Allright boys, got a question for you all....
I bought a dyno'd engine that was sporting a Holley 750. It had its jets played with, timing adjusted etc etc, to get it at the absolute peak of its performance. So I donk it in my Torana. Goes great !
But I have this cool brand new Holley 750HP sitting in my garage off my old motor, AND I dont want to lose any of the fine tuning from my dyno proven engine. Question is....
If I remove all the jets from the Dyno Proven Holley 750, and install them in the same positions in the Holley 750HP (along with the power valve), could that possibly affect the horsepower in a negative way ???
I hope not, the Holley 750 looks way cooler nice and chrome. Thanks in Advance !!
HOLLEY 750 vs HOLLEY 750HP
Started by
_findusparker_
, Nov 29 2009 12:22 AM
21 replies to this topic
#2
_oldjohnno_
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Posted 30 November 2009 - 06:00 AM
Short answer: try it and see how it goes, if it's slower just swap back again.
Long answer, the main advantage of the HP carbs is their tunability; they are made so that air bleeds, emulsion tubes and so on are removable/tunable as well as the normal jets and powervalves. This may or may not be an advantage depending on how far from optimum the standard Holley calibration is. They are also cleaned up a bit aerodynamically. One thing to keep in mind is that they are rated differently to the normal 4 barrels; the HPs are rated at 28" of water (about 2"hg) instead of the usual 1.5"hg. This means a 750HP would flow somewhere around 700cfm at the normal test pressure.
A few years back every man and his dog started producing tricked up carbs based on the Holley, and usually rated them at 28". Holley made the HP to compete with these boutique carbs, and thats why they also use the higher test pressure (that, and for marketing reasons).
I once bought a tricked up 850DP with "special" calibrations; it took me some time to get it right and when I did I found that I'd basically returned it to factory specs. So I view some of these carbs with a little scepticism. Bottom line: if the flow is adequate, and you have the ability to tune them properly, the potential is there for better across-the-range performance with the HP style carbs. But if the original 4150 calibration was close then the gains will be very small.
They are shiny though.
Long answer, the main advantage of the HP carbs is their tunability; they are made so that air bleeds, emulsion tubes and so on are removable/tunable as well as the normal jets and powervalves. This may or may not be an advantage depending on how far from optimum the standard Holley calibration is. They are also cleaned up a bit aerodynamically. One thing to keep in mind is that they are rated differently to the normal 4 barrels; the HPs are rated at 28" of water (about 2"hg) instead of the usual 1.5"hg. This means a 750HP would flow somewhere around 700cfm at the normal test pressure.
A few years back every man and his dog started producing tricked up carbs based on the Holley, and usually rated them at 28". Holley made the HP to compete with these boutique carbs, and thats why they also use the higher test pressure (that, and for marketing reasons).
I once bought a tricked up 850DP with "special" calibrations; it took me some time to get it right and when I did I found that I'd basically returned it to factory specs. So I view some of these carbs with a little scepticism. Bottom line: if the flow is adequate, and you have the ability to tune them properly, the potential is there for better across-the-range performance with the HP style carbs. But if the original 4150 calibration was close then the gains will be very small.
They are shiny though.
#3
_findusparker_
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Posted 01 December 2009 - 08:57 PM
Short answer: try it and see how it goes, if it's slower just swap back again.
Long answer, the main advantage of the HP carbs is their tunability; they are made so that air bleeds, emulsion tubes and so on are removable/tunable as well as the normal jets and powervalves. This may or may not be an advantage depending on how far from optimum the standard Holley calibration is. They are also cleaned up a bit aerodynamically. One thing to keep in mind is that they are rated differently to the normal 4 barrels; the HPs are rated at 28" of water (about 2"hg) instead of the usual 1.5"hg. This means a 750HP would flow somewhere around 700cfm at the normal test pressure.
A few years back every man and his dog started producing tricked up carbs based on the Holley, and usually rated them at 28". Holley made the HP to compete with these boutique carbs, and thats why they also use the higher test pressure (that, and for marketing reasons).
