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"the engine tuning bible"


Old 10-09-2016, 09:50 AM
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Originally Posted by ironzgti35 View Post
Are there any tell tale signs of having too much or too little head clearance?

A engine with the head too tight will will usually display a strong tendency to hang its idle and no amount of tuning , linkage setup or idle gap adjustment can correct it..Unless you completely flood the needles the engine wants to keep revving when you let off the throttle ....They just become hard to tune when the head is too tight, they will not tolerate being leaned down any and will quickly start acting cranky if you try thinning the mixture...Also too much compression will increase fuel usage....

For optimal performance we want to run the squish as tight as possible however many things can affect this so IMO a little trial and error is necessary to find the sweet spot.. OS tend to go towards the over aggressive side while Nova leans towards the conservative side..there will be conditions where a OS will run better with a extra shim added and with Nova they usually run better with shims removed.

When you have too many shims the engines don't idle as strong, especially when hot, they will have a narrow tuning window on the LSN, they will lack top end power..

Once you find the sweet spot the engines will make the best power, idle stronger , have a broader tuning window, tolerate a richer mixture and not flame out as easy , will run strong even with no mechanical pinch ( OS trademark ) , stronger hot idle etc etc ....

IMO head shims play a pretty big role in how these engines behave and is something that is definitely worth playing with..IMO OS has head shims figured out and realized that the tighter clearance has more benefits then drawbacks...the engine runs crisper with more power has a broader tuning window and a much stronger hot idle at a slight sacrifice to runtime..

As these engines age they can sometimes tolerate less head shims...a freshly broken in engine may run best with a little extra shim but once its piston start to wear the engine may start running better with that extra shim removed... The best approach is to test how few head shims the engine will tolerate, as soon as you start noticing a hanging idle you know you went too far...back it up one step....Basically we want to run the least amount of shims the engine will allow...
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Old 03-17-2017, 02:57 PM
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This is valuable information, thanks again for sharing
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Old 03-27-2017, 01:02 AM
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Hi Guys

Engine O.S Speed Spec 3. runs perfect. But when it ideals for 30 sec. Then you give it full throttle - The engine dies.. What the solution ? Thanks
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Old 05-17-2017, 02:32 PM
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Originally Posted by MassiveMods View Post
It will take about 15 minutes of hard running to saturate a chassis at which case you start to get problems if the engine is not tuned correctly. You will find people who experience the " lower idle " have tuned their HSN first instead of last.

If you were to tune your Idle gap first , then your LSN then your HSN you will avoid this ( if its done properly )

How do you do when you tune idle, LAN and last HSN?
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Old 05-17-2017, 10:00 PM
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It takes a little while to explain, but if you're starting an engine for the first time, be prepared to pinch and release the fuel line if you hear the engine idle down as though it's going to stall. It's a helpful tip to quickly reduce the amount of fuel going into the engine to keep an engine with an excessive rich low speed needle setting, from stalling so you don't have to keep restarting the engine.

You're going to want to observe two things as you're pinching the fuel line. How long it takes before the engine starts starving for fuel, and how much the idle speed increases before running out of fuel and losing RPM. You're going to want to release the fuel line before it stalls, but be ready to pinch it again and again until you can get the idle speed and mixture set properly.

If you pinch and hold the fuel line and the engine revs up and then starts to lose RPM over a period of 10-15 seconds or more (let go of the fuel line at this point), then your LSN is set too rich. So, the length of time it takes for the engine to rev up and then start to lose RPM from the loss of fuel, is an indicator of the mixture setting. Long time = too rich, very short amount of time = too lean. You're going to want the engine to start showing sings of being starved of fuel about 3-5 seconds after you pinched the fuel line. This should get you in the ballpark on the LSN setting that the engine will idle (more on that in a minute) so you can run it and fine tune it.

The amount of increase in the engine RPM is an indicator of an idle adjustment. If there's a very significant increase in RPM, it typically indicates the idle speed is too high. If there is little or no increase in RPM, the idle speed might be a touch too low.

Once you have the idle speed and idle mixture settings close enough to keep the engine running reliably, you can start running it to further refine your settings and to break-in the engine. Don't go full guns right off the bench. Work your way up to full speed after a few tanks.
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Old 05-31-2017, 07:01 PM
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When I change the position of my car the engijne speed changes. Example- holding car wheels off the ground and then tip the front end down the engine elms change same when goes nose high... does this mean anything or is this normal
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Old 05-31-2017, 07:17 PM
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Originally Posted by rjkotzur View Post
When I change the position of my car the engijne speed changes. Example- holding car wheels off the ground and then tip the front end down the engine elms change same when goes nose high... does this mean anything or is this normal
normal. if you cant carry your car level or when picking it up to stop the engine etc, lift the front end not the back, lifting the front makes the mixture richer, if you lift the back it will be leaner and revs will rise
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Old 11-14-2017, 10:45 AM
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just trying to make sure I understand what is going on and I am on the right track with where I need to go tuning wise

so after getting the engine up to temp and pulling off the track and setting car on the box the idle is high and the wheels will spin for about 10 seconds or so, then the idle will drop down to what I feel is a good idle speed and wheel spin stops. Rev engine to clean it out and the process repeats.

Based on what I understand my LSN is too rich and it is loading up which is why the idle speed drops and overall my idle speed is too high which is why there is wheel spin initially?. From what I understand I want it to be at the lower idle speed immediately after letting off the trigger?

thanks for the help
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