1.25 ratio rockers

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benito26
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Re: 1.25 ratio rockers

Post by benito26 » Tue Jun 11, 2013 8:05 am

Some good info given in this thread, the stock oil pump and galleys are plenty big enough for most mild engine combinations if built right.
To answer your initial question, yes you can run 1.25 rockers especially if you already have them but bear in mind you are using 40 year old stock springs.
It's really dependant on budget to what can be done to your engine as you mentioned spitting the case, I would pretty much agree with Marc.
88mm thick walls
Stock crank balanced
Pauter B6 cam for 1.1 or 1.25

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Re: 1.25 ratio rockers

Post by Marc » Tue Jun 11, 2013 10:09 am

advinnie wrote:...the only reason im not interested as yet in making the engine bigger is because its only a single relief case and ive been told that increasing the engine size any bigger than a 1600 twin port on a single relief case is a bad idea due to the fact that the oil ways are smaller.
Might have been a good idea to mention that at the outset. What vintage is this case? (Case ID letters/numbers, please).
Small-passage/single-relief cases were all there were to work with until 1970 - a whole lot of VW performance engines were built before then. IMO it's a bad combination to use a cross-drilled crankshaft (those came along in `68) in one, but they're adequate for a mild engine such as we've been discussing. There are bigger concerns, though - the alloy used in `68/`69 was notoriously soft and prone to warpage/cracking/pulled head studs even in bone-stock form - one of those cases is overstressed as a 1600DP (actually they weren't even very good as a 1500SP) and if you have one that's still a running engine the best thing to do to it is...nothing. Be nice to it, don't hot-rod it, and save your money for the inevitable replacement.
advinnie wrote:...Unleaded is unleaded and its only one price...
Seriously? You only have one grade of fuel available? In the USA it's all unleaded, but there's at least a 5-point spread in the available octane with a corresponding price difference.

advinnie
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Re: 1.25 ratio rockers

Post by advinnie » Tue Jun 11, 2013 10:30 am

Right first I will have to get back to you with the engine case number but it started life as a 1500 single port single relief case witch was made back in 1969. And in the UK you have unleaded 95 ron and super unleaded 98 ron and thats it. Im guessing then I should be looking for a new case

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Re: 1.25 ratio rockers

Post by heliarc » Tue Jun 11, 2013 1:15 pm

If I might suggest something, you're not going to use this car out of town, you want more low end and you're not concerned about high speed, why not go with the smaller tires on the rear end? This will give you a little more snap off the line and it's dead simple.

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Re: 1.25 ratio rockers

Post by advinnie » Tue Jun 11, 2013 1:57 pm

Good idea not thought of that. I running 155/80/15 at the minute that give me an overall diameter of 269mm any suggestions on whatvsize to fit?

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Re: 1.25 ratio rockers

Post by Marc » Tue Jun 11, 2013 9:58 pm

advinnie wrote:Good idea not thought of that. I running 155/80/15 at the minute that give me an overall diameter of 269mm any suggestions on whatvsize to fit?
155/80-15s are approximately 24-3/4" diameter (around 4½% shorter than a stock 165-15). If you have 4½" rims, a Smart Car front tire (175/65-15) will shoehorn on and at under 24" diameter will drop your gearing by (about) another 3%. For anything shorter, other than temporary-use spare tires or dinky Citroen 2CV rubber (neither of which really has the load capacity for the rear of Bug), you'll need to get some wider rims (5½ to 6½").

Again, it'd be nice to present all the details in your initial post. 155/80-15 rear tires change the expected RPM (4.375, .88) at 67 MPH to ~3540. 155/80s would bring that up to ~3620....tolerable, IMO, for highway jaunts of under ~20 miles.

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Re: 1.25 ratio rockers

Post by advinnie » Fri Jun 14, 2013 12:53 pm

Hi all first I have decided to leave the tyre sizes how they are at the moment 145/65/15 up front and 155/82/15 at rear. Second of all ive just fitted some scat 1.25 rockers and dont know why people are saying that you will not see much or an improvement I DID. I thought fitting dual 34 carburetors woke the engine up well fitting 1.25 rockers woke the engine up a lot more it pulls harder and longer in each gear now it can hit 36mph in second, pretty much 60 in thrid and four well I got to 80 (on a private road of course) and it was still going but had to slow down cause I was shi$#ing it. Anyway if thats what a ratio rocker does cant wait to fit a w100 or w110 cam and god knows how it will react when I send of the heads to be ported. Once again cheers for all your feed back.

