Fast81

With Performer intake and LT headers, 1.6RRs should bump lift rates equal to a matching Performer cam.

Thoughts ?

Drawmain

Don't forget to check clearances with the 1.6 ratio rockers.

7t9l82

if the l48 is all stock you need to check the pushrod slots in the head because the higher lift ratio will likely cause interference.put one on the intake and exhaust and turn the engine over by hand and check the slot in the head the pushrod goes thru for clearance.
there shouldn't be a valve to piston issue with that cam and dish pistons. i have an L-82 with 64 cc chambers flat tops and 1.6 rockers and have no issues so i doubt you would have piston to valve issues

cardo0

Yes, 7tl82 is correct u would need to enlarge the p-rod slots for 1.6 rockers - its called the Lewis tool and allows p-rod to rest in the normal slot without guide plates. Intake will come off and some debris control management will be required to control the fillings.

The weak link is the vlv spring. I dont know what spring is on the head. We really need the spring specs before deciding. My 1974 shop manual specs for a '74 L48 vlv spring is 266 lbs/in and close press = 80# same as most sbc L48 springs. But at only 1.61 installed height. Our lo-po L48 springs could have a lower installed height and vlv lift limited for this.

I guess what im saying is u would have to try'm and see if u get vlv float or retainer to guide boss interference.

Or u can install better springs (plenty to choose for that head) and go for 1.7 rockers arm - they would be rollers and need better screw in studs.

Tempting to pop the heads and put in a shim steel gasket for quench and compression too. But if the heads come off then really better heads should go on and while im at it itis begins. It would be cool to see what some vortec heads on steel shim gasket with 1.7 rockers would do to that L48 with the 929 cam. I always felt a head swap was much easier to do than a cam swap.

Good luck,
cardo0

PeteZO6

How can that be right? As long as the cam is the same, the pushrods are going to move the same regardless of the rocker arm ratio. The higher ratio rockers should only affect the valve side. You have to make sure the added valve lift doesn't coil bind the springs or cause valve to piston interference.

Pete

John Holmes

I have done this and there is no issue.
I ran the Comp 1.6 roller tips on a stock cammed L48 for 2 years as my daily driver. With the factory heads there is no interference.

scottyp99

The rocker arm is a lever and its mounting point to the head is its fulcrum. If the spot where the rocker is mounted (the fulcrum) doesn't move, and the valve stem doesn't move (the length of the lever on that side of the fulcrum remains the same), then that means that the pushrod has to be closer to the fulcrum, in order to increase the ratio.....I think.....

Scott

7t9l82

it is a longer lever, it will push the pushrod into the end of the slot causing a bind. and with roller rockers not just roller tiped rockers you will need guide plates too.

scottyp99

Did you use new springs?

Scott

John Holmes

No I did not. Even with the added lift and the stock springs you still have a fairly safe margin of lift before you need to be concerned.

John Holmes

One more thing; with the stock intake, holley 650 spreadbore, recurved distributor, long tube headers, auto trans, 3.08 gears, and the afore mentioned cam and rockers the car ran consistent 15.0s @ 91 MPH in the quater mile at sea level.

63mako

My thought is it is not worth the effort. This does nothing for your duration numbers. Stock heads and sub 200 duration cam is in no way a performance combination. The intake and headers need better flowing, smaller chamber heads and more cam duration to optimize the combination. These cars ran around 15.4, 91 MPH from the factory with ramhorns and convertor, crap timing curve and all emissions in place.

7T1vette

You might net 5 hp or so with just the rocker ratio change. Not really worth the trouble. Recurving the distributor could net you 20-30 hp, depending on how you presently set your timing.

Also, verifying that your accelerator pedal will REALLY produce a complete full-throttle opening of the carb is a MUST thing to do. Lots of C3's don't fully open with the factory adjustments to the throttle cable. Opening the throttle by hand doesn't simulate reality!

John Holmes

Nope.
The L82s did run in the low to mid 15s, but the L48 cars w autos were high 15 second cars and had trap speeds in the mid 80s. Road & Track, Car & Driver, and Motor Trend have the original road tests available on the web. My '79 w auto and 3.08 rears ran 15.9 @ 86 when stock. Headers, rockers, and timing knocked almost a full second off that. I'm sure a decent Qjet would have put the car solidly in the 14s, but it came with the Holley 4175 and it worked great so I left it alone.

Fast81

This was my thought. The most cam stock l48 heads (.500 lift) should handle is a Performer 2102 which is pretty close to the stock duration and also on 112. So without going into the heads, the 1.6RRs would multiply the stock lifts to match a Performer cam and get the better breathing without a cam swap but using the 2101 intake.
Cuz if I'm adding a different cam, I'm adding different heads too and all bets are off!

Just following the combined recommendations of many "how can I upgrade my L-48" threads to brainstorm quick, simple upgrades without skipping to heads/cam.

gkull

The l-48 cam specs: .390/.410 lift, 196/202 duration @ .050

Lots of stupidity about binding push rods and guide plate requirements. It is pretty simple math to figure out the lift gain changing from 1.52 -1.6

Going from .390 to .4105 Do you really think that 2 hundredths of an inch will increase cylinder filling or anything to do with valve train angularity?

427Hotrod

Just put some sort of real cam in it. This exercise isn't going to be worth messing with.

There's a lot more to a cam than just .050 numbers.


JIM

Strokemyaxe

I think this is something I'm going to do. My neighbor is a big hot Rod guy and just gave me a pair of comp cams 1.6 inch roller tipped rockers. I've never done this before and it seems like something I want to learn how to do. I will let you guys know how it turns out. I'll test the valve clearance by hand turning the motor with one set on.

bluedawg

When I did intake and heads on the l48 with the stock cam, it can tons better, I went 1.6 rockers even better, went xe262h even better, xe262h with the 1.6s better yet, added the 2400 rpm stall, night and day difference.

Strokemyaxe

My L48 is pretty much brand new. I'm actually not sure if the factory correct Pistons or cam were used. It's not matching numbers I can't for the life of me figure out why in the hell someone would rebuild his exact motor. It's worthless. Lol