What are the cons to using high-ratio rockers?
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From: Central Cal.
The reason is pretty simple... stock rockers are like 1.4:1 at the seat and increase to 1.7:1 throughout the ramp. Roller rockers are 1.7:1 throughout the movement.
It's a pretty small change overall... but it's a change nonetheless.
The cons are mostly around weight over the valve. You just need a spring with more seat/open pressure to accommodate the added weight. Usually add about 25lbs of seat pressure and 50lbs open to whatever your combo calls for and that should be enough.
So, most aftermarket lobes call for a 150/380 with stock rockers or so... you'd need 170+ and 425+ to be good. But usually that ends up being 175/450 or so. Stock cam would be less. But then I'd use the standard dual valve springs with a stock cam and aftermarket rockers... or shim up something like PSI1511s.
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From: over dere
Stock rockers aren't a true 1.7 either. They just finish at a 1.7 ratio
Springs aren't just required for lift. The speed of the valve movement and valvetrain weight come into play as well. That's where you need more pressure to control the movements of the valves
None of it is a waste. If you ever do want to cam in the future you can contact a vendor like cam motion and they can easily design you a cam to work around higher ratio rockers
Springs aren't just required for lift. The speed of the valve movement and valvetrain weight come into play as well. That's where you need more pressure to control the movements of the valves
None of it is a waste. If you ever do want to cam in the future you can contact a vendor like cam motion and they can easily design you a cam to work around higher ratio rockers
You might look for a set of used slp 1.85's. They are identical design to stock 1.7 other then the push rod cup is moved to increase ratio. I have had a set on my car for years. I ended up buying a cam that was designed for the higher ratio a few years back when I did H/C/I.
The LS7 and gen V LT1 both use 1.8 rockers. Jesel just released a set of pedestal mount rollers in 1.8 & 1.9 ratio for the Gen 5 LT. So evidently higher ratio has it's place.
That being said, I would not put Pro Comp anything on my car. My dad installed a 383 into a 62 Impala for a guy. This guy bought the engine off a ebay builder. Almost everything was pro comp(distributor, carb, rockers). It all ended up getting swapped out for good parts because it ran like trash.
The LS7 and gen V LT1 both use 1.8 rockers. Jesel just released a set of pedestal mount rollers in 1.8 & 1.9 ratio for the Gen 5 LT. So evidently higher ratio has it's place.
That being said, I would not put Pro Comp anything on my car. My dad installed a 383 into a 62 Impala for a guy. This guy bought the engine off a ebay builder. Almost everything was pro comp(distributor, carb, rockers). It all ended up getting swapped out for good parts because it ran like trash.
Great question. I have a rebuilt LS1 with new replacement type pistons, 243's from an LS6 with factory yellow valve springs and valves milled 15 IIRC, and the 385hp version of the LS6 cam. This was done because the parts were available and cheap. Obviously I'd rather have a "good" cam, but I don't want to get new springs etc. It's just too much money. Would a set of 1.8's be a worthwhile solution to getting a little bit more out of the motor?
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First, the yellow factory springs would likely not control the 1.8 rocker. Second, you really need to get those springs out of there as they are the ticking time bomb of the original LS6 heads. If you are sticking with the setup you have, the GM replacements (now blue) will be fine but as stated by Darth_V8r get the PSI 1511 ML's if you want a rocker upgrade.
Some of the yellows had a issue with breaking. Idk how widespread it was. But they seemed to start failing at about 80k miles from my research on it. That's why i changed mine initially to the psi 1511. Then i added the 1.8 rockers because there was enough spring there. I have run 1.7s rr on stock ls6 springs also. The only thing i noticed was smoother high rpm. Like 6k + it just ran smoother.
Hmmm. I don't know the mileage on these springs. Was going for a budget build here, had the heads milled, 3 angle valve job and some bowl work done....thought I'd be fine with factory valves and springs. I figured the LS6 springs had to be pretty good, why change them if running a stock cam? Doubt the heads have crazy miles on them.
Don't say that! I've never heard that about LS6 springs, but then I've never really heard anything about LS6 springs. Why are they a ticking time bomb? What is the issue with them? Also keep in mind that this engine is going in a heavy 4wd truck. And while it may see moderate throttle up to 5 grand getting on the highway, it very, very rarely sees WOT. Just saying that if this was going into my car it would be a different story. I beat that thing like it molested my little sister every time I drive it. (sorry) Because that's what it's for - WOT and 6grand plus a lot.