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Re: 1.25 ratio rockers

Post by Marc » Fri Jun 14, 2013 9:01 pm

With your trans and rear tire size, a true 36 MPH in 2nd is 4406 RPM - about 100 RPM below the HP peak of a bone-stock 1600DP with a single carburetor...so it's hardly impressive that your dual-carb engine can rev that high...and a full 60 MPH in 3rd would be 4492 RPM, right about what one would expect of a healthy stock engine. When my `69 was new, I once drove it up a steep grade with a full load (me and a friend plus all our stuff headed to college; not a cubic foot of unfilled space left in the car and more strapped on the back) at 65 MPH...with the radio blaring and back seat area crammed full I was oblivious to the fact that I was still in third for several miles, and that was about 4450 RPM with a bone-stock 1500 singleport.

So, if you're that impressed by your new-found performance (realistically, 1.25 rockers could not have added more than 2 HP, tops) I'd have to surmise that either you serendipitously corrected some other problem while replacing the rocker arms, or you have an extremely sensitive "butt-dyno".
If the latter, you're really going to like it with the ported heads and a little more cam duration...but don't forget my caveat about H5 cases, with the dualport heads and ICTs it's already being overstressed when driven hard.

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Re: 1.25 ratio rockers

Post by advinnie » Sat Jun 15, 2013 3:41 am

Marc wrote:With your trans and rear tire size, a true 36 MPH in 2nd is 4406 RPM - about 100 RPM below the HP peak of a bone-stock 1600DP with a single carburetor...so it's hardly impressive that your dual-carb engine can rev that high...and a full 60 MPH in 3rd would be 4492 RPM, right about what one would expect of a healthy stock engine. When my `69 was new, I once drove it up a steep grade with a full load (me and a friend plus all our stuff headed to college; not a cubic foot of unfilled space left in the car and more strapped on the back) at 65 MPH...with the radio blaring and back seat area crammed full I was oblivious to the fact that I was still in third for several miles, and that was about 4450 RPM with a bone-stock 1500 singleport.

So, if you're that impressed by your new-found performance (realistically, 1.25 rockers could not have added more than 2 HP, tops) I'd have to surmise that either you serendipitously corrected some other problem while replacing the rocker arms, or you have an extremely sensitive "butt-dyno".
If the latter, you're really going to like it with the ported heads and a little more cam duration...but don't forget my caveat about H5 cases, with the dualport heads and ICTs it's already being overstressed when driven hard.
Hi there right just been speaking to the vw specialist here and yes they do agree with you that fitting 1.25 rockers to a stock engine would see you may be 1 BHP ish. But they also agree with me that the rockers have made an improvement to the performance ( the people at the vw specialist are my dads friends and they have driven the car thats how they know before anyone asks) and they are saying that there can only be two real reasons. 1: the least likely is that the camshaft had warn so much that fitting the 1.25 rockers has brought the cam profile back to what it should of been roughly when new.
2:the most likely, that fitting the dual carbs would of seen an increase in performance straight away but with the stock cam, heads and rockers the changes are the the engine was only capable of using may be 80% of what the carbs could offer but fitting new rockers would allow the engine to be able to dip in to the other 20%.
But they are saying that it is easily possible to get 80-85 BHP from a 1600 twin port using dual 34 carburetors a w100 cam with 1.25 rockers and a balanced crank.

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Re: 1.25 ratio rockers

Post by aussiebug » Sat Jun 15, 2013 5:36 am

advinnie wrote:What do you mean Would you like to be able to run the least-expensive petrol? Unleaded is unleaded and its only one price.
Advinnie

For info

You are in the UK and Marc is in the USA. In the UK, normal unleaded is already 95RON Octane which is fine for a stock compression VW engine - in fact it's fine for VW engines up to about 8:1 compression ratio.

In the USA they have more choices in fuel types - at different prices.

Fuels are not the same all over the world. In the USA they measure octane ratings using the (r+m)/2 method. That's RON + MON divided by 2 (for an average of the two test methods). This is called AKI (anti knock index) or "pump" octane. They have several grades of gasoline (petrol), some of which contain alcohol and some which don't (differences between states), and have fuels starting with lower equivalent octane ratings than the UK.

