[FastBuick]

Hello everyone,

I am thinking about changing to a higher rocker ratio in order to get more valve lift. I have a 1.7 ratio on the intake and exhaust now. I was going to go up a 1.9 ratio, or at bare minimum a 1.8 ratio on both intake and exhaust.

What are the pros and cons when doing this? Am I going to create any problems by doing this? Any information on this is greatly appreciated.

Thanks
John

 

[69chicken]

Man your going to have to give a ton more info on your combo but really your cam builder should guide you with rocker ratio.

 

[FastBuick]

My combo is: 400 ci (4.195 x 3.625) SBC 15.5:1 Compression
CFE 18 degree heads with 268cc intake runners 90cc exhaust runners and 2.180/1.600 titanium valves 54cc combustion chambers
Custom Comp Cam 281/290 duration @ .050" 314/328 Adv duration .471"/.451" lobe lift .800"/.765" w/1.7 rocker 108 LSA
3150# car with me in it
5.83 rear gear, 1.76 powerglide trans (will be changing to 2.48/1.48/1.00 lightened TH400 for next season)
Shift at 9000 RPM go through traps at 9200-9400 depending on the air.

Thanks
John

 

[MrRedfish]

^^^^^^^^ That little SBC sounds like steam roller ^^^^^^^^


Wish I Could answer your question but truth is I was thinking the same question so I will stay tuned

 

[fast66]

I'd try 1.8 on the intake and leave the 1.7 on the exhaust. You are trying to get more air in the motor and the exhaust is already creating a vaccuum to get the air out. Most combos see the RPM range moved up a few 100 RPMs and a small increase in HP and torque. Check piston to valve, coil bind and make sure your pushrods are the correct length. Drawbacks to higher lift are extra guide wear and valve spring wear.

 

[68 nova 10.5]

My combo is: 400 ci (4.195 x 3.625) SBC 15.5:1 Compression
CFE 18 degree heads with 268cc intake runners 90cc exhaust runners and 2.180/1.600 titanium valves 54cc combustion chambers
Custom Comp Cam 281/290 duration @ .050" 314/328 Adv duration .471"/.451" lobe lift .800"/.765" w/1.7 rocker 108 LSA
3150# car with me in it
5.83 rear gear, 1.76 powerglide trans (will be changing to 2.48/1.48/1.00 lightened TH400 for next season)
Shift at 9000 RPM go through traps at 9200-9400 depending on the air.

Thanks
John

what has this run so far?

 

[FastBuick]

I'd try 1.8 on the intake and leave the 1.7 on the exhaust. You are trying to get more air in the motor and the exhaust is already creating a vaccuum to get the air out. Most combos see the RPM range moved up a few 100 RPMs and a small increase in HP and torque. Check piston to valve, coil bind and make sure your pushrods are the correct length. Drawbacks to higher lift are extra guide wear and valve spring wear.

Ok so more of the gains come from the intake side. The exhaust side isn't worth the change?

Thanks
John

 

[FastBuick]

what has this run so far?

The car has run a best of 9.28 @ 143.50 mph at a track that is 997 ft. above sea level.

Thanks
John

 

[68 nova 10.5]

thats bad ass!

 

[T-flow]

I run a cam very close to that in one of my 15* motors. It's a Comp Cam's deal, I have ran both 1.7 & 1.8's on it with no problem on the Intake side only. .481"/.461" Lobe Lift But everything else the same. Don't know if it would of picked up going from one to the other, but ran good either way.(To different combo's, same cam)

T-flow

 

[FastBuick]

thats bad ass!

Thank you. Just like every other drag racer I'm never happy until I maximize a combination lol. If there's room for improvement I try to find it. Supposedly there's room for improvement with the trans. That's why it's being changed for next season. CFE said there is room for improvement with more valve lift also. That's why I'm thinking about trying higher ratio rockers.

Thanks
John

 

[CFMCNC]

Would go to 1.9 int.1.8 exh.Bill C.

 

[69chicken]

I think I would run more on the Intake side and leave exh as is. Comp should be able to tell U if a 1.8 or 1.9 will give you any problems.

 

[FastBuick]

I run a cam very close to that in one of my 15* motors. It's a Comp Cam's deal, I have ran both 1.7 & 1.8's on it with no problem on the Intake side only. .481"/.461" Lobe Lift But everything else the same. Don't know if it would of picked up going from one to the other, but ran good either way.(To different combo's, same cam)

T-flow

Thanks for the info. It sounds like the 1.8 ratio is still reliable. Have you ever tried a 1.9 ratio rocker on anything? Was that cam cut on a .900" base circle? Was that used in a standard SBC cam journal? The one issue I have is being able to put a bigger lobe in the engine. Just wondering how big of a lobe I can fit in the standard journal?