This is a good one and will give you more low end power. Most cams are gonna lose low end and gain top end, not what you want in a truck.
https://www.briantooleyracing.com/tr...age-i-cam.html
This is too. Not sure why it's $299 vs $389 or why it's called low lift when it has higher lift than the above cam but this one would be great too.
https://www.briantooleyracing.com/bt...truck-cam.html
Inverse Cam Lobes = "conn" Hi *LUG, the "tech" above is fine with good reports, just NOT about your question 1.8 "conn".
My report is about professional race engine camshaft requirements :
WE REDUCED the Rocker Ratio to 1.6 for best results. (1.73 original)
The reason was the Inverse Lobe Design caused a TOO GREAT Valve Acceleration AND too much stress on the rocker studs. (Roller Camshaft)
NEXT, understand the a Solid Tappet camshaft can accelerate the valve faster than a Roller Tappet camshaft.
This is the reason MANY Pro-Stock engine's have fit a lifter with a LARGE Roller Bearing.
The larger the "roller" the faster the acceleration is of the lifter with lower stress.
THUS, as stated above, it depends on the lobe size, use, spring, etc.
I only state this because of the "bigger=better" is not the best case.
Lance
My report is about professional race engine camshaft requirements :
WE REDUCED the Rocker Ratio to 1.6 for best results. (1.73 original)
The reason was the Inverse Lobe Design caused a TOO GREAT Valve Acceleration AND too much stress on the rocker studs. (Roller Camshaft)
NEXT, understand the a Solid Tappet camshaft can accelerate the valve faster than a Roller Tappet camshaft.
This is the reason MANY Pro-Stock engine's have fit a lifter with a LARGE Roller Bearing.
The larger the "roller" the faster the acceleration is of the lifter with lower stress.
THUS, as stated above, it depends on the lobe size, use, spring, etc.
I only state this because of the "bigger=better" is not the best case.
Lance
Ditch the LS6 cam and grab a stage 1 or stage 2 drop in truck cam and be done with it.
This is a good one and will give you more low end power. Most cams are gonna lose low end and gain top end, not what you want in a truck.
https://www.briantooleyracing.com/tr...age-i-cam.html
This is too. Not sure why it's $299 vs $389 or why it's called low lift when it has higher lift than the above cam but this one would be great too.
https://www.briantooleyracing.com/bt...truck-cam.html
This is a good one and will give you more low end power. Most cams are gonna lose low end and gain top end, not what you want in a truck.
https://www.briantooleyracing.com/tr...age-i-cam.html
This is too. Not sure why it's $299 vs $389 or why it's called low lift when it has higher lift than the above cam but this one would be great too.
https://www.briantooleyracing.com/bt...truck-cam.html
My earlier LS6 cam = 207/217 @.50 .525/.525 lift 116 LSA
Stage 1 Truck Cam = 206/212 .525/.534 114+2
SO they are pretty damn close, no sense in changing to that. And if I'm gonna have cam it I'm gonna make sure it sounds like it too, lol. Again, I have a stall and gears.
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Joined: Jun 2016
Posts: 22,306
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From: Central Cal.
Just to keep things level- The EARLY LS6 cam is 204*/211*@ .050, .525/.525, 116*
The LATE LS6 cam is 204*/218*@.050, .551/.547, 116*
Which one do you have? You show the early lift and close to late duration.
The LATE LS6 cam is 204*/218*@.050, .551/.547, 116*
Which one do you have? You show the early lift and close to late duration.
Pretty close in specs, not as close in performance. You'll gain a lot more with the truck cam than you will with the rockers and you'll spend close to the same. Especially if you go with the $299 truck cam. That LS6 cam will shine in all the areas you said you don't drive the truck.
Hmmm. I don't know the mileage on these springs. Was going for a budget build here, had the heads milled, 3 angle valve job and some bowl work done....thought I'd be fine with factory valves and springs. I figured the LS6 springs had to be pretty good, why change them if running a stock cam? Doubt the heads have crazy miles on them.