North American Turbocoupe Organization



How does boost work?
birdstang Offline
Junior Member
#1
I know alot about Fords. I do not understand boost.I need too know, where is it measured at with a gauge,how do you control it,how do you increase it, and how do you cut it off. I rebuilt a 2.3 turbo, and read everything about turbos,but I still do not understand it. Please help.
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Walsted Offline
Posting Freak
#2
Boost is the amount of pressure above atmospheric pressure. Since it is a pressure, it can be measured using the same units, including bars (or the more common millibars,) pascals (or the more common hectopascals,) inches of mercury, or pounds per square inch (psi). Standard atmospheric pressure is about 1013.2 millibars, 1013.2 hectopascals, 29.92 inches of mercury, or 14.7 psi. So, if you have 15 psi of boost, the pressure (where measured) is about twice as great as standard atmospheric pressure.

The turbo (powered by the engines exhaust gasses,) compresses the air, and thus forces more air into the cylinder on each stroke, and the EFI system makes sure that there is the right amount of fuel. This amount of air and fuel is now greater (and hotter) than would be present in a normally aspirated engine, and thus more power is generated. Since the turbo is powered by the exhaust, the amount of boost available is a function of the amount of exhaust, which is a function of engine load and rpm. The wastegate is used to control the boost by bleeding off exhaust gases.

This probably doesn't explain it as well as others can, and also probably doesn't answer all of your questions.

I hope this helps, though.

------------------
Mike Walsted - NATO member
1986 5-speed TurboCoupe and 1985 5-speed XR7
Mike Walsted - Sold my 1986 5-speed TurboCoupe
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SteveX82 Offline
Posting Freak
#3
A+++, Walsted
Estoril blue 1987 TC 5spd, 148k mi, a237, Bailey BOV, spec stg3 clutch, spearco FMIC, 50 trim t3/t4, 3" exhaust, Bamafuel, LM1, 55pph
Best 1/4 mile: 12.31 @ 110mph on 25psi
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Pete D Offline
Administrator
#4
Way to go Mike.
Pete Dunham


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KMcGrathNJ Offline
Senior Member
#5
Thanks Mike, I just got back from an evening spent in trigonometry playing with vectors, polar equations and imaginary numbers, and I come home to relax a little, see whats going on in the TC world and get slapped upside the head with hectopascals.

Great explination though!!
Kevin


88 TC T5;White/Red; All options exept Leather; Front Mounted K&N cone filter; 140 Speedo; Superchip; Gillis Boost Valve; Custom vac/boost-volt-temp gauge cluster in console Ground Effects; Spoiler; Blaupunkt H/U; Boston Accoustic 3 1/2" in dash; Polk 6" in doors; Infinity 5 1/4 component in rear deck;
Rockford 10" sub; (2) Alpine amps


Near Future -Paint
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oldraven Offline
Senior Member
#6
Only recently did I realize that the compressor is the part of the turbo that is actually creating power. I was under the impression that a turbo SUCKED exhaust and so created higher flow of air. Well, I'm better versed now. My mechanic cousin explained that the power comes from the compressed air going into the chamber. Since I read that our engines use a 8.3:1 compression ratio, I assumed that it stayed that way. *shakes head with disbelief* So it's 8.3:1 before boost, and with boost added this compression ratio gets higher. So a turbo really is forced air then, isn't it.

Learnin is fun.

(heh. just realized why a ported exhaust manifold would increase spool time.)

------------------
I'd like to think my life has a soundtrack, and it sounds just like the white album.

1987 Turbo Coupe, 5-spd. Burgundy, k&n drop in, 3" d.p., 2.5" duals. Going into hibernation.
I'd like to think my life has a soundtrack, and it sounds just like the white album.

1987 Turbo Coupe, 5-spd. Candy Apple Red w/ Charcoal Smoke Accents, k&n drop in, 2.5" duals. Stirring from her winter slumber.

http://www.cardomain.com/id/oldraven

http://www.cardomain.com/id/doasa
http://www.cardomain.com/id/jeepishltd

CAW!!
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Pete D Offline
Administrator
#7
Yes it's forced air. Compression ratio does not change because of turbocharging, it is a fixed mechanical measure. It's tha ratio of the volume within the cylinder when the piston is at bottom dead center as compared to the volumn when the piston is at TDC. The thickness of the head gasket and the volume of the combustion chamber in the head are part of the volume measurements. Unless your rods are flexing or the head is lifting off the block, compression ratio does not change. I think it is closer to 8:1 stock in our engines. Compression pressures can change due to forced induction.

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NATO Member. it's not a vice, it's an obsession
"The nice thing about each new day is nobody ever used it before" Barnaby Jones
88 TC X 2, 86 SVO, mods list at
http://www.turbotbird.com/showroom/pd_88tc.htm
Pete Dunham


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natmac3 Offline
Administrator
#8
While the forced induction of a turbocharger does not effect static compression, it does, in effect, change the compression ratio under boost. Each psi boost is effectively equivalent to increasing compression ratio by 1 point.

i.e.
8.0:1 plus 10psi is effectively 18.0:1

I do believe I remembered that correctly...
1987tc
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oldraven Offline
Senior Member
#9
That's what I assumed. Displacement doesn't change, but compression would. Is there a different measurement between piston travel compression and combined stroke+boost compression?
I'd like to think my life has a soundtrack, and it sounds just like the white album.

1987 Turbo Coupe, 5-spd. Candy Apple Red w/ Charcoal Smoke Accents, k&n drop in, 2.5" duals. Stirring from her winter slumber.

http://www.cardomain.com/id/oldraven

http://www.cardomain.com/id/doasa
http://www.cardomain.com/id/jeepishltd

CAW!!
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