Bryce-o-rama
True Classic
Are those made of Glastic/Haysite?
New 1600 stroker build
- Thread starter Agnelli
- Start date
fiatfactory
Steve Cecchele
but that was when you had an estimated combustion chamber volume of 31.5cc.... now you have the head "in hand" and measure it at 27cc it changes this a little... add to this the fact that skimming the piston crown will also reduce the measured flycut volume.
If your tame machinist has a piston roll over vice then enlarging the inlet flycut (2 on the left and 2 on the right side) of the KS pistons isn't a difficult job and will add some volume back.
Still aim for that SQ value of 1mm to 1.2mm max, so you need to choose a head gasket and determine what it's compressed thickness is likely to be and base the CH you want to achieve on falling into that SQ measurement window.
Al was well known for over estimating the valve open duration of the cams he sold, a bigger number looks more impressive and will probably sell more... so if you choose the faza 40/80 as the cam you'll use, it would pay to actually measure the valve open duration at running clearance (I guarantee it will be less than 300 degrees) and then you can easily determine your simple dynamic compression ratio... I think Ulix had a spread sheet where someone in germany had actually measured this particular cam grind.
SteveC
Agnelli
True Classic
Thank you Steve and Ulix.
I won't be running the Faza 40/80, sold it to Greg in CT. Will instead use a factory Fiat 24/68 Euro 1500 cam. Machinist definitely has capability to enlarge the inlet flycuts as above and expect he will. Two questions:
(1) how to measure / achieve the 1-1.2mm SQ value?
(2) Give the 24/68 cam choice, what static and dynamic CR values do you recommend assuming 91 octane best case?
Agnelli
True Classic
Meanwhile, ordered a multi-layer steel head gasket.
https://www.midwest-bayless.com/Fia...ayer-steel-fiat-bertone-x19-128-yugo-new.aspx
https://www.midwest-bayless.com/Fia...ayer-steel-fiat-bertone-x19-128-yugo-new.aspx
fiatfactory
Steve Cecchele
Is the prisma block M12 fasteners?
Not sure why but the listing doesn't recommend using this gasket with m10 bolts, possibly not enough clamping force available at 61ft/lb with an M10 bolt to get a good seal? I guess you could always go the ARP stud route
One thing not mentioned in the listing is surface finish, generally MLS gaskets require a much finer finish on the block / head faces (a much finer Ra number - your machinist will understand that) to ensure a seal ... the standard Fiat finish on the block is not smooth enough for an MLS gasket.
If you do use the MLS gasket you don't need to worry about working out the compressed thickness, as they don't compress, so at 1.3mm thick your going to be aiming for 0.3mm of plus deck (piston protrusion past the deck face) to get 1.0mm SQ value.
with the euro cam I would be aiming for around 10.5:1
trouble is at the moment with 86.4 bore / 67.4 stroke / 27cc comb chamber/ 1.3 gasket (7.9cc) / 2.cc valve flycut after skimming 1.2mm of the crown - (a guess)/ 33.7 piston CH (so 0.3mm pop up after the block has been decked 0.1mm to get it smooth) which is minus 1.8cc... is that my rough calcs put you at 11.4:1
you need add approx 2.5cc in the combustion chamber to get down to 10.5:1 with your current configuration...
SteveC
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Agnelli
True Classic
Thank you Steve appreciate your high value input. Yes, M12 fasteners on the Prisma block. I will inform machinist on guidance.
And I read up on SQ value (distance from piston top @ TDC to flat section of the combustion chamber).
Will report on the dome shave and SQ metrics, predicted CR, and requisite added cc's to get us to 10.5 static, and how it gets done (flycuts / combustion chambers)
Agnelli
True Classic
Dropped off the multi-layer steel head gasket with the machinist yesterday. He schooled me about engine rebuilding and our next steps. First, at least according to him new cars utilize MLS head gasket technology. I then asked about how we'll approach optimizing compression ratio for the build, and came prepared with documentation and printed photos from this forum on squish quench and de-shrouding the compression chamber near the inlet valve. He's got an application on his phone used to calculate compression and apparently also accounts for cam profile and dynamic compression. He also noted the need to contemplate rod stretch under RPM as that relates to piston height. There was discussion about modern fuel blends (oxygenated / ethanol) and how those are optimized for electronic fuel injection, and the challenges presented by carburetors operating at low fuel pressures vented to atmosphere. He showed me examples of Chevrolet blocks and heads (closed and open port) and demonstrated that relieving the top edge of the cylinder will aid in inlet valve flow. Will report again once decisions are made as to dome height, flycut volume increases, any further modifications to compression chambers, and dynamic compression estimates.
Agnelli
True Classic
Spoke to the machine shop this morning, finally, I'm at the head of the queue after 16 months. They've run all my components through the large steam cleaner, and laid out the internals and the block. Two subsequent phone calls so far today - to positively identify the stroke metric (67.4mm), think through the amount of protrusion of the pistons from the deck, and informed the combustion chambers are 27cc. Compression software says we're at around 12:1 and pistons will require quite a shave. They're looking at all the possible variables, then will get back to me with the go forward plan.
Lowtechprime
Retro Grouch
Compression ratio is spot on, but aren't you giving up 100cc's displacement?
Agnelli
True Classic
I am. Also giving up the marginal advantage of the lighter 1600 crank. That said the setup should make a lot of power relative to the lightness of the car and flexibility of the frame. Big valve head, euro cam, header, Alquati intake w/ twin 36 dcnf.
Lowtechprime
Retro Grouch
Why not just come up with different pistons to get the ratio up, and keep the other benefits of the 1600?
Agnelli
True Classic
You and Ulix are both on point. Explanation: the Kolbenschmitt pistons are quite high quality and rare. No need to re-bore with this set. I happen to have another set of pistons but with same compression height, so that wouldn't have helped. The head is from Europe and fully configured ready to go so to either / or / both change pistons and modify the head wasn't really worth the extra 100cc. Besides, I can save the crank for the next iteration of my X engine. Or, use it in the 1300 coming out of the 128. Fiats are like Legos!
Had I opted to stick with the 1600 crank I would have reverted to another Euro 10 bolt head I have in stock and started from scratch, leaving the complete BV head for the next build. I will report again next time I speak to the machinists.
Agnelli
True Classic
Retrieved block and head from the machine shop with the 128 wagon. The fresh block is now safely mounted to its engine stand bagged and ready for assembly. Cleaned, honed and decked. New main, thrust and con rod bearings.
Machinist noted that the original NOS pistons look great - prior owner sourced the NOS Ritmo block so I know it is low mileage. Anyone need 86.4mm 1500 pistons? Happy to ship them to anyone willing to fund the postage.
Machinist noted that the original NOS pistons look great - prior owner sourced the NOS Ritmo block so I know it is low mileage. Anyone need 86.4mm 1500 pistons? Happy to ship them to anyone willing to fund the postage.