Triumph TR7, TR7V8 & TR8 Information

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My V8 Conversion PDF Print E-mail
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Sunday, 19 September 2010 17:52


If you are thinking of converting your TR7 to V8 power then it is worth reading the rest of this document. I am going to outline the jobs I've had to do and also give some pointers on what to look out for that may cause problems. I will also give details of some of the options you may have.
I am not a professional, but a keen amateur who has read about many conversions and know a few people who have been through it successfully. What follows is certainly not a comprehensive list of options, but hopefully a starter for the first timers.

The first piece of advice is that when considering a V8 conversion, buy the full kit. You will find that all of the large TR suppliers sell a V8 conversion kit, but will use different components. It can be very hard to mix and match. The main problems come when trying to make the exhaust clear the subframe. I bought everything separately over a space of about 12 months, and had trouble with some of the parts.


The most commonly used V8 is one from a SD1. You can use one from a P6 or Range Rover but the earlier ones aren't as strong and the Range Rover/Land Rover ones have lower compression. If you do decide to get a SD1 engine, then try and get the latest model you can. SD1's changed over years including stronger blocks, better distributor and various other improvements. It's definitely worth checking out the David Hardcastle book on the Rover V8.
As far as mounting the engine, it can be bolted on either side of the subframe bracket. The preferred way is behind because of weight distribution. This means that you will need a shortened prop-shaft and you will also need to re-drill the gearbox mounting bracket holes on the car. This does mean however that the gear lever sits a couple of inches further back. TR8's have shortened gearbox extensions which takes the lever back to its original position, but are very difficult to get hold of.
Having said the above, it is possible to mount the engine the other way.
If the engine you are using originally came from an automatic car, then you will have to change the metal spigot bush. The hard part is to remove the old one, which I did by using a hacksaw blade and cut through opposite sides until the spigot bush collapsed and could be withdrawn.


When buying the V8 kit, you generally don't get any uprated suspension parts, but everyone agrees that this should be one of the first areas you look at (with the brakes) even before uprating to V8. The most common upgrade is to put 200lb springs on all corners and add adjustable dampers. You may find that these are too stiff unless you are rallying/racing. A friend of mine has tried numerous settings both at the front and back and he thinks that the ideal setup for the car is :

Length Weight
Front -1" 135lb
Rear -1.5" 180/200lb

Because the rear of the car sits slightly higher, the car tends to look better if you lower the back more than the front.

There are some shortened rear springs on the market that are far too short and will result in the car bottoming out. The reason why some companies sell these is because they have been copied off the original BL rally springs, and the rear trailing arms were mounted higher up.


If you buy the full V8 kit, you will get a wiring diagram with it, however because I never I got a local auto electrician to come and do the wiring. He used both the existing TR7 loom and the SD1 V8 loom to make one TR7V8 one.
I was told that due to the extra amps that the starter motor draws to start the V8, the standard battery has to struggle to. With this in mind I decided to have the battery mounted in the boot as the TR8's have. This allowed me to get a much larger battery and does seem to do the trick even though you loose a bit of power due to the extra length of cable between the positive terminal and the junction box.
You also need to re-calibrate the rev counter (which means adding a resister) which is easier if you buy one because the red-line mark is different as well.


To uprate the overall braking, you can replace the servo with one from a SD1. This gives an increase in pressure going to the master cylinder. To change the servo you will need to shorten the push-rod so the brake pedal sits in the correct position.
You will also find that the brake pipes attach on the opposite side which just means you will have to re-route them. Front
This is the most important area which you must look at, even if you're not considering a V8 conversion. The standard brakes on a TR7 are barely adequate. Even the other Harris Mann creation - the Ambassador had bigger brakes, which can actually be used on the TR with a little engineering. The mounting holes will need to be filled and re-drilled otherwise the pads will not cover the disc.
If you want the best, then go for the SD1 Vittesse type, which have 4 pots and vented discs.
A compromise is to go for the Ford Capri 2.8 calipers and discs. These have only 2 pots but are larger and use vented discs.
You will have to check which calipers can be used with which wheels because clearance can be a problem.
You don't have much choice when it comes to rear brakes apart from :
1) Replace with rear discs, either using the S&S kit, or by getting hold of one of the BL rally type - if you can.
2) Put the rear drums from a 4-speed car on as these are supposed to have smaller inlets which mean that when the brake fluid compresses more pressure is put on the brake cylinders.
It's interesting to know that somebody who has been racing TR7V8's for a while says that you do not need rear discs because they are hardly ever used anyway. Just having a good set of calipers and discs are enough. He also says that you do not need the rear anti roll bar.


