1.25 ratio rockers on intake 1.1 on the exhaust?

[buglover34465]

Has any body done this? What were your results? building a miliage motor simular to Hot Vw's 76x85.5 with a CB performance cam simular to the 110. thanks.

[SamT]

wouldn't be a problem, would probably promote some low end torque. Swaping rockers would be an easy drive it for a few tanks test to see if mileage improves, but I haven't done it...

[gt1953]

That engine is under my hood. 73 standard. 76mm counter weight crank, balanced rods, cheater cam, stock heads worked over, dual single barrel solex carbs, 010 distributor, header, lightened flywheel. Rotating mass was balanced. 1st 125 miles stop and go was 25mpg. Then the next 200 miles was driving home 1000 feet elevation to 6100 feet elevation average speed was about 60 to 65 up and down 6% grades. 34.5 MPG Next tuesday another road trip.
_________________
Volkswagen: We tune what we drive.
Numbers Matching VW's are getting harder to find. Source out the most Stock vehicle and keep that way. You will be glad you did.

72 type 1
72 Squareback
({59 Euro bug, 62, 63, 67, 68, 69, 73 type ones 68 & 69 type two, 68 Ghia all sold})

[fusername]

mileage is really bad on a fresh rebuild, stuff settles in and then it all comes back in glory.
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Need something custom bent up? shoot me an email, maybe we can make it work!

FORSALE: Thrust cut T4 and 1.9 main bearings

[gt1953]

Oh forgot to say is has 1.5 quart deep sump for a total of 5 quarts of oil and full flowed with a 1 quart filter.
_________________
Volkswagen: We tune what we drive.
Numbers Matching VW's are getting harder to find. Source out the most Stock vehicle and keep that way. You will be glad you did.

72 type 1
72 Squareback
({59 Euro bug, 62, 63, 67, 68, 69, 73 type ones 68 & 69 type two, 68 Ghia all sold})

[buglover34465]

I have a stock weight flywheel. The engine is also set up for full filter flow with the Bob Hoover oil mods, with a type 4 cooler, 5.5" rods, demellow full circle race weight 76mm crank, 4 in one header with a vacume pipe mod for the centermount carb preheat, and a dual vac distrubitor and it's matching 34 picti 3 carb. I have a jag crank harmonic balancer pully like John Karcey (but with an alternator instead of a generator). I am slowly setting the heads up, aiming for a .040" deck and 8.5 to 9 ish compression. What compression are you running? I am considering running exhaust port extensions like "The Old One". From the man himself: "The principal reason for originally developing these extensions was to combat reversion back in the mid 70's. As program dollars permitted more and more port/system R&D, I found that on some applications, extending the exhaust port length (before dumping into a larger primary header pipe) caused significant torque increases over shorter ports. Equalizing port wall lengths to equalize surface friction was next, and of course, combining all three followed.
I never came up with any formula's for doing this, and today, I still determine the best combination the old fashioned way....on the dyno in both acceleration runs (ramped by time) and the more effective acceleration runs ramped by a diminishing load, where elapsed time from point A to point B in the RPM scale is the read-out. This later method equates more closely to real-world.
Larry"

[buglover34465]

[DarthWeber]

[madmike]

With the mismatched rockers I would keep a close eye on the Temp gage
_________________
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Rail Buggy 1915 turbo
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"

[vugbug68]

Wouldn't you have to run different length pushrods to get your rocker geometry right?
_________________
71 Super - Backroad Thrasher
66 Corvair - Weekend Cruiser
90 4 Runner - Muddin

[buglover34465]

yes the exhaust pushrods would be of a different length from the intake pushrods. I am wondering why would I have to keep close eye on the engine temps? How's your engine temps GT1953? Has anybody else run this combo of rocker arms?

[buglover34465]

http://www.1800vw.bizhosting.com/raito_rocker_arms.html :

Genuine VW 1.25 Ratio Rocker Arms Genuine VW You can run them with stock adjusting screws or with the Captive Ball adjusters. No Special Push Rods Needed
Drop forged, precision machined and heat treated. Set of 8 rocker arms. "As sold by CB (10% More HP) for $119.95"
Note: We have very good results with some cams running 1.25 rockers on intake and 1.1 or 1 to 1 on ex.

