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Old 07-11-2012, 04:49 PM
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Over adjusted valves?

Got my engine (sbc with gt45 turbo 5 psi) to a point where it runs good... At least good enough to drive out on the street ... Just feels like its lacking power it's a got maybe 20 miles on it so the engine is fresh and i did a good cam break In. It has a smooth idle vacuum at 15 inhg... It has plenty of torque to spin the tires from a dead stop but I feel like it lacks acceleration timing I set at 15 intial and a conservative 30 to avoid detonation with boost... My main question is if it's possible to over adjust valves to a point that the valves never close and bleed off some power. Reason I ask is because I recently added roller rockers and adjusted them... I don't have a very good snap throttle vacuum peak when I hit WOT an let off the vacuum only spikes to about 20-21 inhg... That doesn't seem right to me shouldnt it spike to at least 26-27 and I wanna know if that could be the cause
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Old 07-11-2012, 05:20 PM
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I assume you are running hydraulic lifters. You can over adjust them. How did you adjust them the first time? A turbo takes a few seconds to spool up, it's not like a supercharger where you have instant boost.
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Old 07-11-2012, 06:34 PM
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Usually if the valves are to tight it will pop through the carb or exhaust. Did you change the cam, if so are you sure the dots were aligned.
A compression test would show leaking valves
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Old 07-11-2012, 07:26 PM
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yes theyre hydraulic lifters and im curious about the vacuum reading not the boost ... yes i triple checked the dots on the cam and crank im a paranoid mess when i put my engines together
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Old 07-11-2012, 08:03 PM
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Quote:
Originally Posted by Pupsvette76 View Post
yes theyre hydraulic lifters and im curious about the vacuum reading not the boost ... yes i triple checked the dots on the cam and crank im a paranoid mess when i put my engines together
If you had any valves adjusted too tight the vacuum gauge needle would be bouncing and the performance would be very bad, along w/the aforementioned popping through the carb and/or exhaust.

Did the carb ever run right? The float level could be either too high or too low. It could be the float is hanging up or the needle valve/seat is sticking or there's a possibility something (a piece of gasket or teflon tape) is causing the needle to not stop the fuel flow and the carb fuel level is too high.
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Old 07-11-2012, 09:04 PM
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im running a professional products efi throttle body
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Old 07-12-2012, 01:06 PM
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i just adjusted the valves again this time doing one half turn after "0" lash as weird as it sounds the engine smells better i.e. it smells like its doing a more complete combustion however im not getting a good snap throttle vacuum like i mentioned im worried that means i have a problem
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Old 07-12-2012, 03:02 PM
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Adjusting valves gets tricky. Tighting the lash quarter turn will cost you low end power. Losening them will increase low end and mid range.The best way I found is to adjust the valves enginer running until the ticking stops. After reaching operationg temp of coarse. depending on the valve rain the poping will start when you are too tight or the geometry is incorrect.

How much does changing cams help on your supercharged sbc?

I just rebuilt a 144 and installed it on a camaro. It had a small cam and we upgraded to a larger profile. Honestly I could not tell if it made any difference.

My 305 has a performer cam and a E force charger. I never swapped the cams but thought about it.
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Old 07-12-2012, 06:22 PM
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The car I'm talking about isn't supercharged but I do have a a corvette with a weiand 177 on it with a supercharger cam in it the cam helps because it has a larger lsa(lobe separation angle) its 114 between center lines with less overlap in the valves it retains more cylinder pressure than a smaller lsa cam especially at lower rpm
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Old 07-13-2012, 06:06 AM
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Quote:
Originally Posted by Pupsvette76 View Post
im running a professional products efi throttle body
Had your post mixed up w/a post where a guy was stalling on cornering, etc.
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Old 07-13-2012, 07:12 PM
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im ruling out worn rings just based on hopes and on the fact that the engine has literally just been rebuilt... what else could cause a poor snap throttle vacuum
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Old 07-14-2012, 09:46 AM
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First thing I would do is blow the engine down(will tell you about ring seal)
also about comp goin past valves
If the above checks ok and providing you dont have any manifold or boost leaks
Could be
1 a bad lifter
2 your timing is off(You have to give the engine the timing"it" wants
Id like to know more like
What did u time the cam at
What is the T.I.T.(turbine inlet temp) at wide open throttle
What is boost at wide open
What plugs you r running?
Its hard to guess at timing on a turbo engine,really should use knock sensors on a dyno
You actually need to run more advance and retard the timing when you get your boost
Only way I know to do this would be an "E" curve dizzy
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Old 07-14-2012, 11:52 AM
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Cam is installed straight up I couldn't tell u the inlet air temp about 5 psi at wide open and I'm running and w curve dist with 15 initial and 30 total
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Old 07-28-2012, 03:02 PM
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spinn how does adjusting your hydraulic lifters to different heights change your low mid range and upper power levels?
If it was this easy why even bother moving the cam around.
As far as I know different pre loads will effect the way you engine reacts to valve float
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Old 07-29-2012, 01:00 AM
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Advancing the cam is not changing the reaction and timing of the events. They stay the specified duration , you are only adjusting the IVO moment.

If you set the perload at .002 clearance, or .008 preload that is a difference of around 10 degrees crank rotation. You are shortening the cams effective duration. That increases low end. The opposite is true tighting the preload in that it is slightly depressing the plunger will lengthen the duration. The crank will not have to turn to as far to initiate the bump. These inital events of valve at open and close are crucial and make a big difference.

You asked why, how am I supposed to say what other people do? Not an appropriate question. I can list reference notes and books / pages to confirm my statement. Pm me if you need that reference, and guidance to the knowledge.
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