Tuning Max possible bhp

[Bigvtwin996]

I just wondered..... (not that I can see the point)
but, I have seen ohc heads and sequential gearboxes for our beloived 500s
800/840cc conversions Dino rods etc etc...
but just as a lets do it, what do you think the absolute max bhp you could get from a twin cyclinder 500 based engine..
not interested in reliability or driveability.. just te absilute max...

 

[the hobbler]

I just wondered..... (not that I can see the point)
but, I have seen ohc heads and sequential gearboxes for our beloived 500s
800/840cc conversions Dino rods etc etc...
but just as a lets do it, what do you think the absolute max bhp you could get from a twin cyclinder 500 based engine..
not interested in reliability or driveability.. just te absilute max...

Letus start with the largest engine "D'angelo Motori" make---a 1,000cc variant of the 500 engine--83 BHP, naturally aspirated on carbs. Put that onto Fuel-injection (Jenvey's?) and you could expect just over 90bhp. They do a 'twin over-head cam' version, but that is only 800cc. Go on a bit further, put a turbo onto the 1.0 litre engine and I expect close to 120 bhp would be available, but as to how long it would last is debateable.

 

[Bigvtwin996]

I thought 90-100 may be possible but over 100 would be an engieering feat, as you say but for how long....
I guess the weak lik would be the crank without a central bearing that would be flopping about.. even with the New Abarth ones...

 

[the hobbler]

If

I thought 90-100 may be possible but over 100 would be an engieering feat, as you say but for how long....
I guess the weak lik would be the crank without a central bearing that would be flopping about.. even with the New Abarth ones...

If you were going to the lengths required to chuck out that much power, it was because among other things, you have DEEP pockets! You would therefore have a special steel crank made for you---which would cost in excess of £2,000!

 

[Toshi 975]

I have lost contact with the guy now but a 126 owner developed his engine over a number of years to a 700cc turbo charged with Intercooler set up. Making & modifying many parts himself. On a rolling road test it put out 100hp + and that was not on full throttle. The weak point was the crankshaft when he bent one then snapped another. Last time I heard he was converting to a steel three bearing crank

 

[Bigvtwin996]

i have thought... in this day and age....
I have a mate who makes tooling for injection moulding, he has a CMC milling machine that is ultra accurate and does it's own tool changing and the final tooling basically polishes the metal so it is super smooth...
It can take huge chunks of Alluminium probably the size of a 500 Block, I guess it would be possible to CNC a 3 bearing block, and then for someone to machine a 3 bearing crank....

 

[the hobbler]

i have thought... in this day and age....
I have a mate who makes tooling for injection moulding, he has a CMC milling machine that is ultra accurate and does it's own tool changing and the final tooling basically polishes the metal so it is super smooth...
It can take huge chunks of Alluminium probably the size of a 500 Block, I guess it would be possible to CNC a 3 bearing block, and then for someone to machine a 3 bearing crank....

As Austin found out with the "7"---putting an extra bearing into a crank isn't always the answer. The Austin "7" 2-bearing crank is actually a stronger crank than the 3 bearing version----the reason? In the 3 bearing crank, the length of the crankshaft dictated a very narrow centre bearing---and that is where they normally break! Sure, the 2 bearing crank flexes (I believe about 1/16th of an inch at high revs), but a 2-bearing crank survived even the tuning of Colin Chapman (Lotus 3). I would have thought that the very short length of the 500/126 crank would suffer the same engineering conundrum.

 

[the hobbler]

As Austin found out with the "7"---putting an extra bearing into a crank isn't always the answer. The Austin "7" 2-bearing crank is actually a stronger crank than the 3 bearing version----the reason? In the 3 bearing crank, the length of the crankshaft dictated a very narrow centre bearing---and that is where they normally break! Sure, the 2 bearing crank flexes (I believe about 1/16th of an inch at high revs), but a 2-bearing crank survived even the tuning of Colin Chapman (Lotus 3). I would have thought that the very short length of the 500/126 crank would suffer the same engineering conundrum.

As a thought re. David's colleague with the ultra tuned 126----if you want a 126 to go REALLY fast, you take a leaf out of the Poles tuning-book---you stuff a Fiat 4-pot water-cooled engine (the Fiat "FIRE" engine) into the car's bum. The Poles do this conversion a lot----modified bell-housing and a "sky-hook" style engine mount at the rear of the car. The donor engines for this conversion are out of any of the cars that Fiat fitted the "Fire" engine into---then they tune it! Initially, the only way to know this conversion has been carried out is that the exhaust comes out the "wrong" side---the left side of the car.

