Questions on tuning a 598 bbc
Moderator: Team
Fuel Systems
The Dyno operator said the rear float bowl was running out of fuel.
I have been giving this advice since about 1978 because my unsymmetrical cams have been running float bowls out of gas, when equipped with small lines, small regulators, or small fuel pumps.
Oddly enough, the engines always pick up after switching from the old system to the new.
The way I design cams, I have a delayed opening point for the intake, then open the valve very fast to make up for the delay.
While the intake valve is still closed BTDC, the exhaust gas has more time to exit the combustion chamber, lowering the volume and pressure of the residual exhaust gas.
When the intake valve finally opens, there is less exhaust gas, and at a lower pressure, which has reduced the effect of reversion.
Reversion is much more disruptive as the RPM goes up. This is why most of you have to lean your carbs out on the top-end. Reversion lessens the amount of clear-air flow, and requires a leaner jet to keep air/fuel mixtures correct.
When my designs lessen the effect of reversion, they flow more cleaner air, and require more fuel to maintain the proper air/fuel mixture.
This is generally more pronounced in roller cams than in hydraulics or solids, but all of my solids generally require an upgraded fuel system.
This is without considering the effects of intertia loads on the fuel in the lines, etc, etc, etc.
This has worked in 11-sec and faster cars, for about 31 years.
UDHarold
I have been giving this advice since about 1978 because my unsymmetrical cams have been running float bowls out of gas, when equipped with small lines, small regulators, or small fuel pumps.
Oddly enough, the engines always pick up after switching from the old system to the new.
The way I design cams, I have a delayed opening point for the intake, then open the valve very fast to make up for the delay.
While the intake valve is still closed BTDC, the exhaust gas has more time to exit the combustion chamber, lowering the volume and pressure of the residual exhaust gas.
When the intake valve finally opens, there is less exhaust gas, and at a lower pressure, which has reduced the effect of reversion.
Reversion is much more disruptive as the RPM goes up. This is why most of you have to lean your carbs out on the top-end. Reversion lessens the amount of clear-air flow, and requires a leaner jet to keep air/fuel mixtures correct.
When my designs lessen the effect of reversion, they flow more cleaner air, and require more fuel to maintain the proper air/fuel mixture.
This is generally more pronounced in roller cams than in hydraulics or solids, but all of my solids generally require an upgraded fuel system.
This is without considering the effects of intertia loads on the fuel in the lines, etc, etc, etc.
This has worked in 11-sec and faster cars, for about 31 years.
UDHarold
662-562-4933
brookshire@panola.com
brookshire@panola.com
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travlinman572
regulators
What regulators would You recommend? I have an old old Grant with 4 outputs. Are Yours alky friendly just in case? Hope this might help the origional poster also. Would it be possible to feed a small plate kit NOS between the regulators? Thanks TC
I went to the dyno yesterday . I was running out of fuel badly . I had the bary grand 2 port regulator and it doesn't matter what we do to it the presure wouldn't go below 12 psi . We tried 3 of the same regulator and they all would stay high . But that wasn't the problem . The problem was that when on load , from the beginning i can see the tank on the carbs get splashi and drops (demon with the glas on the side to see the fuel level) .
It doesn't matter what we do with the pump (bg400) with high return or low it would be the same thing . Its not the same pump I went to the track with . I bought a brand new pump with filter from a friend that had it laid around for a long time . The most power it made was 566 hp . It wouldn't rev more then 7000 rpm , it would just hold there . At the track I was hitting the limiter at 7600 . I called bg and they said that the 2 port regulator is rated for up to 650 hp and that I needed their 4 port regulator . The 4 port uses 6 an to the bowls , the 2 port uses 8 an . Well we put it on , the same thing . Even on Park with no load by reving it , it would empty the tanks . I was getting frustrated . So we wanted to put the old pump and filter back . The pump and filter was realy old , but atleast it ran 8.70s first pass . When disassembling the the new pump and filter , there was lots of whites pieces from the filter . The filter was ristricting the fuel badly . The filter problebly because it was sitting in a container and inside was realy hot and it said there for about 2 years . By removing the filter everything worked perfect .
We couldn't make any more pass after that . At the beginning of the dyno it had 96 jets in the carbs and we kept raising the jets because it was so lean . We put 100 jets at the end . Tomorow i'm gonna test it at the track , should I put it back to 96 or leave it at 100 for now and work my way down ?
I wanted to put 2 regulators but after seeing a friend that have 598 with 12 degree profiler heads making about 1050 hp with the same 4 port regulator and 6 an steel braided to the tanks I don't think i'm gonna have any trouble with that .
GJ
It doesn't matter what we do with the pump (bg400) with high return or low it would be the same thing . Its not the same pump I went to the track with . I bought a brand new pump with filter from a friend that had it laid around for a long time . The most power it made was 566 hp . It wouldn't rev more then 7000 rpm , it would just hold there . At the track I was hitting the limiter at 7600 . I called bg and they said that the 2 port regulator is rated for up to 650 hp and that I needed their 4 port regulator . The 4 port uses 6 an to the bowls , the 2 port uses 8 an . Well we put it on , the same thing . Even on Park with no load by reving it , it would empty the tanks . I was getting frustrated . So we wanted to put the old pump and filter back . The pump and filter was realy old , but atleast it ran 8.70s first pass . When disassembling the the new pump and filter , there was lots of whites pieces from the filter . The filter was ristricting the fuel badly . The filter problebly because it was sitting in a container and inside was realy hot and it said there for about 2 years . By removing the filter everything worked perfect .
