Zetec revs

Suppose the best bet really, would be to get it Dyno'd, see where it makes peak power, and where it will drop the revs to after each gear change, and set the red line sorta around the peak power line, assuming it allows the revs to drop into a good torque area in the next gear, and set the limiter about 500rpm after.

I think going higher than 7k will require uprated item's, from what i've read about the zetec. Your idea would work in a rally/race environment Dan but not for top speed or what he is actually asking, which is where to put the rev limit at its highest possible safety margin. Unless Megasquirt allows you to program a rev limit per gear?

But he hasn't given us an engine spec apart from its a Zetec and it is running on Megasquirt, if he has JE forged pistons, Arrow Rods, ARP bolts, steel head gasket and an uprated oil pump then of course he could push 8k without worrying too much about the engine going pop providing he had the car set up properly.

I assumed it as stock as no other upgrades were mentioned, and i'd guess peak power was about 6k. I didn't give maximum revs over that because i couldn't see the point in revving over the peak power, as once you're past that power the curve drops very quickly.

We need to know more about what he wants the set up for really.

stock engine?

set it where ford did plus a couple of hundred.

If you need more because you modded head/cams etc then you need stronger bits too! The ford rev limit is extensively researched by a big factory!

If it's all standard, then you can't really set it much higher than Ford do, for obvious reasons.

Although if it makes peak power at 5000rpm, then there's no point revving upto 6500. To put it another way - you aren't gonna make any extra power by raising the rev limit, if the peak power figure is made at less revs than said rev limit (which it probably is). Peak power at 5000rpm will still be peak power, whether you rev to 6000rpm or 7000rpm. You need to get it on some rollers and see what's going on. Set the rev limit to about 500rpm higher than peak power (although obviously not at

10,000rpm or anything silly :)

If it has stock inlet and exhaust manifoldery and stock cams, max power is at around 5750rpm and the factory rev limit is 6500rpm;by which time the power has severely dropped away anyhow.

Tim..

Depends entirely on how you've modified the bottom end. It's OK sticking in a performance cam but if you're still running standard crankshaft bearings and con rod bolts on that 70,000 mile old oilpump, it isn't going to last too long at 8000RPM.

ISTR my 1.8 revved to somewhere in the region of 7 grand.

Thanks for all the replies so-far. Apologies for the missing info.

The engine is in an unfinished Fisher Fury, so I've yet to drive it on the road. It is indeed bog-standard internally, but I've had to change most of the external bits to make it fit. The obvious performance-affecting changes would be the tubular exhaust manifold, single straight-through silencer, the Trust Electrical inlet manifold, the lack of a catalyst and of course, the mappable fuel and ignition.

I've no idea where the power peak will turn out to be once I've got it on the road and started mapping it properly. For now I'm just after a rev limit that allows me to see as much as possible when I'm mapping, whilst having a good chance of keeping it all in one piece for a while. If it turns out to peak at 3K or something, it's all academic of course, but I'd expect it to move up if anything because of the short inlet runners. Also, wouldn't Ford have rolled off the ignition timing a bit near the top end to encourage gear changing at sensible revs?

I realize that Ford are much better qualified than me to decide what the limit should be, but they have some restrictions that I don't, like warranties, angry customers etc. That said, If the original limit was 6K and it really does stand a good chance of disintegrating at

6001, then I'll happily stick to 6K. It's just that I would hate to think that I was missing out on some performance just because Ford wanted to reduce the percentage of con-rods they need to weld back together under warranty from 0.1% down to 0.05%!

The engine doesn't owe me much. It's served well as a space model for fitting everything under the bonnet and it'll get me through SVA on the pre-cat emissions test. After that, if it throws it's toys out of the pram, it'll be an excuse for me to get a decent black-top.

So does, say, 7K sound like certain death to a bog-standard silver-top (hydraulic tappets) 2.0? The rev-counter is going to be a bargraph, and I need to know how many green LEDs and how many red to get...

Cheers,

Colin.

Almost exactly the same as it was before because you have not really changed anything of any relevance unless the oem manifolds were especialy crap!