I once bought a tricked up 850DP with "special" calibrations; it took me some time to get it right and when I did I found that I'd basically returned it to factory specs. So I view some of these carbs with a little scepticism. Bottom line: if the flow is adequate, and you have the ability to tune them properly, the potential is there for better across-the-range performance with the HP style carbs. But if the original 4150 calibration was close then the gains will be very small.
They are shiny though.
Thanks for the 'long answer', thats handy to know some of that makes sense and the rest im trying to make sense of lol. Obviously Im attempting to make the HP emulate the Non-HP so i dont have to go re-dyno-ing things. Kinda new territory for me so forgive the basic questions please..
The air bleeds and emulsion tubes seem to be the only x-factor in my purpose here. I just consulted my owners manual for the carb (LOL), alas neither is mentioned in it. Can u please shed some light on how I can check these to ensure they are identical to the Non-HP ?
The 2"hg vs the 1.5"hg.... what the ? What tuning need I do to allow for this difference ?
Thanks mate...
#4
_oldjohnno_
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Posted 03 December 2009 - 05:04 PM
The flow rating of a carb is dependant on the pressure that it's tested at, and if you're gonna compare two carbs then you'd want to compare the flows at the same pressure otherwise it's apples and oranges. At the usual test pressure of 1.5"hg the standard 750 flows 750cfm while the 750HP would flow just a bit less at about 710cfm. Not a huge difference, but something to be aware of. Incidentally, two barrel carbs are tested at twice the pressure of four barrels.
The main function of the air bleeds is to help maintain a uniform a/f ratio over a wide range of speeds - without them a carb will tend to run progressively richer as the engine speed increases. The standard factory supplied air bleed jet is nearly always so close to the optimum that it rarely needs to be fiddled with, but if it is too big or too small then it's hard to change cos its pressed into the carb body. Thats the reason for the replaceable bleeds - if you jet for the best top end and then find that the bottom end is a little rich or lean then it's easy with the HP carbs to change them. I think some of the carbs also have replaceable emulsion tubes which can also be used as a fine-tuning tool to help get the best a/f ratio over a very wide speed range.
Now this all sounds good, but unless you are using a carb for something it wasn't designed for you'll usually find that the factory jetting and calibration is very very close. I always like to start jetting with the out-of-the-box settings because it provides some clues as to how the engine is running - say for example the standard jets are 70s and you find that it's still lean with 80s or 82s you might want to stop and think for a minute before you stick 84s in.
Could the engine be over-carbed perhaps, or maybe the plenum volume is too big? Or if the engine wants unusually small jets this could also be an indicator of something being not quite right. This is not to say there is always something wrong if you stray too far from the original jetting; just that it can provide a valuable baseline and be a handy tool in determining where future gains might be made.
Short answer: I think the two carbs are different enough that I wouldn't worry about transferring the settings from one to the other. I'd just stick the HP on as it came out-of-the-box and then jet it normally if required. Unless you have some weirdo engine combination it should run quite well with minimal tuning.
The main function of the air bleeds is to help maintain a uniform a/f ratio over a wide range of speeds - without them a carb will tend to run progressively richer as the engine speed increases. The standard factory supplied air bleed jet is nearly always so close to the optimum that it rarely needs to be fiddled with, but if it is too big or too small then it's hard to change cos its pressed into the carb body. Thats the reason for the replaceable bleeds - if you jet for the best top end and then find that the bottom end is a little rich or lean then it's easy with the HP carbs to change them. I think some of the carbs also have replaceable emulsion tubes which can also be used as a fine-tuning tool to help get the best a/f ratio over a very wide speed range.
Now this all sounds good, but unless you are using a carb for something it wasn't designed for you'll usually find that the factory jetting and calibration is very very close. I always like to start jetting with the out-of-the-box settings because it provides some clues as to how the engine is running - say for example the standard jets are 70s and you find that it's still lean with 80s or 82s you might want to stop and think for a minute before you stick 84s in.
Could the engine be over-carbed perhaps, or maybe the plenum volume is too big? Or if the engine wants unusually small jets this could also be an indicator of something being not quite right. This is not to say there is always something wrong if you stray too far from the original jetting; just that it can provide a valuable baseline and be a handy tool in determining where future gains might be made.
