New 1600 stroker build

Restoring the Prisma steel oil pan now (recall this stroker will reside in my 128). First scrubbed lightly surface rusted / paint failed areas with Barkeeper's helper and a scuff pad. Further treatment with liquid rust remover, the pink stuff. Finally, rotary wire brushed with large 115V buffer. Just applied SEM grey epoxy self etching primer.
 
Started working on the induction system while awaiting machinist's analysis of block bores and crank journals, due in about a week.

Pulled 2 x DCNVH Webers from storage in the garage. The super clean one had a bit of resistance to butterflies snapping cleanly shut. This was solved in less than a minute with Marvel oil. Pulled the jets which may have been original to Maserati BiTurbo application. These won't work for SOHC 1600, so ordered up all new jets from eBay "Alfa1750". 185 air correctors, F24 emulsion tubes, 120 mains, 46 idles. Also was pleased to see both carbs have 30 venturis. Needle air bleeds look good.

Anyone venture to guess what float height is correct for dual DCNVH 36s on a vintage Abarth manifold (thanks Bernice) in a 128?
 
Proceeding to test fit the DCNVH Webers to vintage Abarth intake, with custom made spacers. 50mm studs screwed in to carb mounts, discovered I need to acquire shorter (45mm) studs so as not to interfere with carb bodies.
abarth mani.JPG

spacers.JPG
 
You might find you only need to shorten one stud for each carb.

One will be touching under the accelerator pump assembly, slice 5/10mm or so off that one and leave not just enough room for the nut to get in and out when the carby is seated... It means you need to start that nut first and wind it on a little while you support the carb, but not too fiddly.

DCNVH carbs I've always wondered how they would work in a dual / mltiple situation, as they have no idle air corrector mechanism to help get the balance right... doesn't mean they can't work as I know they were used in a factory dual setup on a Matra, but I think the manifold on that engine had a balance port between the inlet runners.

SteveC
 
You might find you only need to shorten one stud for each carb.

One will be touching under the accelerator pump assembly, slice 5/10mm or so off that one and leave not just enough room for the nut to get in and out when the carby is seated... It means you need to start that nut first and wind it on a little while you support the carb, but not too fiddly.

DCNVH carbs I've always wondered how they would work in a dual / mltiple situation, as they have no idle air corrector mechanism to help get the balance right... doesn't mean they can't work as I know they were used in a factory dual setup on a Matra, but I think the manifold on that engine had a balance port between the inlet runners.

SteveC
Good feedback Steve I will shorten one stud for each carb with a Dremel cut off wheel.

Interesting point that I had not contemplated, the lack of idle air correctors. It'll be fun to see if I can get them to work without a balance port between inlet runners.

Serial numbers here for your review:

36 DCNVH 24-100 4B
36 DCNVH 24-100 4C

Wondering what difference between the B and the C.

dcnvh.JPG
 
Good feedback Steve I will shorten one stud for each carb with a Dremel cut off wheel.

Interesting point that I had not contemplated, the lack of idle air correctors. It'll be fun to see if I can get them to work without a balance port between inlet runners.

Serial numbers here for your review:

36 DCNVH 24-100 4B
36 DCNVH 24-100 4C

Wondering what difference between the B and the C.
If I had to guess on those Weber numbers, I'd say they were manufactured for the same application (car) and the last two digits indicate the position. If they are different at all, it could be a function of what linkage hardware is on each one.
 
Update - dropped in on the machinist (great reason to run the X) to nudge him. Poor guy has been slammed, as another veteran machinist has diverted all his jobs to this shop due to a chronic health issue. The stroker crank has been cleaned. Measured the journals then and there, no need for turning the crank just a polish. Measured the bores, and fortunately I brought the Kolbenschmidt 86.4s along. Calculated bore diameter and read the spec engraved on the piston, determined all we'll need is a block hone. He will also pull the head studs and lightly skim the deck. We then had a conversation about shaving the crowns to arrive at a reasonable compression ratio. In looking at the distance between the crown and the first ring, we'll opt to enlarge flycuts to adjust CR. He doesn't want to shave the crowns, idea being the top edge of the piston develops the most heat. If need be we can dish the pistons. Ordered OE NOS main bearings, Clevite rod bearings, and thrust bearings this morning with all the seals and gaskets I don't already have in stock for the build. Once the block is cleaned we'll mock up the build to check compression height, then modify the pistons, then final build. Learned that Kolbenschmidt means "piston maker" in German. So literal!
 
