Tuning Stroker Crank

[dangfiat]

Hi Fiat Modding Folks!

I have a 652 currently and about to tear it down to rebuild (staying 77mm bore, 40/80 cam, 32/28 FZD. port & polish the head).

Question: I see there's 76mm cranks available... Debating building a stroker to get to 700(ish)cc. The torque from the long stroke might be interesting. Has anyone here built a 77mm bore x 76mm stroke motor? How's the reliability? How's the drivability?

I'm wanting a fairly reliable daily, but the hot rodder in me can't stop thinking "just a little bit more!"

Thanks all,
Daniel

 

[the hobbler]

Hi Fiat Modding Folks!

I have a 652 currently and about to tear it down to rebuild (staying 77mm bore, 40/80 cam, 32/28 FZD. port & polish the head).

Question: I see there's 76mm cranks available... Debating building a stroker to get to 700(ish)cc. The torque from the long stroke might be interesting. Has anyone here built a 77mm bore x 76mm stroke motor? How's the reliability? How's the drivability?

I'm wanting a fairly reliable daily, but the hot rodder in me can't stop thinking "just a little bit more!"

Thanks all,
Daniel

The honest answer to your question is----if it was good enough for Abarth, it should be OK for you! Due to the machining limitations of the 500 crankcase, as against the 126 crankcase, Abarth couldn't go too big with the barrels that he fitted. So, in order to get to "695" (or to be exact, 689.548cc), he used a bore of 76mm and a stroke of-----76mm! The maximum 'oversize' that his barrels could take was +0.55mm, which gave a capacity of 699.570cc. Maximum power was 38bhp at 5,000rpm for the "SS" variant. I would have thought that if you don't go above the 77mm bore, you should have no problems, if driven sensibly.

 

[Goldnrust]

No help with the crank, but just as a slight word of caution, might be worth speaking to @Bounding Bambino , as I think his recently built set up uses the same cam, carb, mild head work combination and I have a feeling he felt it wasn’t quite balanced right as a package?

He was using a stock crank and 540cc kit though, would the stroke crank also allow you to rev the engine harder than stock?

 

[the hobbler]

No help with the crank, but just as a slight word of caution, might be worth speaking to @boundingbambino, as I think his recently built set up uses the same cam, carb, mild head work combination and I have a feeling he felt it wasn’t quite balanced right as a package?

He was using a stock crank and 540cc kit though, would the stroke crank also allow you to rev the engine harder than stock?

Jacques (Bounding Bambino) wasn't using a FZD carb in his set-up (I know because he got the carb he DID use off me!). I can see no problem with the specifications that you have desribed. Balance IS a problem with well tuned 500/126 engines and just to add to the problem (even in the UK), VERY few people are able to balance 2-cylinder engines. In the UK we have "Vibration Free" in Bicester. If you can't find somebody who really DOES know how to balance a 2-cylinder engine (as against somebody who THINKS that they know how to do the job) my suggestion would be to get the flywheel balanced (and possibly lightened--4-1/2kg minimum for a road-use-only engine) and make sure that the bits that go up and down are of equal weights

 

[Bounding Bambino]

Bingo. yes right now im running a 70x70 engine. Stock crank stroke, forged con-rods, but 540cc cylinders which is 70mm bore Which makes it a square engine. Performance has been somewhat inconsistent, but im working thru it, i haven't given up the effort on trying to wrangle in the weber ich 32 carb. I believe my issue is, that the carb is slightly too large for the engine displacement, and causing me grief with tuning.I do have a few plan B's and C's come this spring.

The 40/80 cam, does seems to really liven up past 3000 rpm, and the engine really wants to rev. But it does seem to somewhat fall flat on its face below 3000. Having a lower displacement for such a sporty cam i believe isn't doing me much of a favor. Having a larger displacement will definitely help in keeping intake flow velocities high, and hopefully smooth out these weird power bands i am having. In a few months once i have the time, i will have flow bench values for all to see how a stock head compares to a modified head and so on. We can then make conclusions from there on in.

Gear ratios also make a big difference in drive ability. I always found that i was running out of gears on the stock setup, mine being iirc 8/41 final ratio.. I just ordered a 9/39 final drive to help lengthen first gear, and drop cruising rpm's without having to go 5 speed yet. I wont say the car is a dog, it does get up and go somewhat over a stock 500. But having driven Toms car for a short sprint with this massaged peppy 594cc engine even with 2 of us in the car, its night and day, i still have work to do on mine to get remotely close lol.

