1.6 or 1.7 rockers?

[83 Capri 5.0]

Man there is so much confilicting info on this. I just talked to a guy at a Hi Po retail store (will remain nameless) who says 1.7s will not work with stock block, GT 40 heads and Crane 2040 cam without fly cutting the pistons.

I've got a Hi Po 5.0L reference book that says yes they will but alway take measurements to make sure.

And a tech support guy at Crane says no problem.

I can't afford to guess at this and then grenade my motor, but I'd also like to go with the 1.7s if it's safe.

Input from anyone who is or has run this combo would really be appreciated.
Thanks!

 

[SYLENTBUTVYLENT]

Do a search for anderson ford and call rick's tech line. Give him the cam specs and what you have and he'll give you your answer. He is the cam guru.

 

[9 Deuce GT]

I would just go with 1.6 rr. It will give you more choices if you decide to go with a different cam later.

 

[Michael Yount]

The Crane 2040 is identical to Ford Racing's E303 camshaft. Piston to valve clearance should always be measured on a swap like you're contemplating as both the larger than stock valves in the GT40's, and the longer duration of the 2040 cam are gonna reduce the stock clearance. The rocker ratio difference actually has only a very minor effect on clearance -- 3 or 4 thousandths of an inch is the clearance you'll lose by going to the 1.7 vs. 1.6. Unless you're right on the edge of acceptable clearance, the rocker choice won't make much difference - so it's up to you. But you won't know if you're on the edge or not unless you measure. You're looking for a minimum of .080" on the intake valve and .100" on the exhaust valve. Those amounts are enough that even if you miss a shift and over rev the motor floating the valves no hard parts should come in contact. The 2040 w/1.7's is gonna have .528" lift - I'd consider upgrading the valve springs on the GT40 heads. If they're old/tired, you could have valve float issues at low enough rpm to impact power production.

By the way, other folks with similar combos will often tell you that 'it worked in mine, it will work in yours'. Two things to think about - 1) often, they haven't actually measured clearance; they simply haven't had a problem -- YET. They might find the first time they miss a gear and over rev that the exhaust valves hit the pistons; 2) when it comes to dimensions this tight, no two combos are ever identical, even those with exactly the same parts. So clearance can be fine on one and not on another with the same parts. While well intended, the fact that it worked on another motor isn't helpful in determining if you'll actually have enough clearance. You need to measure if you don't want to take any risk.

Remember - peak lift is not the issue when it comes to p to v clearance - the pistons are WAY down the cylinder when the valves are open all the way. It's during overlap when the piston is passing through tdc and the intake is beginning to open, exhaust is just closing that p to v is at it's minimum. So, bigger valves, heads that have been milled, blocks that have been decked, cams with earlier opening intake valve timing/later closing exhaust valve timing (bigger duration, tighter LSA, more overlap) are the things that reduce clearance. You have 2 of those working with your combo - that means you should measure to be certain. I'm with your 5.0L reference book - measure to be sure - but you'll probably learn that you're fine when you do. By the way, you can buy the tools you'll need to do the measurement for about $50, and you'll learn so much about how your engine actually operates that it's well worth the money for that alone. With those tools you can also degree the cam to be certain that it's installed with the timing that you want. Simply putting it in dot to dot means it could be spot on, or it could be as much as 4 to 6 degrees off. Unless you measure (degree it) you just don't know. Here's a link that describes one easy way to measure with just feeler gauges. Good luck with it. http://www.geocities.com/jjonibones/PVC.html

 

[83 Capri 5.0]

Thanks, the link is very helpful. The 96 Explorer 5.0L motor my GT-40 heads came of had valve relief on the the piston tops. I wonder if the 93-95 Cobras had the same and if they ran 1.6s?

I am tempted to go 1.7s and measure to be sure.

 

[wildstang347]

you can measure with existing 1.6 rockers subtracting .032 to the equation afterwards for the 1.7, provideing each rocker is within specs. and decide if you have enough clearance and decide from there wether you can or cant.

 

[5spd GT]

I would just go with 1.6 rr. It will give you more choices if you decide to go with a different cam later.

Yeah man just go 1.6RR's...for when you step up to that custom cam

 

[86Cobra]

you can measure with existing 1.6 rockers subtracting .032 to the equation afterwards for the 1.7, provideing each rocker is within specs. and decide if you have enough clearance and decide from there wether you can or cant.

Do you guys ever read the previous replys before typing yours?

What you're saying doesn't work. Read Michael Younts post above for an explanation.

 

[wildstang347]

what i just recommended was in the same line as yount, measureing p2v clearance with existing 1.6 rocker and subtracting additional lift gained from going to 1.7 from measurement so you should lay off the crack pipe dude and re-read it yourself!

 

[87gtconv]

I wonder if the 93-95 Cobras had the same and if they ran 1.6s?

No, they ran the 1.7 Cobra RR thus giving them their name!!

 

[Michael Yount]

The Cobras had 1.7's.

Wildstang - read more closely (after you put your crack pipe down ). What you're recommending will not work. First of all, the difference you're speaking of is the difference in PEAK lift. The pistons are way down the cylinders when the valves are at peak lift - there's no clearance issue at all then. The issue occurs during overlap when the valves are barely open -- at that point the difference in clearance between 1.6's and 1.7's is approximated by (1.7/1.6)/100 X valve lift at tdc during overlap. That lift varies with each cam - but for the E, it's about .08" -- so, (1.7/1.6)/100 X .08" = .005", or 5 thousandths of an inch. As you can see, that's an order of magnitude different than 32 thousandths of an inch you referenced above.

 

[86Cobra]

what i just recommended was in the same line as yount, measureing p2v clearance with existing 1.6 rocker and subtracting additional lift gained from going to 1.7 from measurement so you should lay off the crack pipe dude and re-read it yourself!

Feel better now that you've made a fool out of yourself?

 

[wildstang347]

true, i did make an mistake in what i said. i too do realize it isn't max lift that dictates p2v clearance, but amount of duration and overlap when both valves are open at same time when piston is nearing them on exhaust stroke.
when i mentioned .032 i was intending 2 point out the difference in ratios and didnt have the time or spend the time needed 2 give a proper description or explanation 2 what i was trying 2 get accross measureing with clay in what i have posted before on subject.