2L: Why such a low redline?

[maxm50]

Could anyone enlighten me about why the redline on a Fiat 2L FI engine is so low (6000rpm)? I'm mostly curious from an engine design / engineering standpoint. It's such a smooth engine in operation. Cams acting directly on the valves without rockers (which is good for high rpm operation, correct?) So what is it that's limiting the RPM so much?

Related question: Is there an actual rev limiter on the fuel injected engines? ie. does the ECU cut spark or fuel at some RPM? if so, what RPM? I've never taken mine above ~5700rpm.

I'm certainly not unhappy with this engine - it has fantastic low end torque and is one of the smoothest 4-cyls I've ever driven. Just curious about what in its design gives it a relatively low redline.

Cheers,
Max

[18Fiatsandcounting]

Good question. The original 1438cc engine in my '69 was rev happy and would easily surpass 7000 rpm in stock form with no apparent ill effects. When I switched to a 2L engine in this car, I rarely go above 5500 because there's no reason to. There's plenty of torque from 2500 to 5000 and power seems to taper off after that. Likely due to carb or intake issues, not because of any limitation in crankshaft speed.

Just guessing here (I'm good at that), but the 6000 rpm redline may be based more on engine performance than a chance it might blow apart beyond that. Still, I'd be reluctant to hold my 2L engine at 6000 rpm whereas the 1438 could sit there for hours. And it did, in one trip from Phoenix to Los Angeles in 4 hours. Interstates were much more deserted back then.

-Bryan

[SteinOnkel]

You are correct, solid lifters generally allow for higher redlines. I suspect the issue is with the bottom end on this engine.

It most likely cuts spark. Almost no fuel injection system that's older than 25 years cuts fuel. I don't know too much about the fuel injection on these cars, but if the ignition is separate, you could swap in an icu from '79-'80. The redline on those is 6500rpm, I believe.

They always pad in a little extra from the factory. Stock redline on my VW 1.6 16V is 6800, I bumped that up to 7200 (because I can). No issues; it's got roller lifters. I've seen people bolt on solid-lifter 16v heads onto those (you lose vvt) and the bastards spin to 8.5k. Or, if money is plentiful - bolt on a motorcycle cylinder head and the stock crank is good to 11k.

A few weeks ago I money shifted my partner's Fiesta ST on track. Damn 6-speed. Grabbed first instead of third on a downshift. Every single warning light came on - the little beast must've spun to 8k, albeit briefly because I didn't let the clutch all the way out. Stock redline is 6400 with a really harsh rev limiter. Limped it back to the pits, cleared the codes, it was right as rain and did another 5 sessions that day no problem. Well, until we wore the brakes down to metal on metal that is.

[DaveA]

I guess there is a element of not suited to rev so high either. If I read correctly, the 2.0 block is taller, so I can only presume it has a longer stroke, therefore more rotating mass to move. The smaller engines are more “square” - less stroke, less mass and therefore happier revving higher. But torque is generally higher in a longer stroke engine and thats the 2.0’s gain. Remember, HP/revs is how fast you hit the wall..torque is how far you push it before you stop!!

Add more controlled fuel delivery and you have the FI engined car. That said, id love to be able to rev mine upto 7k, the noise would be too tempting, and the tickets would soon follow!!

[RRoller123]

The 2L is a stroked 1800.

[maxm50]

Ah, yes, it looks like the bore x stroke is 84 x 90mm on this 2L engine. Not TERRIBLY oversquare, but a bit. Anyway, I agree that there's really no reason to go beyond 5500rpm on the 2L stock engine. It completely runs out of steam. But it's quite happy to torque along from 2k-5k rpm. I do wonder how high compression pistons would affect the powerband. Someday when mine needs a rebuild, I guess I'll find out.

DaveA, you've fallen prey to automotive internet forum nonsense! Torque is NOT "how far you push the wall". That's determined by your momentum (mass x velocity), coefficient of restitution (ie. do you bounce off the wall or not), energy absorbed in the vehicle structure through material deformation in the crash, and mass of the wall. Among other things. But torque ain't one of the variables in that equation

[Nut124]

I think the reason for the factory 2L redline is that with the FI, early into the emissions controls, std cams, low compression, there is not much more power to be had beyond 5500.

There is nothing wrong with the Fiat twin cam bottom end. Quite the opposite. It is stronger than most. The Fiat twin cam is one of the best ever performance engines. It is still being used in club racing all over the world. I recently corresponded with a racer in Finland who said they use the Fiat TC in auto-cross(?) racing. 1650cc displacement limit. Their engines make 170+HP and spin to 9000.

Carburated 2L performance engines can sustain running at 7000+ making peak power at 7500rpm according to Guy Croft.

In my 1800, I upshift at 7800 when on the track or pushing it, which pretty much happens every time I drive it.

[SteinOnkel]

I think the reason for the factory 2L redline is that with the FI, early into the emissions controls, std cams, low compression, there is not much more power to be had beyond 5500.

