You are here:

Triumph Repair/1974 Triumph Spitfire


Where can I get a (readable) vacuum diagram. None of the lines were on my car when I bought it.

EGR 3  
Hi John,

Good vacuum diagrams are difficult to find. Even in the dealerships we had a hard time getting accurate diagrams partley because BLM had made so many different changes. The only thing that saved us was that most of the BLM cars had a vacuum diagram sticker under the hood. The problem with that now is that the digram usually didn't survive the years. The 74 spitfire did have a few emission control items like the EGR valve and they had several changes in the vacuum routing. Unless you are trying to restore this car back to original you may have a difficult time finding what actually matched your car. Depending on your state laws for emissions you may have to chase a lot of ghosts to find accurate vacuum diagrams. The enclosed photos are copies of a service bulletin I received in 1974 about the EGR vacuum system on the TR-6 and Spitfire.

In the early days of emissions on BLM cars, they didn't know how to correct the emissions so they raised combustion chamber temperatures in an attampt to get a cleaner burn. However, this method caused a larger problem then HC and CO. They now had NOX (burning of the Nitrogen in the air which was more poisonous then the HC and CO.) So they intorduced exhaust gas into the intake to dilute the fuel air mixture. This too has a side effect of reducing horse power thus forcing the driver to use more throttle to go the same speed which then polutes the air more then if they left it alone. ha! So BLM and most of the cars in the world at the time had to chase their tails trying to meet emission standards. The humorous part was that some of the motorcycle manufactures had seen the writting on the wall and had an emission control section and had very clean exhaust emissions with no emission control items on their engines. They achieved this by having an advanced engine design of the combustion chamber and intake and exhaust system. But they found it easy to do because motorcycle engines mostly were 10 to 20 years ahead of the auto engine design.

If your local emission laws allow and you are only building a "Driver" rather then a show car. You would be far better off just putting on the required emission systems like evaporative loss system and eleminate EGR and all the things that caused the engine to over heat the combustion chamber in the first place.

Inclosed are three photo copies of the service bulletin about the hose routing of the EGR valve.


Triumph Repair

All Answers

Answers by Expert:

Ask Experts


Howard M. Fitzcharles III


Triumph TR-4 up & Spitfire, and Engine theory


Dealership line mechanic on MG, Triumph, Jaguar for 15 years, Instructor in commercial mechanics school 2 yr. Product information manager for piston and valve manufacture, Instructor & hotline answer man for import car parts importer 15 yrs.

Associate member SAE EAA member

Import Car magazine

ASE Master Auto with L-1 certification up to 2000

©2016 All rights reserved.