aren't necessary to achieve desired results for most folks. To commend it the P.I. cam has an unsurpassed track record, good for up to 170 BHP ( according to some ), has a gentle ramp to the lift for excellent longevity and accepts the 0.010" tappet clearance vs. looser settings for virtually all other " performance " cams. Lumpy as it is at idle, it's tractable enough to give good TRaction from 2000 rpm up.

 

'72 and later heads have the P.I. port spacing; they're just a lot thicker. Furthermore, the later blocks have recessed cylinder bores ( P.I. too ). The P.I. cars' head gaskets have a brass/copper ring to fill that recess; I don't know about the U.S. spec gaskets. Empty will surely give lower c/r. For the unrecessed engines, head thickness of ~ 3.400" will give 9.5:1 without porting/ combustion chamber rework.

 

For the basic " 150 BHP " conversion I'd mill the head, fit a P.I. cam / valve springs and fit 3X40DCOEs. That should get it about on par . Sounds simple enough, and is if you know Webers or have a specialist dial them in for you .

[Austin Branson]

Hi, Tim. I've got one, it's a 74 ex-California car with no rust, but no horsepower either. As I understand it, the 6 cylinder TR engine was developed for PI, as Lucas promised Triumph that that would solve the US exhaust emission problems. It didn't. So the TR250 was introduced with a cylinder head that COULD NOT be retro-fitted with the PI system (Inlet valve ports are different). It also had a wierd distributor that had vacuum advance and retard (two of those bell-shaped vessels connected to the disi cam). As far as I know, these were not fitted to TR6's. Again, as far as I know, all US TR6's were fitted with vacuum RETARD, not adavance, and this means that the ignition timing is set up as 4 degrees AFTER TDC. Wierd. I disconnected mine. To restore the 9.5:1 CR as used on the European TR6, the head will need a lot of meat removed, but that's all. According to Neil Revington, the cams are all the same for the TR6. He knows much more about it than I do. The car has difficulty out-accelerating a scooter, so I am in the process of fitting an Eaton M62 supercharger, and leaving the low compression ratio - at least for the moment. This will give me about 150HP at the flywheel, but enormous grunt at low revs. Peter Cobbold has done this, is an expert, and has been an enormous help to me in the project - in fact I believe without him, I probably would not have been able to do it. The low back axle ratio is up to you, it was the standard ratio in all the previous TR's, and was only increased for the PI cars. Late US cars were all fitted with overdrive. The Stromberg carbs were actually far more accurately made than the SU's, but by 1974 certainly, they have very limited facility for mixture adjustment, and have to be adjusted using a special tool. I could not get mine working, but you must remember that in those far-off days when Ralph Nader was busy condemming a lot of 4 wheeled bolides - the venerable VW bug included, that the US government were making pollution targets that the motor industry simply did not know how to deliver. Stromberg released about 4 different versions in one model year trying to comply, US imported Toyotas would simply not run (the problems were eased by judicious blocking of some of the hoses using beebee pellets), and even giants such as GM were strapping air pumps on, that simply injected raw air into the exhaust manifold to reduce the concentration of pollutants in the exhaust. Putting PI on an ex-US car will be difficult, expensive, and although it is probably better than most carburettor set-ups, will not give as much bang for your buck as going to a blower. PI will mean new fuel tank, lines, disi, pump, wiring, injector bodies etc etc etc. Lots of money, and it still is only really calibrated for about 2000 rpm in the total rev range. My project is not yet completed, and I am expecting several problems, but I am confident it will work, and with Peters help, it will be bloody good fun! My advice - go for a rust free ex_US car, get it converted to RHD, then start looking for a blower. Talk to Peter. Good luck, and let us know how you get on.

Best wishes,

Austin

[Tom Fremont]

Just a couple of points re: the above post:

 

Vacuum retard function on the U.S. cars is operational only at idle, being de-activated once the throttles begin to open. The published timing values refer to the retard condition; off idle they will switch to ~ 10 degrees BTDC.

 

TR6 cams were either "150" bhp ( 35/65/65/35 ) or 125 ( 18/58/58/18 ). The latter is common to later P.I. and U.S. carb engines. Early U.S. TR6s and TR250s shared the 10/50/50/10 cam.

 

A blower will likely give more low-end grunt than normally aspirated engines but remember, if it lets go the engine eats the bits. It is probably the quickest way to 150+ bhp when mounted on a ready engine, i.e. fresh everything, unleaded, suitable c/r etc. If you're removing the head anyway that advantage evaporates.

[Tim D.]

Hi guys

Problem solved. Have bought a 150bhp with injection!!

(lotus was sent to new owner in australia at 10 am yesterday, TR6 was bought to replace it at 10 pm, so garage was empty for only 12 hours !)

Will no doubt have lotsof questions for the forum in the coming years.

Cheers

Tim

[foster461]

Hi guys

Problem solved. Have bought a 150bhp with injection!!

(lotus was sent to new owner in australia at 10 am yesterday, TR6 was bought to replace it at 10 pm, so garage was empty for only 12 hours !)

Will no doubt have lotsof questions for the forum in the coming years.

Cheers

Tim

 

 

Congrats Tim. I'm sure the TR6 will have its own set of quirks and issues but you will be in good company here. Post some pictures when you get a chance and lets see what you have.

 

Stan