My understanding of the answer to my questions about the above statement. The exhaust does not need the extra flow, the advantage is on the intake side. Exhaust duration is longer so not much effect due to the lower lift as compared to the intake. The exhaust speed is slightly higher due to the smaller opening which builds a slightly higher backpresure. Thus better for a miliage motor.

Hoping to hear from real life results/experiencies.

[buglover34465]

my websight, http://sites.google.com/site/buglover34465/ please check it out. I am told that the stock Vw cam came with different grinds for the intake and exhaust valves. simular to my idea. Is any body else running this setup?

[sergVDUB]

i did it and they work good
you get more lift and you get some performance for it but not a lot, but it is a step to making a bigger motor


right now i working on my motor...
making it a 1915cc and i am going to use the 1.25 arms

[buglover34465]

From the great Bob Hoover "The stock Volkswagen cam uses
less lift for the smaller exhaust valves. (Maximum effective lift is
PROPORTIONAL to valve diameter. Any greater lift simply increases the
engine's wear whilst decreasing efficiency.)"

[miniman82]

Bob is referring to was what David Vizard calls 'curtain area', as illustrated by the following picture (the area in red):

The more curtain area you have, the more you can flow through the cylinder head (to a point). This explains why 4 valve heads are so much better than 2 valves, since the curtain area is doubled. More lift is only beneficial so long as flow is increasing, once you get to a certain point it makes no sense to open the valve any farther since the gains to be had are negligable.
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Build thread: http://www.thesamba.com/vw/forum/viewtopic.php?t=212747

[Bob Hoover]

From the great Bob Hoover...

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Wow! Great, eh? House falling down, mean case of cancer trying to do me in and all I get is GREAT? Sheezzz. Shoulda been at least a grate & a half.

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But as for the topic, all I can say is that I REPEATED it. The fundamentals of poppet-valve operation have been well understood for more than a hundred years and as you may have guessed, a lot of very smart cookies have applied a lot of thinking to the charging issue.

That's what it is, by the way.... charging. You open the intake valve so you can CHARGE the chamber with your combustible mixture, and right in there -- in the charging of the chamber -- you can get about 99% of your automotive education.

The charge has mass. Open the valve, say come on in, the charge just lays there and looks at you. It won't move unless some energy gets applied somewhere. You can PULL it in or you PUSH it in or you can just stand around tapping your toe waiting for it to wake up and come in on its own... which is about what you get with a Volkswagen. Figure out how to get the charge moving earlier... and faster... and you run a good chance of getting MORE charge into the chamber. Right off the bat all the monkies twirl their wrenches and make the valve open higher. Which doesn't do a damn bit of good. Charge is STILL just laying there, looking at you. Indeed, the task is trickier than it appears.

Because the fuel/air charge has MASS it also has INERTIA. Like in physics and all that jazz. If you want to improve on the charging problem you'll need to delve into the physics of the problem. But bigger valves sounds way kewl. Gotta be something there. (Actually, bigger valves can be a huge mistake. And yes, there's a little play on words there.) Think about charging the chamber as an event that takes place over a given amount of TIME. You can see some benefit from larger valves only aft the charge begins MOVING. The real bell-ringer is how to get it moving earlier. To that you need a bigger difference in the pressures involved. If you can reduce the pressure in the chamber so as to create a bigger DIFFERENCE in pressure, then you may benefit from larger valves. But larger valves typically require more energy... they have more area that needs to be sealed and that dictates the use of a stronger spring. And of course, you have to COMPRESS that spring to begn with, which is why, after doing all the kewl trix you may end up with a turkey instead of a screaming eagle.

Since charging is a time-related event you may want to look at its finish as well as its beginning, since the higher the rpm, the less TIME you will have to charge the chamber.

All of this is skirting around the problem of Volumetric Efficiency. But I'll leave that for another day. Right now I'm trying to teach a kid in Bombay how to make a table saw out of a cardboard box and an old ceiling fan.

-Bob Hoover

[Jengel451]

[buglover34465]

Food for thaught ( Norris cams ) Their milage maker is 218 duration @.050, lift at the cam is 352 on the intake and 330 at the exhaust on a 107 lobe center.