In the past i might have mentioned that i had plans for a much larger engine. I have a few 126 engine blocks and "planning" to do a big bore stroker engine. 82mm bore. with either a 76 or 80mm stroke crank. Unfortunately trying to hunt down the crank has been a journey. Yes they do exist, but options are limited, and info/feedback about them is sparse. Balancing is also another aspect/adventure. In Europe and the UK it might not be very difficult to find someone who can balance a parallel twin crank properly, in North America no one has a clue about them. The real trick is finding someone who knows what proper "balance factor" to use on these engines. Technically they are balanced to a desired rpm range and use case. And you need to already have the piston, rings, con-rods already to weigh and do accruate calculations.

I am trying to hunt down a forged 76 or 80 mm stroke crank for my 2nd engine. With that for now, a twin duct modified panda 30 head with larger valves will be the go too for its first variant.

To close, i would say the trade off with a longer stroke is peak RPM. But that tradeoff also is based upon the crank strength, and "balance". I would assume those insane high powered hill climb 500's that are revving to the moon (7000+rpm), are more then likely running a variant of a stroker crank and big bore kit, and those engine are absolutely singing up the Italian hillsides. A high revving 500 engine is definitely a treat with the proper exhaust

 

[the hobbler]

Bingo. yes right now im running a 70x70 engine. Stock crank stroke, forged con-rods, but 540cc cylinders which is 70mm bore Which makes it a square engine. Performance has been somewhat inconsistent, but im working thru it, i haven't given up the effort on trying to wrangle in the weber ich 32 carb. I believe my issue is, that the carb is slightly too large for the engine displacement, and causing me grief with tuning.I do have a few plan B's and C's come this spring.

The 40/80 cam, does seems to really liven up past 3000 rpm, and the engine really wants to rev. But it does seem to somewhat fall flat on its face below 3000. Having a lower displacement for such a sporty cam i believe isn't doing me much of a favor. Having a larger displacement will definitely help in keeping intake flow velocities high, and hopefully smooth out these weird power bands i am having. In a few months once i have the time, i will have flow bench values for all to see how a stock head compares to a modified head and so on. We can then make conclusions from there on in.

Gear ratios also make a big difference in drive ability. I always found that i was running out of gears on the stock setup, mine being iirc 8/41 final ratio.. I just ordered a 9/39 final drive to help lengthen first gear, and drop cruising rpm's without having to go 5 speed yet. I wont say the car is a dog, it does get up and go somewhat over a stock 500. But having driven Toms car for a short sprint with this massaged peppy 594cc engine even with 2 of us in the car, its night and day, i still have work to do on mine to get remotely close lol.

In the past i might have mentioned that i had plans for a much larger engine. I have a few 126 engine blocks and "planning" to do a big bore stroker engine. 82mm bore. with either a 76 or 80mm stroke crank. Unfortunately trying to hunt down the crank has been a journey. Yes they do exist, but options are limited, and info/feedback about them is sparse. Balancing is also another aspect/adventure. In Europe and the UK it might not be very difficult to find someone who can balance a parallel twin crank properly, in North America no one has a clue about them. The real trick is finding someone who knows what proper "balance factor" to use on these engines. Technically they are balanced to a desired rpm range and use case. And you need to already have the piston, rings, con-rods already to weigh and do accruate calculations.

I am trying to hunt down a forged 76 or 80 mm stroke crank for my 2nd engine. With that for now, a twin duct modified panda 30 head with larger valves will be the go too for its first variant.

To close, i would say the trade off with a longer stroke is peak RPM. But that tradeoff also is based upon the crank strength, and "balance". I would assume those insane high powered hill climb 500's that are revving to the moon (7000+rpm), are more then likely running a variant of a stroker crank and big bore kit, and those engine are absolutely singing up the Italian hillsides. A high revving 500 engine is definitely a treat with the proper exhaust

Thank you for your comments regarding my engine, but I have to confess---it is a 659cc engine (652 +0,4mm over-bore). I agree with what you are saying with regard to the 40/80/80/40 cam that you have in your engine---possibly a tad TOO wild for the 540cc. Can you let me know what choke size you have in your 32 ICH carb----I will look and see if I can lay my hands on a '32' with a smaller choke size for you

 

[dangfiat]

Thanks all for the replies, one other question would be: is the 32//28 FZD enough carb for a 707cc engine with a 40/80 cam? Of course I'd enlarge the valves/ports (might just buy a D'Angelo head - they seem to know what they're doing)

I know Tom has one on his 652, just looks like all the 700's and up go to the 40DCOE Webber - which seems like too much carb

Thanks for the input and advice, As always it's much appreciated

Daniel

 

[the hobbler]

