GHOSTOWLGRID

Specs on my cam:
Operating RPM Range: 1,500-5,500
Intake Duration at 050 inch Lift: 218
Exhaust Duration at 050 inch Lift: 218
Duration at 050 inch Lift: 218 int./218 exh.
Intake Duration: 268
Exhaust Duration: 268
Duration: 268 int./268 exh.
Intake Valve Lift with Factory Rocker Arm Ratio: 0.456 in.
Exhaust Valve Lift with Factory Rocker Arm Ratio: 0.456 in.
Valve Lift with Factory Rocker Arm Ratio: 0.456 int./0.456 exh.
Lobe Separation (degrees): 110
Computer-Controlled Compatible: No
Grind Number: OL 268H-10
Valve Springs Required: Yes


I have the stock rockers in the 1968 C heads, and my pushrod lengths are all the same:
Intake Overall Length (in): 9.550 in.
Exhaust Overall Length (in): 9.550 in.

Compression test gave 150 PSI on all 8.

Should I be using different rocker arms/ratios or different pushrod lengths to optimize this cam? Or do you think I'm okay with pushrod length?
My plan is to upgrade to flat top pistons with valve reliefs in the future.

How much longer can I go for pushrod legnths and/or rocker ratios if I wanted to get more lift with my current dished pistons?
Do you think more valve lift will help my performance?

My trans is a turbo 400 auto and my differential is a 2.73 ratio, no posi.

Fun71

To me that cam seems to be short on lift for the amount of duration (my 217º cam has .485" lift), or conversely, too much duration for the amount of lift (most "RV" style cams with about .450 lift have 204º duration).

While that cam would likely run well with your current setup, I wouldn't use it with the compression you'd likely end up with flat top pistons.

GHOSTOWLGRID

Yah I was considering flat top pistons but I'm not sure, that wouldn't happen until many years later still.

The cam is already in the engine, it does run great, I was only curious if I could get better loopy idle and better hp from some more lift.

I read that the stock rocker ratio in the olds 455 is 1.6:1 ratio. Is that correct?
If I wanted to increase valve lift should I go to a 1.5:1 or 1.7:1 ratio rocker?

Do I need to change my pushrod length if I do that? Do you think my pushrod will clear the heads?

Fun71

You would need to go with a 1.7:1 rocker ratio.
I have no idea about your other questions.

GHOSTOWLGRID

Ok, just to verify so I'm sure, keeping the cam and keeping the same pushrods, Moving from 1.6:1 to 1.7:1 will increase lift/duration?

The only thing though, I Have this style rockers on my 455, this link is a stock replacement (1/6 rockers) for my engine:
https://www.summitracing.com/parts/c...ake/oldsmobile

I found this for 1.7 Rockers:
https://www.summitracing.com/parts/c...ake/oldsmobile

I'm not sure if these 1.7 rockers will bolt onto my C heads, they look different. Am I missing something?

cutlassefi

Don't waste your money on 1.7 rockers. With a stock or nearly stock configuration I doubt you'll feel any change at all. And rocker design will have as much to do with pushrod length as anything else.
Kenneth- lobe profiles do not necessarily come in even graduations for lift. You have large duration low lift designs or higher lift shorter duration ones as well as everything in between. There are different lobes for different applications, even with similar lifts and durations. That's why you need to know how one design will effect a combination.
Hope this helps.

GHOSTOWLGRID

So if I want a 1.7 rocker to be effective, I should get different pushrods to match?
I was thinking I could get a little more lift/duration from the existing cam that I got to help with airflow.

I'm mostly doing things with my 455 to learn. But 500 dolars for 1.7 rockers is a lot. lol I thought they'd be 150 for a set like the 1.5 and 1.6 are.

I see you have EFI listed in your signature, do you think changing my dual plane intake to a single plane intake and going with fuel injection will improve my performance? I know a properly tuned MSD spark controller will work better because my distributor still isn't optimal.

cutlassefi

Don't waste your money on ANY 1.7 rocker, not worth it for your build.
Efi on its own does not ADD hp. However if you increase airflow due to an intake and/or throttle body change, then you'll increase hp. And timing control really just enhances driveability more than anything.

olds 307 and 403

What is your compression ratio? You either need a conversion stud, retap the head for a larger stud or pedestal rocker arms like these. https://www.summitracing.com/parts/scc-scp1096
Also guide plates are needed and there can be contact between the pushrod and head with a bigger ratio, mine was super close with 1.72 ratio rocker arms. You can try your pushrod but it is hard to say if it will close enough to work OK.
Using the proper cam is easier. Aftermarket cams due to the smaller base circle, do sometimes need an adjustable valve train, can cause a ticking, I am dealing with that right now.

Fun71

Understood. It just has always seemed to me that particular cam had mismatched lift and duration (based on all the other Olds cam profiles I have seen over the years).

cutlassefi

Gotcha. But I'm guessing you mean OEM Olds cams?
No one today makes Olds specific profiles, really no need to as they share common lifter diameters and rocker ratios with other manufacturers.
Only Mopars have "their own" profiles, basically just to take advantage of the .904 lifter diameter.

GHOSTOWLGRID

My rockers have the bolt style, no studs, not adjustable at all.

Like you said, lots of duration but less lift, I was reading that I can get more airflow from more lift.
Thats why I was wondering if I can sneak a little more lift from the cam I have with a different set of rockers because they are easy to swap out on the top.

I'm not hard up for it because it runs very well as it is, but I was thinking if I could find rockers for cheap I could try it because they're easy to swap.

cutlassefi

Knock yourself out. It seems like you're just hoping someone will give you the answer you're looking for anyway.

GHOSTOWLGRID

I like trying things for fun and for learning. Even if they don't always work. lol :P I was more so curious/concerned about valve/piton clearances

cutlassefi

Gotcha. You'll still have a mile and a half between the valve and piston.