TheSamba.com :: View topic - 1957 Euro Semaphore/Ragtop Vintage Speed Project

Tue Nov 23, 2010 7:01 pm

Oval56
If you dont mind will you share your head and carb specifications with us?
88 hp means you did a lot of things right.
I still have those items to work out.
Thanks

Tue Nov 23, 2010 10:51 pm

no problem, i had all here online...

http://www.thesamba.com/vw/forum/viewtopic.php?t=3...p;start=20

74x82,5
okrasaheads ww modified 36/33, solex 40pbic singel crabs, rockerchange (porsche super 90) porting, regrind custom cam, 356 rods balanced, crank reworked.....

my 1433 singelport:

[/url]http://www.thesamba.com/vw/forum/viewtopic.php?t=327411&highlight=oval56[url][/url]

Wed Dec 01, 2010 8:33 am

Update on my Engine Build
I have put a lot of thought in what to have done to the Stock Okrasa heads. A memeber on here sugested i talk with Ron Chuck in CA. I gave Ron a call and he seems to think we can massage a good bit more performance out to the Heads.
So today i have shipped my heads to him.
We are going to
Bore heads to get the Compression Ratio that i want
Port and polish
Look at increasing the size of the Valves
Replace the stock valve springs with heavier ones

Any other suggestions are welcome?
Thanks

Thu Dec 02, 2010 1:26 pm

With my heads off to Ron Chuck I thought I would focus on the Okrasa Manifolds Maybe to get some ideas on how to get more flow out of them. Any suggestions from the Forum would be nice . I am no engineer so hopefully someone will chime in. As I have a couple Questions.

The stock Okrasa manifolds consist of a 32 mm Carburetor flange that feeds a 32 mm tube that is 2.75 inches long, Then it splits or Y's into two 28.5mm tubes 5.5 inches long that feed the two ports on the heads

It seems to me that the two 28.5 mm tubes can flow more than the single 32mm tube that feeds them. If so my question is this What Size single feed tube would supply the two 28.5s to there maximum potential?
Thanks to you engineers
Rick

Fri Dec 03, 2010 3:29 pm

what is your hp goal with this engine?
valvesize, cam? carburetor?

to your question. yes two 28,5mm holes flow more than one 32mm hole ;) but in a 4 cylinder 4 stroke engine. only one cylinder will suck at one manifold pipe at the same moment so it suck on the 28,5mm and on the 32mm and on the venturi of the carb...that will be the smalles area. so the manifold is good how it is. bigger single pipe will change nothing.
its a question of flow. i beginning with easy to calculate things but good to understand how engines work.
your piston goes down with a specific mean piston speed that is easy to calculate in your case i would say 12m/s here you start(this is at max. peak at 4500rpm).
this is also your mean port velocity in the cylinder. with a stock valve of 33mm the thinnest area would be...lets be optimistic and say 28mm this is about 8 times smaller than your bore of 80mm in square. so the speed of gas would be 8 times faster so you are at about 100m/s. alot of people found out that at about 80-90m/sec you will have best flow VE and so your peak hp. normal... flow and so volumetric efficency (VE) will go up with rpm up to 110-120m/s ...depends on ... and than it run into pumping losses and the VE will decrease rapidly. to use the engine over peak hp make only sense on races...so 80-90m/s is for peak hp on engines like we have.
how you see with your kind of parts an engine rpm over 4500 is not usefull the port and intake valve is the restriction. for the most 36 it is very hard to go over this RPM mark with peak HP.
this are the limits of the heads. what you want at the end is that heads, cam, manifolds, exhaust and carbs are all in a range arround this limit.
same calculation for your carb. the venturi is the smalles area and also an restriction. with a venturi of about 28mm it would work great how it is maybe smaller for driveability.
if you want more you could also use steffi.g 's manifolds for zenith carbs.
they have and also give more potential to the heads.
one thing that you can do with the okrasa manifolds is to shorten the bigger pipe. this could transfere the powerband a little up or could give a little more top end and a little less low end. but this will not be really much just a little. the manifolds are long and that is good for low end power. and 4500 is no high rpm. you want as much as under the curve how you can get.
you could also try to mount bigger and better flowing carbs so with a bigger big pipe on the manifold but this could be tricky to make it work. but if the carb is the most restrictive part in your build it will free some HP.

lets see what your head porter will do with your heads ;) maybe after that you have 2x 30mm holes ;) than you need a new manifold ;)

first you have to know what you want. than you can find out how to get it.

wishes

Fri Dec 03, 2010 4:40 pm

Hello-

I'm in the same boat. I've been slowly collecting parts for an engine that's a 356 1600 wannabe (356 crank rods, 82.5mm pistons, Zenith carbs, and modified Okrasa heads). Experimenting with DesktopDyno has helped, but I still feel very uncomfortable committing to a particular head/cam. What would be a good resource for this kind of information?

