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Discussion Starter · #1 ·
I have an appointment next Wednesday with a speed shop in the Chicago area to have my motor dyno'd & tuned.

Please excuse my ignorance on the subject but I want to have some general knowlege before I show for the tune up.

1. I understand they will adjust accelorator pump and jets on the carburator.

2. Timing will be adjusted as well.

3. I have heard that "valve lash" can be looked at as well. What exactly is "valve lash"? I assume it is the adjustable setting on the rocker studs that maintains the pressure or setting on the rocker arm. How important is this to have set? I asked the company doing the dyno today and they acted as if though they do not normally adjust this but would do so if I was willing to pay for the time involved.

The purpose of the dyno is not to see how many horse I am pushing but rather to finalize the tuning of the car. It is a 351W with a 670 Bigs carb; 4 into 4's, Edelbrock Performer RPM, cast iron heads and 9:1 compression. I get about 12 miles to the gallon and think it is burning ritch. Rear end is a 2:73 with a Richmond 5 speed with a 1:1 5th gear.
 

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Former Roadster Owner
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1,861 Posts
Valve Lash is the clearance you have beentween the rocker arm tip/roller and the valve stem. If you have a hydraulic cam that is set a 0 lash then the lash is taken-up from the hyraulic lifter.

You need to specify what type of cam you have if you want any help on lash requirements. If you have a hyraulic lifter cam, the lash is eaiser to maintain as it usually doesn't need to be re-adjusted once it is set properly. If you have a solid lifter cam, then frequent adjustments to last are needed.

Is this an engine dyno or RearWheel Dyno? Personally I like Rear Wheel dyno's because they show the number that counts...at the ground.

As far as what the shop will do, that just depends on their experience and willingness to preform the job.

You want to have a air fuel ratio that is neither to lean or to rich---I know... a very profound statement. If you are too rich you are losing power and if you are too lean, you can do damage--especially if you run a power adder--which I assume you don't.

Keep us posted!--Dan
 

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Discussion Starter · #4 ·
The cam is a flat tappet hydraulic lifter cam. Non-roller. Rocker arms are roller tipped though.
 

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Discussion Starter · #5 ·
Rear drive dyno as well.
 

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FFR Craftsman
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5,834 Posts
agree with fordmandan. to add to the lash issue, (doesn't apply to you it seems) is the fact you need to do both a cold-lash (initial build) adjustment and then a hot-lash adjustment. The later being a bit messy.

I did hydraulic rollers. Didn't want to have this much hassle for a street-mostly car.
 

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Former Roadster Owner
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Accobra66,

Since you have a hydraulic flat tappet cam with roller tiped rockers your lash will be in the lifter. The adjustment of lash on your set up will come from the length of your push-rods.

At zerolash between the rocker tip and valvestem and the lifter contacting the backside of the cam lobe (valve 100% closed) the lash (plunger pushed down) in the lifter should between .020-.060 of an inch.--if I remember right. Anything more than about .060" and the valve COULD hand open and cause problems.

This means the dyno shop shouldn't be able to adjust your lash unless they change pushrods.-- This means unless your engine is running rough (pushrods to long) and or makes very noticable ticking or clattering sounds (pushrods to short) --then I'm sure your lash is fine and you have the proper length pushrods.

In reguards to THIS DISSCUSSION the only differnece between setting up a hyd. roller and a hyd. flat-tappet cam is the break-in procedure.--The lash setting on both cam styles comes from the right length pushrods.

I've ran several hydraulic flat-tappet cams and have had great success with them. Good Luck, Dan
 
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