Fiat Uno 1580 SOHC competition engine prep

[andy97]

Hi Guy

I am about to try to get a 1580 SOHC engine from a Fiat Tipo prepared and installed in my race Fiat Uno (to replace the one I blew up at Brands Hatch earlier in the year!). The car is a club racing car with which I compete in the 1300-1600 2valve per cylinder class of the Classic Sports Car Club's "Tin Tops" series of 40 min "mini enduro" races for 1 or 2 drivers. The car is the ex Neil Smith Auto-Italia championship winning car from 2002 which is light and stiff and handles extremely well.

The "new" engine will retain its original bore/stroke (86.4/ 67.4) but I intend to fit the following valves:
inlet - 39.5, exhaust - 33.0 (originally Inlet of 39.5 and exhaust of 31.0). (These are bigger valves than on the head that came off the old 1372 cc engine which were 36 & 33 and seem to be the max that will fit)

The existing inlet/exhaust port size is 29/30mm and 27/28mm - seem to be slightly oval in shape, hence the two different diameters - and I have been advised elsewhere (!) to open up the inlet ports to about 35-36mm and 30mm on the exhaust and de-shroud the area around the valves. You mentioned 32-31 mm ports so I am wondering whether the bigger ports recommended are desirable or even possible.

The engine will be refitted with my Weber Twin 40s (not sure of choke sizes) and the FT9 Kent Cam from the original race engine. I have spoken to Kent Cams and they advise that the FT9 was a race spec cam designed to operate in a 3-7000rpm power band. It is a 52/82 82/52 cam with 314 deg duration, lift = 441 thou, full lift posn = 105 deg and valve clearance of 8 thou on inlet and exhaust (cold).

I am hoping for a CR of about 11:1 and may have to have valve pockets cut in the existing pistons.

I am also considering fitting the engine with a PBS windage tray which i have acquired.

I'd appreciate your comments on this spec.

I know that you are not comfortable with talking about budgets but I will say that the budget isn't huge - hence I am happy to have an engine which is affordable and to an OK spec rather than have to spend a lot of money to build the ultimate, and properly optimised engine.

I am afraid that I am not capable of doing the work myself so I am farming the work out.

thanks

Andy

[Guy Croft]

Take the inlet ports to 33mm parallel from outer face to wherever the port starts to enlarge beyond that size, that's plenty big enough and will ensure a high Mach number and good filling with that cam. Anything over 34mm will be too big and yes, on that little engine, the port velocity will be poor and cylinder filling will suffer dramatically. The guides on inlet and ex should be removed to port it properly. Deshrouding around the inlet valve is a good idea, yes.

Cam timing and type looks OK to me.

A bit of basic arithmetic: The valve area ratio is not that at good ex area 70% of inlet - a bit borderline really and ideally we'd want more - 75%. But, you will just get away with it. The port area ratio if you have 33mm inlet and go to 28mm ex (average diameter) is OK at 72%. The ex port should - if it's possible without breaking thru, have the same cross sectional area as the ex valve throat - which will be about 29mm on a fully spec'd seat with a 33mm valve.

The most important thing, that you have not spoken about, is the pistons, you've got to go forged, or else keep the revs below 7500. On a big bore unit like that the tops will come off the pistons at higher rpm and all your work will be wasted. I would, similarly, not just rely on the windage tray. Get an accumulator fitted too, 1.5 qt Moroso (I have them).

Bit of fun: I'd like to meet the 'guy' who hands out all the advice everyone seems to have before they write to me! I get no-end of calls where they begin 'I've been told...' Invariably wrong!

But - good post, well detailed, easy for me to work thru. Some photos would add interest, never get to see 'em in GC Q&A.....

GC

[andy97]

Guy, Thanks for your reply, that's very useful.

You are right about "someone", he's responsible for a heck of a lot of trouble!

I'll let you know how it goes, although it will be a few weeks, yet, before it gets sorted. It will be interesting to see how the car performs compared to the old engine. I'll definately be keeping the revs to below 7500 this time!

Thanks again

Andy

[guenter]

Hello Guy,

I'm currently working on my first real engine job. I own a Fiat X1/9 and I'd like to realize my dream from the last 20 years. Since this time we've been trying to get more power out of the 1500 engine with little success.

Here's my question. I bought a 1600 unit out of a Fiat Tempra station-wagon with oil cooling for the pistons.
I like to keep the head 37,5 inlet and 33 ex valve. I am opening the inlet port to 33mm and the ex port to 30mm. I will send you pictures next week.
I'd like to use the camshaft I have used in my 1500 engine in recent years. It is some kind of aftermarket cam - but I have no detailed information about it. All I know is that I been using the cam for the last 6 years and it worked really fine. Hopefully I will be able to give you the details after measuring soon.

