I am running 470 CID (.070 over JE flat tops) Twin turbo drawing threw A holly 850 with open chamber square ports the compression ratio is 8 to 1, donÂ’t have cam specs in head any more but it is a clay smith Hydraulic H9080.o.b from what I can remember it has about 0.310 lift and about 230 dur. I have it advanced 3 degrees so it is on 107 lobe center I am running at 10-11 PSI of boost. Holly 850 list #4781c 89 primary jets and 99 secondary jets. With a power valve that has been modified to boost reference on the primary side only. I was running it at 37 degrees timing with it retarding 0.6 degree per pound of boost for a total of 31deg.btdc I am running straight AV gas (101 low lead). It still seems to be lean The plugs (autolite AR13) are still bright white after wide open pass, I am backing out of it when The EGT temps reach 1600 degrees. It already feels rich in mid range 2000-4000. How big can I go on secondary jets before I max out the passages? I need to step down the primaries 1 or 2 sizes but I am hesitant. Should I go to a power valve in the secondary also? If so should I modify it for boost reference similar to primary side? Another question is just went to MSD distributor with about 26 deg mechanical advance. Its retarding under boost, just wondering what changes if I lock out all mechanical advance, and retard under boost and starting only?
Any Help is greatly appreciated Ken B
http://www.***boat.com/image_center/showphoto.php?photo=28532&password=&sort=7&thecat= 500[/IMG]
That looks like an old BAnks set up but with a wast gate added.
I would add the secondary power valve. If that is not enough you can open up the power valve hole. If you are all ready fat in the midrange I would not jet up any more!
Just my .02
Timmy
I would make sure the carb is getting enough fuel.
Float levels. Fuel pressure. Fuel line sizes etc.
Thanks for ALL THE INPUT! I am running -10 fuel line to pump then -8 line to holy regulator. The regulator is next to carb and I am using the regulator as my tee which then drops down to -6 line to each float bowl. I am running 7 psi with big needle and seats. at wide open throttle 11 psi of boost (aprox 850 hp)my fuel pressure is dropping down to about 4 psi. I went back to my old holly 750 which I ran last year. It has 86 primary jets and 93 secondary jets with a power valve on primary side. And it seems to run perfect. Little less power and it lost about 300 rpm. At this point I think I will just leave it till I have time to dyno it again. With some one who has little more experience than me with tuning and reading plugs. As far as my turbo set up itÂ’s a PFM set up that I added the waste gates and dumped them into two stainless mufflers that I made.
Ditch that holley reg, have you seen the size of the hole the fuel goes thru?? it is very small and a big restriction. I set up a bypass system on both my blown motors and love them, full volume to the carbs, and regulate on the way out.
Yesterday, when I was testing out the Schiada, I was only pulling 4500 rpms and it seemed way flat on the top end. I am thinking the same thing Blown. I have a holley blue and with the holley FPR. I might need to throw on my BG.
The difference between a holley and a BG pump can be compared to the difference between a gentle love making session and scull f*&$ing. The BG flows so hard you can SEE the voltage being sucked from you battery and you are afraid the steel braided lines are going to burst.
A sexual overtone to everything, got to love it.
Mr.curious:
Holly 850 list #4781c 89 primary jets and 99 secondary jets. With a power valve that has been modified to boost reference on the primary side only. It already feels rich in mid range 2000-4000. How big can I go on secondary jets before I max out the passages? http://www.***boat.com/image_center/showphoto.php?photo=28532&password=&sort=7&thecat= 500[/IMG] When you've reached a size 99 jet and she still wants more than you need to get into a more precise carburetor set-up. The 850 Holleys come stock with 0.150" Down-leg boosters. If you were to step up into a 0.160" version downleg, lean out the primary high speed air-bleeds and idle air-bleeds you might find this cures your dilemma. For example....alcohol carbs use alot more fuel volume, so when setting one up it needs to be modified with 0.178-0.190" boosters. These boosters would drown an 800HP BBC with no problem. But you got the point...
You have to remember that setting up a carburetor for forced induction isn't a general blanket template. For turbo and centrifugal supercharger set-ups, blowthrough and drawthrough (non-roots style), you need to set the primaries for normal aspiration use (slightly richer) and the secondaries for roots style blower use. This could show a 7 or 8 jet size spread or even a booster calibration of 0.150" Primary/0.158" secondary (very common up to 850HP.
If you use the roots style calibration on both primary and secondary, you will have a very rich bottom because the boost isn't all the way on yet. Generally that's the story, but every application is different and needs to be treated as such.
With respect to your lean top-end.... you need more fuel. That can be from carb adjustment (boosters/jets/floats), fuel volume, and very important fuel pressure.
Hope this sheds some light.
Mr Curious, I run basicly the same set up as you on a BBF [466"] 2 Rayjay 370-E-10 with intercooler. I run an old 850 centersquirter Holley with 83s in the primarys with p/v and .070" pvcr [boost referenced] and 93s in the secondarys [no p/v] the carb work great and the system will make about 14 lbs of boost. I also use a B/G bypass fuel regulator and a B/G pump. If you experence ANY fuel pressure drop at the carb it is leaning out and no jet changes you do will make any difference. Correct your fuel delivery problem and you may find your carb is now rich with the jets that are currently in there. Also av gas is a lighter specific gravity and will always be slightly lean compaired to automotive fuel, try jetting to automotive race gas and stick with it. Av gas works good at 12000' but its not formulated for automotive use on the ground. [you don't need de-icing additive for your boat] I use ERC 110 at 100% and it is slightly rich from the mix I used to use of 50/50 race-pump 92.
One more thing, don't put a lot of faith in plug color, it is deceiving. Unleaded and low lead fuel will not color a plug like leaded gas. Read the heat tracks on the ground electrode and the heat coloring on the plug body threads. That is a better indicator of whats going on inside the cylinders.
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