effect of a 1.6 rocker change

[Gene 64 2dr]

I’m thinking of replacing my rocker assembly with a 1.6 roller rocker. The cam I have installed is a 268/274 (110) running a T5 trans and a 3x1 offy set up. It is going to be driven on the street but not as a daily driver and will find it’s way to the drag strip.

My question is how much of an effect will changing the ratio have on this setup. I’m wondering if it will be too much.


Thanks
Gene

 

[AzCoupe]

We plan to dyno test one in the next week or two, to see just how much power can be had with the swap. I'll post the result once we're done testing.

 

[wsa111]

Gene, the 1.6 roller rockers will reduce some valve train friction.

The advertised camshaft duration will not change but the duration @ .050 will be about 2 degrees more & you will gain about .030" lift.

I would guess at least a 5-8 HP gain. Bill

 

[rbohm]

8) you wont gain a lot of peak power, like was111 said about 8hp or so, but you will get a slightly fatter power curve through out the rpm range. one thing though, the larger ratio will stress the valve springs more than the stock ratio will, but not enough to worry about.

 

[Gene 64 2dr]

Thanks for the feedback. My main concern is since it’s already a pretty aggressive cam I was wondering if the added lift would push it over the edge for driving on the street. I see that the 280 cam should only be used in a racing application and would bumping the 274 up the 2 or 3 degrees be too much for the street.

By the way rbohm “dittoâ€￾


Gene

 

[BIGREDRASA]

8) you wont gain a lot of peak power, like was111 said about 8hp or so, but you will get a slightly fatter power curve through out the rpm range. one thing though, the larger ratio will stress the valve springs more than the stock ratio will, but not enough to worry about.

That's one kind of "fat" I'll go for! Will it have a similar effect with the stock cam?

 

[wsa111]

Tony, you still run a stock cam! Those cams are obsolete.
I think the 1.6 rocker will also help you. In fact it may help you more because the stock cam is so mild & the lift is below poverty level that any increase would be appreciated by your engine. Bill

 

[XFlow_Fairlane]

it will not effect the ovrlap too much which will help keep it tame (IE not require a stupid idle speed) you get a faster opening of the valves for the same duration but more lift.

the only worry would be if you are going to bind the springs any which I doubt on that mild of a cam.

 

[rbohm]

8) you wont gain a lot of peak power, like was111 said about 8hp or so, but you will get a slightly fatter power curve through out the rpm range. one thing though, the larger ratio will stress the valve springs more than the stock ratio will, but not enough to worry about.

That's one kind of "fat" I'll go for! Will it have a similar effect with the stock cam?

8) yes it will, the effect of higher ratio rockers is pretty much universal. some engines will see a bit more peak power, and some a bit less, but usually only a couple hp. one more thing you can do is to use say a 1.6 ratio on the intake side and a 1.7 ratio on the exhaust side to pick up a bit more exhaust flow, and an extra couple of hp as well.

 

[AzCoupe]

We will be testing it on Gene's 250, which has a stock cam. So we'll find out.

 

[66 Fastback]

I remember seeing some dyno runs in a hot rod magazine years ago that showed there was negligible difference. But I would suspect it depends on the engine. I would think that an engine like ours that has a difficult time breathing, the additional lift may help more than one that has been ported and blue printed.
There is also a powertrain engineer on a Corvette site I visit that notes that stock 1.5 rockers are not really 1.5 (at least on small block Chevies). I forget the exact numbers, but it seems they were more like 1.45 on average and the stamped steel ones varied quite a bit.
Doug

 

[rbohm]

8) doug you are right, and ford is just as bad. the stock rockers on a ford V8 also measure out to be between 1.42 and 1.45 like the small block chevy. i think part of the reason is the wear you find on the dies as they age. there have been stock rockers measure out at spec, but they tend to be few and far between.

 

[CZLN6]

Howdy Back Gene and all:

With a high lift performance cam like you have with lifts of .455" intake and .480" exhaust, your gains going from stock type 1.5:1 rockers to 1.6:1 roller tips will be slight. THis amount of cam lift will likely exceed the flow capacity of all but the finest flowing heads. At this point, I'd be doubly careful to check valve to piston clearances too. You would likely see gains in mid range where the additional lift can be used. IF you're talking the roller tipped rochers, the roller feature will also help with valve tip alignment and valve stem side rock.