Thanks
John

 

[FastBuick]

Would go to 1.9 int.1.8 exh.Bill C.

Thanks for the reply. That will give me .895"/.812". Just so I know the reasoning behind it. Why would you use so much stagger in the lift. Is it because the duration is more important than the lift?

Thanks
John

 

[Lobes]

Buy some dyno time.

 

[79rustbucket79]

My combo is: 400 ci (4.195 x 3.625) SBC 15.5:1 Compression
CFE 18 degree heads with 268cc intake runners 90cc exhaust runners and 2.180/1.600 titanium valves 54cc combustion chambers
Custom Comp Cam 281/290 duration @ .050" 314/328 Adv duration .471"/.451" lobe lift .800"/.765" w/1.7 rocker 108 LSA
3150# car with me in it
5.83 rear gear, 1.76 powerglide trans (will be changing to 2.48/1.48/1.00 lightened TH400 for next season)
Shift at 9000 RPM go through traps at 9200-9400 depending on the air.

Thanks
John

At the very least I would be talking to the cam designer to see if it would be stable with the bigger ratio at that RPM.

 

[melsie68]

Jumping from 1.7 to 1.9 is rather significant on a lobe like you have now and on the stock SBC base circle. Only the lobe designer would know for sure if the valvetrain will still be under control in the case of the 1.9 ratio. Surely you can get more lift by changing rockers and that may make more hp, but not if springs cannot keep the valves from bouncing and keep the lifters on the cam. You may have to switch to a different lobe which will give you the lift benefit you are looking for with a rocker change and will still have a ramp rate that is feasible with the high rocker ratio. Or just buy another cam with more lobe on it to get the lift your after with your current rockers. Call Steve Lowe at LSM. The 108 lobe separation seems rather tight to me too...I bet she sounds trashy (in a good way). If it is a Dart block, I would look at going 55mm babbit bearings on the cam to get a decent lobe in there and you might as well go to .905 or .937 lifters at the same time. With your short stroke, you should have the clearance for the larger base circle cam.

Nice motor and good heads by the way. They are right in saying the more lift, the more power you will make.

 

[FastBuick]

Jumping from 1.7 to 1.9 is rather significant on a lobe like you have now and on the stock SBC base circle. Only the lobe designer would know for sure if the valvetrain will still be under control in the case of the 1.9 ratio. Surely you can get more lift by changing rockers and that may make more hp, but not if springs cannot keep the valves from bouncing and keep the lifters on the cam. You may have to switch to a different lobe which will give you the lift benefit you are looking for with a rocker change and will still have a ramp rate that is feasible with the high rocker ratio. Or just buy another cam with more lobe on it to get the lift your after with your current rockers. Call Steve Lowe at LSM. The 108 lobe separation seems rather tight to me too...I bet she sounds trashy (in a good way). If it is a Dart block, I would look at going 55mm babbit bearings on the cam to get a decent lobe in there and you might as well go to .905 or .937 lifters at the same time. With your short stroke, you should have the clearance for the larger base circle cam.

Nice motor and good heads by the way. They are right in saying the more lift, the more power you will make.

Thank you for the reply. You do make a lot of good points. Those are all things I would like to do. The limitation I have is the block. In order for me to get a bigger base circle and a bigger lobe I would have to go with a raised cam block. I have a World Products Motown block now. I can go with the bigger journal but I would still have to use a small base circle like I have now (.900"). The problem is the rod to cam clearance. I have .095" clearance now on the 2 tight cylinders. I know it is said that you can go as tight as .050" but I'm not sure if I want to chance that not knowing how much the cam flexes at the RPM I run. Although I did read last night that a higher rocker ratio will cause more stress on the valve train and cause the cam and pushrods to flex more. This is because the pushrod is moved closer to the shaft on the rocker which gives it less leverage. I do have the .904" lifters now and I have the 1.500" PAC springs that have 400# on the seat with 1050# open. Those should be ok with the rocker change I would think.

Thank you for the compliments on the engine. I think it does run really well. I just enjoy tweaking it so I'm always trying new stuff.

Thanks
John

 

[T-flow]

Thanks for the info. It sounds like the 1.8 ratio is still reliable. Have you ever tried a 1.9 ratio rocker on anything? Was that cam cut on a .900" base circle? Was that used in a standard SBC cam journal? The one issue I have is being able to put a bigger lobe in the engine. Just wondering how big of a lobe I can fit in the standard journal?

Thanks
John

No, dont have any 1.9's. Only have 1.85's, thats the highest that I have. They pretty much stay on another motor, I bought them because the cam guy wanted that for his deal...
Standard base circle cam with 1.7's-1.8's. The 1.85's are on a small base circle cam, standard cam location.

T-flow