In most of the rest of the world, octane ratings use the RON method only.

Your UK 95 RON unleaded would be rated about 91AKI in the USA.

Then I think you still have 4-star or premium - which has an octane rating of 98 or so?

Here in Australia, we have 91 (normal unleaded), 95 premium and 98 ultimate - still unleaded of course. There are also 10% ethanol mixes (E10) here of 91 and 94 at selected service stations, and they are talking about an E85 (85% ethanol) fuel coming soon - 95 octane I think.
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Re: 1.25 ratio rockers

Post by Jim Ed » Sat Jun 15, 2013 5:45 am

Did you ever try using premium gas? My Beetle's engine seems like it is happier with it!

aussiebug wrote:
advinnie wrote:What do you mean Would you like to be able to run the least-expensive petrol? Unleaded is unleaded and its only one price.
Advinnie

For info

You are in the UK and Marc is in the USA. In the UK, normal unleaded is already 95RON Octane which is fine for a stock compression VW engine - in fact it's fine for VW engines up to about 8:1 compression.

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Re: 1.25 ratio rockers

Post by Marc » Sat Jun 15, 2013 8:24 am

Higher compression ratio, carbon buildup, lean fuel mixture and excessive spark timing advance can all increase the requirement for a particular engine to avoid detonation, but there's no more energy contained in higher-octane pump gas than in Regular. In fact, if the octane is raised by blending in alcohol the energy content per gallon is less than that of "straight" gasoline.
A stock VW engine is designed to operate on 91 RON gas, US 87 meets that requirement - and as Rob pointed out, "Regular" in many parts of the world exceeds it.
Any modifications which increase the peak pre-ignition cylinder pressure will increase the octane requirement. Basically, that means higher static compression ratio and anything which increases the volumetric efficiency, such as cam or head modifications - to put it simply, how much air/fuel mixture gets in, and how hard it's squeezed.
Gasoline refiners have encouraged the public perception that "Premium" fuel is better for all engines for one simple reason - they make more profit per gallon on it. If your engine actually needs higher octane for some reason, of course that's what it should be fed...but if not there's no benefit in running it (other than to the oil companies' bottom line).

http://en.wikipedia.org/wiki/Octane_rating

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Re: 1.25 ratio rockers

Post by aussiebug » Sun Jun 16, 2013 5:39 am

The wikipedia entry Marc notes above is wrong in one respect - it equates pre-ignition with detonation. In fact, pre-ignition means the fuel ignite BEFORE the spark (hotspots in the cylinder etc) but detonation normally occurs AFTER the spark but before the flame front has finished racing across the cylinder head and burnt all the fuel - the remaining fuel-air mixture self-ignites and causes a "hammer blow" to the piston, rather than a steady push. Otherwise it's a good article.

Pre-ignition CAN result in detonation if part of the fuel mixture self-ignites after the pre-ignition starts the burning process, but the two are not the same.

Another way of looking at it is that pre-ignition refers the the initiation of fuel burn, where detonation refers to the final burn parameters.

The wikipedia Octane article also mentions the Cetane rating, which is NOT used in reference to gasoline/petrol.
A Cetane number refers to the EASE of self ignition of a fuel and is used in reference to diesel fuel, which MUST self-ignite as diesel engines are compression ignition - no spark plug. They would have been better not mentioning Cetane - it might confuse some folks.
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Re: 1.25 ratio rockers

Post by Marc » Mon Jun 17, 2013 1:26 am

aussiebug wrote:...Pre-ignition CAN result in detonation if part of the fuel mixture self-ignites after the pre-ignition starts the burning process, but the two are not the same...
All technically correct of course, but if all you're concerned with is the minimum required fuel octane it's kind of a moot point - pragmatically speaking, they're both the result of cylinder pressures too high for the fuel being run, and in either case the solution is the same (buy better gas).

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Re: 1.25 ratio rockers

Post by madmike » Wed Jun 19, 2013 7:08 am

You guys didn't catch that his 2 tip GT exhast is probably holding back a bunch of ponys :lol: :lol: :lol: :lol: :lol:
Get a true 4 into 1 merged with a good flowing muffler 8)

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