74X85.5-Pushing a pencil - decided on 1745cc

[Ravivos]

Hi,
Would like to run the number with you guys, since i realized that it is important to order the right parts in order to have a decent working, reliable engine.

So, here goes…
After a long wait, I finally have the time and financial resources to build my Type 34 KG's engine.
I've already posted a few questions here and got some great answers that enlightened me.
One of the major issues with the type 34 is its ability to properly cool down the engine, so I want to build a reliable street engine with a good low end torque without going too big.
Furthermore, since I live in a rather worm country, with 8 month of summer, I am building an AC system for it, so the engine needs to be able to turn the AC compressor and the driving wheels at the same time
I am trying to avoid ant head or case machine work (line-bore excluded) thus want to stay with the 85.5mm P/C.
With a 74mm counterweight crank, the engine will be a whopping ( ) 1699cc engine.
Will probably go with the W100 cam
Compression ratio will be set to approx 8.5:1, deck height will be set accordingly, with a minimum of 0.05" (approx 1.5mm)
Now – a few questions –
Would I need longer rods or the stock 5.4" will suffice?
Using longer rods (5.5") might help with the clearance work, but will require a rather thick barrel and head gaskets, which will set the engine a bit too wide for the cooling tin.
So, any one with experience with a 74mm crack on stock length rods, what kind of clearance work is needed? Have no problem working with my trusted Dremel tool and do the clearing, as long as it's not too much.
Do I need a different fly-wheel? any recommendations?
Any other thoughts?

I know most of you will say that i need to go with a larger engine, but since i am trying to avoid opening the case and heads (larger bore), this is probably the largest displacement i can go without thinning the cylinder's wall too much.

Thanks
Ravivos.

[gearheadgreg]

Aircooled.net has a write up that answers all of your quesions: http://www.aircooled.net/vw-type-1-mileage-engine-mpg/

I got an engine with a Bus project recently, it was built back in the 90's, but brand new. 74 Scat Volkstroker x 88mm thick wall cylinders, 8.5:1 compression, Norris 336S cam, pocket ported heads, etc. I put it into a Baja project recently, with large tires and an 091 transmission and it works really well.

I would suggest going to the tick wall 88s, as it will help unshroud the valves and give another 100ccs of displacement. If you truly don't want to open the bores, I would go with a 76mm crank, and make sure to get the best head work done with stock size valves possible. That will likely determine the real power level of the engine, given your displacement and cam/powerband restrictions.

[Ravivos]

Hi Greg,
thanks for the answer, your link sure helped wrapping my head around the needed parts... but... (there is always a but...)
aircooled.net, as great as they are, trying to maximize their sales, which is of course a good thing but i really dont want to find myself spending money on parts i dont need, so a still trying to find the best value combo.
your engine descriptions sounds really good, and it is pretty much what i am looking for - a torquey engine with a good pull at low and mid range, somewhere in 80-90 bhp range with a flat torque curve.
i know ill have to port and polish the heads, and will probably go with the OTT exhaust :http://vwparts.aircooled.net/Tri-Mil-Tu ... -a-way.htm

i wonder, if i use the original con-rods, what kind of clearance job would i need to do, it would be great if i can get some picture of it...
is the clearance needed on a 76mm crank is similar to the 7mm one?

any thoughts would be appreciated,

Thanks
Ravivos.

[madmike]

If torque is what u want go with even shorter rods like Porsche length,then the motor tins fit because it will be stock width you might need to dremal the piston skirts then re-balance them you will know when you do the mock-up,Madmike

[Ravivos]

If torque is what u want go with even shorter rods like Porsche length,then the motor tins fit because it will be stock width you might need to dremal the piston skirts then re-balance them you will know when you do the mock-up,Madmike

Hi MadMike,
fail to see the connection between the con-rod's length and the engine's torque,
a "Stroker" is defined by the piston travel-to-bore ratio, the con-rods length will not have any influence on the engines torque curve nor its power curve...
as i see it (correct me if i am wrong), the rod length is selected according to a mechanical needs and restrains, and in order to minimize the needed shims for height adjustments...

is the 76mm crank requires the same amount of clearance as the 74? or is it involved a more complex work?

