Two questions-carb and compression

PolishSasquatch · May 12th, 2009, 02:04 PM

1) why is my carbs bufferfly vavle sitting like this? Car is off, nobody is touchging the throttle...

2) what is the standard compression on a 9.0:1 302? in psi or kPa

1slo5.0 · May 12th, 2009, 03:05 PM

Originally Posted by PolishSasquatch

1) why is my carbs bufferfly vavle sitting like this? Car is off, nobody is touchging the throttle...

2) what is the standard compression on a 9.0:1 302? in psi or kPa

1- That is the choke. Touching the throttle has nothing to do with it.

2- Compression ratio and cranking compression are two different things.

PolishSasquatch · May 12th, 2009, 03:10 PM

Originally Posted by Darrell

1- That is the choke. Touching the throttle has nothing to do with it.

2- Compression ratio and cranking compression are two different things.

im referring to cranking compression then. as you mentioned before I think my car has blowby, so I want to double check the cranking compression against some standard baseline figures to see where im at

also, i was running the stock headers and Y pipe, cut off riht before the second cats (im still building the car) and when i took it above 4000 rpm id get crzy backfiring and it felt like it lost power. Am getting a lean out backfire? If so how do i fix it? (i had some fuel leaks before, but i replaced the lines, and havent had a chance to run the car yet) could it be carburator jetting?

1slo5.0 · May 12th, 2009, 03:15 PM

Originally Posted by PolishSasquatch

im referring to cranking compression then. as you mentioned before I think my car has blowby, so I want to double check the cranking compression against some standard baseline figures to see where im at

also, i was running the stock headers and Y pipe, cut off riht before the second cats (im still building the car) and when i took it above 4000 rpm id get crzy backfiring and it felt like it lost power. Am getting a lean out backfire? If so how do i fix it? (i had some fuel leaks before, but i replaced the lines, and havent had a chance to run the car yet) could it be carburator jetting?

What year is the engine? Is it a high output or not? Backfiring can be caused by many things.

PolishSasquatch · May 12th, 2009, 03:20 PM

Originally Posted by Darrell

What year is the engine? Is it a high output or not? Backfiring can be caused by many things.

its an 85 HO

1slo5.0 · May 12th, 2009, 03:40 PM

Originally Posted by PolishSasquatch

its an 85 HO

120psi roughly and each cylinder should be within 10% of the highest cylinder.

PolishSasquatch · May 13th, 2009, 12:17 AM

btw my fuel pressure gauge byt eh car is reading 4spi at idle...isnt this a bit high?

1slo5.0 · May 13th, 2009, 08:55 AM

Originally Posted by PolishSasquatch

btw my fuel pressure gauge byt eh car is reading 4spi at idle...isnt this a bit high?

Mechanical or electric fuel pump?

PolishSasquatch · May 13th, 2009, 10:22 AM

its a mech pump

superbean · May 13th, 2009, 10:43 AM

carbs like 6-7 pounds of fuel pressure.

1slo5.0 · May 13th, 2009, 11:30 AM

Originally Posted by PolishSasquatch

its a mech pump

Does the pressure increase with rpm? 4psi is definitely not too much fuel pressure, it is more along the lines of too little fuel pressure. You should see 7psi.

PolishSasquatch · May 13th, 2009, 01:52 PM

ill have to get ym dad to look at the gauge as i rev it. how do i go about bumping the fuel pressure on this?

superbean · May 13th, 2009, 02:01 PM

you need a higher volume pump and a regulator set to 7 psi.

PolishSasquatch · May 13th, 2009, 02:11 PM

do i absolutely need a higher volume pump? Cant i jsut get a regulator? im sure tons of guys can support modest horsepower on a stock v8 pump..

1slo5.0 · May 13th, 2009, 02:16 PM

Originally Posted by PolishSasquatch

do i absolutely need a higher volume pump? Cant i jsut get a regulator? im sure tons of guys can support modest horsepower on a stock v8 pump..

You might need a new stock pump. Does the pressure goe up with rpm?

PolishSasquatch · May 13th, 2009, 09:06 PM

yeah the pressure goes up, was at 5 spi at 2000 rpm

also, when i fire it up, even if i keep it at 2000 rpm, when the eienge is cold it sounds liek tis running on 6 or 7 cyl only, but sosudns fine ocne warm...

just looked at the backup fuel pump spec sheet and it says it supplies up to 6.5psi only...

PolishSasquatch · May 15th, 2009, 12:53 PM

well i fired it up today, and noticed the fuel pressure was at 5.5 at idle...?

May 12th, 2009, 02:04 PM	#1
PolishSasquatch Regular Join Date: Mar 2009 Posts: 97 iTrader: 0 reviews	Two questions-carb and compression 1) why is my carbs bufferfly vavle sitting like this? Car is off, nobody is touchging the throttle... 2) what is the standard compression on a 9.0:1 302? in psi or kPa

May 13th, 2009, 10:43 AM	#10
superbean Hardcore Enthusiast 1998 Cobra 13.24@105.66 Join Date: Aug 2008 Location: North Carolina Posts: 1,778 iTrader: 0 reviews	carbs like 6-7 pounds of fuel pressure. __________________ weeee foooord!

May 13th, 2009, 02:01 PM	#13
superbean Hardcore Enthusiast 1998 Cobra 13.24@105.66 Join Date: Aug 2008 Location: North Carolina Posts: 1,778 iTrader: 0 reviews	you need a higher volume pump and a regulator set to 7 psi. __________________ weeee foooord!

May 13th, 2009, 09:06 PM	#16
PolishSasquatch Regular Join Date: Mar 2009 Posts: 97 iTrader: 0 reviews	yeah the pressure goes up, was at 5 spi at 2000 rpm also, when i fire it up, even if i keep it at 2000 rpm, when the eienge is cold it sounds liek tis running on 6 or 7 cyl only, but sosudns fine ocne warm... just looked at the backup fuel pump spec sheet and it says it supplies up to 6.5psi only... Last edited by PolishSasquatch; May 13th, 2009 at 10:24 PM.

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May 13th, 2009, 12:17 AM	#7
PolishSasquatch Regular Join Date: Mar 2009 Posts: 97 iTrader: 0 reviews	btw my fuel pressure gauge byt eh car is reading 4spi at idle...isnt this a bit high?

May 13th, 2009, 10:22 AM	#9
PolishSasquatch Regular Join Date: Mar 2009 Posts: 97 iTrader: 0 reviews	its a mech pump

May 13th, 2009, 01:52 PM	#12
PolishSasquatch Regular Join Date: Mar 2009 Posts: 97 iTrader: 0 reviews	ill have to get ym dad to look at the gauge as i rev it. how do i go about bumping the fuel pressure on this?

May 13th, 2009, 02:11 PM	#14
PolishSasquatch Regular Join Date: Mar 2009 Posts: 97 iTrader: 0 reviews	do i absolutely need a higher volume pump? Cant i jsut get a regulator? im sure tons of guys can support modest horsepower on a stock v8 pump..

May 15th, 2009, 12:53 PM	#17
PolishSasquatch Regular Join Date: Mar 2009 Posts: 97 iTrader: 0 reviews	well i fired it up today, and noticed the fuel pressure was at 5.5 at idle...?

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