New 1600 stroker build

[Agnelli]

The engine that came out of my X was sourced by the prior owner, a 1500 Lancia Prisma NOS shortblock he had installed in the car. I've torn it down to just the block, crank and pistons, all other peripherals are off. Internals look very good, consistent with low mileage and frequent oil changes. The cylinder bores look great, which is good news, as I'm hoping to install a 67.3 / 1600 crank with Kolbenschmidt pistons with just a hone, no overbore. It will be dropped at the machinist Saturday for a thorough jet washer cleaning and measurement of the bores. I have a European Fiat cam and Euro ten bolt head head in stock ready to mount. Also have ready a vintage Abarth 2 x DCNF manifold, and 36 DCNVH carbys which need to be reconfigured. Plan is to run this in my 128 to replace the very good running 1300, which will come available in the springtime if anyone may have an interest. The 1300 had been maintained for years by its prior owner at Wine Country Motors. It consumes the least oil of any SOHC I've owned.

 

[ghostdancing]

interesting plan.. what trans are you planning to mate with the prisma block?

 

[tonyism7]

Will you have to do any machine work to the pistons, or were you able to find some with the correct compression height? (Selfishly asking because I have a stroker crank waiting in the wings, but haven't seen the correct pistons around in the last few years).

 

[Agnelli]

Will you have to do any machine work to the pistons, or were you able to find some with the correct compression height? (Selfishly asking because I have a stroker crank waiting in the wings, but haven't seen the correct pistons around in the last few years).

I was with some effort able to find pistons with correct compression height, acquired from the UK back in 2016, and have also found supply no longer available since. I have a second set of correct compression height pistons, also Kolbens, which are oversize 86.8mm. Depending on what the machinst measures, one or the other set will be employed, and I may or may not sell the unused set. And, I have a set of stock Fiat European small flycut stock pistons (86.4mm). These with a 1500 crank yield about a 9.2:1 CR, and with a 1600 crank and minor machining may yield 10 - 11:1 CR.

The question for you is, do you have a low mileage block available with bores in spec that may employ 86.4mm pistons? If so and you are interested there may be a way to use your stroker crank without major machining costs.

And to the prior question about which trans, it's the four speed 128 new internals 3.76 final drive built for me last year by SteveH. It's in the car now mated to the existing 1300, lightened flywheel. When I swap in the 1600, I will change out the flywheel to the unit that came out of my X, a lightened 1500 flywheel with correct 1300 ring gear, and upgrade to a new 1500 clutch.

 

[Agnelli]

Crankcase now @ machine shop. In discussions with the machinist, gained advice:

1) though the engine is low mileage, we're going to use new main bearings and large connecting rod end bearings. Reason: bearings bed in over time and become egg shaped. So the conclusion is, don't re-use main and rod end bearings.

2) water galley 'freeze' plugs are steel. The oxidize. They're cheap. If you remove before cleaning the water jackets have a better chance of removing debris. Change, them too.

3) same goes for the oil galley plugs.

Block should be cleaned and stroker crank measured in a week's time. Meanwhile I sent the factory specs for the block, bearings, pistons and crank to the shop for reference.

 

[fiatfactory]

mains and big ends were never going to be any good anyway...cheap insurance to use new.

if the crank is new you'll find the 1600 measures up a little different anyway, if it's used and you regrind then it doesn't matter.

water core plugs absolutely, crank core plugs absolutely, the block oilway plugs unless the block has been sitting in a field rusting I don't usually bother with removal, seldom is there anything in there, plus the flat welch plugs are a bit of a PITA to refit neatly.

core plugs in the crank , absolutely if the crank is used... all the crud centrifuges out and sets like cement in there...

A tip with plugs, small ones, most people use a small flat punch to drive them home...that can work but it can also pierce the plug.
A flat faced round punch will have a square sharpish edge, the cup plug has a rounded inner... you need to round off and dress the punch faces edge before use.

SteveC

 

[PaulD]

Will you have to do any machine work to the pistons, or were you able to find some with the correct compression height? (Selfishly asking because I have a stroker crank waiting in the wings, but haven't seen the correct pistons around in the last few years).