[dorkie]

pretty good article about how rod length affects power:

http://www.stahlheaders.com/Lit_Rod%20Length.htm

[FJCamper]

Hi Ravivos,

The connecting rod is a lever. Longer rods make more torque if all else is equal.

We have the complexities of calculating "rod ratio" which is vital to engine performance. This is one of the engine building areas that separate the winners from the losers.

CONNECTING ROD RATIO of STROKER ENGINES

(rod length divided by stroke length equals ratio)

The lower the ratio number, the more power the engine can produce

5.394" (137mm) VW ROD
5.352" (136mm) PORSCHE ROD

69mm 2.7165" VW STROKE
74mm 2.9134" PORSCHE STROKE

1.98 VW ROD RATIO, STOCK
1.99 PORSCHE ROD RATIO, STOCK

Stroke (in mm) times rod length (in mm)

69mm X 137mm = 1.98
74mm X 137mm = 1.85
76mm X 137mm = 1.80
78mm X 137mm = 1.75
82mm X 137mm = 1.67

Rod length moves the power band higher or lower in the rev range. The length of the rod and the length of the crankshaft stroke give the rod ratio. Rod length (mm) divided by the crank stroke (mm) = Rod Ratio.

The lower the ratio, the lower the power band, the higher the ratio the higher up the range the power band will move.

As a comparison the stock 1600cc set-up is 137/69 = 1.98 (considered high). If you wish to hill climb (torque) you will require a lower ratio (such as 1.76) and to drag race (rpm), a high one.

Standard VW rods are type 311. This is cast into the bottom of the big end. 311's are good for most engines up to 100 BHP, with a 69mm stroke crank. A stroker crank will either require these rods to be machined, or buy a set of previously cleared rods. The advantage of buying a set of rods is that they will have been balanced end for end and as a set, which will help engine longevity.

Like crankshafts, con-rods are available with different journals. You have no need to change from the stock VW 55mm diameter.

Chevy 327 rods are 145mm long, but require machining as the big end is only 51mm instead of the 55mm of the VW. This does save on changing the crank just to match the rods. These used with a stock length crank will give a high revving engine with a high power band, giving a rod ratio of 2.10, ideal for a small bore drag engine.

The Porsche 912 rod is a little shorter than the VW, but the VW is stronger, not a bad length, and it fits.

A long rod will give a slower piston speed, and therefore a longer life for the rings and cylinder walls, but this also causes the cylinders to fill up slowly when the piston moves down during the inlet stroke.

Of course, once the rpm builds this is overcome, hence the higher power band. A shorter rod will fill the cylinder much faster and therefore give more power at lower engine speeds, but be limited to a lower rev range.

Stock rods are nominally 137mm center-to-center (5.394") and get slightly shorter each time they're rebuilt. So with a stock 69mm stroke the ratio is 1.985, and with a 76mm stroke it's 1.80.

Many factors come into play when considering the "ideal" rodlength-to-stroke ratio. The lower the number, the faster the piston moves near TDC (and since it has to cover the same total distance in the same time, that means it's moving slower in the lower part of the stroke. This affects the port velocity and cam selection; with short rods a given engine will need bigger intake ports to keep from "running out of breath" at high RPM.

A lower number also increases the rod angularity near TDC - that promotes better torque due to the added "leverage".

Most production engines will make more total horsepower with a higher rod ratio - but that's because they tend to come with too short of a rod to begin with in order to reduce the total height of the engine. A 350ci Chevy, for example, has a rod ratio of 1.64 and people go to a great deal of trouble to squeeze in longer rods just to get that up to 1.72 - they'd be delighted if they could get even close to what the ACVW has stock.

