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Author Topic:   alcohol holley jets and power valve
Dirt Maniac

Total posts: 190
posted May 02, 2005 08:59 PM  
4150 holley, has 136 jets and 8.5 power valves, is this close, or way out?
12 to 1, 355, with 250-260 duration.

Dirt Forum Champ
Total posts: 753
posted May 02, 2005 09:32 PM  
136 jets???? if I remember right my alky carb had like 98 jets.... isn't 136 kinda high most especially when using a power valve??

Dirt Maniac

Total posts: 102
posted May 03, 2005 05:10 AM  
Originally posted by FlyNLoIMCA17:
136 jets???? if I remember right my alky carb had like 98 jets.... isn't 136 kinda high most especially when using a power valve??

right. I run a 355 and have holley 65's with 90 jets. Not even close to ruining anything. Trying to get carb info = trying to pull teeth. (at least for me!) Hope that helps

[This message has been edited by dirtzone (edited May 03, 2005).]

Dirt Maniac

Total posts: 190
posted May 03, 2005 06:12 AM  
are you both running a 4150? i read recently that 136 is close.
this carb came off an engine with two broke pistons, that look like detonation was to blame. i have had nothing to do with methanol, and need some info.

Dirt Forum Champ
Total posts: 1019
posted May 03, 2005 07:24 AM  
Jet sizes in the 90's are because they are using the old standard style metering blocks with auxiliary holes drilled above (or sometimes beside) the regular jet holes. Those older blocks take standard 1/4" thread Holley jets.
The HP series carbs that use HP series metering blocks that were purpose-built for alcohol use are using 5/16" alcohol jets that are much larger in size and in numbering than the standard Holley jets, and they do not require aux holes to be drilled in the blocks.
Therein lies the differences in numbers, and there's NO way to recommend an accurate jet size unless ya know exactly what size those aux holes are and every single thing about both the carb sizes internally and full engine info as well as air quality info (temp, humidity, altitude, etc).
And if the carb has HP series metering blocks, the same thing applies - you'd need to know everything about the carb itself, as well as engine info and air info in order to even come reasonably close to a recommended starting point on jets.

Hope that helps, and since I really didn't answer the original question..... I would start with jetting anywhere from 136's to 156's and go with a 6.5 alcohol power valve and tune accordingly. If the carb has 1.75" butterflies on a 750 body, then your jetting is more likely to be near or above the 170's.

Good luck and if ya need more help, just hollar.


Dirt Maniac

Total posts: 190
posted May 03, 2005 12:14 PM  
thanks, it is a 4150 hp series 750 cfm.
the power valves are actually 5.5, i was stupid when i read them.
you have cleared a bunch up for me, we have a couple guys here running jets in the 90's, so i was thinking this may be high, but it detonated two pistons, which could have been something else, its not my engine.
i will order a jet kit for him, and try something larger.

James Birmingham
Dirt Full Roller

Total posts: 28
posted May 04, 2005 08:41 AM  
Something else needs to be check. That would be the supply system. In most of the problems I have seen it comes down to not being able to supply enough fuel to the carb to meter. You can take the jets out but if the fuel supply is metering the system you will still lean out.

Dirt Freak

Total posts: 390
posted May 04, 2005 08:16 PM  
Good carb builders know to get a correct fuel curve requires power valves otherwise you have to over jet which makes the bottom end too fat. Example: Braswell,C&S, Willy's,
Barry Grant,Gary Williams, etc. Not a backyard builder in the bunch! To do it right you need power valves. **** ! Even Holley says to,And they invented the darn thing! Alcohol jets in the 90's range usually have the metering block drilled with an extra 1/8 in. hole above the jet. This was the old school method before they started enlarging the jets and passages in the old gas metering blocks. All the newer stuff runs the larger jet numbers with the better or billet metering blocks. It makes for a new market of jets you need to buy.

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