Chris Obert has a set for sale here:

Fiat Parts and Supplies

I have a set of these sitting around that I will be posting in the FS&W section soon. After I got them I decided to go with custom forged pistons as they were lighter and stronger

 

[fiatfactory]

easy to machine... I did these.

began life as small flycut 34.5 flat tops, now 1mm half dome 33.5ch enlarged flycut on the intake side.

Stock dished top 1581 type piston will only give 9.2:1 static with the euro volume combustion chamber

SteveC

 

[Ulix]

Yes, don‘t use 1600 pistons.
With the move to the 1600 crank you have the chance to gain CR and squish by using modified 1500 pistons.

 

[fiatfactory]

Yes, don‘t use 1600 pistons.
With the move to the 1600 crank you have the chance to gain CR and squish by using modified 1500 pistons.

Well it depends Ulix... the dished pistons would work very nicely with a USA spec decmpression head to build a low compression 1600...


..... and then push about 10psi into it with a turbocharger to get some performance out of it.

SteveC

 

[Agnelli]

Past and forthcoming input appreciated. If the bores spec out such that I can use the attached KS pistons, I will. Welcome your calculations on projected static compression with 1600 crank, original bore dimension 86.4mm, stock crank length. Photos of pistons with markings below. You can see the diameter stamped in 86.36. Compared to stock Euro small flycut pistons, you can see these have a slightly lower CH. Wondering if they are 34.15 like Mahle 8082's. I measured the depth of the valve recesses aka flycuts, though these are cast in - 5.7mm. Assume no change to stock Euro 10 bolt head other than light skim to it and the block ( ~ 15 thousandths"), and Matt's baseline head gasket. Aim is CR of 10.5:1 no more than 11:00-1. Thanks in advance.

 

[fiatfactory]

Nice slugs... KS are (IMO) about the best quality production pistons available, so a very good choice for a stroker engine.

They are "almost" the same as mahle 0872 (34.15CH small flycut) and the one and only set I have identical to the set you have I was actually wrongly supplied. I had bought a bunch of KS pistons from a dealer closeout in Switzerland, and despite having the same part number on the (still factory sealed) box I got one set of the large 5.7mm deep flycut pistons in among the ten sets or so of small flycut 0872 pistons I bought from the guy...

I hung onto them thinking they would be a good slightly lower compression alternative for a more street build, and / or for a motor with a cam that had a lot of lift at TDC.



I actually machined these myself a couple of months back when I had some mill time available, as these are going in the lemon engine which will also be a 1600 (the machine time would have been off my lemons dollars budget)

bare weight is now under 400grams (395g) which is pretty light for a cast piston. With the half dome and the SQ at 1.0mm, I did the rough calcs on these at 10.6:1, and I'm planning to drop anther couple of CC's from the combustion chamber to deshroud it a little, so my target is 10.4:1 (1599cc) so that with the cam I'm running the dynamic CR will be what I want

If you already have a set of SCAT rods, pony up for a set of the lightweight Ross gudgeon pins and your bottom end will be the same basic components as my lemon engine.

SteveC

 

[Agnelli]

Nice slugs... KS are (IMO) about the best quality production pistons available, so a very good choice for a stroker engine.

They are "almost" the same as mahle 0872 (34.15CH small flycut) and the one and only set I have identical to the set you have I was actually wrongly supplied. I had bought a bunch of KS pistons from a dealer closeout in Switzerland, and despite having the same part number on the (still factory sealed) box I got one set of the large 5.7mm deep flycut pistons in among the ten sets or so of small flycut 0872 pistons I bought from the guy...

I hung onto them thinking they would be a good slightly lower compression alternative for a more street build, and / or for a motor with a cam that had a lot of lift at TDC.

