Hi all,
Can anyone tell me what it is safe to rev a stock A14, and a stock A15 up to?
Thanx.

Hello

My A engine is almost stock and I overrev it on a daily basis to over 7000 RPM. No problems until now.

Ricardo

Riclage, what engine do you have?
I'm trying to find out how much the extra stroke in the A15 affects the ability to handle high RPM's.

What is "safe" to rev it to? If you rev it to 6,000 rpm on every shift, that engine will wear out soon. I wore my A12 out in a few months, it started smoking pretty good. That was over 100 6,000 rpm pulls a day (hey, that was fun while it lasted). I put in the A14 and kept the revs lower (usually under 3,000) and it lasted a loooong time.

The A15 revability is gonna be limited by the valve springs, not the stroke.

The stroke of an A15 is a lot shorter than that of a V8 engine and those can run over 10,000 rpm ... so the stroke itself is not the limit. Longer stroke means higher peak piston ring speed, higher wear, quicker ring failure ... but the A15 stroke is not long in the world of gasonline piston engines.

If you upgrade the valve springs and cam to rev higher, then the limit becomes the strength of the crank, rods, piston assembly. Forged cranks like the A12 are stronger (and so can rev higher) than cast cranks. I think A15s came both ways.

Engine theory says that a longer stroke engine gives more torque than shorter stroke but the small-stroke engine has an advantage in rate of piston acceleration (assuming the overall CCs are the same). Also, the bigger bore can have an advantage in air flow. But displacement is even more important. If you are racing in a class, you may have no choice. But for the street, more displacement is almost always better (unless the larger engine has some specific flaw). An A15 will make almost exactly the same peak HP as an A12 if the same intake system (including cam), cylinder head, exhaust and ignition are used. Plus it will make more torque than the A12. Therefore more overall performance. The A15 won't "feel" as fast because it will make peak HP at a lower rpm and so feels "flat" above a certain rev (flatter torque curve). The A12 will increase in torque as you keep revving so "feels" more sporty. Nevertheless, the bigger engine will win out with a stopwatch.

Now if you are talking about building an extreme race engine, a smaller engine can have some specific advantages. But the for a road car that's not an issue.

I have a A12 engine

Ricardo

little off-topic but while were talking about over-reving, i was dragging my brother in his 1600 escort rally car and i missed second gear, she revved to over 8000rpm screaming! but no damage or bad noises at the time shes all good!, mind you once i found second i dumped the clutch and the old sprund load locker kicked in and the arse end attempted to overtake the front , i beat my brother cause as this happended the front of my car has walked accross the lane cutting off my brother and forcing him to brake, i wonder if this technique could be mastered and used regularly