Fiat Seicento 1,4 16v head and intake and exhaust mods

[Guy Croft]

hi Tomasz

you have emailed me indeed re pistons,thanks.

I am going to spell out the key decisions in engine building - I suggest you tell your owner the facts from GC and take personal control of this project. nothing worse than an engine built by committe.

The bhp increase will come from an increase in torque and rpm capability. To get more power we have to run a normally aspirated engine to higher rpm, this is invariably true, given similar cubic capacity of course.

More torque comes from cams, CR, head and valve mods. It also depends on cam timing, inlet and ex configuration. It is dependent too on fuel system but that is not a primary consideration.

Higher CR usually means a new piston and given that we are going to run it higher the best way is always forged. If the rpm will be significantly higher - I mean 1000 or more over peak std redline - then race rods are almost a no-brainer. This is to ensure the rods don't break and take the whole engine with them

The cams will determine (in the main) what is possible, they are, after all, a mechanism for letting the fuel/air into the cylinder and the more power you want the bigger the lift integral (not duration but area under the curve) and rate, peak lift and dwell are all factors but essentially we will run more peak lift, more overlap and more LATDC. It is inevitable (unless you are only seeking a 12% increase in power that the cams to make this engine powerful will have to have solid lifters.

Springs and buckets will follow (and often dictate) cam choice - and such a cam pair may have to be specially made and may have to be steel billet.

Any difficulties involved in determining setup height of valves and bucket clearance/design must be determined before any other work. The available space for the new setup and available lift will - to a great extent - govern what valve/seat mods are possible and as a precondition the existing setup must be drawn out on cad to define what's possible.

Once the valve train setup (valve height, spring and base, cap, bucket) is thought thru then the cam can be considered but not until that is done, otherwise you can end up with a cam whose base circle/lift characteristics will simply not fit. There will either be a range of cams available that suit or will they will have to be made from scratch.

Then and only then it's time to do some head work and figure out the kind of flow regime that's possible. The behaviour with valve in will entirely dictate the cam choice. Following this the pistons can be designed and if you do them first they won't be right.

It is amateurish to set as a 'pre-condition' that you're running EFI - the gain is some improved overall driveability and maybe 10% increase in peak power, broader spread of torque but more_often_than not the wrong throttle bodies are selected and it's not mapped up properly - I mean in sufficient depth - to capitalise on the work that's been done. And the cost of those conversions - over_and_over often greatly exceeds the cost of more_important components. I see this all the time efi efi efi and then using cast pistons and a header that simply doesn't work.

I write most often for the education of people checking into this site.

The regime is how I operate all the time, fixed logical sequence and it always begins with development, cad work and then costings, trimming or expanding the budget or power targets to suit. You and your team would be well-advised to go thru all of this before going any further.

Until that point I am locking this thread, not because I don't like the thread but because it is an important one and can be used as a model of how to proceed and I don't want it any more complicated than it needs to be. Drop me an email or pm when you have progressed matters with your team along the lines I have described.


GC