Thanks all for the replies, one other question would be: is the 32//28 FZD enough carb for a 707cc engine with a 40/80 cam? Of course I'd enlarge the valves/ports (might just buy a D'Angelo head - they seem to know what they're doing)

I know Tom has one on his 652, just looks like all the 700's and up go to the 40DCOE Webber - which seems like too much carb

Thanks for the input and advice, As always it's much appreciated

Daniel

Hi Daniel;
I honestly can't see any problem with putting a FZD 32/28 onto a 700cc engine. As I mentioned, my engine has been slightly enlarged to 659cc. (with a pair pf BORGO pistons, as per Abarth factory original---what a find!) and I have no hesitation/poor running problem with the 32/28. For a 'road-use-only' in the UK (and ESPECIALLY up here in Wales!) the big side-draught Webers are just too much---combined with the problem that few people (in the UK) know how to set them upon such a small engine. If somebody really does want a twin-side-draught carb on their 500/126, the smaller and lighter, Solex (32 or35 PHH) or Dellorto (DHLB 35) would be a more sensible way to go---but I still think that the Dellorto FZDis a very good and sensible carb

 

[Bleeding Knuckles]

Hi Daniel, welcome to the slippery slope of modding the 500/126 engine!!! My first attempt at modding a 500/126 hybrid was using a Panda head with standard valves but a great deal of material was removed during the porting and polishing, the final head capacity was 35.7cc giving a C/R of 9.8:1. Valve springs too were standard. Cam is a 35/75-75/35 with standard timing gear and followers. After a slight rebore we ended up with 712.6cc using 80.5mm flat top pistons from Italy. But, I elected to use a Solex 35phhe 10 from a citroen visa as my carb. After a long trial and error period the final rolling road figures gave 36.2bhp at the flywheel at only 5000rpm. My main point here is that a twin choke carb will work if you limit the venturi to around 32mm - the Solex is a fixed venturi carb with two at 31mm each, A smaller Solex (32phh) has venturi of 29mm each. The engine tune must be sufficient to draw enough air during operation. Don't discount the weber 40 DCOE on these engines as the choke may be 40mm BUT you can interchange the removable venturi down to 24mm IIRC. The weber is big and heavy and must be supported, the Solex are smaller and lighter but can be challenging to setup. People in Italy have long long experience in getting their engines to sing at high rpm, but they don't have to drive them home or on the road, they just rebuild them!!!!
Ian.

 

[Bounding Bambino]

Of course I'd enlarge the valves/ports (might just buy a D'Angelo head

So. ive spent a fair bit of time looking and researching the progression of upgrades and performance for these cars. The D'angelo head is honesty very intriguing.

Im assuming your talking about the lavazza split head.. https://www.dangelomotori.it/en/pro...-head-complete-with-new-lavazza-tappet-cover/

Ive spent a few long nights browsing the Italian fiat 500 forum, trying to discover what secrets they have hidden there.
Ive come to the general conclusion that typically head modifications progress as follows:

-Std500 head
-Std 500 head with porting
-Std 500 head with porting and valve size increase

-std Panda 30 head with twin duct
-std Panda 30 head with port/polish, and maybe valve size increase.

Then racers start to get creative:
-Std 500 head that has been machined to accept a dual intake
-panda 30 head with significant port machining

The most extreme versions are some folks who have made fully custom dual overhead cams for these little engines.

The lavazza head seems to take all these design trials and tests into a complete package if you want to go near full race.
Obviously these heads come with a price, but it would be nice to dream, who knows
Definitely looks like a well designed pc of kit.

With all of this said, i am disappointed in the fact that there are absolutely no test values or flow graphs for anything sold on the market for the 500. To me this is odd and uncommon, as most companies that sell aftermarket heads/cams in the North American car market typically have flow charts and actual dyno results showing some form of % increase. Obviously there's a lot of different customization options one could have as a completed engine for the 500 (displacement, cams, exhaust etc), but i wish the market had some sort of baseline comparison for those of us shopping for aftermarket goodies with actual comparative values, especially for the $$$ stuff like the lavazza head... nearly 2000€ but no real figures, like ??..

Im in the process of building a flow bench, and i have a stock 500 head, along with a ported one, one with larger valves and a few panda 30 heads (stock and modified), that i would like to bench test and share the research on the forum for folks to reference to. The italian forum likes to keep all this info hidden unfortunetly from what i could see.

 

[the hobbler]

So. ive spent a fair bit of time looking and researching the progression of upgrades and performance for these cars. The D'angelo head is honesty very intriguing.