For drag-racing, most ACVW builders go with a ratio considerably lower than stock (in the 1.7 ballpark) - to keep it up near stock with a big stroke requires really long rods which makes the whole package come out a couple inches wider than stock. Only a very small percentage of engines have ever been built this way, so almost all development of heads, cams, etc. has historically been done with lower rod ratios....in other words, the tail has wagged the dog here - the popularity of low rod ratios has much more to do with what fits than with what's best.

FJC

[gearheadgreg]

is the 76mm crank requires the same amount of clearance as the 74? or is it involved a more complex work?

As expected, the larger the crankshaft - the more clearancing of the case required. That said, the 74 is none or almost none, and the 76 is just a little more. I haven't clearanced for a 76, just educated guessing here - I'm sure there will be others on here that have done it 100 times.

[Ravivos]

Hi FJC,
That is an excellent educating explanation, although kind of hard to wrap my head around the concept.
i do get the stroker concept and its affect on torque and engine breathing (i.e power curve vs rpm).

so, in order to sum up the numbers and use your information, i've decided to go with a 76mm crank (on a set of 85.5mm B pistons) with a rod length of 5.5" (139.7mm), so the rod ratio should be 1.83, that will produce a torquey engine with the power at the low-mid range, correct? is rod ratio of 1.83 is a good number or i should ignore this issue as i am not competing? just looking for a decent street car with a good pull (and sometimes good "green light throttling")

by the way, pushing a pencil sure did the trick and gave me a better understanding on rod length, piston pin height and crank stroke.
all in order to try and build the engine as close as possible to its original width.

Hi Greg,
i've decided to go with the 5.500" I-Beam con-rod that suppose to clearenced
http://vwparts.aircooled.net/5-500-I-Be ... ournal.htm
so i guess the clearance work will not be a major issue.

one of the problems of building a performance (well, comparing to the original) engine here in Israel, is the price of the parts.
whatever you guys are paying for the parts (CIP1 or Aircooled.net) we pay exactly double the price (shipping and taxes).
that is way i am trying to find the most suited parts for my needs without the need to reorder things.

truly appreciate all you guys help, and any other thoughts or inputs are much welcomed.

Ravivos.

[gearheadgreg]

Bravo - in my opinion, every engine build should be scrutinized as much as you are. Is there any way for you to get around that high cost? Buy the parts and have them shipped to someone in the US and ship them to you as a personal gift? Just saying...

[Ravivos]

Hi Greg
when ordering the small bits and bobs, it is usually o.k, the problem starts when you order the bigger/heavier parts, that is when the shipping prices goes through the roof (even for a sea freight, that takes more than a month to get the parts) and the taxes sure builds up (we suppose to pay the tax for the full amount including the shipping).
but hey, that's life here at sunny Israel

i have another question regarding full flow oil filter (and adding a cooler) -
it seems it is almost impossible to use an off-the-shelf oil pump cover with two fittings on a type 3 engine, because of the fan shroud and the engine mount.
beside drilling and tapping the case side, is there any other way to implement an external oil filter (and cooler) without the hassle of drilling-tapping-plugging-re drilling - re tapping the case (oil galley)?
i saw people mounting the geneBerg oil pump cover, but still have problems with the clearance of the shroud and engine mount.
any input on this issue? would sure love to have a proper filter on the engine, and a decent oil cooler, and dont mind tapping one of the oil galleys, just dont want to end up with a ruined case.

Thanks.

[Marc]

...i've decided to go with a 76mm crank (on a set of 85.5mm B pistons) with a rod length of 5.5" (139.7mm), so the rod ratio should be 1.83, that will produce a torquey engine with the power at the low-mid range, correct? is rod ratio of 1.83 is a good number or i should ignore this issue as i am not competing? just looking for a decent street car with a good pull (and sometimes good "green light throttling")...