For now I'm just after a

A ford factory engineer once told me that the 2 litre pinto engine was ok continually all day long at 5700 rpm for thousands of hours with no problems... Intermitently at 5900, but would have a life measured maybe 40 to 80 hours.

Rely on their development testing (or actualy recardo) as they know what they are talking about. Use the factory figures as they are correct. It may survive short periods up to 7000 but that does not mean that you are not getting 20,000 miles of wear in a few seconds! Nothing may break but fatigue damage and bolts stretch etc happens.

If you need to rev it harder (and with your mods you wont) then you need to speak to the people experienced in tuning that specific engine. It may only mean some different lighter pistons, or some stronger big end bolts or a bit more running clearance, with a better oil pump, but whatever bit fails needs fixing first!

Maybe but more likely the cam timing is just designed for nice tractable bottom end so runs out of steam at high revs. If this is the case your bigger fatter shorter manifolds are going to cost low down power, and fail to do much at the top due to the cam! Cam swop next! Engines are a careful balance of matched "things" designed for a purpose. Grocery getting comfortably.

All engines are different so unless you are unlucky a couple of hundred extra shouldnt hurt.

It's just that I would hate to

Well if power keeps climbing on the dyno as you run up to the limiter then you need stronger bits! It wont though.

It wont explode or throw a rod, more likely it will wear out very quickly and become rattly low oil pressure and buggered unless it does actually break. Remember the forces on the big ends for example increas with the square of the rpm. The oil film will fail.

You better get a fan so you can see it through the oil smoke!

Get a big red one for zero rpm because sooner or later a 7000 rpm you will see it come on suddenly!

But it doesn't need to still be climbing surely? I'd expect it to be falling away still, but hopefully not as fast as with stock manifolds and ignition timing. I'm clinging to the hope that that might push the power up enough to make it worthwhile opening up that area of the power band for use.

That's actually quite encouraging. I hadn't considered the prospect of completely knackering the engine, and still being able to drive home afterwards ;o)

Hmmm. I think I'll leave the red line where it is then and set the limit at the same place for road use - I've dug the Mondeo's instruments out of the back of the garage and, as Tim says, the red line is already at 6K5. If it turns out after mapping that there's any power worth having up at that level, then I might up the limit to 7K just for track days.

Perhaps I need to think about getting a trailer too...

Cheers,

Colin

In my 1.8 Mondeo, the redline was 6.5k but the rev limit is higher. Why not ask a Ford spannerer what it is?

That sounds like the best plan of action.

As Tim said in his post :

So it's unlikely you're gonna raise the peak power from 5750 to >6500.

I doubt it will matter in this case, but there is a reason to raise the redline and strengthen the engine so it can survive there.

When you go through a gear, you want to get the maximum power under the graph over that range, i.e. if you change up too early, the engine is labouring along at the short end of the power curve until it comes on cam.

The standard gearing will probably be well arranged to give you gears that start off reasonably high up the curve, pass the peak power and down the other side, before you change up and arrive back reasonably high up the curve ready to do it all again.

As soon as you tune the engine - which is almost always for more power, which is developed higher up the rev band - you are moving the range over which the gears work. Simply changing the ratio on the diff will help here but it makes more sense to extend the useful range above the peak so that when you now change up, you are also higher up the revs prior to the peak to the same extent as before, and just leave the gears alone.

As a sort of rough guide, if you have an engine that goes on song at 4,000 rpm and redlines at 6,000, peaking across about 5,000 for the best acceleration, then if you tune it up to develop this peak at 5,800 rpm and raise the point at which you come on cam to 4,800 or thereabouts, redlining at 6,000 still is no use because when you now change down, you're 800 rpm before your engine is on cam and you won't get that 800 rpm back from the guy you're racing however long the straight might be. Basically, you might get a little more acceleration around 5,800 rpm with the tuned engine, but real world performance will be lower than the untuned, lower powered car.

This is partly why lazy v8 engines with the old style four speed gearbox are pretty competitive even though their headline power figures are a lot less.