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TR2/3/3A Hypothetical: Big bore TR3/4 engine

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Bremer

Bremer

Jedi Hopeful
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We know that 89 mm is the largest bore that pistons and liners are readily available for. I read about engines with 92, 92.5 and even 94 mm. I'm looking for some information on what would be involved in such modification.
I found that solid info on this is few and far between. I know the block has to be machined, but what features exactly? Can the bore centers still be on a straight line, or would they have to the offset?
How about cooling efficiency? Liners touching each other? Just a few of the issues that come to mind.
I totally realize that the most practical upgrade is the 89 mm bore kit. The benefits of a bigger bore may not be worth the amount of headache and cost to build the engine. Nevertheless, just wondering...
 
:iagree:
And he loves to talk!

ISTR him talking about keeping the cylinders in-line; but having to 'siamese' the liners together. Strictly racing stuff, he doesn't recommend more than 89 for the street (although I know some have done it and seem to get away with it).

He also used to have a motto : "Speed costs money, how fast do you want to go?"
grin.gif
 
The first 25% increase in power is relatively inexpensive, the next 25% can be what you spent up to that point. After that, the $$/hp goes up exponentially. Keep in mind you reach a point the car is not street drivable.

There is only so much you can get out these lumps.
 
Of course, there's more than one way to skin a cat ...
 

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I just saw in the "British Motoring" magazine from Moss Motors that came today, that they have an Eaton blower set-up coming soon for the TRactor motors. :smile: I couldn't find any info on there web site yet.
 
martx-5 said:
I just saw in the "British Motoring" magazine from Moss Motors that came today, that they have an Eaton blower set-up coming soon for the TRactor motors. :smile: I couldn't find any info on there web site yet.
Click to expand...
They were showing a TR4A installation at TRfest, but I didn't get a chance to ask about it. Looked very sanitary, but maybe wouldn't fit a TR3 as it very nearly touched the inner fender on the wider 4A.
 
I love all of the turbo pics & excitement. Considered that myself. Went with 89mm with custom liners. The ones purchased from normal channels proved to be slightly out of round & kept coming in damaged. My engine builder made custom units, way cool.
The issue, I think is with the crank & only 3 main bearings. How much power can it take? Also, think of the harmonic vibrations of the large 4 cylinder engine.
I have a German car with a 3.0 liter 4 cyl. It has 2 balance shafts.
Sure, you can bore away but what will you have when it is done?
 
IMHO if you are going to go to this extreme, you must invest in modern forged or machined rods.These are much lighter than stock rods and will reduce the loads on the old 3 main lump.While you are ordering the rods up ,send out the crank for a heat treating.Then lighten and polish it before the final work on the journals,try to stay at 020 under if possible.
The factory never had a harmonic balancer unless you counted the fan and its rubber grommets.But at the end of the day no crankshaft will last forever,you can only give it the best chance by reducing the loads.Custom pistons are not as high dollar as you might think and the 100 grams saved on forged pistols is 3 ounces of weight each journal will not have to fight.The rods can save as much as 210 gr each. A low end with this kind of prep can easily exceed 6000rpm reliably for many years.NOW you can punch it out to what ever you feel confidant with.
MD(mad dog)
 
I can't speak for the big bores, but..

You need a harmonic balancer. We use an ATI unit.

The bottom end can take A LOT of rpms (well over 7000rpm) when set up right, even as wet sump. Granted, you're looking at a lightweight, all forged set up. The thing to watch for on the bottom end is the center main flexing. Run the biggest main cap strap you can fit. You're probably going to have to custom machine something.

I think most people with stock cranks try to limit themselves to 6000 and once in a while they will hit 6500rpm.
 
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