In looking at the distance between the crown and the first ring, we'll opt to enlarge flycuts to adjust CR. He doesn't want to shave the crowns, idea being the top edge of the piston develops the most heat. If need be we can dish the pistons.

A slight dish on the piston will assist flame propagation as well as compression reduction.
 
A parcel arrived from Europe. Ten bolt European head. Big valves. Ported. Bronze guides. Machinist happened to (finally) call back starting work on the mock up and modifying piston tops. More to report forthcoming once I bring the head to him, cam, cam tower.

head1.JPG
head2.JPG
 
In looking at the distance between the crown and the first ring, we'll opt to enlarge flycuts to adjust CR. He doesn't want to shave the crowns, idea being the top edge of the piston develops the most heat. If need be we can dish the pistons.

Given that the pistons (from KS at least) are precisely the same casting for all variants from 34.15 to 35 CH, taking material from the top of the crown isn't an issue IMO, I myself have taken a regular Mondial and KS pistons from 34.7 and 34.45 piston and reduced the CH to 33.5 with no issue several times. Many more modern engines, and variations of the sohc architecture (like the bravo dohc engine) use a much smaller width above the top ring land, the sohc engine by comparison is very wide, and that's dead space you want to minimise, for both performance and emissions.

Personally I would be aiming a little higher with the static CR ... and that will open up more options for camshaft choice (longer duration) as it's not really static CR that's the be all and end all, it's the dynamic CR you achieve when you factor in the fact that the inlet valve closes well after the piston is on it's way back up the bore after BDC.

The 1600 I built for Mark in Sydney was a measured 11.4:1 static. For that engine I started with Mondial 34.45CH small flycut pistons and machined the CH down to 33.5 and left a 0.95mm half dome, after th block was skimmed the piston crown was 0.05 plus deck so the top of the dome was 1mm plus deck, with the 42/82 10.6 lift cam I fitted the simple dynamic was 9.75:1 from memory... if your running twin carbs and at sea level you can work on a simple dynamic of 9.5 - 9.75 pretty safely with regular pump premium fuel... if the static CR isn't around 11:1 the dynamic CR will be quite low if you use a cam of 300 degrees duration or more.

you need to measure your combustion chamber volumes, and perhaps rethink your choice of a 1.5 crushed head gasket, you really want to get the SQ down to approx 1mm - 1.2mm.

If you alter the CH of the pistons, be certain to clamp the piston via the gudgeon pin / pin bores... don't use the ring grooves as they have a much bigger potential for variation and not being quite square (as I found out the hard way)

Even with the deep / large flycuts in the KS piston crowns you will need to enlarge one side for the intake valve... that's if you are aiming for a decent output of more than 100hp at the wheels.

SteveC
 
Given that the pistons (from KS at least) are precisely the same casting for all variants from 34.15 to 35 CH, taking material from the top of the crown isn't an issue IMO, I myself have taken a regular Mondial and KS pistons from 34.7 and 34.45 piston and reduced the CH to 33.5 with no issue several times. Many more modern engines, and variations of the sohc architecture (like the bravo dohc engine) use a much smaller width above the top ring land, the sohc engine by comparison is very wide, and that's dead space you want to minimise, for both performance and emissions.

Personally I would be aiming a little higher with the static CR ... and that will open up more options for camshaft choice (longer duration) as it's not really static CR that's the be all and end all, it's the dynamic CR you achieve when you factor in the fact that the inlet valve closes well after the piston is on it's way back up the bore after BDC.

