Grumpy.... rocker ratio and change on cam events info needed

[Guest Night_rider_383]

Grumpy or anybody that knows the answer to this, could you please try to give me the real info on it.

 

I know that going from 1.5 to 1.6 rocker ratio will add lift, and heard it adds 2 to 3 degrees of duration at .050'' lift. Is this true? If so how will it change the rest of the cam events like IVO, and advertised duration?

 

Thanks for any insight on this

John

[Mudge]

More time spent at a higher lift is akin to more overall duration.

[grumpyvette]

it depends on the cams ramp rates and total durration and lift, it can be as much as 7-8 degrees of effective durration or as little as 3-5 degrees, from what Ive seen, keep in mind that 1.6 ratio rockers tend to work much better on mild cams and lower lifts because the total flow change is greater and the stress levels on the valve train is relatively low. once you get over about .550 lift and about 235 dur.@.050 lift and 5000rpm the resulting improvement in flow tends to be less than the resulting stress on the valve train compared to just getting the correct cam with a slight durration and lift increase that is better designed to run above 5000rpm due to the more controlled rate of lifter acceleration which can in a cam orriginally designed to run 1.5 ratio rockers get to valve float rpm.

look what your trying to do,... what 1.6 rockers are is a nice tuneing aid that allows tweaking the cam timing, they are in no way a valid replacement for the correctly matched cam and 1.5 ratio rockers but they ARE an easy way to get a few cfm of extra airflow in the ports IF the ports potentially flow better than the cam your useing allows. where I see the best results is in nearly stuck engines where the cam severly restricts airflow at the higher rpms, Ive even seen LOSSES in hp in engine with fairly hot roller cams when 1.6 ratio rockers are added. also sometimes only adding the 1.6 ratio rockers to the intake or exhaust can sometimes gain more than adding the rockers to both

when I was running a crane #114142 cam they helped , when I swapped to a 119661 roller cam they added zero hp over 1.5 ratio rockers in my 383

here look this over but keep in mind PONTIACs have restricted exhaust ports

 

http://www.lmengines.com/rocker_arm_changes.htm

[Guest Fast Frog]

Hey G Vette!

 

I was just surfing the HybZ website this morn when I read your 1.6 ratio response. At one time I was considering a 119661 for my 383. Currently,

I'm running a Crane 119821 (214/222@ .050 .488/.509) with 1.5 ratio. Could I expect a comparable increase in performance if I just simply changed from a 1.5 to a 1.6 set of rockers?

[grumpyvette]

NO!

look at the specs of the 119661

 

http://dab7.cranecams.com/SpecCard/DisplayCatalogCard.asp?PN=119661&B1=Display+Card

 

they are 230/238 dur..538/.558 lift

your cam

http://dab7.cranecams.com/SpecCard/DisplayCatalogCard.asp?PN=119821&B1=Display+Card

 

your cam with 1.6 rockers would be about

220/228dur. .520/.540 lift

 

now it should give you a slight increase in both hp and tq ABOVE 5000rpm but not what a cam change would potentially give you, but it will get you close to the next larger crane cam, specs, the 119831 so you might want to try it but only if your present combo lacks power above 5000rpm and has too much wheel spinning torque at just off idle with your cam now.

http://dab7.cranecams.com/SpecCard/DisplayCatalogCard.asp?PN=119831&B1=Display+Card

[Guest Fast Frog]

HMmmmm! Thanx G Vette!

[Guest Night_rider_383]

Grumpy... thanks for the quick answer..

I think 1.6's will help my combo alittle. It's a milder 355 for street performance/daily driver in a 88 camaro with a th-400 trans, 2800 stall converter, 3.42 gears

 

Engine specs are....

9.83:1 SCR, crane power-max hyd. flat tappet 216/228@.050'', 278/284 adv., .454''/.480'' lift, 112 lsa, 462 heads, manley 1.94''/1.50'' valves, port work, performer intake, 1'' open spacer, edel. 600 cfm carb. I also have a set of elgin 1.6 ratio roller tip rockers

 

Alot of the parts are "left over" parts with about 4k miles on em that I used in my truck's 327,bought new then, now re-useing in this 350 for a cheap priced build

 

Why I asked about the change is cause I was playing with desktop dyno 2000, (I know it aint the real truth as to the engine's power) useing the cam events, then added 3 deg. @.050'' and 3 deg adv. to cam duration and the extra lift for the 1.6's. It showed pretty good power across the board with and with out the extra duration, but once I added the extra duration and advanced the cam 2 deg. it showed a big hp gain, gain in torque across the board.

 

Here's what dd2000 shows. These are both with the extra 3 deg duration added in and the extra lift. With the cam I listed above and 1.5 rockers hp peak was 373, but the torque did'nt look as good

RPM HP TQ VE%

2000 136 358 77.7

2500 171 360 78.3

3000 208 364 79.6

3500 256 384 84.4

4000 305 401 88.8

4500 352 411 91.5

5000 363 382 88.9

5500 343 328 81.7

6000 323 283 76.6

 

2 deg. advanced

RPM HP TQ VE%

2000 137 360 79.5

2500 173 364 80.0

3000 212 371 81.8

3500 260 390 86.5

4000 308 404 90.5

4500 353 411 92.8

5000 393 413 94.7

5500 341 326 82.0

6000 319 280 76.9