Technical RPM of tuned engines.

fiat500

Patinated Peter
Joined
Mar 7, 2005
Messages
5,820
Location
Nairn
I'm aware that the 500 engine spins pretty quickly at any given speed and, to preserve it, that's why I generally stick at around 50 mph.
I know that tuning an engine is a pleasure in it itself and that top speed is not the only aim when increasing performance. But I presume that without gearing modifications, a tuned 500 must really scream when hurtling along at the speed limit.
Although, with my own car, that would freak me out and make the whole job pointless, does anyone have any videos of their car at full belt?
 

AndrewHarvey

New member
Joined
Jan 17, 2015
Messages
1,471
Original engines rev to 4700
Balanced and lightened to 6500
Steel cranked to 8000!
Mine has five speed and higher final drive diff
We will find out what it's like soon....?
 

Toshi 975

Well-known member
Joined
Jun 30, 2009
Messages
1,427
No videos I am afraid but my 499ccs 500L engine with modified head, 28imb carb, late 126 camshaft and sport exhaust would peak out at 6,500 rpm. I found out the hard way that the original fan will not take those revs as it rotates 50% faster than the crank so getting on towards 10,000 rpm. My fan gave out at max revs and some parts pierced the steel cooling housing. Alloy or composite fans now fitted. Yet to test my 662ccs engine with head mods, Abarth cam, twin choke Weber and exhaust upgrade but the guy I got the original Abarth camshaft from used to race 500s back in the 70s. He told me that he had an engine with a roller bearing crankshaft set up that would rev to 10,000 rpm.
 
OP
OP
fiat500

fiat500

Patinated Peter
Joined
Mar 7, 2005
Messages
5,820
Location
Nairn
my 499ccs 500L engine with modified head, 28imb carb, late 126 camshaft and sport exhaust would peak out at 6,500 rpm.

So is that what you would call mildly tuned?..sounds an interesting and relatively straighforward way to approach it.
But with the extra top speed wouldn't that mean the thing would be screaming? (delightfully of course).
 
Joined
Dec 27, 2014
Messages
979
Location
Ripon
Hi All,
I'm running 704cc, slightly modified Panda 30 head with weber 30 DGF and a 75/35-35/75 cam with a large bore exhaust. The rig pulls easily to 4000rpm showing just over 90kph (it sings a little at that speed!) - it's not been on the rolling road yet, but I have a BIS gearbox with the high ratio diff that will be fitted soon to make things gentler on the ear (thanks Tom) not too sure what to push the rpm to??????? but I think that excursions beyond 5500rpm will be the exception and not the rule!!

Ian.
 
Joined
Sep 22, 2010
Messages
780
Location
Cambridge
I'll look to take a video next time I'm out. It's a lightly reworked 660cc and a 9/39 synchro gearbox. IIRC it does about 4,000 rpm at ~60mph.

cheers, Steve
 
Joined
Dec 27, 2014
Messages
979
Location
Ripon
Thinking of RPM and tuned engines and was wondering if I have heard right, the 126BIS crankshaft is better (stronger?) at taking higher revs than the standard item? Anyone care to comment on this????

Ian.
 
Joined
Sep 22, 2010
Messages
780
Location
Cambridge
Sorry Peter, no video as I was on my own and no way to rig up phone etc. However I did note revs at various speeds in top, 4th, gear...

30mph/50kph ~2,000 rpm
40/60 ~ 2,300
50/80 ~ 3,000
60/90 ~ 3,600

So 50mph is a relatively relaxed cruise hovering around 3,000 rpm.

It's a lightly reworked 660cc and a 9/39 synchro gearbox.

cheers, Steve
 
OP
OP
fiat500

fiat500

Patinated Peter
Joined
Mar 7, 2005
Messages
5,820
Location
Nairn
Thanks Steve, that's bit less across the range than I imagined; so good news.
Maybe I just got too used to driving a diesel.
I've always found it hard to believe that all those little components are capable of doing what they do at high speeds; particularly so when they have all been in my hands at some point.:eek:
I've just put a new piston and barrel in my chainsaw and that will be revving at over 10,000!
I'll worry less about putting my foot down; I'm sure i could cruise at 60mph if I wanted to.
 

the hobbler

Well-known member
Joined
Jul 25, 2012
Messages
3,325
Going by Steve's observations, it would seem that with the BIS final-drive fitted (9/39) the car will be geared for 15mph per 1,000rpm (30mph at 2,000rpm), although this does seem to 'wander' a bit as the speed increases
(?). With your final -drive (which I think is 8/39), I reckon that you will be quite safe at 60mph---probably about 4,200rpm. Maybe the mathematically endowed amongst the forum members would try and work that one out? I have a standard 126 box (8/39 final-drive)in my 500 and normally cruise at just over 60, traffic and law allowing!
thumb.gif
smile.gif
 
Joined
Sep 22, 2010
Messages
780
Location
Cambridge
The wander is probably more from the cheap rev counter and me trying to read it. ;)

Looking at the revs for 40,50 & 60 they are pretty linear, and extrapolating these for 30 it should be ~1800. It could have been as I was concentrating on the higher speeds more, and as I say, the gauge is not that accurate.

cheers, Steve
 
Top