 

[Goldnrust]

If you want to keep it to the original style 2 cylinder engine then, bottom end strength is going to be the limiting factor.

Lets say we're using that 1000cc capacity, and if you say you're going to replace the head with a modern style OHC 4 valve head, then you should have the breathing and detonation resistance of a modern engine. There's plenty of road going, every day reliable engines making 100hp/litre, think Honda K series. So if your 1 litre engine could have a head with those characteristics and the right cam it should be able to make 100hp. If you venture into the world of motorbikes, then if you can rev high enough there are bikes you can walking into a show room today making 200hp/litre.

Once you add forced induction to that, just think the modern standard Abarth 500 engines will do 250hp with the right turbo, so thats 180hp/litre. And thats a road going engine that will do thousands of miles and have sensible service intervals. Nissan skylines and Toyota Supras can be modified to over 1000hp, so we are talking 300hp/litre and more.

So when you look at it that way, the real limit is not the top end or the breathing. The issue is in the bottom end strength, which as mentioned by @the hobbler, is not always an easy thing to fix as there can be unexpected consequences, and the limit of how much heat the air cooled engine can dissipate.

Not to say you can't make your own bottom end, or do a water cooled conversion, but when does it stop being a 500 engine, and when would you be better off, again as @the hobbler mentions, just bolting a different engine in!

Interesting to hear your story @Toshi 975 of the turbo 126. When the crank design means revving high like a motorbike is not an option to make power, then forced induction does seem the obvious route. When you look at engines like this: https://www.dangelomotori.it/prodot...n-testa-per-fiat-500-f-l-r-e-fiat-126-depoca/

€12k of OHC converted race engine, ,making 65-70hp. To make 100hp with the turbo is a good chunk faster than that! And in theory could be made much more 'usable' and tame than the 700cc racing engine would be.

These are all dangerous thoughts on cold dark winters nights, especially when I've got a good chunk of the parts I'd need to turbo my 500 sat in my shed...

 

[the hobbler]

As Austin found out with the "7"---putting an extra bearing into a crank isn't always the answer. The Austin "7" 2-bearing crank is actually a stronger crank than the 3 bearing version----the reason? In the 3 bearing crank, the length of the crankshaft dictated a very narrow centre bearing---and that is where they normally break! Sure, the 2 bearing crank flexes (I believe about 1/16th of an inch at high revs), but a 2-bearing crank survived even the tuning of Colin Chapman (Lotus 3). I would have thought that the very short length of the 500/126 crank would suffer the same engineering conundrum.

As a thought re. David's colleague with the ultra tuned 126----if you want a 126 to go REALLY fast, you take a leaf out of the Poles tuning-book---you stuff a Fiat 4-pot water-cooled engine into the car's bum. The Polesdo this conversion a lot--modified bell-housing and a "sky-hook" sty;eengine mount at the rear of the car. The donor engines for this conversion are out of 'Pandas'

If you want to keep it to the original style 2 cylinder engine then, bottom end strength is going to be the limiting factor.

Lets say we're using that 1000cc capacity, and if you say you're going to replace the head with a modern style OHC 4 valve head, then you should have the breathing and detonation resistance of a modern engine. There's plenty of road going, every day reliable engines making 100hp/litre, think Honda K series. So if your 1 litre engine could have a head with those characteristics and the right cam it should be able to make 100hp. If you venture into the world of motorbikes, then if you can rev high enough there are bikes you can walking into a show room today making 200hp/litre.

Once you add forced induction to that, just think the modern standard Abarth 500 engines will do 250hp with the right turbo, so thats 180hp/litre. And thats a road going engine that will do thousands of miles and have sensible service intervals. Nissan skylines and Toyota Supras can be modified to over 1000hp, so we are talking 300hp/litre and more.

So when you look at it that way, the real limit is not the top end or the breathing. The issue is in the bottom end strength, which as mentioned by @the hobbler, is not always an easy thing to fix as there can be unexpected consequences, and the limit of how much heat the air cooled engine can dissipate.

Not to say you can't make your own bottom end, or do a water cooled conversion, but when does it stop being a 500 engine, and when would you be better off, again as @the hobbler mentions, just bolting a different engine in!

Interesting to hear your story @Toshi 975 of the turbo 126. When the crank design means revving high like a motorbike is not an option to make power, then forced induction does seem the obvious route. When you look at engines like this: https://www.dangelomotori.it/prodot...n-testa-per-fiat-500-f-l-r-e-fiat-126-depoca/

€12k of OHC converted race engine, ,making 65-70hp. To make 100hp with the turbo is a good chunk faster than that! And in theory could be made much more 'usable' and tame than the 700cc racing engine would be.