Short answer: I think the two carbs are different enough that I wouldn't worry about transferring the settings from one to the other. I'd just stick the HP on as it came out-of-the-box and then jet it normally if required. Unless you have some weirdo engine combination it should run quite well with minimal tuning.
Edited by oldjohnno, 03 December 2009 - 05:06 PM.
#5
_Bomber Watson_
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Posted 03 December 2009 - 05:48 PM
On a side note, what kinda damb engine do you have to need a 750????
A 454 at 7000rpm and 80% volumetric efficiency (would need a pretty decent cam head and manifold setup to get that efficiency at those revs, were talking 9000rpm redlines here) only consumes 736cfm of air if my calculations are correct....
A 454 at 7000rpm and 80% volumetric efficiency (would need a pretty decent cam head and manifold setup to get that efficiency at those revs, were talking 9000rpm redlines here) only consumes 736cfm of air if my calculations are correct....
#6
_oldjohnno_
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Posted 03 December 2009 - 06:04 PM
On a side note, what kinda damb engine do you have to need a 750????
A 454 at 7000rpm and 80% volumetric efficiency (would need a pretty decent cam head and manifold setup to get that efficiency at those revs, were talking 9000rpm redlines here) only consumes 736cfm of air if my calculations are correct....
Not all that big as it turns out. The Holley four barrels are rated at 1.5"hg and this is the figure Holley use in their application formula as well. In the real world though, it seems best performance is had by sizing the carb to run at not much more than 0.5"hg. In my experience street 400s and 454s have run very well with 750 - 800cfm so that works out about right.
The weird thing is that Holley use the nominal cfm rating of the carb in their application formula and disregard the variations in test pressures completely. It's fortunate that these carbs have been used for about a million years now and it's been pretty much proved empirically what carbs work with what motors.
#7
TerrA LX
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Posted 03 December 2009 - 06:50 PM
On a side note, what kinda damb engine do you have to need a 750????
A 454 at 7000rpm and 80% volumetric efficiency (would need a pretty decent cam head and manifold setup to get that efficiency at those revs, were talking 9000rpm redlines here) only consumes 736cfm of air if my calculations are correct....
The thing you are missing here is that this is rather a mean average, seeing an engine's intake charge is a pulse over the number of cylinders (8 in this case) thru usually an open plenum then the carb might actually see 1472cfm, not a constant 736cfm. (this is not a calculated figure but just an example).
This is why usually drag cars work well over carbed and the same size motor in a short circuit cars run better times with a smaller one closer to te mark.
Edited by TerrA LX, 03 December 2009 - 06:52 PM.
#8
_oldjohnno_
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Posted 03 December 2009 - 07:30 PM
On a side note, what kinda damb engine do you have to need a 750????
A 454 at 7000rpm and 80% volumetric efficiency (would need a pretty decent cam head and manifold setup to get that efficiency at those revs, were talking 9000rpm redlines here) only consumes 736cfm of air if my calculations are correct....
The thing you are missing here is that this is rather a mean average, seeing an engine's intake charge is a pulse over the number of cylinders (8 in this case) thru usually an open plenum then the carb might actually see 1472cfm, not a constant 736cfm. (this is not a calculated figure but just an example).
This is why usually drag cars work well over carbed and the same size motor in a short circuit cars run better times with a smaller one closer to te mark.
Good point. An extreme example would be an engine with an individual runner and carb throat for each cylinder (like a V8 with four IDAs, or a 12 port six with six Mikunis). The optimum total carb flow ends up being about three times what you'd use with a conventional setup.
#9
_findusparker_
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Posted 03 December 2009 - 11:03 PM
The 750HP has had its jets swapped out a coupld of times and Ive lost track of whats standard in it now. Its a 0-82751, I cant manage to find what they are supposed to be...
So Old Johnno, what your saying is that because a 750HP is only rated at approx 710CFM while the 750DP is actuallr rated at 750cfm, would that suggest that the 750HP does in fact require larger jets to compensate for the smaller cfm ?
Ill take the car in for a chassis dyno next week with the new carb and old carb and try a few combos. My understanding of the power valve is that its not perhaps going to make a big difference dyno wise as its more of a fuel saving utility ?
