varying rocker ratios from In to Ex
varying rocker ratios from In to Ex I searched but results were mixed and I'd like some feedback on my combo
so, I am well aware that a tricky rocker setup is never a replacement for a correctly spec'd out cam but I've sworn not to throw anymore money at internals on this motor so I'm looking to squeeze a little more out of it here and there. From past threads about my cam I've learned that it's a single pattern cam which is not optimal for an LT1. In the spirit of doing the best with what I've got right now I've been researching running different rocker ratios on the intake and exhaust valves. Some say running a higher ratio on the exhaust is good as LT1s need help on the exhaust side but then I see others going bigger on the intake side and smaller on the exhaust. I have 1.6s on both right now but I have a set of 1.7s sitting here and am wondering if putting 1.7 on the exhaust side will help at all versus putting the 1.7s on both intake and exhaust.
My current cam specs are...yes it's a wee little cam
Duration:
Intake: 227
Exhaust: 227
Lift:
Intake: 556
Exhaust: 556
Lobe Center: 112
Centerline: 108
And my head flow numbers are below.
If I were to run 1.7s on just the exhaust. The lift seen at the valve would be
Lift:
Intake: 556
Exhaust: 590.75
If I run 1.7s all the way around it would be .590/.590
Keep in mind, I have springs good to .600
Is .010 enough room to be safe?
so, I am well aware that a tricky rocker setup is never a replacement for a correctly spec'd out cam but I've sworn not to throw anymore money at internals on this motor so I'm looking to squeeze a little more out of it here and there. From past threads about my cam I've learned that it's a single pattern cam which is not optimal for an LT1. In the spirit of doing the best with what I've got right now I've been researching running different rocker ratios on the intake and exhaust valves. Some say running a higher ratio on the exhaust is good as LT1s need help on the exhaust side but then I see others going bigger on the intake side and smaller on the exhaust. I have 1.6s on both right now but I have a set of 1.7s sitting here and am wondering if putting 1.7 on the exhaust side will help at all versus putting the 1.7s on both intake and exhaust.
My current cam specs are...yes it's a wee little cam
Duration:
Intake: 227
Exhaust: 227
Lift:
Intake: 556
Exhaust: 556
Lobe Center: 112
Centerline: 108
And my head flow numbers are below.
If I were to run 1.7s on just the exhaust. The lift seen at the valve would be
Lift:
Intake: 556
Exhaust: 590.75
If I run 1.7s all the way around it would be .590/.590
Keep in mind, I have springs good to .600
Is .010 enough room to be safe?
Last edited by garage_queen; Jan 14, 2010 at 12:07 PM.
from what i understand is yes nitrous motor like more exhaust.
My Tea Heads flow a lot more on the exhaust side and on a TNT 150 shot my car picked up 170rwhp....
I don't know much about what will happen with mismatching rocker ratios..I know that a lot of old school engine builders use that method though...
My Tea Heads flow a lot more on the exhaust side and on a TNT 150 shot my car picked up 170rwhp....
I don't know much about what will happen with mismatching rocker ratios..I know that a lot of old school engine builders use that method though...
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TECH Addict
Joined: Jul 2005
Posts: 2,153
Likes: 3
No. . . what's been done for years by many others is running 1.6i/1.5e, myself included. The increased lift is almost always more beneficial on the intake than the exhaust. Peak exhaust lift makes little to no difference in power. This is very well tested and documented in Vizards camshaft book.
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Launching!
Joined: Dec 2004
Posts: 284
Likes: 1
From: Hebron, Oh
I run a 1.6/1.52 rocker split on the ZZ4 cam I have in my car. I did this to get the lift up, from .474/.510 to .506/.516. I didn't care about the exhaust lift with this cam since there is such a large split in duration 208/221. It's a mild cam, but thought it might help it a bit.
ok, I was reading another thread and people were chiming in on how they were doing it. It seemed pretty split that some went bigger on the intake side and others did it on the exhaust. Everything I find indicates that the LT1 needs all the help it can get on the exhaust side and especially in nitrous combos. I won't be doing it now that I know my springs would not be safe if I switch to the 1.7s. A clearance of .010 just isn't enough.
Glad you mentioned that book, I'll have to check it out as I've been looking for a good one.
Glad you mentioned that book, I'll have to check it out as I've been looking for a good one.
