View Full Version : 1.6 rocker ratio

joseph m. hahnl
02-25-2012, 07:51 PM
If I use a 1.6 rocker ratio , it would change the amount of lift ,duration and overlap?

When adding more lift and duration should the LSA number get larger to prevent reversion?

This is a comparison to the roller 350 Mag to the flat tappet 350 260hp

See how it has more lift, the duration is less,and the LSA got smaller

Specs - roller lifter Merc Part No 431-811658
Duration @ .050:
197 intake,
207 exhaustValve
lift in inches:
.430 intake,
.450 exhaust
Lobe centerline degrees:
106 ATDC,
112 BTDC
Lobe Separation Angle in Degrees:

Specs - Flat-based lifter Merc Part No 431-5943
Duration @ .050:
200 intake,
212 exhaustValve
lift in inches:
.400 intake,
.410 exhaust
Lobe centerline degrees:
108 ATDC,
112 BTDC
Lobe Separation Angle in Degrees:
Stock Marine

Ralph Savarese
02-25-2012, 09:00 PM
That is a small cam I am running 216,228, 454,480 112, and I put 1.6 on the intake ir raised the intake to about 480 made a bit of differenceRalph

02-27-2012, 04:19 PM
To answer your questions... yes.

The reason why SBC have a more aggressive LSA is because the stock rocker is only 1.5 vs 1.7 for BBC. As you go up in rocker height your overlap will be greater. The overlap is what causes reversion. So, if you increase your duration or decrease LSA you are adding to the overlap increasing your chances at reversion. By going to a bigger multiplier with taller rockers you'll get there as well. I thought about going to full roller 1.6's on my Minx but only after doing the long tail EMI thunders. If I had stock exhaust I wouldn't have gone there. I was already on the edge by running a cam with stock exhaust.

joseph m. hahnl
03-03-2012, 11:38 AM
So what do you think? is a 109 LSA to small to add .030 lift

Has anyone put 1.6 on the stock roller tappet cam without issue?

Some one stated that best performance comes from 1.6 on the intake and 1.5 on the exhaust. Is there truth to that?

Should I just go with true 1:5 rockers and put my mind at ease?

My plan is to go with 64cc heads and sticking with a duel plane intake.I'm thinking
I need a little more lift for the 9:7 compression.

"Mop I want to go with stainless full Rollers"

03-03-2012, 04:32 PM
provided the pushrod holes in the heads are big enough, I would do it

Ralph Savarese
03-03-2012, 09:25 PM
Typically if keep your total under 500 you should be ok. If you have the engine apart you could always clay check?