Thanks,

Paul

Sun Dec 05, 2010 1:23 pm

Thanks for the information. I guess with what you have provided i need to wait and see what the final head confiduration will be.
As far as carbs go at this point i have in the works a set of Solex 34PBICs and a set of Solex 40 PICB. I am leaning towards the 40s as that is what Porsche used in there 1500 Super. And my engijne is going to be close to that . Same Crank/Pistons/Cam I may run a little more Compression Ratio.

Again thanks for sharing with me

Sun Dec 05, 2010 1:42 pm

Just found this Picture of a set of Okrasa manifolds that Oval56 modified.

Im not sure what he increased the size to. But i beleive they were modified to fit a set of 40 PCIBs

Thu Dec 30, 2010 7:40 am

After balancing the Rods i decided it would be wise to do the pistons. Then i thought why not do the pistons and pins as a matched pair. So that is what i am doing . I matched the piston and pins to get combos with the least weight spread. Now my thoughts are to remove any needed materital from the Pins and not the pistons to get the matched pairs to .5 of a gram. What are your thoughts on removing the weight from the pins?

Tue Jan 04, 2011 6:54 am

Update on the Body. Ready to start putting things together. Fresh Red Coral paint

Tue Jan 04, 2011 7:57 am

i modified my manifolts op to the 40 pbic's to gat a matching port down to that point where theh 2 tubes hit the singel one... i also had the idea of bigger manifolds, but it make than sens if you can do bigger valves and bigger ports... my valve is 37mm my ports are 36mm my tubes are 29mm
what do i get is a better vacuum flow trough the manifold

the thing is, waht goal of hp do you have and how hard would you like to go on the border of what is possible or what not.

the main point is rockerratio + cam.. and if you do not modifie your rockerarm ratio, all other points will make not much sens.

i have made some lasercuts flanges down for okrasa heads stud pattern for 35x1,5mm tubes means 32mm inside diameter! - they are availible

Mon Jan 24, 2011 2:46 pm

Update: I am waiting on my head work to be completed to finish my build. In the meantime i Rebuilt restored an orignal 56/57 period correcrt Oval Fuel Pump > I am ahppy with the results.

Nice and Fresh looking

Mon Jan 24, 2011 3:58 pm

Hello Rwoodshvac
And,.... after the carb are you going to rebuilt the fuel pump ? :lol: :wink:
Nice thread, by the way.

Mon Jan 24, 2011 5:13 pm

Hello-

Did you have to put in a stronger spring to accomodate the fuel needs of your carbs?

Thanks,

Paul

Mon Jan 24, 2011 5:34 pm

gimmesomeshelter wrote: Hello-

Did you have to put in a stronger spring to accomodate the fuel needs of your carbs?

Thanks,

Paul Would putting a stronger spring in the fuel pump increase flow? My understanding was that you increase flow by removing excess gaskets.

Mon Jan 24, 2011 5:40 pm

Hello-

I don't know. I always assumed it was done with a stronger spring because the Judson guys do it that way.

Paul

Tue Jan 25, 2011 1:40 pm

Paul
You are spot on. The only way i have read to increase fuel flow is to use a Judson Spring. I have not heard of the gasket trick.
Here is a picture of the Judson spring, i have a picture of the stock and the Judson side by side i will post later i think it is still in my camera . You can pick Judson springs up here on the Samba

Thanks for the correction on Carb/Fuel pump

More info comming on my carbs

Tue Feb 01, 2011 8:42 am

Here is a Picture to compare a stock 1957 36 hp spring to a Judson Spring that is designed to provide more fuel delivery from stock fuel pump . There is a big difference in the stiffness

Tue Feb 01, 2011 8:45 am

Where did you get the rebuild items for your fuel pump?
great thread :D

Tue Feb 01, 2011 9:51 am

Changing the spring is the way VW did it for the Type 3 dual carb pumps.
Up with the push rod, and the diaphragm is pulled down. Push rod retracts, and the diaphragm goes up, because of the spring, Pushing gas out of the pump to the carb. Heavier spring = Higher pressure.