best okrasa engine combo..help help needed

[WorkingClass]

i hope that someone can help me a bit futher and give me there 2 cent.

I got these oettinger manifolds
http://www.thesamba.com/vw/forum/album_page.php?pic_id=251290 the use 32 pbic's. the same as the older okrasa setups

I want to build an oldspeed engine for them,
what wil be a good setup for a lot of power / torque...

shout i make a big stroker engine 2276 82x94 or is this to big for the carbs (GWD did the same engine with a stock carb)
or shout is build a stroker small displacement 85.5x 76...with a high CR and big valves ...but this is not enough power/torque..

please help me out with some idea's


thanks

[layinLow Kustoms]

These carbs are to small to run a motor size of 2276. The original Okrasa setup came with the 2 heads which either ran a 7.5:1 or 8:1 comprassion ratio. The 2 carbs 32mm PBIC(36hp kit) or PCIB(40hp kit) have either a 26mm or 28mm venturi. There are several math formulas you can do to figure out airflow of the motor...if you need it I can post it up later. But bottom line is the 28mm venturi would be good for a motor around 1600cc displacement. I am currently building my 3rd okrasa setup right now for a 40hp motor and here are my specs below;

88mm biral p/c
69.5mm crank
scat c35 cam shaft
dual 32mm PCIB's bored to 35mm w/ 30mm venturi
scat lube a lobe lifters w/ SLR treatment
straight cut gears
heads ported and polished with 37.5mm intake valve and 32mm exhaust valve.

With my past experience, this setup should make an easy 80hp with about 60-70 torque.

[WorkingClass]

thanks a lot for the info....
there are not a lot of guys knowing this sort of stufff and staying with a standard out of the box way of building a engine.

I diden't thought of the fact of boring the carburators out to a 35mm....with bigger venturis...mine currently have 28mm verturis.
Webbers uses 28mm until 1800cc (depending of engine setup ofcourse)

Wenn i look a the VW standard engines..vw made a 2 liter type 4 engine with and used small carburators....the restriction always wil be the carburation but don't you not bennefit from a bigger volume??

[layinLow Kustoms]

By bigger volume do you mean displacment of the engine. If so yes you do but at a certain point you are basically starving the engine for air, thus creating more flats spots throughout your power curve. The formula for figuring out venturi size of a given motor i will list below along with a couple other formulas you should be considering before just throwing some parts together.


Engine CFM:
(Engine size (CID) x Max RPM/3,456)= CFM
Will Tell you how much air you engine will flow under perfect conditions. So now that you know what it will flow the next trick is picking the right carbs for this task. And a general rule of thumb is CFM/1.5 will give you your max horsepower, again in a perfect world.

Formula for venturi sizing:
20*SQRT(Cylinder Volume in cc's/1000*RPM of peak HP/1000)
Also note that your venturi size should be around 3-5mm smaller than intake valve for street/mild engines, and almost the same size on all out drag motors.

So since I gave you my okrasa motor specs Ill show you how I came to my setup for the okrasa.

I decided to go with the original okrasa crank in the okrasa kit which is 69mm. Since I wanted to stay with the whole vintage performance look the biggest period correct would have been 88mm Birals. The reason I chose birals is that they have cast aluminum fins on a cast iron liner, which increases the cooling effeciency of the cylinders some 20-40% from the normal cast iron setup. The benefit from this is to keep the head temps as low as possible, as Okrasa heads will crack if head temps get to hot. From here is where the math comes in to figure the rest of your setup.

