800cfm Holley Jetting
 

I recently purchase 2 800cfm dp holley carbs from a board member. They are HP 500s take offs and appear to be factory stock. Jetting is staggered 75 sb primary, 81 port primary, 93 sb secondary and 89 port secondary. Has single power 6.5 power valve.

These carbs are going on 425 to 450hp 454s. Actually dyno 2000 says my engines should be 500 hp but I find that hard to believe. I need advise on which way to go with jetting as I am in the process of freshening the carbs now. I'd like to start somewhere in the ballpark. Should I run the carbs with factory hp500 setup first?

Engines are: 468cid, 8.5:1 compression, rect port al edelbrock rpm heads, 226/234 @050, 544/564 comp cams, edelbrock rpm dp intakes, eickert headers. Planning to spin to 5200rpm.

Looking for specific jet combinations, power valves, squirters and accel pump selection advice

Dave

Dyno and SuperV are currently running these carbs on similar engines as yours, just with a point more c/r and a slightly larger cam and Merlin oval-port heads. Maybe one of them will pop in here and post.

Thanks Crazyhorse. Do you by chance know the theory behind the staggered jets in the hp 500s?

Dave

The staggered jets are necessary with some intakes. What intakes are you using?

Edelbrock rpm performer, dual plane. What did the HP come with?

Dave

Dart single plane I think.

So Tom, you think I should have even prim/sec jetting due to the dual plane? Maybe 81 prim, 93 secondary? Gotta start somewhere.......

Dave

I am not familiar with those carbs, if they were 3310's (780 cfm) I could tell you exactly.

Thanks F31. I guess I will just put my qjets back on and forget it. It was probably a dumb idea to switch to holleys anyway :rolleyes:

Dave

Well, Im gonna try my Quads again this year after I change manifolds and get them set up. There should be quite a few people on here who know the jet setup for those 800's. Ive never been able to get the quads to put out top end like the holleys but Im gonna need fuel economy and engine reliability for a while so thats why Im gonna try and go back.

I put an 800 Holley on my 502 last year and my fuel mileage did not suffer at all. I have 99 secondary jets and 84 primaries. I know that seems rich but it runs good and the plugs look OK. I love the carb. It outruns the previous Weber 750 by 1 to 2 mph and it starts right up after setting for a week. Best bang for the buck I have ever spent. :D

Jetting
 

I am running 86pri/ 98sec. HP 500 .30 over 731 cam at Sea altitude. Don't be shy too start big & work you way down. As Macdad has similar jetting as me. Do a search, there was a thread here before on this exact topic...if it has not been purged. Boat starts easy, don't forget to set your float levels.
John

I had the same carbs on almost the same engine. I had a stock 454Mag bottom, heads,and with a stock magnum intake with a 1"carb spacer, Crane 226/236, .531/.553 cam and Imco exhaust.
I ran 79 primaries and 94 secondaries and would spin the engine to 5400rpms. Left the sock 6.5 PowerValve on the primaries.

Sounds like no one is using the staggered jetting. Sounds like 79-81 primary and 93-95 secondary would be a good start. Griff, did you do a lot of plug readings to end up with the 79/94 jetting or is that just were it was when you got it?

Thanks fellas,

Dave

I got the carb with stock jetting and searched the forum for what others were using or recommending on other similar setups. I started with like 76's and and 90's and after a few plug readings, moved up.
To set the primaries, I ran the boat up to about 100 rpms before the secondaries opened,shut it down, and checked the plugs for color and the heat line on the electrode.
Did the same for the secondaries after WOT runs.

I would shut it down fast, take a couple plug readings, and then beach it to change the jets. Take your plug readings on #1 and #7 initially, as they will be the leanest. When you get it real close, then check some more of them.
The carb was always a little rich at idle.

My 454 with 174 blower and polished and ported iron rectangular heads and crane 241 flat tappet with similar lift duration is running 82 primaries and 94 secondaries with the 800 CFM HP 500 Holley. Power valve is 6.5 with manifold reference. Given your extra cubes but no blower you will probably wind up with something a little less. The accelerator pumps on my carb were unchanged. There is conflicting info on various sites Holley, CP Performance and Summit as to whether the 800 came with 30cc primary and 50cc secondary or vice versa accelerator pumps.