76mm stroke, B pistons and 5.5" rods is a tidy combination. Don't obsess over the rod ratio for a project like this, but rest assured that 1.838:1 will be just fine.
I've run a "conventional" full-flow setup on an IRS Type III and it did involve a bit of whittling on the moustache bar to avoid the use of multiple fittings but IMO it was worth it to avoid unnecessary restriction. The easiest way to deal with the return line is with an aftermarket fitting that brings the clean oil in through the pump-end oil-pressure plunger bore:
http://vwparts.aircooled.net/Full-Flow- ... p/3059.htm
These send all of the oil through the cooler, all of the time, so warmup can be delayed a little - but that's probably not much of an issue in your climate. They are not recommended for a single-relief case, though, since there'd be no overpressure protection other than what would be offered by a pump cover with integral relief.


The 1745 should be a nice engine for your purposes, but if the goal is just to maximize displacement while avoiding machinework to the case there's a far simpler and cheaper way to get to 1679cc. Over the years there've been three available 88mm cylinder sizes. The "slip-ins" which retain the top & bottom O.D.s of stock 85.5 jugs are too thin for anything but a trike or light sand rail. Old-school machine-ins retained the stock cylinderwall thickness (or close to it) so therefore required opening up the case & heads slightly - those haven't been seen on the market in years (there was a Biral version with aluminum fins that's particularly desirable, but those are rare as hen's teeth). Modern "thickwall" 88s require that the case & heads be opened up a little further, to the dimensions required for old-school 90.5s, and they're great for a Bus or Type III motor (the cylinderwalls are a bit thicker than stock). A couple of years ago a 4th size became available from AA - these have the lower spigot diameter of an 85.5 and the upper spigot diameter of a 92/late 90.5 which gives them the thickest walls of any off-the-shelf cylinder. The ~1mm thick lower spigot requires careful handling to avoid breakage, but once assembled it's not a problem - that region is low enough in the bore that it's not subjected to any stress from combustion, and they can handle the piston side thrust just fine.
So far there are no 88B pistons readily available (Berg used to make some by milling off unfinished blanks and squeezing the ring package - I have one set - but they aren't around any more) so 74mm is about the limit for stroke if you want to keep the width nominal. With stock rods the engine's only 5mm wider, and the rod ratio's fine at ~1.85. 88x84 brings you up to 1800cc, which happens to be about the limit for stock heat exchangers. You've got to open the heads up, of course, but there's no need to buy longer rods....just something else for you to consider before you commit to the 1745.

[Ravivos]

Hi Marc
I've read a lot about the thick walled 88s and they sure sounds nice, but i would like to try build it a bit different, although i now that the 1745 is not all that different.
maybe i am wrong but i think that the 1745 will suit my needs a bit better.
beside, not a cognitive dissonance, but i already ordered the parts...

so, it will be a 76mm counterbalanced,
5.5 clearanced i-beam rods,
engle W100
13lbs flywheel
original (solex?) carbs
will p&p the heads and intake manifold,
"over the top" exhaust",

now, i will probably need to re-jet my carbs, just wondering where should i start.

meanwhile, i got a hold of a nice original pulley that fits over the fan for an additional belt to drive an AC compressor, started thinking and designing the compressor's mount.
will probably need to let the original air filter (the one with the oil) go in order to get the comp in.

any recommendation to a set of nice air filters (dual) that will fit under the engine bay lid?

Thanks.
Ravivos.

[Marc]

Your car's still swingaxle, right?

Would you be averse to making an engine cover that offers more room over the carbs/compressor?

Have you considered mounting the A/C compressor in the stock generator location and fabricating a mounting system for a compact alternator?

[Ravivos]

Hi Marc,

My Ghia is 68' so its an IRS based.
If i won't have any other option, i will modify the engine cover for more room, but i saw pictures of a very nice air filters tucked under the lid without a problem... wondering if i can get a hold of such set.

as for the A/C compressor, i did though about locating it instead of the generator, but since the compressor is rather small (used on a small displacement engines like Suzuki swift/Alto), it doesnt really matter if i switch the gen and the comp.

here is a very nice picture showing exactly how i was thinking of mounting the comp, furthermore, this pic shows the nice air filters.

T3AC.jpg

any information is welcomed.

Thanks,
Ravivos.