Doing the math my engine will flow 192.665 CFM under perfect conditions so know the goal is to try and provide this much air to the motor to take advantage of your displacement. So with my CFM/1.5, if this motor is built to perfect conditions the max HP this setup could create is 128.44HP. Which will never happen but its always fun to compare this number to the actual dyno run at the end. So next we need to figure out what carbs to run. Since I wanted to stay with the original setup of the okrasa setup, the difficulty is to make 32mm carbs as effcient as possible. So while measuring up the walls of the throat I found that I could open it up to a max of 36mm while still having a 1/16th wall. But a 30mm venturi only requires a 35mm throat which works perfect. If you run the math I should actually be using a 32-34mm venturi but as you can see not possible without changing carbs. But I have found running a slightly smaller than needed venturi increases driveability, i.e. low end torque. So now that we know the venturi size which is 30mm we should have a 4-5mm larger intake valve size in your heads to take full advantage of the setup. Now with all this said dont get to obssesed with CFM of the motor cause I can make a large hole in anything but it wont have much airspeed. There is a direct relation of CFM to airspeed with out airspeed you lack the turbulance required for the fuel to atomize with the air. Hopefully this helps you out in picking what to put together with your old speed setup.

[WorkingClass]

i sended you an PM....

what make more sense to get to approx 1679cc (69x88) bigger cilinders or a bigger crank.....

[gimmesomeshelter]

Hello-

I'm slowly purchasing the parts required to build a 36hp based Okrasa engine (74mm crank, 77mm pistons). Do you have any experience building these? If so, I'm concerned that the the valve train will be a real weak spot. Do you have any suggestions? Also, what are the big mistakes people make when building these engines?

Thanks,

Paul
_________________
"I would rather have questions that can't be answered than answers that can't be questioned."

Richard Feynman

[layinLow Kustoms]

Traditionaly the kit came with a 69.5mm crank...but everyone has there own twist on engine building when it comes to combinations. But as far as the 74mm crank your probably going to have to do some clearancing in the case to make it work. Also as far as the valve train being weaker it depends on how you have the heads rebuilt. Definitly do not go with any dual springs as you will not need it, the single HD. I have also heard of some making there own ratio rockers for the 36hp setup. But with the normal 69.5mm crank, 77mm pistons, okrasa heads, dual solex 32mm pbic carbs, it was good enough. Best place to point you would be this topic Click Here as there is a lot of info about many 36hp setups.

[scott s]

[WorkingClass]

We think the same scott...

porsche used for the 1600c en the sc 74mm crank and a 82.5 bore...a longer crank will increase airflow at lower revs.


that why i think its better to have bigger crank and smaller bore. Different than VW used...

The difference from "gimmesomeshelter" I use 1600cc stuff so i can go everywhere he has to find his stuff for a 36hp....and is restrickted by this.

The only thing i want to use is mij okrasa manifolds and the 32 carbs..it is a street engine but is has to have "maximum" power output.

[scott s]

Then go 74x85.5 for 1699cc or 76x85.5 for 1745cc. Should add some extra bottom end grunt and cool like a stocker. Throw on a 36HP shroud and make it LOOK like a vintage motor, at least. Use one of the Flat Four Fram style oil filters and an 010 dist., stock pulley, etc. Maybe paint the shroud like the Super 90 engine?

[WorkingClass]

I already have a original fram and a 010 and 019
(depending on the cam). so i'm almost ready for it.

layinlow kustoms is gonne help me with my carburators, he know this stuff more than i do. Hopefully it will work out

[MJMarkham]

[MJMarkham]

ok, started searching...is there a source for 77x69mm P/Cs
_________________
M J Markham
57 Ragtop Oval, 58 Lowlight Coupe

WANTED: Original 58 Ghia Dash Knob

[Alstrup]

http://www.thesamba.com/vw/forum/album_page.php?pic_id=251290

I am not absolutely sure, but the carbs in the above link looks suspiciusly much like a set of 40 mm PDSIT´s.
If that´s the case, they will easily handle up to 2000 cc. They ome factory equipped with up to 30 mm. venturies, but accepts 32 mm. without serius jetting problems.
With the right combination of parts they will support 110 - 120 hp.
T

[WorkingClass]

@Alstup, The carburators i have are 32 pbic's mm like the original setup shout be. The carburators in the pictures are (i think) 32/34 type 3 carburators. these are not original with the set but will problebly work good with the manifolds.

After some talk with brandon from layinlow customs we decided to go with overborering the original 32mm carburators to a 35mm trouth now it wil except a bigger 30mm verturi...this will work better with the 35mm intake. than i decided to go with a bigger, porsche like 74 mm crank with 85,5 bore.