Anyone know what accelerator pump configuration the HP 500 carb comes standard with? Seems to me 30/50 makes most sense for marine applicatio.

Great carb so far responsive and fuel efficient.

Thanks Griff, that is what I will do. I run msd ignitions so a rich idle should be ok.

Dave

I'll check on the factory hp500 carb I have apart this evening and let you know. I think it is 30/50 but want to verify.

Dave

Vmax. The carbs I have had 50 primary and 50 secondary. I'm thinking this carb is perfectly stock, the jetting was factory, so I assume the accel pumps are too. Is 30/50 a common approach to double pumpers?

Dave

Dave,
From what I have seen with the 800 or Holley part number 9022 carburetors there appears to be three levels of marine calibration a universal marine which has 30/50 gives you biggest shot of gas when secondaries open, performance/competition with 50/30 eliminates off idle stumbles and gives biggest boost out of the hole ,
and race with 50/50 throttle responsive at through entire range with big boosts of gas.

The holley dominators all have 50/50 pumps. Super charger 2X4 set ups run 30/30. Supercharger single 1X4 50/50.
Some of the Holleys without choke horn and annular booster run 30/30.


850 CFM Universal calibration runs 30/30.
850 CFM Performance competition runs 30/50.
850 Race runs 50/50.

I'm glad to here the Mercury blue HP500 has the 50/50 set up standard issue since that is what mine started out as. Probably also explains why there is so much black soot build up on these carbs air horns after running a short time. I don't see that out the tail pipes though with my jetting and my blower. If I were you I would try the 50/50. If initial holeshot bogs try 30/50 to lean it up and save a few pennies on gas when puttering around. But I'm not a carb expert just an engineer who likes to analyze things. Myself I tend to stay away from the full throttle start with the blower and an early bravo drive to keep teeth on the gears. The secondary kick on my boat is a grin a minute. Gotta burn the fossil fuel in large quantities with hair on fire.

Good info Vmax. Do you ever take notice to a fuel smell in your motor oil? I am concerned a 50/50 shot may wash down the cylinders.

What year bravo are you running? I've heard tale that early bravos were in fact stronger than subsequent years. I like that idea since I run 1988 bravos and can say, they are indeed different inside than the standard bravo. I'm not pushing the hp you are but am not into the straightarm holeshots either.

Dave

I had just bought the boat and had I believe is a 830CFM auto carb on it without the choke horn and annular booster. Nice looking carb but boat was tough to start and I had an enclosed bilge. I had an ignition issue of wrong ignition module for the blower application that the helpful OSO members here help me straighten out with a V-6 module. That set up was definitely washing down the cylinders. Not sure if it was the carb or the module contributing since she would flood often.

Only got to run my boat once on Thanksgiving Morning about a half hour since an oil change and the new module then put her away. I did check and smell the oil and it was not loaded with gas. Only did a few plug checks for ignition change that day maybe 20 minutes run time.

You can always put a cam on pump for a slower fuel burst if its an issue.

Drive is 89 with cresent nose cone. The early bravos had a cone clutch issue with only three grooves instead of five that let it slip during throttle chops on high HP motors. I don't know if mine was fixed but have not seen it yet. There is a merc bulletin say to use the 5 groove. I think it may have had a speedo pitot prior to nose cone. There is a rubber hose fastens to a plastic plug top plate forward of case. Hose goes through gimbal. Can't find set up in mercury manuals telles waht the hose was and can't see original case. I now have a POS pitot that I can't keep down with my speeds. Unerving running up in RPM guessing your speeds. Think it is mid to upper 80's given RPMs and prop pitch. Sure feels like it.
Darrell

Mine has the speedo tube fitting too. You probably have a hose with a screw in it behind the engine.

Sounds like it is time for a gps. I intalled a garmin 162 and it fills the bill quite well. Only problem so far is it consistently reads about 10mph low :D :D .

Dave