Im assuming your talking about the lavazza split head.. https://www.dangelomotori.it/en/pro...-head-complete-with-new-lavazza-tappet-cover/

Ive spent a few long nights browsing the Italian fiat 500 forum, trying to discover what secrets they have hidden there.
Ive come to the general conclusion that typically head modifications progress as follows:

-Std500 head
-Std 500 head with porting
-Std 500 head with porting and valve size increase

-std Panda 30 head with twin duct
-std Panda 30 head with port/polish, and maybe valve size increase.

Then racers start to get creative:
-Std 500 head that has been machined to accept a dual intake
-panda 30 head with significant port machining
View attachment 439057

View attachment 439055
View attachment 439059

View attachment 439056

The most extreme versions are some folks who have made fully custom dual overhead cams for these little engines.

The lavazza head seems to take all these design trials and tests into a complete package if you want to go near full race.
Obviously these heads come with a price, but it would be nice to dream, who knows
Definitely looks like a well designed pc of kit.
View attachment 439058

The reason that they re-engineer these heads the way that they do is that technically, the Panda30 inlet ports are too close together. When you look at the (for example Lavazza) head,you will see that the inlet tract is a straight line down to the inlet valve--which is usually a fair bit bigger than standard.

 

[dangfiat]

@Bleeding Knuckles Thanks for this. I'm not anti twin choke, it's just that I have a 32/28 FZD already and would probably give that a try first. I know from my Riley, a 38mm (1.5") SU was the best option. Gave a decent 65hp with a big valve head and 266 cam. This was a 998cc 4-cylinder

That being said, I am worried about being a bit under-carbed. Will see

@Bounding Bambino I'm more looking for the single intake head that's been ported/polished and with 36/31 valves from D'Angelo I think it's only 1000euro. I'm not trying to make a race motor, I'm going for something that I can reasonably daily. If I can hit ~40ish hp I'll be happy. Although I am VERY intrigued by building an almost square 77bore x 76stroke motor ! I think I can make something like that reliable and quick(ish), with the longer stroke moving the torque curve lower down.

Thanks everyone, it's a fun debate! I'll keep putting items in and out of the cart... hehehe

 

[the hobbler]

@Bleeding Knuckles Thanks for this. I'm not anti twin choke, it's just that I have a 32/28 FZD already and would probably give that a try first. I know from my Riley, a 38mm (1.5") SU was the best option. Gave a decent 65hp with a big valve head and 266 cam. This was a 998cc 4-cylinder

That being said, I am worried about being a bit under-carbed. Will see

@Bounding Bambino I'm more looking for the single intake head that's been ported/polished and with 36/31 valves from D'Angelo I think it's only 1000euro. I'm not trying to make a race motor, I'm going for something that I can reasonably daily. If I can hit ~40ish hp I'll be happy. Although I am VERY intrigued by building an almost square 77bore x 76stroke motor ! I think I can make something like that reliable and quick(ish), with the longer stroke moving the torque curve lower down.

Thanks everyone, it's a fun debate! I'll keep putting items in and out of the cart... hehehe

If you Do fit the 32/28, drop me a line ( [email protected] ) and I will let you know all the jet settings in my 32/28. I realise that my engine (659cc)is a shade smaller, but it will give you a good "base-line" to start with. One thing that I came to realise with the FZD; you do not want to go too big on the 'pump' jet (aka, the accelerator jet). Sure, it will run fine when cold, but will bog-down in a most embarressing way when hot! Secondly, keep a carefull log of WHAT jet you fit, and WHEN you fit it---that way you can always change something, knowing what you have got in the carb and how it is working. The FZD is a nice simple carb, that works well, is light enough that it does not need any support, and stays in tune. I think that the FZD will give you few problems and be a good choice.

 

[Bleeding Knuckles]

Hi Daniel, All Appreciated, but the one thing I have noticed is that most if not all of the adverts and sales worldwide seem to concentrate on modifications
to the head and timing gear (cam) at the cost of the crankshaft/bottom end of the engine. If you want to change the pistons and rods for something more wild it's a problem sourcing the parts let alone the cost!!!!!!!!! Don't get me started on the cost of a billet crankshaft from Italy, they are only available to the deepest of pockets and you really do need to consider the final use of the engine before going all in????? We can only scan through the pages on-line and wish
Ian.

 

[Goldnrust]

Sorry to go off topic slightly, but that's some helpful research there @Bounding Bambino. Thank you for sharing.

I think it's interesting that with 500s the move to twin port heads happens at a relatively low tune, I guess the once availability of Panda30 heads drove that.

Classic Mini's also share the siamese intake ports, and they can get close to 100hp/litre while retaining the 1 port for 2 cylinders intake design. If we could match that from a 500 engine, then you'd be seeing 60-65hp from a 650cc.

