help with my carb-- Holley 4175 - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Blue_71 · 11-10-2002, 09:00 PM

ok--is this thing supposed to have a power valve or a power valve block off? ive got an open hole.. also, where can i get a gasket to go between the baseplate and throttle body? and last, what size jets do i need? it has 58 on the side of the ones in it

mikep · 11-10-2002, 09:12 PM

It is supposed to have a power valve. What happened to yours? Might want to start with a 9 or so. Hard to give you a real number without knowing what your cruise vacuum is. Also on the jets. 58 sounds about right for getting it started and then checking your plugs. Then you can make an informed decision about your jetting. Was this thing torn apart in a basket when you got it?

Blue_71 · 11-10-2002, 09:22 PM

it had supposedly been rebuilt (according to the ebay description) so i put the gaskets in thinking it was all it needed, then when it shot gas out the top i was like ok what am i missing.. took it apart with a friend who has rebuitl them before and he told me that was missing, i thought the open hole was supposed to be there (first holley i ever tore down) now i need another set of gaskets

mikep · 11-10-2002, 09:38 PM

Ive pretty much learned not to buy anything on ebay thats been "rebuilt" . I bought a 650 cfm double pumper like that . It had been "rebuilt by a reputable shop and chrome plated" Turns out the guy just sandblasted it with coarse ground glass and had never taken it apart. Throttle shaft bores were toast and it lokked like it had been run over by a truck. It was full of ground glass particles. Every jet was plugged. The thing wasnt even good for parts. I did get a partial refund out of the guy..

67shortie · 11-11-2002, 12:54 AM

Where is the hole? If it is in the metering block in the center lower area, YES you need a power valve. The average factory installed valve was rated at 6.5 inches of vacuum. This is what I would start with. Also, no insults intended, a 58 jet is awfully lean for any jet installed by Holley.
Start with 6.5 power valves and 68-72 jetting on both primary and secondaries. This will give you a baseline to start with.

mikep · 11-11-2002, 01:39 AM

AAAHHHH ..Dont do that ! Apples and oranges...

58 is fine for a 4175. Remember thats a spread bore quadrajet replacement carb with teenie weenie primaries and its gets a really strong booster signal so 58 might sound like a small number when you are used to dealing with 4150's and 4160's but to the smaller venturi on the 4175 primary side it works fine.

For a stock cam with a 4175 you probably want to start around 8 or 9 on the power valve as you may never see 6.5 inches unless you are just totally flooring it. Only way to tell what you really need is to run a vacuum line inside the cab and read your vacuum at cruise speed and then size your valve accordingly.With 4175's I generally run 2-3 numbers under what my cruise vacuum reading is. 4175's need a bit more enrichment to make up for the big hole the secondaries give you when they open up. On the 4175 the transition circuit ( power valve ) is probably more important than with the square bore carbs. That is unless you have a double pumper 4175 in which case 6.5 would be a good valve. I believe the secondary jetting on the 4175 is 88 or so. Those are big venturi!

mikep · 11-11-2002, 01:58 AM

By the way I have an extra 750 edelbrock I'll trade you for that 4175 if your throttle shaft bores are in good shape. I like those things.

67shortie · 11-11-2002, 12:53 PM

Mike, I suggested a start not what is suppose to be in there from the factory. As you can clearly see, my experience has been mainly with the 4150/4160 carb style, see what I get by shooting my mouth off?

Typing that post, I did not have my handy dandy Holley book in front of me, sorry for the bad advise

Mike is right, the 4175 has a small main jet, like a 56-58 depending on the PART # not the model # so 58 is fine for that 650. From what I have been reading this morning, that model # carb is listed with a plate in the rear instead of a jet depending on part # again. If it has a metering block, use what jet he suggests and run it.

Also according to the Holley book and website, www.holley.com you can get the rebuild kit, which has your body to base gasket in it under part # 37-741 or 37-742 depending again on part #.

the power valve is listed as an 85=8.5 inches of vacuum reading.

thanks for clearing this up Mike

Blue_71 · 11-11-2002, 08:38 PM

you said for a stock cam, but what if i have this cam--

Chevrolet: 262-400, 234 intake/244 exhaust duration at .050" .488 intake/.510 exhaust lift, 114 lobe speration

in case anyone wants to suggest me a different cam, here the motor specs:

