1.6 ratio rockers. Do they actually hurt the geometry??

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fishy68

Tyr Fryr's Inc.
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I've seen posted before that it is generally thought that 1.6 ratio rocker arms on a LA engine actually make the already bad valve train geometry worse but as I looked over a 360 block and heads I have it appears to me that they might actually help. I don't have any 1.6 rocker arms to compare to my 1.5 arms but I'd think to get the higher ratio they would have to move the pushrod point on the rocker arm a little closer to the fulcrum. By doing so that would actually straighten the pushrod path slightly so therefore it would help the geometry. Any you engine guru's have a thought on this??
 
Yes Fishy, in my experience with 1.6 ratio rockers on a LA headed engine that the pushrods actually sit a bit straighter due to the adjusters being moved slightly in toward the rocker shaft.

I think the complaints about geometry come from people with limited valve train set-up experience that find that the pushrods hit the heads. In my experience, custom pushrods are mandatory with 1.6 ratio rockers. I made a pushrod measuring tool, mocked up my engine with Crane 1.6 ratio rockers with the adjuster showing just 1.5 threads underneath the rocker (Cranes reccomended set up) and adjusted the tool for .040 lifter preload. I then measured the tool and ordered the correct pushrods. Presto, no pushrod interference problems.
 
The biggest problem is getting the tip on the top of the valve just so and correct. This give fits to people. Sometimes, some things are easy for some and sometimes it is a royal pain for others.
 
The biggest problem is getting the tip on the top of the valve just so and correct. This give fits to people. Sometimes, some things are easy for some and sometimes it is a royal pain for others.

Only way to get this correct on a rocker shaft motor is by rocker shaft spacers or not to set the valves too deep in the head. Unlike stud mounted rockers, pushrod length has no effect on this. Like rumble said, it can be a pain.
 
He he h, this shold be a treat for me to do later. I haven't done it in years. Like more than....I'm not even sure when I last had a problem, YIKES!

Could be trouble. LOL
 
Thanks for confirming what I thought Ramcharger.

I went through trying to get the tip on the top of the valve a few months ago and that's when I found out allot I didn't know about Mopar rocker geometry.

Also not sinking the valves far enough when new seats are installed can lead to problems. That was the problem on my heads. It caused the valve stem to be too short. The only correction for it was to remove the heads and have the seats ground in a little deeper where they were supposed to be.
 
Never sink the valve ,it hurts airflow.You should have went to a longer valve or a lash cap if you did not want to buy valves.
 
Never sink the valve ,it hurts airflow.You should have went to a longer valve or a lash cap if you did not want to buy valves.

Yeah I realize that sinking the valves hurts airflow. Sorry but my explanation of why I did that wasn't clear.

They are brand new valves but what happened is the shop installed new exh. valve seats and didn't sink them deep enough to their original location by anywhere from .020-.050". That's the reason I mentioned having them sunk farther. It was to get them to their original location and get them all even. I figured since they're heights all varied by quite a bit that the airflow would be different from cylinder to cylinder and sinking them to their stock location would balance the airflow better. I looked into putting lash caps on them but even then I'm sure the flow difference from cyl. to cyl. would be quite different.
 
UI guess I'm just old fashioned. I'd rather order the cam than mess too much with pushrods hitting. I do have the pushrod holes enlarged on all RPM heads, but run a big enough cam and thick PR and you know why that needs doing. A 1.6 rocker isnt harming anythign if like was said the valve job is done right. I think the majority of isues stems from people cheaping out during the base head restoration. I always just account for all new valves, and I always go oversize. I've never lost power that I can tell from the choice, and it always lets me run the seat out as much as possible wihtout installing new seats on everything. Exh get seats 'cause they almost always need them anyway. Same old adage... You can pay now, pay later, or simply chose to ignore the issues cheap work creates.
 
UI guess I'm just old fashioned. I'd rather order the cam than mess too much with pushrods hitting.

I know where you're coming from moper. When I went to Summit to order my Crane Golds for some reason that I can't explain the 1.6 ratio Cranes were 80 bucks or so cheaper than the 1.5's. They just must of had an overstock that particular week and were trying to move them off the shelf.

I figured what the hell, a little extra lift won't hurt anything since I'm running 2.02 intakes and some home porting. As a bonus I noticed that the pushods appeared to be a bit more in line with the lifters. I actually enjoy setting up valvetrains so the extra work didn't bother me either. I'm hoping that the 1.6's will give me a bit more midrange and top end without degrading the idle or reducing gas mileage. We'll see shortly.

Luckily, the shop that did my heads did a good job and replaced all of exhaust seats as I requested and no, it was not cheap. There were some things that they did that I did not like. For example, when I broke down the heads to double check installed height I found lap compound on the backside of three or four valves, aaaarrrggghhh! Doesn't anyone use prussian blue anymore? Anyway, that's a story for another post. It's tough not working in a shop anymore and having to farm out work I could do it myself if I had the equipment.
 
Thanks for the input Moper.

The main reason I brought this up is
A: to verify that what I was seeing was true, and
B: because I found a good deal on a set of 1.6 rockers.

Now that I'm finally figuring this stuff out I order my cams how they should be in the first place. I also don't like going through the hassles of trying to make something fit the application when it's not correct. I would just like to stay with 1.5 rockers but the deal I found is a good one so it got me thinking.

About my heads. Actually I didn't cheap out at all when doing them. The problem was back when I had them done I didn't know of any performance shop within 100 miles of me so I took them to the only reputable shop around. Unfortunately even though I had every intention of having them done correctly apparently the machinist wasn't as good as everybody said he was cause what I got back wasn't a near perfect job to say the least. That's what caused the problems I had posted in a thread a few months back when I was trying to figure out what was wrong. I'm sure you also read it in my post about flow numbers.