We couldn't make any more pass after that . At the beginning of the dyno it had 96 jets in the carbs and we kept raising the jets because it was so lean . We put 100 jets at the end . Tomorow i'm gonna test it at the track , should I put it back to 96 or leave it at 100 for now and work my way down ?
I wanted to put 2 regulators but after seeing a friend that have 598 with 12 degree profiler heads making about 1050 hp with the same 4 port regulator and 6 an steel braided to the tanks I don't think i'm gonna have any trouble with that .
GJ
Harold, I'm running one of your newer cams in a large BBC. 1350 dom with #6 lines to each bowl from a single 12-803 regulator. I don't see any problems with fuel pressure drop during a pass. However I don't know any way I can study aeration of the fuel. Do you think that a problem like aeration would show up in fuel pressure variation? We're measuring the pressure at the rear fuel bowl inlet.
If you think it's a good idea, I will replumb and put a bigger regulator on it if necessary?
If you think it's a good idea, I will replumb and put a bigger regulator on it if necessary?
I went to the track yesterday and made 3 passes . It had the 1190 king demon on it and the timing was 36 . The first pass was 8.74 @ 153 . We checked the plugs and it was lean . It had 98 jets . We put 100 jets all around and it went 8.66 @ 156 and then 8.62@ 156 . 60 foot was 1.21 .
The plugs looks like it need some more fuel . I tried the car at the track a day before with 37 degree timing with 98 jets and it only ran 8.95@152 mph . So we dropped the timing back to 36 . But it could be that because it was lean , the higher timing would make it even leaner . Oh one other thing , this pass we made it shifting at 7000 rpm and 7600 rev limiter . It would hit the rev limiter before getting to the finish line . So we tried 7400 shift point yesterday with 7800 rev limit and it hit the limiter right at the finish line . Do you guys thing I need a bigger carb ? We want to try the 1250 holley again but we think the venturi is big (2 1/8) . It didn't make any power at the dyno but we had trouble with the fuel system . I wish we had a engine dyno down here .
Thanx
The plugs looks like it need some more fuel . I tried the car at the track a day before with 37 degree timing with 98 jets and it only ran 8.95@152 mph . So we dropped the timing back to 36 . But it could be that because it was lean , the higher timing would make it even leaner . Oh one other thing , this pass we made it shifting at 7000 rpm and 7600 rev limiter . It would hit the rev limiter before getting to the finish line . So we tried 7400 shift point yesterday with 7800 rev limit and it hit the limiter right at the finish line . Do you guys thing I need a bigger carb ? We want to try the 1250 holley again but we think the venturi is big (2 1/8) . It didn't make any power at the dyno but we had trouble with the fuel system . I wish we had a engine dyno down here .
Thanx
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RayJE Carburetors
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Just keep adding jet ....as long as the carb responds to jet there is nothing wrong .....if your high in jet numbers its not always the carbs fault .. i see this so often with customers... ..there are numerous factors that will effect carb signal.
you might have to machine some jets..... a 100 Holley jet is .128
3.3mm drill is .130
, 3.4mm drill is .134
#29 drill is .136
or Purchase some BLP jets in Pin Size
anything bigger than 136 thou and the carb wont respond to jet changes ..... the King demon Blocks have an effective cross sectional area at the bottom of the well that is .140
increase the cross channel size by 5 thou or so .. this will richen the top end ... ...if the boooster stakes are the same size .. you will have to machine them out as well......
you might have to machine some jets..... a 100 Holley jet is .128
3.3mm drill is .130
, 3.4mm drill is .134
#29 drill is .136
or Purchase some BLP jets in Pin Size
anything bigger than 136 thou and the carb wont respond to jet changes ..... the King demon Blocks have an effective cross sectional area at the bottom of the well that is .140
increase the cross channel size by 5 thou or so .. this will richen the top end ... ...if the boooster stakes are the same size .. you will have to machine them out as well......
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Strange Magic
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The best thing you can do is get rid of the BG stuff and make an investment in a real fuel system that will provide adequite fuel for the engine.
Either Product Engineering or Magna Fuel. A single 12 to the pump from the cell, number 10 into a 2 port or 4 port regulator and #6 or #8 lines to the bowls.
The BG pumps are 5 vains and I have seen my share of them fail out there, the entire pump. The biggest problem is when they don't fail but just slowly go away. Once again, i've witnessed this on plenty of occasions. The PE has 7 vains and is continuos duty and the Magna fuel has 6 vains and is also continuos duty.
