Fatheroftwins said:
I think I will probably go for the 2200 block and put the 2000 TC head on it...
I'm afraid I have to agree with Kev's comment:
hermione149 said:
I would go with option A as it's a straight swap,and the only difference between the sc and tc are the compression ratios, use the 2000tc headset, (2000sc and tc head gaskets are the same, )
I've rebuilt my 2000 TC engine with 'SC' pistons (9:1), which is basically option A for you. The principle advantage to this is that it lowers the compression ratio to an acceptable level that modern unleaded can tolerate without pinking.
I've rattled on about this in various posts before, but to summarise all of the advantages in one place:
Compression ratio is not directly linked to 'power delivery' - it was a performance/economy measure in the 1960s/early 70s that can't be replicated easily today.
Compressing the mixture tighter encourages it to combust more readily and more completely, allowing a larger amount of power to be extracted from a smaller amount of fuel. If you keep increasing the compression ratio far enough (say 18 or 20:1), the mixture combusts on its own and you can throw the ignition system away (ie, you have a diesel). The problem with a high compression ratio (>9.5:1) in a petrol engine is that it requires a very high octane fuel to withstand the compression before automatically combusting. Quoting
this wiki article:
"The higher the octane number, the more compression the fuel can withstand before detonating (igniting)." If you don't have a good enough fuel, the engine will suffer damaging pinking under moderate load, as the fuel ignites automatically under compression
before the spark plug fires, thus causing the flame front to push back down on the piston as it is still on the upward (compression) stroke. Short term problem is piston blow-by, long term is scratched bores and knackered bearings.
High compression engines were common in performance cars from the late 1950's and powerful saloons from the mid-60's. At this time, 100 RON 5-star fuel was available on the British market. This was of sufficient octane rating to tolerate the high compression ratio allowing the engine to be tuned for either power (richer) or economy (leaner). In the case of volume production cars (Jags and the like), it was done for economy.
4-Star fuel was 98 RON (so not much lower), but couldn't be used on anything higher than 9.5:1. As such, when the 1973 oil crisis hit, 5-star fuel ceased to be widely available in the UK, and all large car producers lowered the compression ratios of their performance engines for the 1974 model year (Rover's 2000 TC went from 10:1 to 9:1 in the 2200 TC, and the 3.5 V8 went from 10.5:1 to 9.25:1 in Oct 1973).
Modern super unleaded rarely comes in anything higher than 97 RON, with supermarket petrol being about 95. So you are already down on the conditions of the 60's/early 70s, and straight away you can see that running an engine with a 10 or 10.5:1 compression ratio is going to give you serious problems with pinking.
Unleaded fuel also combusts at a much slower rate than old-school leaded, so you need a completely different ignition curve in your distributor (one with greater primary advance to begin the combustion sooner so the flame front can travel down the bore at the optimum point to mimic original conditions). You will also need your carburettors re-needling to get different ratios of fuel/air mixture in under various conditions to replicate the original power delivery of your engine. Without this, you'll end up with flat spots (usually below 2000 rpm for a 4-cyl P6 engine) and probably pinking.
All of that is largely irrelevant if you don't plan to build a fast road/race engine, but it's just to shed a little light on the myth that "higher compression ratio directly means more power!"
Going to 2200 comes with a number of disadvantages. Primarily, you lose the dished (heron) piston design of the 2000 engine (below), which promotes good swirl and focuses the 'squish' area directly under the spark plug. The 2200 is a conventional piston and merely stops 6mm shy of the top of the bore, giving a cylindrical combustion chamber vs the much better 'inverted hemisphere' of the 2000.
The 2200 is also an oversquare engine (bore wider than stroke is long) and consequently needs to reach maximum distributor advance much sooner than the 2000. The effect is a less rev-happy engine that will struggle to make it to the red line.
Regarding valvegear, I'm yet to be convinced the 2200 is a 'big valve cylinder head'. The exhaust valve heads are certainly larger (inlets the same as 2000), but I'm not convinced the ports are increased in size. Regardless, even if they are larger, the tracts and exhaust primaries (on SC and TC) are the same size as the 2000 so any minor breathing advantage gained at the ports is negated further down the line. It's my personal inclination that the 2200 is a 'big valve seat' head. Ie, the exhaust valve heads and seats are larger to make it more efficient at dissipating heat when the exh valve is on the seat. 2000's particularly are known to burn out valves, so this would offer a clear advantage for longevity.
2200 TC's have a strong reputation for being almost as quick as a V8, and a very sweet engine. Most people cite the extra capacity and 'big valves' as the reasons for this, but it is my belief that real advantages come from the modern HIF carburettors (which deliver much improved low end torque and don't go off-tune as much) and the lower 9:1 compression ratio.
I've therefore put 9:1 2000 SC pistons in my engine (to keep the good combustion chamber design) and bolted the 2200's twin HIF6 carbs onto the manifold -
a straight swap conversion.
Demetris and
Hermione149 have done the same.
The result is a very sweet engine with a broad and uniform power curve that doesn't pink under any load, and will idle properly!!
I'd strongly recommend anybody else doing the same if they had the kit available. A 2200 just offers too much compromise for me to live with.
Plenty of food for thought!
Heron headed pistons like those in the 2000 engine.
2200's have conventional 'flat' piston design.