I have since found not 1 but 2 good performance shops so in the future I know where to go so things get done right the first time.

Everybody have a good rest of the week and thanks for all the input.
 
First off, changing from 1.5 to 1.6 gains you about 7% in lift. So a cam that gives you .450 lift with the 1.5 will give you .480 with 1.6. Thats .030 at max lift only, the area under the curve is increased very little. It would take more calculus than I can do in my head tonight to figure it out exactly so think of it like this: You are increasing the size of the nipple, not the whole boob. Ever hear of anyone getting a nipple-job?

The main drawback however is the increased loads on your valvetrain. The loads don't just increase by 7%. Sure, the cam and lifter faces now experience 107% of the force of the valvespring (and 107% of the mass of the valve). But thats static pressure, we are accelerating that valve back and forth so loads increase exponentially. More wear, more HP losses in the valvetrain.

Geometry is a function of the relationship between pushrod length, valve tip height, and pivot point. With shaft mounted rockers the pivot is pretty much fixed, so you either change the length of the pushrod or the valve by using a lash cap. Generally after milling heads you need shorter pushrods.

Fitting oversize valves is a time honored way to raise the valve heads relative to their seats, as you do recess the valve a little every time you do a valve job. If the seat is recessed much at all the seat shrouds the valve at low lift. You'll gain more from a good valve job than you will with fancy rockers, and maybe save enough cash to buy a set of implants (or tires).
 
First off, changing from 1.5 to 1.6 gains you about 7% in lift. So a cam that gives you .450 lift with the 1.5 will give you .480 with 1.6. Thats .030 at max lift only, the area under the curve is increased very little. It would take more calculus than I can do in my head tonight to figure it out exactly so think of it like this: You are increasing the size of the nipple, not the whole boob. Ever hear of anyone getting a nipple-job?

Setting up a valvetrain is not a boob job. If I wanted .600 lift cam @ 260 of duration, I would have bought one. What I wanted was something closer to a hydraulic roller profile without spending a $1000. This is not calculus but basic math. I used my cams profile as an example. Obviously I would much rather have the profile on the 1.6 side.

Cam lift---@Valve w/1.5 Rockers-----@Valve w/1.6 Rockers

.100----------- .150--------------- .160
.150----------- .225--------------- .240
.200----------- .300--------------- .320
.250----------- .375--------------- .400
.300----------- .450--------------- .480
.320----------- .480--------------- .512

The main drawback however is the increased loads on your valvetrain. The loads don't just increase by 7%. Sure, the cam and lifter faces now experience 107% of the force of the valvespring (and 107% of the mass of the valve). But thats static pressure, we are accelerating that valve back and forth so loads increase exponentially. More wear, more HP losses in the valvetrain.

Loads do increase exponentially in a dynamic enviroment but the 7% increase in load will not. The load only increases by a 7% relationship to the valve spring pressure at any given lift. Ford 351C engines run a 1.73 ratio rocker from the factory without any problems. A 351C engine that I had built 20 years ago ran just fine for 70K miles, again with Crane rollers. The same load increases would also be seen from a 7% higher lift cam or 7% stiffer springs.

Geometry is a function of the relationship between pushrod length, valve tip height, and pivot point. With shaft mounted rockers the pivot is pretty much fixed, so you either change the length of the pushrod or the valve by using a lash cap.

Changing the pushrod length does nothing to the tip/stem geometry on a rocker shaft engine. Pushrod length is changed only to establish the correct preload and adjuster screw position.

There are two geometries that are spoken of on a LA engine. One is on the pushrod side, and isn't all that great from the factory. Anything that can be done to straighten it out will add stiffness, strength and increase reliability as well as add power through the reduction of flex.

The other is the relationship between the rocker tip and valve stem as a function of the pivot point at the rocker shaft and the valve stem height. Rocker shaft spacers can be used to raise the pivot point and as you say, lash caps could be used, but a good valve job to start with would have alleviated the situation.


Fitting oversize valves is a time honored way to raise the valve heads relative to their seats, as you do recess the valve a little every time you do a valve job. If the seat is recessed much at all the seat shrouds the valve at low lift. You'll gain more from a good valve job than you will with fancy rockers,

And you'll gain reliability and power when you combine a good valve job with a well set up valve train. My heads flow quite well up to .520 lift and I will gain nothing leaving my lift @ .480. Why not get a bigger cam? Because of my specific application. This particular engine is in a 4WD truck that I need to keep as driveable and as efficeint as possible. In other words, I didn't want to increase my duration. It's all about the combination and application. Higher ratio rockers are not a cure-all and aren't a instant hp bolt on, but they have their place.

and maybe save enough cash to buy a set of implants (or tires).

I saved over $80 by buying the 1.6 Crane Golds vs. the 1.5 Crane Golds. IIRC I paid $225 for them and thats with hardened rocker shafts. That $26 more than a set of crappy Proforms. You also never mentioned how much a poor quality valvetrain will flex under load.

I know nothing about implants, nipple jobs or boob jobs but I do know valvetrains.
 
Well said RamCharger. I have always used 1.6 rockers over the std. 1.5's, when I can. NEVER had an issue with the stability even @ 7800 . Never had to change pushrods when changing over to 1.6's. And yes it does as you say 'straighten' the terrible lifter/pushrod angle a few degrees that the small Mopar is blessed with. 'Straighter' means stiffer. Lift equals power. Makes little sense to have expensive ported heads if you don't get the valve open far enough to 'use' that expensive porting. The ACTUAL lift has to match the flow capability of the heads or you are leaving horsepower on the table.
 
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