Expansion Tank
The expansion tank can be sited in a number of places.
1) Leave it where it is.
2) Mount it on top of the alternator bracket.
3) Move it to the right-hand side inner wing. If mounted correctly the inlets/outlets are in the wrong place. You have two choices :

  • Mount the expansion tank on an angle so it clears the bonnet.

  • You can try and find an expansion tank from a 1979 model TR7 which were mounted on the right-hand side at the factory.

I did the latter.

There isn't a lot I can say about the radiator apart from you need to buy a TR7V8 one, I'm not aware of other radiators fitting. There are however many different upper and lower brackets available which again don't mix and match too well. Some of the lower brackets allow for the original twin fans to be fitted.
When fitting electric fans, you will need to fit a temperature sensor somewhere on the radiator. The original set-up uses a simple clip that holds the sensor in and should resist the pressure. These type of clips are hard to get hold of, so an alternative as I did, is to get the side of the radiator drilled and get a nut welded over it so it can take a standard modern screw-in type sensor.
I used a fan from a modern car which was very thin. I'm not sure which car it came from, but had Japanese writing on and could have come from a Nissan.


It is possible to get hold of a pump from your local scrap yard but make sure it isn't from a fuel injected car and also try and get one from a larger engined car. A lot of early 80's Japanese cars had electric fuel pumps and one from a Nissan Laurel would do.
I know of someone who has a Scimitar GTE with a Rover V8 in and until the end of last year had be running an electric fuel pump from a Morris Minor for about 2 years (he did say he had problems going up hill).
When fitting the fuel pump it should also be mounted through a cut-out switch in case of an accident. An ideal part can be found from a Montego.


There are quite a number of options available and at the end of the day depends on money and taste.
To make it easier when fitting tubular manifolds, you can buy studs that screw into the cylinder head and allow the manifold to slide on easier. This is because they can be slightly out of alignment and stops you stripping the threads.


There are many different subframes on the market and depending on what you intend to do, will depend on which one you choose. If you think you might add power steering in the future then you will need to get an original TR8 subframe so that there is enough clearances between the steering arm, exhaust and the power steering components themselves.
The majority of the rest are uprated/amended TR7 subframes but are done professionally. You should keep clear of subframes converted by amateurs unless absolutely sure.


The Triumph TR7 5-speed gearbox is ideal and you can also use a SD1 5-speed gearbox which are based on the same design but apparently some of them are slightly stronger (or so someone told me). If using a SD1 gearbox I think you need to swap over the gear lever arm.
If you want a better feel to the gear change then you can shorten the gear stick itself and get it re-threaded.
(As an additional item, the gearbox should be filled with automatic transmission oil).


Any 4-speed car needs a tougher rear axle which can be obtained from a 5-speed TR7/8. You can keep the original ratio (3.9:1), which will give good acceleration but a lower top speed and of course higher revs. The most common is the 3.08:1 which you can get from a SD1 (automatic ?). You can use the entire axle if you wish like the Grinnall cars, but they are much wider and have five wheel studs. A nice compromise is a 3.45:1 ratio from a SD1 (2600 ?). When changing from 4-speed rear axle you will need to transfer the trailing arms and links as they are different. The ultimate is a limited slip diff. It is advisable to get a professional to change the differential if you are in any doubts as there are very small tolerances involved.

The following is taken from Mike Jeffrey with additional SD1 information by Jim Robinson.

Axle ratios
Early TR7
Late TR7 (and auto?)
SD1 2000 auto/manual
SD1 2300 auto/manual
SD1 2600 manual
SD1 2600 auto
SD1 3500 (carb) auto/manual
SD1 Vitesse manual
SD1 Vitesse auto/VDP auto


Steering does not need to altered, although you can get a quick rack which helps, and of course you can add power steering but a lot of people say that power steering reduces the enjoyment of the car. This is mainly personal preference.

Last Updated on Monday, 20 September 2010 22:33