going from 1.6 rockers to 1.7

[dragstang86]

With the combo in my sig how much do you think my 1/4 mile time would improve (if any) if i go from 1.6 rockers to 1.7 rockers? And how much if i go from the stock maf to a 76mm maf? Last time at the track before i advanced the timing and got my rear locking up i went a 13.30 @ only 99 shifting at about 5000 with a 1.75 60ft.

thanks for the help

[88workcar]

It should pick up a little, don't get your hopes up too high. In extreme cases it may be 2 tenths. You will never know till you try. I have a set of JBA 1.6s in a bucket in the shed, I am undecided weather I will put them on or not, the old stockers are doing good for now.

[jim_howard_pdx]

If your 1.6 rockers are netting say .480 lift, you can determine the actual lobe lift by dividing .480 by 1.6. Take this number and multiply it by 1.7. This will give you your new lift.

Did you measure the piston to valve clearance when you put the engine together? Are you running aftermarket heads? If so, you could punch the valve, or if they float in the future because the valve springs go soft, you will bend the valve and possibly ruin a head or engine.

Be careful is all I am saying.....

I measured my piston to valve clearance without the head gasket. Intake clearance was .17. Exhaust clearance was .29. I only require 0.08 clearance. My gasket compressed thickness is .039, so I am way safe. Going to 1.7's will be no problem.

Plan on picking up 8-15 hp. Also, do not expect more than a tenth second.

Don't expect a huge improvement from the rockers, but they will add some more lift to your cam specs. You could gain up to maybe 5 more horses from the 76mm MAF though. Are you still running the stock one? If so, you have been seriously choking your air intake. So you actually might feel that, or hopefully it will show up on your time slips. Just guessing here, but I'd imagine you might knock a tenth of a sec. off your 1/4 mile time.

[jim_howard_pdx]

Where I see most people picking up significant time improvements is with the following items.

Change to 3.7 or 4.10 gear ratio
Change to slicks
Improved traction with posi rebuild or going with a locked differential.
Extrude honing the upper and lower intakes
Changing Cams
Port matching heads to intake and exhaust gaskets or going with aftermarket heads.
Going with a larger MAS unit
Going with full length headers
Improving ignition with MSD type provisions
Using improved rear suspension arms
Strengthening the chassis
Adding a roll cage

OBVIOUSLY adding a supercharger or NOS is a simple way to make an additional 25% hp. You can go for more, but not with the stock short block.

Touching on the 1.6 to 1.7 rocker conversion, I perform a trick that was originally performed by a Chevy engine guru back in the 70's. This is simple on a Chevy or Chrysler X shape intake engine such as the small block chevy engine. What we do is run 1.5 rockers on the inside X runner intakes and run 1.6 ratio rockers on the outside of the X runner intakes.

On a FORD you find the cylinders that are running lean and run 1.7 rockers on both the intake and the exhaust valves of that particular cylinder to get equal power. This can dramatically smooth out a racing engine. Most Fords run lean on the corners. Cylinders 1,4, 5, and 8. On my intake and heads, I port these cylinders for about 6% more flow than the interior cylinders. Then I play with the rocker ratios until I get the best power.

To determine which cylinders are running lean, I start by running the car at WOT for about 1/2 mile. I shut down the engine as soon as I can and I pull and index each spark plug. This helps me determine which are ideal, which are lean and which are rich. I jet the car until no cylinders run rich, and then I play with the 1.7 rockers to get them all equal. This is really hard to do with pump gas. Try to get some 106 to 110 racing fuel. This will give you the truest plug reading.

Then, when I think everything is balanced, I run the engine at 3500 RPM for about 5 minutes, then step it up to 5,500 RPM for 3 minutes. Then I take the temperature at the first bend of each primary header tube. If the temperatures are within 3-4% you are good to go. If any one cylinder is running hotter than 6% you know you need to go in and do some porting work to the intake, or index your intake gaskets to make sure they are not reducing flow to any particular cylinder. On one engine, our port work flowed almost 15 cfm greater to cylinders 1 and 7 than the other cylinders just to balance the power. It really can vary that much. I hate to port any cylinder that much bigger than the others until I determine my bracket class, the ET's I plan to run all season, and finalize the intake and carb. Because just a carb change could throw EVERYTHING OFF.

Hope this helps.