1.25 ratio rockers

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advinnie
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1.25 ratio rockers

Post by advinnie » Mon Jun 10, 2013 7:16 am

Hi all I have a 1600 twin port beetle with a stock cam and crankshaft but it has dual 34 carbs and a 2 tip gt exhaust and the head will be sent of soon for porting but I need some rockers. Should I stay with stock 1.1 rockers or get some 1.25 ratio ro rockers? Any advice welcome cheers all

Stray Catalyst
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Re: 1.25 ratio rockers

Post by Stray Catalyst » Mon Jun 10, 2013 11:07 am

Stock cam and crank, you're fine to use stock rockers IMHO.

advinnie
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Re: 1.25 ratio rockers

Post by advinnie » Mon Jun 10, 2013 11:17 am

Sorry im new to this what does IMHO mean

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Re: 1.25 ratio rockers

Post by Stray Catalyst » Mon Jun 10, 2013 11:39 am

In My Humble Opinion.

I use 1.25:1 rockers on my 1835 engine, but I'm also using a W110 cam and a 69mm counterweighted crank. As your engine's internals (cam, crank, etc) are all stock, you should be just fine with the standard 1:1 rockers. If you decide to rebuild the engine for higher performance, the rockers might also need to be upgraded - but at this point, I don't think you'd see any difference except the amount of money you're spending.

advinnie
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Re: 1.25 ratio rockers

Post by advinnie » Mon Jun 10, 2013 12:01 pm

So even with ported heads and dual 34 carbs there is no need to use 1.25 rockers.

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Re: 1.25 ratio rockers

Post by Stray Catalyst » Mon Jun 10, 2013 12:29 pm

Ratio rockers are needed if your cam is trying to lift your valves rapidly and a greater distance - the type of heads or carburetors won't change the valve lift at all. Heads and carbs are the easy way to get more power out of an engine - but you're still using the stock cam, so the valves are still lifting the stock distance. Assuming you're still using single springs, there's very little benefit to getting the ratio rockers for your engine.
I'm not an expert - don't take my advice as gospel - but until and unless you get a more aggressive cam, you're unlikely to see any benefit from ratio rockers. Using them will slightly reduce the wear on the cam, but the difference (with stock cam and crank) is negligible. Use the same money for a split cable linkage for your carbs - you'll see the difference that way, as you're not going to be getting those odd problems as the hex bar linkage responds to heat.

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Re: 1.25 ratio rockers

Post by FJCamper » Mon Jun 10, 2013 1:44 pm

Hi Stray, Advinnie;

The "ratio rocker" will lift the valve a bit higher -- so in that respect it is like a cam with a higher lift, but it doesn't increase duration, the amount of time the valves are open.

Duration is where the power band goes up with RPM. Long-duration cams have that familiar rough idle or irregular lope to them because they are allowing the intake and exhaust valves to be open at the same time, and at low RPM, the gasses mix.

You'd feel (maybe) some better initial accelleration (1000-3000 rpm) because you're getting slightly better breathing from a higher lift, but above 3000-3500, you have no extra duration to extend the breathing into the higher RPM range.

The real hassel in mounting ratio rockers on a stock engine is shimming the rocker arm assembly outwards away from the head so you can use your stock pushrod length.

Where ratio rockers shine is on top of cams that can use them. The Engle 100, 110, 120, all can. They make a good performance cam a little better.

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Re: 1.25 ratio rockers

Post by Devastator » Mon Jun 10, 2013 2:01 pm

You might also consider upgrading the rocker shafts if they are stock, whether you run the ratio rockers or not.
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Marc
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Re: 1.25 ratio rockers

Post by Marc » Mon Jun 10, 2013 2:03 pm

advinnie wrote:So even with ported heads and dual 34 carbs there is no need to use 1.25 rockers.
That's not quite the way I'd put it. The engine would benefit enough from 1.4:1 rockers to justify their expense. Dyno tests have shown around 4 HP gain, mostly from 4500-5500RPM (the upper limit for a stock crank) but only after fitting HD single valve springs. The added lift doesn't change the total time that the valves are off the seats, it's true, but because they are opened at a faster rate the effective duration (time spent open more than ~.050") does increase slightly...enough so, in fact, that there's actually a measurable drop in HP at <1500RPM.
But the performance gain from 1.25s is much less, perhaps 1 to 1½ HP - it's a step in the right direction, but a small step that isn't worth the cost IMO.

It'd be simple to upgrade the valve springs while the heads are off being ported, so you might want to look into whether the cost of 1.4 rockers, springs, and pushrods is in your budget. Bear in mind that you may also introduce some rockerarm geometry problems that could take custom-length pushrods to resolve...more cost and downtime.