350 2 bolt main, bored .30
flat top pistons
487 71/2 LT1 350 heads, 1.94/1.6 valves
Weiand 8004 Aluminum intake
Holley 4175 carb
1 5/8" headers
HEI

mikep · 11-11-2002, 08:59 PM

Minor points really but those heads are not LT-1 heads. 487's are decent castings but theyre not what came on LT-1's. LT-1's had 462's with 64 cc chambers and 2.02 intakes and 1.6 inch exhausts. They also came with screw in studs and straight guideplates. The ports were a little bit larger than 487's as well. The 350 LT-1 being sort of the high water mark of muscle car small block development. There werent many of them so don't feel bad . Not that any of that makes any difference but its nice to know what you have. 487's were the standard LoPo cylinder head with 76 cc chambers and small valves up to 74 I believe. That means that with that edelbrock RPM ( or clone thereof ) cam you are using you will not work well with your combination as you are too low on you compression with those flat top pistons. You can get away with a cam that big in a heavy truck if you have enough compression to back it up but in your case your'e too heavy and your compression is too low. You'd have a dog in the waiting. For your compression ( 8.5:1 or so ) and intake with those heads I'd say any more than 240 or so on the duration would be too much . Most people say less duration is better for trucks but I think thats a bunch of hooey although a summit 1102 or edelbrock performer will put you in the 340 HP region with 380+ ft lbs of torque but you'd have no idle lope. Yes, that is important! The cam I like for overall stock motors such as yours with a dual plane intake and a set of headers is the competition cams copy of the old L-79 cam. Its got a 229/236 duration spread with .468/.462 on the lift which puts your peak torque right at 3500 rpm. Perfect for a heavy street truck. I ran it through the desktop dyno and came up with 326 HP at 5000 rpm with a fairly flat curve from 4500-6000 . Torque would be in the 364 ft lbs area at 4000 but its flat as a board from 3000-5000.
With the RPM cam you loose about 20 HP but worse than that your torque takes a nosedive to about 300 ft lbs. Bigger isnt always better in cam selection unless you have the compression and porting to back it up.

Blue_71 · 11-11-2002, 09:20 PM

hmm mortec is wrong then

thats where i got my head info from.. i had it ran with desktop dyno (bigjiml? i think was his name) and it came to like 250HP and 372 torque with a stock cam (or was it and RV cam? i dont remember now) what's the best torque cam you can recomend for me? this thing has to be able to pull 25K lbs

mikep · 11-11-2002, 09:27 PM

If you are looking for max torque I'd go with the summit 1102 cam. 204/214 duration with .420 and .442 on the lift. Everybody makes a version of this same cam because it's a good cam for trucks and heavy vehicles. I run a slightly higher compression ratio but I'm around 400 ft lbs of torque with half decent mileage to boot. Plus I can light'em up at 40 mph no problemo with the same cam. That cam and a set of lifters will destroy $73 from summit racing. I run one one my truck but edelbrock calls it a performer. Same cam!

11-10-2002, 09:12 PM	#2
mikep Used to have a truck Join Date: May 2002 Location: port orchard WA Posts: 1,552	It is supposed to have a power valve. What happened to yours? Might want to start with a 9 or so. Hard to give you a real number without knowing what your cruise vacuum is. Also on the jets. 58 sounds about right for getting it started and then checking your plugs. Then you can make an informed decision about your jetting. Was this thing torn apart in a basket when you got it? __________________ No truck :-(

11-10-2002, 09:38 PM	#4
mikep Used to have a truck Join Date: May 2002 Location: port orchard WA Posts: 1,552	Ive pretty much learned not to buy anything on ebay thats been "rebuilt" . I bought a 650 cfm double pumper like that . It had been "rebuilt by a reputable shop and chrome plated" Turns out the guy just sandblasted it with coarse ground glass and had never taken it apart. Throttle shaft bores were toast and it lokked like it had been run over by a truck. It was full of ground glass particles. Every jet was plugged. The thing wasnt even good for parts. I did get a partial refund out of the guy.. __________________ No truck :-(

11-11-2002, 12:54 AM	#5
67shortie Green club Join Date: May 2002 Location: Central CA Posts: 1,059	Where is the hole? If it is in the metering block in the center lower area, YES you need a power valve. The average factory installed valve was rated at 6.5 inches of vacuum. This is what I would start with. Also, no insults intended, a 58 jet is awfully lean for any jet installed by Holley. Start with 6.5 power valves and 68-72 jetting on both primary and secondaries. This will give you a baseline to start with. __________________ 71 short/fleet ECE 4/6 drop, LQ4/700r4/3.42 gears 70 SS396 Chevelle 427/200-4R/3.73posi 61 Lincoln Continental, black on black Son you are going to drive me to drinkin if you don't stop drivin that hot rod lincoln

11-11-2002, 01:39 AM	#6
mikep Used to have a truck Join Date: May 2002 Location: port orchard WA Posts: 1,552	AAAHHHH ..Dont do that ! Apples and oranges... 58 is fine for a 4175. Remember thats a spread bore quadrajet replacement carb with teenie weenie primaries and its gets a really strong booster signal so 58 might sound like a small number when you are used to dealing with 4150's and 4160's but to the smaller venturi on the 4175 primary side it works fine. For a stock cam with a 4175 you probably want to start around 8 or 9 on the power valve as you may never see 6.5 inches unless you are just totally flooring it. Only way to tell what you really need is to run a vacuum line inside the cab and read your vacuum at cruise speed and then size your valve accordingly.With 4175's I generally run 2-3 numbers under what my cruise vacuum reading is. 4175's need a bit more enrichment to make up for the big hole the secondaries give you when they open up. On the 4175 the transition circuit ( power valve ) is probably more important than with the square bore carbs. That is unless you have a double pumper 4175 in which case 6.5 would be a good valve. I believe the secondary jetting on the 4175 is 88 or so. Those are big venturi! __________________ No truck :-( Last edited by mikep; 11-11-2002 at 01:50 AM.

