boost levels
I'm looking at buying a guys FD out of Miami. it has about 5K on rebuilt engine, compression is fine, I want to know what boost levels are acceptable. I know to look for 10/11 at around 4500, then a drop, and back up in second. what about at idle? and what if the boost ih higher or lower? like running 14 with no dropoff?
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Re: boost levels
Originally posted by man_of_steel I know to look for 10/11 at around 4500, then a drop, and back up in second. what about at idle? |
Re: boost levels
Originally posted by man_of_steel I know to look for 10/11 at around 4500, then a drop, and back up in second. what about at idle? uh are you asking what the boost should be at,,,,,, at idle?? |
EXACTLY. This is why I'm confused. I was told something about negative something, and the fact that a boost at idle was even mentioned threw me off guard, and I was thinking that damn, maybe I have no idea whats going on. I just wanted to double check.
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there's no boost at idle. boost is manifold pressure higher than atmospheric.
now... you should be concerned with manifold *vacuum* at idle (which is NOT boost) which is usually read on the same gauge. i think the factory spec is the engine needs rebuilt if idle vacuum is lower than 15 inches. of course if the car has a vacuum leak or a ported engine that's going to mess up the readings. also keep in mind that FDs don't have boost gauges, so you're goingto have to install one to check it. |
15 inches? whats that on a real boost gauge? what kind of boost gauge are you using metric/standard-rest of the world/american?
I have heard the norm is about 12(dont know what the measure is--inches or what) but a reall strong engine does about 18...again, vaccum is what you should read at idle. If you are boosting 14psi sustained w/o fuel enrishment you may be leaning out the engine which you dont want! be ready to have some extra cash for a rebuild just in case the guy you are buying the car from already damaged/didnt break it in correctly--or just flat out you may very well do that on your own. its a cool car though! if you got the cash get it!!!!!!!!!! |
US BOOST/VACUUM Guages (Like AUTOMETER) are calibrated in INCHES of Mercury for Vacuum and PSI for Boost.
A STOCK FD 5 spd should pull 15"-16" Vacuum (Automatic Trans cars will run 12-14") at Idle in neutral. On WOT (Check In 2nd or 3rd) the boost should peak at 10-11psi on the primary, from 3000-4500 rpm, dip to 8 psi during transition (for about 1/2 sec) to both turbos then hold 10-11psi from 4500-7000 rpm and drop slightly (but not less than 9 psi at redline this is called the 10/8/10 (stock) boost pattern 2-3 airflow mods can up this pattern to 12/10/12 and that absolutly is the Highest BOOST you should run on a stock ecu. |
so if this FD I'm looking at actually does push 14 psi, do I need to upgrade the ecu, get/improve the wastegate, or what?
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