These are all dangerous thoughts on cold dark winters nights, especially when I've got a good chunk of the parts I'd need to turbo my 500 sat in my shed...

Very interesting engine, and so it ruddy well should be at E12,000+! I have looked at this engine before, and one thing that crossed my mind is---"how long will that cam-belt last"? Running that close to an exhaust pipe (the belt runs both sides of the exhaust pipe) which has only just exited the cylinder-head I would have thought could lead to trouble---the belt is going to exposed to a LOT of heat

 

[MalcolmfromMoffat]

That cylinder head on the linked engine, I don’t see it in the lists of parts they offer? There’s another very nicely cast cylinder head in their range which I think I’d choose over a belt driven overhead cam version but I’d be interested to hear opinion or experience on these fancy looking billet cylinder heads.

I see the attraction of turbocharging but can’t help but think it’s already very hot in there!

Like any highly engineered component a billet crank would be expensive, very expensive quite possibly but would it cure the inability to sustain high rpm? Is that maybe just the nature of a parallel twin?

 

[Goldnrust]

I presume @the hobbler that as that engine is essentially a purely racing engine, you'd be inspecting the belt after every race and possibly change it a couple of times a season anyway? I guess it's a compromise to get the gains in valve geometry afforded by OHC.

Billet cranks do make a big difference, from what I've read, @MalcolmfromMoffat. Stock cranks can't rev past around 6,000rpm safely, engines like the one linked in my previous post have a billet crank and can be taken to 8,000rpm or more even. Modern motorbikes with parallel twin engines can rev past 11,000 rpm without destroying themselves, so it's not necessarily a parallel twin issue but it could still be a crank design issue. I believe the motorbikes have switched to a 270° crank, rather than the 360° crank that our Fiats use, I don't know if that helps the balance or is more to do with how the power is applied to the road, which I know is a consideration in racing motorcycle design. Not to get too far off track, but some of the modern super bikes use different firing orders and timings to change the gaps between combustion events, as it changes how the rear tyre can fight for traction when the bike is exiting corners.

In dream land, with a custom cam shaft and crank, no reason you couldn't build a 270° Fiat engine... Again you'd have to question why bother though! Things like that race engine are developed to meet race rules, that stipulate things like 'must use stock crank case'. If you're building something outside of the rules, putting the motorbike engine in would be mechanically easier than re-working the original architecture.

 

[Bigvtwin996]

I think the "why bother" is my attitue to be honest, if I wanted something small and quick I'd spend a couple of £k on a BMW mini or even a modern fiat 500...
For example I don't get the obsession with trying to fit a porsche engine in a VW van "to make it quick" but it's a brick and will always handle like a brick....
A fiat 500 has a crumple zone of 2 sheets of 1.5mm steel so you are not going to get out....
However I do like what Allen Millyard does when he adds a couple of extra cylinders to a motorbike as the engineering is superb when it looks like it left he factory that way...
for me my max 52mph is more than enough from my 500.

i only asked the question because someone asked me...

 

[Goldnrust]

I think the 'why bother' is often because for some the hobby they enjoy is the problem solving and engineering behind making it work. Often this is more important than the driving even.

The other thing is that when you spend time with other enthusiasts it can become a little tribal and so to be the coolest guy in the club because you have the fastest, or most unusual, or shiniest, or most original, etc... becomes the goal.

As you say, any modern performance car would run rings round even a heavily modified 500. The experience of driving the two cars would be vastly different though!

 

[Bleeding Knuckles]

OOOO I do like dark thoughts on a winters night !!!!! The fun (if you can call it that!) with the classic 500 is the solving of problems that modern cars don't have. Driving my car hard is fun - But your brain needs to be way ahead of things to make sure you stop or manoeuvre in time to avoid a coming together and when the rear end decides it's swing axel time !!!!! I have read of a polish chap who frequently rally's a 126, he fitted a wild engine of some 700cc but took time to help the crankcase and bottom end survive the onslaught. He fitted a bracing plate of alloy between the crankcase and sump mating faces with suitable cutouts to enable engine rotation and then welded alloy webs all over the crankcase and sump to simply brace the assembly, I suppose this engineering work helped stop distortion at high rpm but I don't know if he used a billet crank. Funny though I never did hear if it all worked and for how long if it did????
Ian.