The 1600 I built for Mark in Sydney was a measured 11.4:1 static. For that engine I started with Mondial 34.45CH small flycut pistons and machined the CH down to 33.5 and left a 0.95mm half dome, after th block was skimmed the piston crown was 0.05 plus deck so the top of the dome was 1mm plus deck, with the 42/82 10.6 lift cam I fitted the simple dynamic was 9.75:1 from memory... if your running twin carbs and at sea level you can work on a simple dynamic of 9.5 - 9.75 pretty safely with regular pump premium fuel... if the static CR isn't around 11:1 the dynamic CR will be quite low if you use a cam of 300 degrees duration or more.

you need to measure your combustion chamber volumes, and perhaps rethink your choice of a 1.5 crushed head gasket, you really want to get the SQ down to approx 1mm - 1.2mm.

If you alter the CH of the pistons, be certain to clamp the piston via the gudgeon pin / pin bores... don't use the ring grooves as they have a much bigger potential for variation and not being quite square (as I found out the hard way)

Even with the deep / large flycuts in the KS piston crowns you will need to enlarge one side for the intake valve... that's if you are aiming for a decent output of more than 100hp at the wheels.

SteveC
Your feedback much appreciated Steve. I've measured the combustion chamber volume: 27cc. Two cam choices I already have are (1) Euro 1500 factory cam and (2) Faza 40/80. Carbs now will be 36 DCNF on the aforementioned vintage Abarth manifold. Yes it will be run at sea level. Any further thought toward static and dynamic CR figures given these cams, or do you suggest something with greater duration with a thinner head gasket?

I imagine next steps would be enlarge the inlet flycuts, measure new flycut volume, then recalculate static CR with an eye toward your thoughts on final dynamic CR. This is a street application so I don't want to sacrifice drivability.

Good eye Greg, to your question above: Intake ports measure 30mm at the manifold end, exhaust 31mm.
 
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Your feedback much appreciated Steve. I've measured the combustion chamber volume: 27cc. Two cam choices I already have are (1) Euro 1500 factory cam and (2) Faza 40/80. Carbs now will be 36 DCNF on the aforementioned vintage Abarth manifold. Yes it will be run at sea level. Any further thought toward static and dynamic CR figures given these cams, or do you suggest something with greater duration with a thinner head gasket?

I imagine next steps would be enlarge the inlet flycuts, measure new flycut volume, then recalculate static CR with an eye toward your thoughts on final dynamic CR. This is a street application so I don't want to sacrifice drivability.

Good eye Greg, to your question above: Intake ports measure 30mm at the manifold end, exhaust 31mm.
That cam will be happy with about 10.5 to 11:1. Its a hot cam.
 
"Intake ports measure 30mm at the manifold end, exhaust 31mm."
That is a bit odd, to go to bigger valves and have the intake ports smaller than the exhaust.
Do you mind if I ask who did the head work?
 
"Intake ports measure 30mm at the manifold end, exhaust 31mm."
That is a bit odd, to go to bigger valves and have the intake ports smaller than the exhaust.
Do you mind if I ask who did the head work?
Agree with your observation. Classic Performance provisioned the head. We'll see how it works. Some time ago I had a big valve head from Europe (same size valves, don't recall the port measurements) on an SL Coupe. That head performed incredibly, even though it was a used race head, until it suffered leaky guides and a broken spring which wiped out a cam lobe. I don't know who built that one, but it did provide remarkable power relative to the standard Euro head mounted after it. That one had 7mm stems.
 
Update- Finally received an apologetic phone call from my over-clocked machinist. KS piston mounted with original stock 1500 crank, dome resides flush with top of engine block. KS piston then mounted with 1600 stroker crank protrudes .055" / 1.397mm from the top of engine block. Machine shop has a special lathe mount which is a ring securing piston pin to enable a true face (dome) cut. He will relieve to piston top to reduce protrusion / compression ratio. Then CC the head and check flycut clearance, we'll run numbers to optimize compression then increase inlet flycut accordingly. Progress report forthcoming.
 
How much piston stickout are you shooting for?
Zero?
Not sure, really. Any advice?

EDIT- looked back at my build spreadsheets. Estimate shaving .75mm from piston dome yielding .65mm pop up.
 
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