P.S. Forget the bigger carb, set the timing at 33, jets at 100, a new set of plugs. Get yourself a real good baseline and then move 1 degree into it (34) and see if it responds with mph. A,B,A, test this timing to understand what it likes. I really can't see it wanting anything more than 33 degerees with a 4.5 stroke and fast piston speed from rod angle. If the dome was 44-46 I could see 35 or 36 degrees but it's not, it is 39 cc's which requires less leed.
Set your rev limiter at least a minimum of 400 rpms over max trap rpm. Bouncing it off the limiter will allow for parts to be bounced right out of the engine block.
Either Product Engineering or Magna Fuel. A single 12 to the pump from the cell, number 10 into a 2 port or 4 port regulator and #6 or #8 lines to the bowls.
The BG pumps are 5 vains and I have seen my share of them fail out there, the entire pump. The biggest problem is when they don't fail but just slowly go away. Once again, i've witnessed this on plenty of occasions. The PE has 7 vains and is continuos duty and the Magna fuel has 6 vains and is also continuos duty.
P.S. Forget the bigger carb, set the timing at 33, jets at 100, a new set of plugs. Get yourself a real good baseline and then move 1 degree into it (34) and see if it responds with mph. A,B,A, test this timing to understand what it likes. I really can't see it wanting anything more than 33 degerees with a 4.5 stroke and fast piston speed from rod angle. If the dome was 44-46 I could see 35 or 36 degrees but it's not, it is 39 cc's which requires less leed.
You are burning this engine up with too much timing and a bad fuel system. It takes about 25-28 hp to move a tenth. If you think about how much power you are killing to slow it up that much, it is doing some harm to that engine.I tried the car at the track a day before with 37 degree timing with 98 jets and it only ran 8.95@152 mph .
Set your rev limiter at least a minimum of 400 rpms over max trap rpm. Bouncing it off the limiter will allow for parts to be bounced right out of the engine block.
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revolutionary
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GI
Lot's of good info here and some not so. Once you have all of the issues resolved YOU NEED TO LISTEN TO THE CAR, IT WILL HAVE THE LAST WORD!
On your carb, my advice is to have one built for your combo! Out of the box holley or BG is just that, a good carb shop can do wounders for you!
Converter sounds way too tight, did you mentioned what trans you were using? If it's a glide you need it much looser stall, 5800 - 6300.
Timing, let the MPH on the time slip tell you, start w/36 and go from there.
Fuel system, a good 400 pump from any will do the trick, I like the pruduct engineering stuff myself. One good 4 port regulator is fine and #6 line will work to the bowls, the needle and seat is the restriction once the regulator is sized correctly. 7 to 7.5 psi is all you shoulde ver need, if you need more there's other problems and your just band aiding the deal. Too much fuel pressure airates the fuel in the bowls.
Take your time and don't rush it, good luck.
Lot's of good info here and some not so. Once you have all of the issues resolved YOU NEED TO LISTEN TO THE CAR, IT WILL HAVE THE LAST WORD!
On your carb, my advice is to have one built for your combo! Out of the box holley or BG is just that, a good carb shop can do wounders for you!
Converter sounds way too tight, did you mentioned what trans you were using? If it's a glide you need it much looser stall, 5800 - 6300.
Timing, let the MPH on the time slip tell you, start w/36 and go from there.
Fuel system, a good 400 pump from any will do the trick, I like the pruduct engineering stuff myself. One good 4 port regulator is fine and #6 line will work to the bowls, the needle and seat is the restriction once the regulator is sized correctly. 7 to 7.5 psi is all you shoulde ver need, if you need more there's other problems and your just band aiding the deal. Too much fuel pressure airates the fuel in the bowls.
Take your time and don't rush it, good luck.
I've been following this post with much interest as I'm having growing pains with a 598 also but a couple of things stated by Strange Magic and Top38 knocked me over. After starting at 36 degrees timing, working up to 38 and back down to 28 I ended up dead on 33. Tried a 8" 5000 converter (trashed it), then a 10" 5500 (too tight on the shift to high) and have just ended up with a 9" 5800 that has worked the best (glide). (Exactly as they said) Car weight is about 2540 and best 60 ft has been 1.113. MPH is down 6 or 7 from what it should be (1/8) and I suspect fuel/scoop issues but the plugs don't indicate lean.
George
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Strange Magic
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One more thing to add:
Do not use a nitrous fuels on a normally aspirated engines. Some common nitrous fuels are listed below:
C-16
C-15
Sunoco Red Maximal
VP Nos
If you are using one of the above for a normally aspirated engine you should consider the below (fuels below will be dependant on compression ratios and cubic inches:
VP C14
VP C14+
Sunoco Blue Supreme
VP C12
VP 113 (low compression, max power)
VP C25 (max power under 600 cubes, very costly)
Do not use a nitrous fuels on a normally aspirated engines. Some common nitrous fuels are listed below:
C-16
C-15
Sunoco Red Maximal
VP Nos
If you are using one of the above for a normally aspirated engine you should consider the below (fuels below will be dependant on compression ratios and cubic inches:
VP C14
VP C14+
Sunoco Blue Supreme
VP C12
VP 113 (low compression, max power)
VP C25 (max power under 600 cubes, very costly)