11-11-2002, 01:58 AM	#7
mikep Used to have a truck Join Date: May 2002 Location: port orchard WA Posts: 1,552	By the way I have an extra 750 edelbrock I'll trade you for that 4175 if your throttle shaft bores are in good shape. I like those things. __________________ No truck :-(

11-11-2002, 12:53 PM	#8
67shortie Green club Join Date: May 2002 Location: Central CA Posts: 1,059	Mike, I suggested a start not what is suppose to be in there from the factory. As you can clearly see, my experience has been mainly with the 4150/4160 carb style, see what I get by shooting my mouth off? Typing that post, I did not have my handy dandy Holley book in front of me, sorry for the bad advise Mike is right, the 4175 has a small main jet, like a 56-58 depending on the PART # not the model # so 58 is fine for that 650. From what I have been reading this morning, that model # carb is listed with a plate in the rear instead of a jet depending on part # again. If it has a metering block, use what jet he suggests and run it. Also according to the Holley book and website, www.holley.com you can get the rebuild kit, which has your body to base gasket in it under part # 37-741 or 37-742 depending again on part #. the power valve is listed as an 85=8.5 inches of vacuum reading. thanks for clearing this up Mike __________________ 71 short/fleet ECE 4/6 drop, LQ4/700r4/3.42 gears 70 SS396 Chevelle 427/200-4R/3.73posi 61 Lincoln Continental, black on black Son you are going to drive me to drinkin if you don't stop drivin that hot rod lincoln

11-11-2002, 08:38 PM	#9
Blue_71 Bloo Join Date: Feb 2001 Location: Barren County Kentucky Posts: 6,283	you said for a stock cam, but what if i have this cam-- Chevrolet: 262-400, 234 intake/244 exhaust duration at .050" .488 intake/.510 exhaust lift, 114 lobe speration in case anyone wants to suggest me a different cam, here the motor specs: 350 2 bolt main, bored .30 flat top pistons 487 71/2 LT1 350 heads, 1.94/1.6 valves Weiand 8004 Aluminum intake Holley 4175 carb 1 5/8" headers HEI

11-11-2002, 08:59 PM	#10
mikep Used to have a truck Join Date: May 2002 Location: port orchard WA Posts: 1,552	Minor points really but those heads are not LT-1 heads. 487's are decent castings but theyre not what came on LT-1's. LT-1's had 462's with 64 cc chambers and 2.02 intakes and 1.6 inch exhausts. They also came with screw in studs and straight guideplates. The ports were a little bit larger than 487's as well. The 350 LT-1 being sort of the high water mark of muscle car small block development. There werent many of them so don't feel bad . Not that any of that makes any difference but its nice to know what you have. 487's were the standard LoPo cylinder head with 76 cc chambers and small valves up to 74 I believe. That means that with that edelbrock RPM ( or clone thereof ) cam you are using you will not work well with your combination as you are too low on you compression with those flat top pistons. You can get away with a cam that big in a heavy truck if you have enough compression to back it up but in your case your'e too heavy and your compression is too low. You'd have a dog in the waiting. For your compression ( 8.5:1 or so ) and intake with those heads I'd say any more than 240 or so on the duration would be too much . Most people say less duration is better for trucks but I think thats a bunch of hooey although a summit 1102 or edelbrock performer will put you in the 340 HP region with 380+ ft lbs of torque but you'd have no idle lope. Yes, that is important! The cam I like for overall stock motors such as yours with a dual plane intake and a set of headers is the competition cams copy of the old L-79 cam. Its got a 229/236 duration spread with .468/.462 on the lift which puts your peak torque right at 3500 rpm. Perfect for a heavy street truck. I ran it through the desktop dyno and came up with 326 HP at 5000 rpm with a fairly flat curve from 4500-6000 . Torque would be in the 364 ft lbs area at 4000 but its flat as a board from 3000-5000. With the RPM cam you loose about 20 HP but worse than that your torque takes a nosedive to about 300 ft lbs. Bigger isnt always better in cam selection unless you have the compression and porting to back it up. __________________ No truck :-( Last edited by mikep; 11-11-2002 at 09:48 PM.

11-11-2002, 09:27 PM	#12
mikep Used to have a truck Join Date: May 2002 Location: port orchard WA Posts: 1,552	If you are looking for max torque I'd go with the summit 1102 cam. 204/214 duration with .420 and .442 on the lift. Everybody makes a version of this same cam because it's a good cam for trucks and heavy vehicles. I run a slightly higher compression ratio but I'm around 400 ft lbs of torque with half decent mileage to boot. Plus I can light'em up at 40 mph no problemo with the same cam. That cam and a set of lifters will destroy $73 from summit racing. I run one one my truck but edelbrock calls it a performer. Same cam! __________________ No truck :-( Last edited by mikep; 11-11-2002 at 09:30 PM.



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