1.6 vs 1.7 RR?

[jmd2914]

so i'm kinda new to the whole engine building thing, so let me see if i have this right. if i swapped from a 1.6 to a 1.7 it would be like swapping a cam with more duration right?

 

[Mustang78]

kinda, a 1.7 pushes the valve down .031" more(on a .500" lift cam) than a 1.6 ratio..you can divide the lift by 1.6 or 1.7 to find the actual size of the cam and the differences it makes

~Mark~

 

[Maryland Stang]

You get increased lift but the total duration stays the same.

 

[jmd2914]

so would it be more beneficial to use a different cam and use 1.6rr's?

 

[Maryland Stang]

It depends on what you're trying to accomplish. Putting more cam into an otherwise stock engine can have undesirable results like loss of low end torque and valve float on the high end. You have to build a package of parts that match to get good results. For example:

I have the mods listed in my sig line. In addition to those I'm getting ready to do a H/C/I install on my stock block that includes a B cam, Explorer intake, ported GT-40P heads with Manley 1.85/1.55 valves and double springs, FRPP 1.7 roller rockers, new lifters, Explorer 65MM TB and 26# Vette injectors. All of these parts are known to work well together with the exception of the Vette injectors and I'm going to get a custom burned chip to iron out that issue.

 

[88mouse]

I heard that 1.7 add 3* of duration to.

 

[Maryland Stang]

Total duration is fixed by the cam and cannot be altered. The amount of duration that the valve is open beyond a specific point may be changed, either for the good or bad.

 

[Twisted306]

0.480 lift divide 1.6 times 1.6 = 0.480
0.480 lift divide 1.6 times 1.7 = 0.510
0.500 lift divide 1.6 times 1.7 = 0.531
0.500 lift divide 1.6 times 1.6 = 0.500
0.500 lift divide 1.6 times 1.8 = 0.562
0.512 lift divide 1.6 times 1.7 = 0.544
i was shown like this can be pain n the butt to get right i was told 550 is max lift for the stock 5.0 short block any more valve will hit pistons and alway leave room if some thing happes like valve flow or missed a gear i dont run any more then 0.530 in a stock 5.0 short block valve braking off in the cly make one BIG mess

 

[90bluegt]

I'm running higher than .550 lift on a stock 5.0 block, (out of an explorer) and i'm not hitting the pistons. My lift is around .577 that's with 1.7 rockers.

 

[85_SS_302_Coupe]

IMO 1.7 rockers are a waste because even on a stock engine, you can benefit from a mild cam and get better results than you'll ever see with a stock cam and 1.7s, also 1.7s put more of a bind on the valve geometry than is necessary. I've seen tons of otherwise bone stock 5.0s gain from E303 and equivalent cams. As mentioned, you're only gaining lift, which you can get plus duration from a cam swap.

 

[Chietala]

Great info here.

http://www.popularhotrodding.com/tech/0607phr_camshaft_basics/lifters_pushrods.html

 

[Foxfan88]

i use 1.7 with a b-cam and it works well.

the b-cam has pretty low lift compared to other cams, it has.480 with a 1.7 rocker arm its around .510-.512 which works for me.