74 x 90.5 vs 78 x 90.5....and stuff....

[RandyV]

A couple considerations......(Since the money part doesn't really matter)....

#1.) Physical dimension management. Since this motor is or an oval....engine compartment is a little tighter. 74 x motor with stock (or shorter) rod length = compact motor?

#2.) To me....78 on down is always a little more "everything" friendly (minimal case mods, safe head mods, etc.) so I'm almost convinced 78 x 90.5 is just the perfect engine size for equal money spent.

All things equal does 78 or 74 carry a worthwhile advantage over the other?

[Lingwendil]

74 stroke with 5.325" rods should be just about stock width, and not require any crazy work to fit into an early car, at least not more than fitting a 1600 in.
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[RandyV]

[modok]

AA brand B pistons should be just right for 78 stroke

Mahle 90.5 B pistons are 1mm shorter, so, maybe deck the case 1mm if you use those.


74 stroke with 5.325 rods should be .030 wider per side, but you won't notice, how deep the heads are cut is a bigger factor in the actual engine width.

1904CC is a good size to max out "stock size" heads IMO

If you go with larger valves, 78 stroke for sure, and also consider thickwall 92 if using the panchito heads. Plenty of flow and they were made for big bores

[Alstrup]

ALWAYS deck the case. If you use shims of a zecent quality it doesnt matter.
If you go 78 x 94 bore you can chose the csp/Mahle "c" pistons. Along with a stock length rod that will give you an egine approx 4 mm narrower than a stock 1600
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https://www.thesamba.com/vw/forum/viewtopic.php?t=435993

[RandyV]

I like 90.5 because you get a "plenty thick" cylinder without having to punch out case & heads so much. (planning to use AS41 case on this one)

Heads will be mildly custom 40 x 35.5 setup running either W110 or FK-65 cam. (Gonna be a torquey, smooth running sleeper)

[Alstrup]

Fair enough. Just giving options for a narrower engine with a little displacement.
But AT LEAST get yourself a proper cam, instead of something from 1970. There are several better ones on the market in the same segment.
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https://www.thesamba.com/vw/forum/viewtopic.php?t=435993

[evanfrucht]

I'd go with 78. B pistons are lighter than A pistons...

X2 on considering thickwall 92s...

They make thick walls that are 90.5 opening at the case and are only larger at the head mating surface... something to think about.
- So it would be the same machine work to the case... thicker cylinders... bigger engine... Win, win, and win...
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1964 Fury Wagon ( the pavement shredder )

[madmike]

I built a 78 x 92tw over the winter , 5.5 rods(can't pass up free H-beams)
1970 ish? FK8 cam advanced 4*
t3/t4 turbo
Holley Quick fuel 680
all I can say is this thing is 'Snappy quick'
but it's wider then my 2180 (Porsche rod length)
_________________
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76 Drag/Street bug 2180cc 'Turbo' 11:85 @113 mph"If I go any faster I'll burn up the Hamster" ,gets 28 mpg. also 10/09/22 11.90 @115 mph
"If I'm ever on Life Support,UNPLUG Me, Then Plug me back In see if that Works"

[bugguy1967]

This day and age, you're not confined by simple "A" and "B". Order 90.5 cylinders, and custom-order your pistons to make the engine as narrow as you want. Or buy oversize Ford Modular pistons that have clips instead of press-fit.
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[RandyV]

[modok]

At a basic level it's a fine plan.
But then again it isn't.
So you've got 25% more displacement, and make your heads 25% bigger, sound logic.
You'll get something that runs like a 1600 with an engle 100 cam, except 25% bigger. Which is OK but not very exciting. BUS motor? put a single carb on it? offroad? Pretty good for that, but not the most exiting "sleeper"
At times it can be a struggle to find heads with chambers large enough to get the compression LOW enough to use a mild cam, at least was 10 years ago .
Don't know if you like chinese heads or not, some of those have bigger chambers, the panchito has a BIG chamber, so you can flycut that DOWN to your desired compression, instead of HUNTING for uncut heads and having to enlarge the chambers.
Which one is "narrower"?

40x35.5 valves is another "standard" that we have ALWAYS had the ability to customize. Why is it a standard? I don't know. Would re-arrange that a little.
More port velocity brings the powerband down and torque UP, valves just the right size for the ports and 75% flow ratio, maybe you only need 39x34 valves..... less chance of cracking, more cam duration can be used, more compression can be used. MORE exciting than custom cutting cylinders and head studs and tins to make your engine 5mm narrower per side than a 1600, when you can make your engine compartment that much wider with a mallet REAL QUICK

And the other thing is, on a STREET car, I think there is such a thing as too much low end. It's kinda jerky. I have a 2007cc in a 1960 bug, web 110 cam, Plenty of low end IMO, but could use MORE mid range torque, always.
And another thing is your IDF carbs can HANDLE cam duration, and more compression helps the carb signal, so, it kinda goes together.
But they are sensitive to exhaust system misbehavior, too much exhaust flow can send you to chasing jetting problems that aren't jetting problems.
My new set of heads have 40x34.5 valves, maybe I am overly obsessed with ratios.....but it's working so far.
Pat Downs is putting panchito heads with TINY 40x35.5valves on a bunch of 2275cc monsters.....for STREET cars. See what I'm sayin?
big valves &small cam VS big cam smaller valves? What's the difference? the cam after all just controls the valves. The difference is velocity, and flow ratios, or what kind of intake and exhaust system it has may work better one way or another.

WIDTH? Only real thing that hits is the valve covers might get close to the lower edge of the inner wheel well. You can trim the cylinder tins pretty easy. Where the carbs end up depends on the manifolds. If you use a 36hp style shroud, get manifolds so the carbs can be tilted inward. It's a stale air car anyway. Tho would be cool to have a 36horse width engine, but that's like, 10mm per side? I don't see it happening.

[StefansBus]

[RandyV]

[txoval]

If you want to stick with Engle, I’d go with the W125 or FK8…especially if 78x90.5 or 92

The W125 provides plenty of torque down low and runs strong to 6500ish

It idles smoothly with dual IDF’s…

I recently used the W125 in my 78x90.5 engine with CB Panchito heads…9:1 CR, dual 40 dells

[MuzzcoVW]

[UK Luke 72]

[c77owen]

[RandyV]

[RandyV]