Bomber its a 355 stroker, Vn heads, big cam etc, makes 488 proven hp at 6900 rpm on engine dyno with old carby.
So Old Johnno, what your saying is that because a 750HP is only rated at approx 710CFM while the 750DP is actuallr rated at 750cfm, would that suggest that the 750HP does in fact require larger jets to compensate for the smaller cfm ?
Ill take the car in for a chassis dyno next week with the new carb and old carb and try a few combos. My understanding of the power valve is that its not perhaps going to make a big difference dyno wise as its more of a fuel saving utility ?
Bomber its a 355 stroker, Vn heads, big cam etc, makes 488 proven hp at 6900 rpm on engine dyno with old carby.
#10
TerrA LX
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Posted 04 December 2009 - 12:11 AM
#11
_oldjohnno_
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Posted 04 December 2009 - 06:01 AM
So Old Johnno, what your saying is that because a 750HP is only rated at approx 710CFM while the 750DP is actuallr rated at 750cfm, would that suggest that the 750HP does in fact require larger jets to compensate for the smaller cfm ?
No, this is a common misconception. It actually works the other way, using an oversize carby requires larger jets and vice versa.
The standard jets for the HP are 72s in the primaries and 80s in the secs. I'd start from there and be very surprised if you had to deviate far from those sizes.
#12
_sbc57lx_
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Posted 04 December 2009 - 02:32 PM
Just leave it as it is ...... If it's running so nice - why swap it with the UNKNOWN.?????
I know shiny stuff looks nice ..... if the old carb is CLEAN and hiding under a chrome air cleaner that's good for most of us .
Unless it's going to showed - then who cares about HP ???. Keep it simple, save some bucks.
I DO LIKE CHROME ...................
I know shiny stuff looks nice ..... if the old carb is CLEAN and hiding under a chrome air cleaner that's good for most of us .
Unless it's going to showed - then who cares about HP ???. Keep it simple, save some bucks.
I DO LIKE CHROME ...................
#13
_rorym_
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Posted 04 December 2009 - 07:22 PM
Got a member with a 363 Chev in a boat...been chasing cooler header temps for 18 mths...It had a 750HP...swapped it out for a STD 750 Holley...gained 30 HP...and temps dropped 400 degrees..
As said...If it works...leave the shit alone..or polish the carb on it now to make it look pretty....you are asking for trouble....and trust me...you will get it...
R
As said...If it works...leave the shit alone..or polish the carb on it now to make it look pretty....you are asking for trouble....and trust me...you will get it...
R
#14
_Bomber Watson_
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Posted 04 December 2009 - 07:49 PM
On a side note, what kinda damb engine do you have to need a 750????
A 454 at 7000rpm and 80% volumetric efficiency (would need a pretty decent cam head and manifold setup to get that efficiency at those revs, were talking 9000rpm redlines here) only consumes 736cfm of air if my calculations are correct....
Not all that big as it turns out. The Holley four barrels are rated at 1.5"hg and this is the figure Holley use in their application formula as well. In the real world though, it seems best performance is had by sizing the carb to run at not much more than 0.5"hg. In my experience street 400s and 454s have run very well with 750 - 800cfm so that works out about right.
The weird thing is that Holley use the nominal cfm rating of the carb in their application formula and disregard the variations in test pressures completely. It's fortunate that these carbs have been used for about a million years now and it's been pretty much proved empirically what carbs work with what motors.
Mate i was thinking about this today at work and actually stumbled upon the same conclusion as what you have just said, and the two posts after it.
Good point, i now feel like a knob haha.
Cheers.
#15
_findusparker_
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Posted 05 December 2009 - 01:20 PM
I thought for humours sake I would demonstrate Holleys answer to my question...
"Jetting is 3% fuel. 1 jet up will increase fuel 3%. WOT Both carbs have the same BSFC"
Good thing for forums hey ?
"Jetting is 3% fuel. 1 jet up will increase fuel 3%. WOT Both carbs have the same BSFC"
Good thing for forums hey ?
#16
_Bomber Watson_
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Posted 05 December 2009 - 03:37 PM
Hmmm, usefull......
Cheers.
Cheers.