There is nothing wrong with the Fiat twin cam bottom end. Quite the opposite. It is stronger than most. The Fiat twin cam is one of the best ever performance engines. It is still being used in club racing all over the world. I recently corresponded with a racer in Finland who said they use the Fiat TC in auto-cross(?) racing. 1650cc displacement limit. Their engines make 170+HP and spin to 9000.

Carburated 2L performance engines can sustain running at 7000+ making peak power at 7500rpm according to Guy Croft.

In my 1800, I upshift at 7800 when on the track or pushing it, which pretty much happens every time I drive it.

Let's not get crazy with it. It's a fine engine and great from the factory (hellooo standard equipment oil pan baffling). Its downfall is the lack of 8 more valves. 170hp out of 1650cc* is respectable without a doubt. For a racing engine, I would look at a 4 valve setup. With that you can break 200hp. Not easily and not cheaply, but certainly doable.

*I wonder what the Derby's new power plant will do on the dyno. Programmable EFI, 16V, ITBs, pretty much exactly 1650cc, 11.5:1 compression and a redline of 7200.

[Nut124]

Steiny, yes, you are correct.

Obviously, there are many "better" engines available today. Back in the -70s and -80s the Fiat TC was special. Widely available and relatively cheap with good tuning potential. Not many similar 4-cyl engines back then, other than the Cosworth, which was expensive.

[maxm50]

Does anyone know if there is an actual ignition-cut rev limiter on the Bosch FI 2L Spiders? I'm scared to take mine beyond 5500 to find out until I get around to checking the valves...

[tima01864]

I have been trying to reach the 6000rpm limit. 83 2.liter, Large valves ported polished intake, 5/75 intake cam, Exhaust stock cam.
High compression piston 10:1.
Maybe it is the way I am driving the engine. Other than not revving to red line the engine is woke.

[18Fiatsandcounting]

So I'm not getting it. If you warm up your Fiat engine (whatever model year), put it in neutral, stomp on the gas, the engine should easily (repeat: easily) rev to 6000 rpm and beyond. If not, something is wrong with your engine.

In all the Fiats I've had, the only thing limiting the engine speed is me, not wishing to blow the engine. 6000 rpm = happiness . 6500 rpm = still happy. 7000 and above = OK, pushing things on a stock engine but just getting started on a race/performance engine.

-Bryan

[DaveA]

DaveA, you've fallen prey to automotive internet forum nonsense! Torque is NOT "how far you push the wall". That's determined by your momentum (mass x velocity), coefficient of restitution (ie. do you bounce off the wall or not), energy absorbed in the vehicle structure through material deformation in the crash, and mass of the wall. Among other things. But torque ain't one of the variables in that equation

Haha, love your comments!! To be honest Im hoping never to prove either of our explanations!

The twin cam is a dream of an engine and when you put it into context with others of it day - I build, race and rally Classic Mini’s, Mk2 Escorts and Mgb’s. Im a relatively new owner of the classic spyder (for my sins I own a 2019 124 Abarth too, great car). The difference in the technology from the MGB and the Fiat which first was manufactured within the decade, is unbelievable.

As others have said, with wilder cam’s, inlet and exhaust ports and valves (maybe even more of them!!), lightened and balanced components and a little more compression, I'm sure it could hit the dizzy 7k + heights, but I think the fuel injection in standard form would struggle with fuel supply. Even if that was addressed, the drivability would be affected.

Horses for course I think, some of the quickest point to point cars Ive driven didnt have the highest HP figures. I guess fiat thought that the 2.0 torque made it a hoot on those twisty back roads north of Turin.

But Id still love it to be able to spin up to 7k, maybe i cant have my cake and eat it!!

[18Fiatsandcounting]

Just a curiosity question here. I've heard people mention not being able to spin up their Fiat twin cams past 6000 or 7000 rpm or so. So if you put it in neutral, put a brick on the gas pedal, the engine just spins up to those rpms and hovers there?

I'm just asking because every Fiat that I've had would keep going up in rpm, until it was me who blinked first and let off the gas. I've never actually kept going because the engine showed no sign of slowing down and I didn't want to end up with a blown engine. If you believe the tach, the highest I ever got on my stock 1438cc was about 8000 rpm, and on the 2L, about 7000 rpm. Very briefly, usually because of missed shifts at redline. Admittedly, all my spiders except one were carbureted, and so I can't speak for fuel injection.

-Bryan

[SteinOnkel]

Does anyone know if there is an actual ignition-cut rev limiter on the Bosch FI 2L Spiders? I'm scared to take mine beyond 5500 to find out until I get around to checking the valves...

Why? Pretty sure even Dieselspider spins his engine faster than that

It's a solid motor - you can take it past 5500 all day, every day.
Here's some info on the L-Jet rev limiter from * ugh * rennlist: https://rennlist.com/forums/928-forum/3 ... miter.html

Probably the worst english speaking car forum. I want to take a shower now.