View attachment 40886View attachment 40887View attachment 40888

I actually machined these myself a couple of months back when I had some mill time available, as these are going in the lemon engine which will also be a 1600 (the machine time would have been off my lemons dollars budget)

bare weight is now under 400grams (395g) which is pretty light for a cast piston. With the half dome and the SQ at 1.0mm, I did the rough calcs on these at 10.6:1, and I'm planning to drop anther couple of CC's from the combustion chamber to deshroud it a little, so my target is 10.4:1 (1599cc) so that with the cam I'm running the dynamic CR will be what I want

If you already have a set of SCAT rods, pony up for a set of the lightweight Ross gudgeon pins and your bottom end will be the same basic components as my lemon engine.

SteveC

Thanks for your affirmation of my pistons Steve, and your experience with your mislabeled set. Also insightful to see your modifications and associated head and cam information. I'm leaning toward leaving the deep flycuts at their original circumference with my refreshed though stock 10 bolt Euro head and cam for maximum compression. This should make plenty of power for a relatively stock 128 chassis. I do have a set of new SCAT rods I may use in this build.

Question: where do you suggest sourcing lightweight Ross gudgeon pins, and do you have the correct part number?

 

[Agnelli]

Below are calculations for the build to ascertain compression ratio and how much to shave off the piston crowns. Below are numbers assuming shaving 0.755mm from the crowns. I may shave up to 1mm, or, less than the earlier 0.755mm value if machinist and I opt to enlarge the inlet valve cast flycuts, which would enable (a) fitting a big valve head later without removing the engine and rotating assembly or (b) fitting a big valve head with the initial build. Flycuts affect the CR a lot. I did measure CR height with Vernier caliper, and cc'd the flycuts and combustion chambers with oil and graduated hobby syringes. All this is predicated on the forthcoming measurements from the machines shop informing viability of use of OE diameter pistons, stroker crank, or alternatives based on findings.

Swept Volume of the cylinder.
Pi x R squared x Stroke			cc
3.14285​	43.2​	43.2​	67.4​	395322.1​	395.3221​
Volume of the piston 'pop up'
3.14285​	42.95​	42.95​	0.65​	3768.5​	3.768455​
Volume of the head gasket.
3.14285​	43.6​	43.6​	1.5​	8961.6​	8.961648​
Volume of the ring land clearance
3.14285​	43.2​	43.2​	6.5​	minus	3.14285​	42.95​	42.95​	6.5​
			38124.53​					37684.55​
					439.9794​
					0.439979​
Flycut Vol	3​
CmbChbr	31.5​
Volume at BDC
438.1581​
Volume at TDC
42.83604​
CR
10.22872​

 

[fastx19]

10.23 is getting up there. Super only, and even then maybe an octane additive. I am excited to see how this turns out for you.

 

[Ulix]

Are you figuring in the piston (pin) height somewhere?
Do you know this measurement for your pistons.
It is KH in this drawing:

 

[ghostdancing]

it's the four speed 128 new internals 3.76 final drive

is this tall enough for the torque of a 1600?

 

[Agnelli]

10.23 is getting up there. Super only, and even then maybe an octane additive. I am excited to see how this turns out for you.

Eric -
Super constructive feedback I am completely receptive. Detonation is definitely the enemy, so I will heed your advice and aim for a figure between 9.5 and 10:1. Likely by shaving a full 1mm off the crowns and enlarging inlet fly cuts to get there.

 

[Agnelli]

Are you figuring in the piston (pin) height somewhere?
Do you know this measurement for your pistons.
It is KH in this drawing:

View attachment 42194View attachment 42195

Thanks Ulix. Compression height is figured in to the volume of pop up calculation. This is my first attempt at doing the math, I replicated the method from the Ultimate SOHC thread. The three different piston sets I have available are all 34.9 CH. With the 67.4 1600 crank, a better starting point would have been 34.15 CH pistons - hard to find, I would probably have to order custom made pistons. Once I hear from the machinist, I will re-calculate CR and confer with him on the piston machining.

 

[Agnelli]

is this tall enough for the torque of a 1600?

I think it will be. Plus, without resorting to more extreme measures, that final drive is the highest commonly available. My former SL Coupe had a Yugo five speed, I would love to find another one for the 128 wagon.