#17
_findusparker_
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Posted 05 December 2009 - 06:17 PM
I put the approiprite jets in the hp and will post the chassis results on monday. Funny, the bowls in the hp had some kind of light greenish/white creamy corrosion looking slop on them on the bottom. Could that be just fuel additive (octane boost)?
#18
_oldjohnno_
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Posted 05 December 2009 - 08:30 PM
I thought for humours sake I would demonstrate Holleys answer to my question...
"Jetting is 3% fuel. 1 jet up will increase fuel 3%. WOT Both carbs have the same BSFC"
Good thing for forums hey ?
A man of few words eh?
At the risk of explaining how to suck eggs, the first bit means that for each increase of one jet size flow increases 3% (I always thought it was more like 4.5% but there ya go). The second bit just means that both carbs are jetted to give the same Brake Specific Fuel Consumption at wide open throttle. This is just a measurement of the amount of fuel consumed per horsepower/hour. In other words they should both give roughly the same f/a ratio at their maximum rated flow even though they have different jet sizes. I'd imagine all the Holley performance carbs (or performance carbs of any brand really) would be jetted to give roughly the same BSFC at full throttle.
It kind of underlines why you should always start with out-of-the-box jetting rather than try something that worked for you in a different carb - a 72 in one carb may give you a much richer or leaner mixture than it does in another.
ps. Bomber if I had a dollar for every time I felt like a knob I'd be richer than Billy Gates...
pps. I'm a bit worried about the white creamy stuff in the bowls findus. You don't find the shiny finish that exciting do you?
#19
_findusparker_
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Posted 05 December 2009 - 10:05 PM
Ahh yes I knew the 'ol door was left open on that comment....
Well, the charts on the engine suggest that the BSFC range from .390 to .440 throughout the rev range, which im lead to believe is not so bad. Im not curious on that the standard jets are on a 4779-2 then. Google here I come..
I just found your lair old Jonny boy...
http://www.mopar1.us/carbs.html
Well, the charts on the engine suggest that the BSFC range from .390 to .440 throughout the rev range, which im lead to believe is not so bad. Im not curious on that the standard jets are on a 4779-2 then. Google here I come..
I just found your lair old Jonny boy...
http://www.mopar1.us/carbs.html
#20
_findusparker_
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Posted 07 December 2009 - 12:19 PM
Thanks to all that replied to this thread... here are the results of a chassis dyno with regards to the difference in the carbs...
750 Jetted 70/70 made 335 RWHP. A/F was perfect 12.8
750HP Jetted standard (72/80) made 348 RWHP. A/F showed too rich.
750HP Jetted at 72/70 made 352 RWHP. A/F showed too lean.
750HP Jetted at 74/75 made 364 RWHP. A/F was perfect 12/8.
Also, was going to save this for another thread but for a matter of information in terms of drivetrain loss on HP...
The first setup listed above made 488HP on an Engine Dyno, therefore was 335HP on Chassis Dyno. That was thru TH350 and 9" 4:11 plus 5200 converter. Im told the converter and diff can rob a bit of power, so these figures will give some of you a guide as to exactly how much it took.
Thanks
750 Jetted 70/70 made 335 RWHP. A/F was perfect 12.8
750HP Jetted standard (72/80) made 348 RWHP. A/F showed too rich.
750HP Jetted at 72/70 made 352 RWHP. A/F showed too lean.
750HP Jetted at 74/75 made 364 RWHP. A/F was perfect 12/8.
Also, was going to save this for another thread but for a matter of information in terms of drivetrain loss on HP...
The first setup listed above made 488HP on an Engine Dyno, therefore was 335HP on Chassis Dyno. That was thru TH350 and 9" 4:11 plus 5200 converter. Im told the converter and diff can rob a bit of power, so these figures will give some of you a guide as to exactly how much it took.
Thanks
#21
_sbc57lx_
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Posted 07 December 2009 - 01:26 PM
25 - 30 % HP loss with an auto sounds right . Nearly 30 HP with a change of carby - Hm. impressive.
#22
_findusparker_
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Posted 07 December 2009 - 01:46 PM
Ill take it to Heathcote on Sunday to see if those improvements reflect on track times. The 335RWHP's best time for the day a feew weeks ago was 11.09.
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