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I thought I'd rekindle this topic for a turbo "what-if?"
The 96 cams are the same, just ground 4 deg. ADVANCED from the earlier engines (going off numbers found here somewhere: 108ICL, 115ECL for the 96 vs. 112/111 for the 94-95). I'm sure this was for emissions purposes. INteresting how the engine made more hp at higher rpm than the earlier with cams ADVANCED! Opposite normal expectations. It must be all in the heads.
Anyway, by retarding the exhaust 13*, one adds that much overlap, which helps in scavenging, which helps high end, blah, blah... actually, retarding the intake about half that would even open it up more.
BUT, on a boosted engine, you want to keep the overlap to a minimum, otherwise you're just blowing off your intake charge. So, you want the exhaust to open sooner (within reason... if it opens too soon, you get too much reversion and kill power everywhere). The earlier exhaust opening event helps to build boost quicker.
Lastly, the way to increase effective rpm on a boosted engine is to retard the intake. Something like 4-8deg. Or, on a 8000rpm max race engine, as much as 15deg. A side benefit is reduced overlap which as mentioned above, furthur helps the turbo build cylinder pressure.
Now, all of this assumes one is attempting to gain the most out of stock cams for cost reasons, racing class rules, etc. Aftermarket cams will have these timing changes ground into the profile and should always be set to manufacturers specifications.
So, I am going to start with a 4deg retard on the intakes to see what I get. Using Michael Smiths Fiero project, he retarded the intake 8deg. and peaked at 7500, 2000rpms higher than stock, so I hope 4deg. will give me about 1000 more, from 5500-6500.
How's all this sound????
The 96 cams are the same, just ground 4 deg. ADVANCED from the earlier engines (going off numbers found here somewhere: 108ICL, 115ECL for the 96 vs. 112/111 for the 94-95). I'm sure this was for emissions purposes. INteresting how the engine made more hp at higher rpm than the earlier with cams ADVANCED! Opposite normal expectations. It must be all in the heads.
Anyway, by retarding the exhaust 13*, one adds that much overlap, which helps in scavenging, which helps high end, blah, blah... actually, retarding the intake about half that would even open it up more.
BUT, on a boosted engine, you want to keep the overlap to a minimum, otherwise you're just blowing off your intake charge. So, you want the exhaust to open sooner (within reason... if it opens too soon, you get too much reversion and kill power everywhere). The earlier exhaust opening event helps to build boost quicker.
Lastly, the way to increase effective rpm on a boosted engine is to retard the intake. Something like 4-8deg. Or, on a 8000rpm max race engine, as much as 15deg. A side benefit is reduced overlap which as mentioned above, furthur helps the turbo build cylinder pressure.
Now, all of this assumes one is attempting to gain the most out of stock cams for cost reasons, racing class rules, etc. Aftermarket cams will have these timing changes ground into the profile and should always be set to manufacturers specifications.
So, I am going to start with a 4deg retard on the intakes to see what I get. Using Michael Smiths Fiero project, he retarded the intake 8deg. and peaked at 7500, 2000rpms higher than stock, so I hope 4deg. will give me about 1000 more, from 5500-6500.
How's all this sound????
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