Not to say they can't get more from custom individual intake runner heads, but my question to myself is how much does the single intake port really limit power in the 500 engine, or are other factors at play? e.g. the crank that limited high RPM.

Also learning from the Mini guys, another potential carb option could be a 'split' 40 DCOE. Where on a single port engine you can use just one choke of the twin choke carb, with the other one deactivated. Then you have all the tuning available for those carbs, things like the wide range of Venturi sizes, but with a single 40mm throttle plate more suited to our small engines than twin 40mm plates. Again something I've wondered about while idly considering options for more power from my own 500.

 

[the hobbler]

Sorry to go off topic slightly, but that's some helpful research there @Bounding Bambino. Thank you for sharing.

I think it's interesting that with 500s the move to twin port heads happens at a relatively low tune, I guess the once availability of Panda30 heads drove that.

Classic Mini's also share the siamese intake ports, and they can get close to 100hp/litre while retaining the 1 port for 2 cylinders intake design. If we could match that from a 500 engine, then you'd be seeing 60-65hp from a 650cc.

Not to say they can't get more from custom individual intake runner heads, but my question to myself is how much does the single intake port really limit power in the 500 engine, or are other factors at play? e.g. the crank that limited high RPM.

Also learning from the Mini guys, another potential carb option could be a 'split' 40 DCOE. Where on a single port engine you can use just one choke of the twin choke carb, with the other one deactivated. Then you have all the tuning available for those carbs, things like the wide range of Venturi sizes, but with a single 40mm throttle plate more suited to our small engines than twin 40mm plates. Again something I've wondered about while idly considering options for more power from my own 500.

Goldenrust----I competely agree with you, it is possible to get 100bhp per litre AT THE FLYWHEEL with 'siamised' inlet ports. However, the big difference between the engines that achieve this and the 500/126 family is---revebility. Unless one fits a steel crank into a 500/126 crankcase, 6,000rpm must be the maximum that one regularly uses. The BMC, Imp and Ford engines (to name but 3) that achieve the 100 bhp per litre level are ALL engines that one can rev the nuts off! Ford and Imp in particular regularly have in excess of 10,000rpm as their limit. In my own 'field of interest', the Abarth 850tcr (based on the Fiat 600) engine used to be regularly taken to 8,000rpm---and that was in the mid-sixties!
When I was in my 'yoof,' the Formula 3 engines were 1,000cc and limited to a single choke of carburettor. The normal trick in those days was to use a twin down-draught Weber carb , with one choke blanked off. The top F3 engines of that period all developed in excess of 100bhp (at the flywheel)---and that was with a restrictor in the inlet tract as well! No, the main restrictor of economical big bhp from the 500/126 family of engines is its inability to be highlyrevved.

 

[Toshi 975]

Seems that the Fiat 126 Bis crankshaft has been overlooked again. Said to be more stable and stronger at higher revs. The profile is also very similar to some that cost four figures. I have fitted a few of these on engine builds in 499, 594 and 650cc crankcases and not heard of one breaking yet.

 

[Goldnrust]

Is the BIS crank a direct swap @Toshi 975 ?

Or are there other mods that must be done to make it work?

 

[the hobbler]

Is the BIS crank a direct swap @Toshi 975 ?

Or are there other mods that must be done to make it work?

The BIS crank is a straight 'swap'. I am in the process of building a '595' engine for my friend in Italy, and as I had both a '126' crank and a 'BIS' crank available, I asked him which he would prefer to have fitted. The answer, after consulting with the experts in his local Cinquecento club was---the BIS crank. This surprised me as I had been led to believe, by leading Fiat and Abarth people in this country, that the BIS was so called because it was aBISmal! I wish I had known that the BIS was the better crank---I would have fitted into the '695' engine that I am building (and have had expensively balanced!)

 

[Bleeding Knuckles]

I agree with Tom, the BIS crank is a good alternative and I have used one in my 'Hot' engine, you can see from the pic that it has been extensively lightened during the balancing process and I thought that they would have to add weight to the crank to achieve good balance!!!! It is probably due to the use of lightweight H pattern alloy conrods even though the flywheel is some 4.5kg, the pistons are standard 80mm BIS with standard compression height and three rings. The use of ARP 2000 bolts was advised by my engine man. The only slight drawback is that with a 40/80-80/40 cam the tickover is lumpy below 1200rpm but overall the engine response is quick. Don't forget to weld the crank core plugs if you are going to use high revs as they tend to pop out - guess how I know that!!!!!!!!!!!!
Ian.