"Solid" rocker shafts are always a worthwhile upgrade. Although they aren't really needed below ~5000RPM, they do eliminate the possibility of a stock springclip or wavy washer failing. With a stock oil pump pickup not equipped with a magnet, those bits can do a surprising amount of damage to your engine.

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Re: 1.25 ratio rockers

Post by advinnie » Mon Jun 10, 2013 2:10 pm

The reason im looking at ratio rockers is because my 1600 twin port with dual carbs will be having it heads ported and flowed but its bolted on to a gearbox from a 1200 so it already nippy and it will sit at 75 mph all day nicely so im not after any more top end speed just more pulling power. The problem with fitting a performance cam is that it moves the max torque up the rpm range and that is not what im after I want all the torque low down the rpm range the beetle hardly ever gets out of town thats why I want of the mark power. Hope this make sence. Ps before any one says it I want to keep it a 1600 im not interested in going bigger well not at the moment. So surly if I keep the stock cam the torque and power should stay low down the range but the extra valve lift should allow more fuel air mix in and let the extra exhaust gas out right especially after the heads are done

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Re: 1.25 ratio rockers

Post by Marc » Mon Jun 10, 2013 2:28 pm

So you have a 4.375:1 trans and drive at 75MPH, but think you don't want to move the engine's operating RPM up? That's over 4000RPM, BTW, pretty busy for cruising. I wouldn't want to live with that, even if the price of fuel was lower.
There is so much more to take into consideration than the limited concerns you've expressed. How far apart is this engine going to be?

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Re: 1.25 ratio rockers

Post by advinnie » Mon Jun 10, 2013 3:07 pm

im splitting the engine this winter if thats what you mean why. And as I said the car never really goes on the motorway but last month I done a 758 mile round trip in her sitting at 70 mph most of the way and no problems at all but im neger doing that again ky body hurt for weeks after not to mention my hearing. If the 1200 engine could do 80 mph theres no reason why a 1600 cant do 75 mph

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Re: 1.25 ratio rockers

Post by advinnie » Mon Jun 10, 2013 3:48 pm

Marc wrote:So you have a 4.375:1 trans and drive at 75MPH, but think you don't want to move the engine's operating RPM up? That's over 4000RPM, BTW, pretty busy for cruising. I wouldn't want to live with that, even if the price of fuel was lower.
There is so much more to take into consideration than the limited concerns you've expressed. How far apart is this engine going to be?
Hi there sat down and worked out what speeds I would be doing in all gears at 1000, 2000, 3000 and 4000 rpm and at 4000 rpm in four I would be doing exactly 75mph and the aircooled engines were designed to run flat out or 4000 rpm all day and can sit for a limit tike at 4500 rpm. Plus theres one thing I for got about I have smaller tyres at front so my speedo over reads by 10 percent so 70pmh will really be 63 and 75mph is In reality 67mph sorry. So on the motorway im not at 75mph im at 67 witch is 3541rpm

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Re: 1.25 ratio rockers

Post by Marc » Mon Jun 10, 2013 5:18 pm

~3550's not so bad; in fact, with a 25.4" rear tire, 4.375 R&P and .88 4th it's more like 3410 @67MPH.
Are you going to be needing new pistons/cylinders or are your present 1600s in good shape? Would you like to be able to run the least-expensive petrol?
If you don't intend to replace the crank with a counterweighted one, around 5000RPM should be the maximum RPM that you hit regularly. Occasional excursions up to ~5500 won't shorten life dramatically, but don't go higher. If you'll be going through the whole engine consider having it balanced.
These days you can buy Chinese-made (seriously, their quality is pretty good for the price) thickwall 88mm pistons/cylinders which only require cylinderhead machining. If I was going to try to get a perceptible boost in low-end grunt without spending much more than it takes to build a stocker, I'd use a set of those. If the present cam & lifters are in great shape there's no need to change them, but if I needed a new cam anyway I'd put one in that's just a baby-step bigger than stock (with the added 100+cc displacement there's no need to fear losing bottom-end with a little stick that's anywhere in the Engle W-100 to Bugpack 4061 range). NEW stock valve springs, shimmed ~.030"; the rest of the valvetrain can remain stock (although I still like solid shafts). Static C.R. of ~7.8:1 (vs 7.6 with a stock cam) will allow burning Regular with impunity. And as for the head porting, for your purposes it should be kept pretty mild. The exhausts shouldn't be enlarged at all, and the intakes only need to be as big as the I.D. of a stock metal gasket with a good port-match to the manifolds.

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Re: 1.25 ratio rockers

Post by advinnie » Tue Jun 11, 2013 3:18 am

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

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