change from 1.6 to 1.7s
- Thread starter steel1212
- Start date
brianj5600
Active Member
I'm retarded its in my sig.
duration goes up in a small percentage of the net increase in lift. it is small enough that i usually ignore it personally. as far as lift specs go, take the valve lift and divide it by the rocker arm ratio, then multiply that result by the new rocker arm ratio. that will give you the new valve lift. example;
.480/1.6=.300
.300x1.7=.510
.480/1.6=.300
.300x1.7=.510
fasttback
New Member
Comps cam 280H for the 289/302 is 0.512" lift using the 1.6 ratio rockers with a 230 duration at 0.050 (this is from their web site). Your cam lobe (I and E) measures 0.320". Multiply the cam lobe by whatever Ford SB ratio rockers you want to try = your new lift. As for more duration it is minimal and I usuall do not add it in either.
No matter what, there will be an increase overall, and this is essentially "free" horspower, being that the 1.7's cost the same as 1.6's do, if you're swapping from stock rockers to rollers. Only thing you'll need to watch for is exceeding the maximum compressed height of the springs you're using ( if not changing them at the same time) I think, 70Nitrous eater's observation may have been in error, the gains with a stock cam shouldn't be any more different than with a bigger cam, the specs he saw may have been due more to a change in rocker type ( stock to roller)
69Rcode_Mach1
Active Member
You will probably not feel a sotp difference. It will give you more power though. If you are planning on changing rockers anyway, you might as well go with 1.7's.
D.Hearne said:
Nope.. Think of it this way: After you open the valve a certain distance, there will become a point where opening the valve any further won't make much of a differancein airflow. With a high lift cam and 1.6:1 rockers you are already getting to that point..stepping up to the 1.7:1 rockers gives more lift but this extra lift doesn't make much of a difference anyway. But with a stock lower lift grind, the added lift of the 1.7:1 rockers makes for a larger increase in hp.
An analogy: You take a V8 that's built for a 650cfm carb and you replace the carb. Stepping up to the 750cfm might gain you a few extra hp, but stepping up to a 900cfm carb wouldn't make any more power that the 750cfm.
69Rcode_Mach1
Active Member
70_Nitrous_Eater said:
Well that is true, but it takes a lot to reach that point. That has to correlate with the compression and total lift on the cam. Usually when the lift is too much you will be close to .600 lift depending on the engine. I wonder how that stock cam would respond what you are saying makes sense to me, but it doesn't seem that the stock cam is so terrible that the .032" of lift would make that big of a difference.
Similar threads
