In the spring I am changing to 1.6 rr's. What springs should I replace the stock ones with? My friend says to go with some "beehive" ones. Or should I leave them alone?? The car has 73k on it so I'm thinking they could use a replacing. Also the car runs at 3000 rpm on the highway at 70. What kind of gears would I have to make that rpm? Yes it is in overdrive to...

 

Some suggest to change the springs, I had 94,000 miles on my '89 when I went to 1.6 roller rockers and I didn't change springs. I had no problems running the stock springs, and I doubt you will as long as you don't increase your redline. Make SURE you remove the drip tabs that are sticking down from the top on the inside of your valve covers. I suggest grinding them off, or you can just snap them off, but if snapping them off be careful not to crack the valve cover.

As far as the gearing do a search for a gear calculator. It will let you enter tire size, transmission, etc. and should tell you your rear gear ratio. Also you can mark the driveshaft, then jack the rear up and turn a tire exactly 1 full turn while counting how many times the driveshaft goes around. Example, 1 turn of the tire = 3 1/2 turns of the driveshaft would be 3.45:1 or 3.54:1 gears.

 

At 73k if its all stock Id just leave it alone.
Some like beehives, others dont.

 

Ok. The next time I have it in for an oil change I will do the mark the driveshaft idea. I figure as long as the shim pockets or whatever isn't wore down then I will leave the springs alone. With this automatic first gear is non existent due to wheel spin anyhow. I want to post a picture of my car but I guess I have to pay to do that. Oh well the car is in the garage, if I want to see it I will open the door. But I want to show it off!!!

 

I know a member on this board who's valve springs measured less than half their original rating in 1996. His car is an '89. That's when he milled the head and went to 1.6 rockers.

Currently, I'm struggling with the issue of whether to change springs -- just as old-age maintenance. (Actually, trying to decide if I should pull the heads, mill, do valves, etc.... but that's besides the point. Mine is an '89 (also) with 55k miles).

The owner's car in question only had 36k when the springs had fallen to 50lbs. (vs 110 new). For '89's those cars would now be over twice the age!

Is it REALLY O.K. to leave factory springs in at that age? Moreover, if you work them harder with 1.6rr, isn't that "asking for trouble"?

Or do you think the car I mention was factory-installed with the wrong springs?

 

Maybe he got weak springs from a bad lot shippment. If I go to the point of changing heads I will put on my angle plug castings I have for a '70 350...

 

I never tested them, I can only give my real world experience. I had 94,000 on mine, put on 1.6 narrow body self aligning rockers from Summit and ran it. Was shifting at 5000rpm on the digital tach, which is really about 5200. No valve float, no problems at all. Will you have trouble, I have no idea. I know there is alot more concern for trouble than there actually is trouble with running the stock springs and 1.6 rockers and keeping the stock redline.

 

That rpm does not sound right at a cruise. Your shifter may show you are in OD, but the transmission sure doesn't sound like it. What gears are you using?

 

I think the rpms range of the OP's car sounds too high as well! Mine runs 1750 rpms at 70mph on my 6spd. Any other car I've owned with a 4-spd auto ran between 2200-2500 rpms in OD. Maybe it's got something in the 4-ratio range?

BTW: What effect does 1.6 rr have on flow? I assume the valve depresses a little further while the duration can't change with the same cam lobe.

Since stock cams have a lift in the .415 range, does is create a "psuedo-lift" of .442 or thereabouts? (1.6/1.5 * 0.415)

gp

 

There is no "psuedo-lift" effect. It will actually increase the lift.

 

That and $4 will get me a Starbuck's coffee.

I used the phrase "psuedo-lift" where I could have said "effective-lift". The actual lift of the cam (lob) does not change. Since head flow data is based on cam lift, I wanted to know how to figure what 1.6's would do. Your answer did not help.

(Also, I assume the stock rockers are 1.5's but I'm not sure).

gp

 

I don't know the gears. The car is fast though....

 

Assuming you are running a stock L98 or LT1, the rocker ratio is 1.5. It is 1.6 on the LT4s. Think of a lever or fulcrum. The 1.6s will "open" the valve slightly higher and faster, even if the cam specs are the same. So yes, the lift is higher on the valve, but still the same on the cam. Hopefully that explains it better.

 

To the layman, yes. But, I already knew that too.

I'm wanting to know how much affect it has. What's the new effective lobe lift?

How else can I ask the question?

gp

 

Someone with an auto trans (who knows their gear ratio and rpm's at 70mph) will need to chime in to get this figured out.

 

Let's say the "actual" lift on a cam lobe is .300". The 1.5 rockers will "multiply" the lift by 1.5 so that's a total of .450" of lift applied to the valve from the lifter to the pushrod. So with 1.6s, the valve will open .480", even though the cam would have the same "actual" specifications.

When I'm cruising in OD down the highway at 70 mph, my tach reads exactly 2000 rpms with stock 3.07 gears. The calculation with 2.59s at 70 mph in OD would be 1650 rpms and with 2.73s it would be 1750 rpms

 

my pickup runs 3000 RPm's with 3:38 gears it's a 4 speed with no overdrive.

 

Cam and rocker ratio school, here it is....... I'll use my stock '89 cam for example:

Lift with 1.5 rockers is .415 intake, .430 exhaust. Divide those by 1.5 to find the cam's gross lift = .277 intake, .287 exhaust. Multiply those by 1.6 to find the net lift or total lift with 1.6 rockers = .443 intake, .459 exhaust. Still peanut numbers but better than before.

Advertised duration doesn't change no matter what rockers you are running, as that is the point where the cam first starts to raise the lifter. Most cams are measured by duration at .050 because any lift less than that is so very miniscule. Duration at .050 lift does change with rocker ratio changes. Going from 1.5's to 1.6's increase the duration at .050 by about 2. The stock '89 durations at .050 are 207/213, so now with 1.6's they are about 209/215. This is because the increased ratio lets the valve open sooner and holds it open longer. Not a huge amount, but every little bit helps.

The lobe separation (LSA) is the angle between the peaks of the intake and exhaust lobes on the cam. It has nothing to do with the rockers and therefore does not change. Cams with a tight LSA, say 110 or less, tend to be lopey and I've heard are hard to tune with a fuel injected computer controlled engine. Higher LSA's are more computer friendly and mild mannered, possibly having more torque down low and better part throttle driving and throttle response, but sacrifice some mid and high end power. 110 to 114 LSA seems to be the range most street driven fuel injected 350's work best in. Lower if carbureted and not daily driven, higher if emission laws must be met. There are exceptions, I'm sure some have a 108 lsa and it is tuned perfectly, and I'm sure some have a 115 LSA with gobs of top end, but what I said is a general rule.

I hope this helps clear some things up and assists some in cam choice.

 

I thought the cam was .415 (as you say). And, you can not change it's "gross lift". I would think the cam lift multiplied by the rocker ratio would equal the valve travel (in inches).

So, .415 x 1.5 = .6225" of valve travel for a stock '89 intake valve
And .415 x 1.6 = .644" of valve travel for a stock '89 with 1.6 rockers.

Effectively, this would be the same valve travel as if you'd left the stock rockers on the car and changed to a cam with .443 (intake) and .459 (exhaust) lobes. And, since head flows are based on cam lift (right?), then you need these numbers to predict flow.

We are saying pretty much the same thing -- except for the gross lift part.

gp

 

'87 auto with 3.54 rear is 2300 at 70mph.Thats with 35 profile tyres on 17"rims.