The real problem is, which piston to choose?
I don't want to work on the head to increase CR as you wrote. I wish to use lighter forget pistons. The original bore is 67,4, Fiat recommends a oversize of 67,8. Can I go for 67mm without risking to much? Are pistons and rings available and how high should I go with the CR? I have no knowledge about all this. I considered sending the original piston to some piston maker and they will build me one on my/your specifications. I will lighten the con rods as well.

In the final stage the car will be equipped with a new fully programmable engine management system. I wish to keep the original look of the engine and to built a road car.

For any help and suggestions I will be very thankfull.

Yours sincerely and Merry Christmas

Guenter

[Guy Croft]

Hi Guenter!

Thanks for your Xmas Greetings and I wish the same to you!

Why not talk to me in the New Year? I do a lot of forged piston design and my forged items are some of the lightest and best around! Naturally I need certain design criteria but this is easy enough for us to work out with one or two emails and some basic dimensions..

Your proposed head mods are fine! If the cam is good and the calibration of the new fuel injection system correct that little motor will fly!

GC

[Acki]

I think the stroke is 67,4mm not the bore?!

@Guy: What's they weight of your pistons for a 1581 SOHC turbo?

[guenter]

This is what happens when a "non expert" gives details.
Thank you for the correct details.

I`m following your detail in the german forum. Looks like we have the same goal in mind. How fare are you?

I will talk to Guy next year about his pistons and camshaft.
I guess his help will ensure us the best chance for a reasonable performance of that engine.

Happy New Year an may the "engine" force be with us.

[guenter]

Hello Guy, Hello Andy,

why not work with the experts. It seems we have the same goal.
I do not have to widen the bore of my engine to 87 mm. I can keep the original 86,4 mm
So why dont we let Guy design us the pistons. 11.1 cr is fine for me.

The pistons you use on the tipo should be the same as the ones I had in the tempra.
My inlet valve is 37,5mm and ex is 33 mm. Maybe Guy can design the pockets a little bigger so they will fit us both.

This is just an idea to prefend guy from doing 100 million piston designs.
I´m afraid of using something else that my not be suitable.

What you think?

[andy97]

Guenter

Thanks for the reply. This is a good idea but unfortunately my work is already underway. Sorry.

[Guy Croft]

members, hi

Guenter, yup, thanks for the kind words!

The immutable law of piston design (and yes, I really do design them, see pics) is that no sooner have you done one and got the prod underway than along comes another user who wants it all different! You can't do 'em all! If you don't buy from me, that's cool, but you'll get off the shelf parts or copies. I know that because that is what i used to get, a long time ago. But exp has taught me that if you actually design them you get exactly what you want and if they are wrong your design is wrong or they've been made wrong so it cuts out all the arguments about whose fault it is. When you consider how many variants of every engine there are in the world and how costly it is to stock even a few of the same type (never mind keep the rings that you fondly imagine the user is going to need, you can imagine how my spirits sag when a caller says 'Oh - don't you have them in stock then?' !! The most common problem (frankly) is the guy who 'gets his block bored' without checking on ring pack availability and bore finish... ho hum.


Anyway. Here are some pics of the latest medium comp GC forged piston for the SOHC X19.

[Acki]

Thanks GC for the pictures. Do you have some for a 1.6 turbo? ;)

[Guy Croft]

No, I don't keep stock unless I get an order for one set and then I order a spare set. Eg: So far I've only sold 2 sets of the model above..

However, I can do the design (which you don't pay for) in a day or so and if I have the required client info (comp height, valve size, camlift at tdc, bowl volume or CR&head volume) I can get very readily. A lot actually depends on the availablity of ring packs so I have to figure out the right size at an early stage. My standard lead time from order is under 4 weeks but with a surcharge (you pay) I can genuinely get in around 10 days.


GC

[Acki]

Hi Guy,

Would you shorten the pipe of the crankshaft housing venting?
Or did you get problems with the venting in high revs? ~8000rpm



Regards, Martin

[Guy Croft]

hullo Martin,

that pipe is the one that returns liquid oil from the cyclone separator on the block and it is supposed to be placed adjacent to the oil pump pickup to get suction and make sure the oil (separated from vapour and gas) gets back to where it belongs. No there is no value in shortening it unless of course the sump has had the base reduced in height. It must sit in the oil. If you shorten it for any other reason you'll end up throwing oil out of the breather.

In case you are wondering if there is more crankcase blowby with forged pistons, well that has nothing to do with the piston material.

GC

[Acki]

Thanks Guy.
I was just wondering because the pipe is IN the oil and I thought when I drive high rev's I could get problems.
But when you tell me there is no problem I don't think abput anymore :)

Regards, Martin