View Full Version : TR2/3/3A Horsepower increase for TR3 engine

11-16-2004, 09:36 AM
I'm in the middle of a ground up resto on my TR3. I have to rebuild the engine and was thinking about adding some more grunt. Nothing outrageous, just a nice kick in the pants. What would yeild some good results without spending a huge sum of money. I already have an 87mm piston and liner set to go in. What head work (milling?? to increase compression) and cam would be suitable. I plan to retain the SU carbs.

Simon TR4a
11-16-2004, 11:50 AM
Martx I have the same engine in my TR4a, and have done basically what you are planning.

First, since you are putting in liners and pistons you obviously are going to have the engine apart, so I feel a fast road cam would be worthwhile, and you may need to replace your cam and lifters anyway.My cam is from Kent cams, the Sprint 88 grind, might be a bit too much for most people, they have milder ones, as do Piper cams, Web cam in California etc. (I would advise against regrinding your stock cam as it is symetrical, a compromise made presumably to control production cost, modern cam designs give different intake and exhaud\st timing and perform better.)

Second, you are increasing the compression anyway by increasing the displacement; if you had 86mm pistons you are going from 2138cc. to 2188cc., about 2.5%, so if you had 9:0 to 1 compression you now have 9.2 approx. If your pistons were 83mm. you are going from 1991cc. to 2188, an increase of nearly 10%, raising your compression from 8.5 to 1 to about 9.35.
My advice is to take the head to a machine shop and cc. the combustion chambers so you know where you are now, as the head may have been skimmed as part of a previous rebuild. You also need to measure the depth of the pistons below the deck height and allow 1mm or 40 thou for the compressed thickness of the head gasket.
A reasonable ratio for pump gas is 9.5; mine is at 9.75 and I use 94 octane Sunoco.
Keep in mind that a moderate power increase is fairly easy and not too expensive, a really big increase will be very costly and make the car less driveable in traffic.
I am still using SUs on my car, with a range of needles, and find they work well for a car in "fast road" tune, as the English refer to it.
Good luck with your project.
Simon, WOFTAM Racing.

11-16-2004, 09:51 PM
Simon gave you some great tips that should help alot.

For your use, I would think the "D" grind camshaft would probably be a good choice. It's mild enough to use for the street.

If you do want to mill the head, .090 is a moderate amount which should leave a very reliable and street-worthy engine. .125 to .150 is possible, but can be pushing it. On the other hand, I drove my TR4 on the street for ten years with .125 milled and Weber carbs (among other things) without any problems.

The TR3 head has a couple concerns when milling and may not be possible to mill all the way to .125 or 150. One concern is clearance at the coolant outflow/thermostat housing. Another is re-shaping the "squish area" within the combustion area of the head. The earlier head casting limits the amount of work that can be done in there. It's possible to break through or weaken so that it collapses later. You could also use a steel shim-type head gasket (the best price I've seen is from britishframeandengine.com). This gasket is thinner than stock and could be used in conjunction with milling, or not, depending upon how much you want to boost compression.

Keep in mind that milling the head and/or the thinner head gasket will mean replacing the stock push rods with shorter ones to match, or the tubular type that can be shortened to custom lengths. Alternatively, it's possible to shim up the rocker arm pedestals to re-establish correct valve train geometry.

Other ideas would be to do some porting, polishing and match the manifolds carefully so that you insure the engine breathes well, both on intake and exhaust. Larger valves aren't necessary for street use.

A header would likely be the biggest single improvement you could make, especially if it's fitted to a free flow exhaust. Fitting a header on a TR3 can be a problem, depending on whether you have the earlier or later type of starter and gearbox.

I strongly suggest you pick up a copy of the TR4/TR4A Performance Tuning Manual that was produced by Standard Triumph and later reprinted by Leyland. This little book contains tons of detail on maximizing engine performance within "Production" racing limitations, i.e, keeping the cars reasonably stock and using the SUs. The TR3 and TR4 are similar enough that most of the same info can be applied, plus the TR3 is discussed to some degree. I don't believe a similar book was ever offered specifically for TR3. The book is written by Kas Kastner and based upon the factory supported US race program and performance parts that were originally available through the dealers. The manual is currently available from some of the usual TR parts providers and shows up on eBay every so often.

Have fun with your project!

11-16-2004, 10:07 PM
Not to lead you, but here is a little something you might want to keep an EYE on. Wayne https://cgi.ebay.com/ebaymotors/ws/eBayIS...me=STRK:MEWA:IT (https://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&rd=1&item=4504132948&ssPage Name=STRK:MEWA:IT)

11-17-2004, 02:43 PM
Agree with the original post and add that you could also consider roller rockers and balancing the crank.