It is my opinion that the greatest value from increased rocker ratio is with an engine with a stock cam with valve lifts of .348" to .372". An additional .030" lift across the board would be worth doing.

I'm looking forward to Mike's before and after tests on Gene F. engine with a stock cam.

With an OEM log head flow flatten out at around .400" lift. Very little increase in flow is seen above .400". Now with the Oz, Argentine heads that would likely be a different story. Mike's new head is still finding limits and absolutes, so that's a different story.

What head are you using Gene? Valve size? Porting? exhaust? trans?

That's my two cents. for what it's worth.

Adios, David

 

[wsa111]

David, i agree with you that the log head is maxed out at .400" lift.

But if you go above the .400" for a longer duration that maximum limit is extended at that peak flow for a longer time.

All i can say with the modified log any time i increased the rocker arm ratio the engine ran stronger. Even going to the 1.65 over the 1.6 you could hear the difference at full throttle from the exhaust & it was slightly stronger in acceration, possibly being a full roller rocker maybe the less friction made the difference. Bill

 

[Gene 64 2dr]

Dave,

This is the setup as it is now:

200 bored 40 over with flat top pistons
Compression ratio about 8.5 to 1
268/274 cam with matching springs and retainers
Dual roller timing chain
Dual out long tube headers
DUI distributor with matching wires
Later year large log flat top head with a 1.75 intake bore
3-angle vale job on I believe are 1.75 intake vales
Head ported and polished by me (machinist said I did a good job)
3x1 offy setup using single Weber ICT carbs
Trans being used is a T5 to a 8â€￾ rear end (have not made a decision on gearing yet)

I think that’s about it

Gene

 

[AzCoupe]

Gene's log head has been modified for a direct mount 2V carb, which is the primary reason for our testing. The head has 175/150 valves, and was cleaned up in the bowls. They also ported up into the intake runners as far as they could, cleaning them up as well. Once we run the modified log head with the stock rockers and various 2V carbs, will see what happens with the rockers. Pony Carbs is sending us a couple extra Autolite carbs to test, a 287cfm and a 351cfm. Plus we'll be testing the Holley 350 and Autolite 240 that we used during the baseline runs.

If I can afford it, I'd like to have Steve bring his Falcon back. Since we have the baselines on his 200ci, it would be nice to test the bigger Autolites and the rockers. Based on the previous dyno runs, I'm pretty sure the Autolite 240 was to small. I'd really like to see how the Autolite 287 and 351 compare to the Holley 350. ???

Should be fun, and some great info.

 

[69.5Mav]

Any Progress?

 

[Gene Fiore]

Any Progress?

Yep! http://fordsix.com/forum/viewtopic.php?t=54061

 

[AzCoupe]

Results using the Holley 350 with a 2V adaptor; verses the Holley 350 on a modified head (direct mount 2V) with 1.5 rockers; verse the Holley 350 on the modified head with 1.6 rockers.
Carb - CFM - Rockers - Max HP (Gain/Avg) - Max TQ (Gain/Avg) - C/O
Holley 350 - adaptor - 1.5 - 80 @ 3950 (5/68hp) - 120 @ 2600 (10/109lbs) 6%
Holley 350 - modified - 1.5 - 98 @ 3850 (23/70hp) - 140 @ 2500 (30/112lbs) 6%
Holley 350 - modified - 1.6 - 100 @ 3900 (25/80hp) - 142 @ 2450 (32/129lbs) 6%

Note the gains in average HP and TQ. Peaks gains were slight, which means the low and mid range gains had to be higher than the average gain.

 

[Gene Fiore]

I've noticed that the 1.6 rockers have made a difference in driveability as there is more seat of the pants difference with them driving around town. I'm hoping to prove that there is a difference at the drag strip this weekend. I did go to the track with the 1.6 rockers already, but the weather conditions were much hotter than my last time out plus I found that I wasn't quite getting full throttle due to a problem with my linkage, so my et's were a little off. We'll see how it runs this Sunday.