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1 boat's never enough
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Discussion Starter · #1 ·
I just finished installing an Edelbrock tunnel ram with two Holley 600's and have a question about jetting. Everything's setup really nice, idles at 1,000 rpm, quick off the line and hits 4500 rpm instantly but falls flat from there. I have plenty of throttle left but it inches up very slowly and doesn't go beyone 4500. I turned my scoop around (open to the rear) and picked up 300 rpm. I turned it forward and put a piece of paper over half the scoop and picked up the same 300 rpm. I'm not sure how to read plugs and frankly am a little worried about shutting the engine off at WOT (low free board). I'm thinking I need to jet up a bit but it seems that 2x600 cfm should be plenty for a BBC 402, 10.5:1 compression. Any ideas? I'm not familiar with tunnel ram setups and am baffled that it seems to be lean.
Thanks!!
 

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Did you pull a spark plug to see what's going on inside the cylinder.? What carbs are they (double pumpers, vac sec etc) Do they have power valves??
What was the RPM before the tunnel ram setup? What jets are in the carbs now??
 

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On my 565 I have the same manifold and 600 doule pumpers, 67 pri jet, 73 sec jet, 6.5 power valves. Mine idles in gear at 900 and pulls strong to 7K+. Nothing trick in my carbs, and I'm running K&N air cleaners and velocity stacks. As suggested a plug report would be helpful, as well as how the carbs are setup now. Have the choke butterflys been removed or locked in the full open position? An excessive lean condition would probably cause popping in the exhaust.

What was on the engine prior to the TR, and what did it pull then?
 

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just a ski boat with bark
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I just finished installing an Edelbrock tunnel ram with two Holley 600's and have a question about jetting. Everything's setup really nice, idles at 1,000 rpm, quick off the line and hits 4500 rpm instantly but falls flat from there. I have plenty of throttle left but it inches up very slowly and doesn't go beyone 4500. I'm thinking I need to jet up a bit but it seems that 2x600 cfm should be plenty for a BBC 402, 10.5:1 compression. Any ideas? I'm not familiar with tunnel ram setups and am baffled that it seems to be lean.
Thanks!!
I assume this is in a jet by looking at your avatar? If so what rpm did it run before the tunnel ram, When I switched from a large 4bbl on a single plane intake to my tunnel ram I only saw 100-150rpm increase on top end. I'll post a picture of how I like my plugs to look after a WOT pass but like the other guys I find it hard to believe your lean, whats your total timing set at?

 

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1 boat's never enough
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Discussion Starter · #5 · (Edited)
I'll do a run this weekend and pull the plugs to see what they look like and even take some pictures. I put the engine together and installed the tunnel ram so don't have numbers prior to setup I have now. Pulled around 5200 with previouse engine. The carbs were reworked with smaller bowls to fit end to end and the tops have been machined off and I have flame arrestors inside the scoop. I'll take photo's this weekend to show what I'm talking about (boat's in Havasu and I'm in CA). I believe the jets are stock, carbs are 4150 600's. Plenty of fuel pressure at WOT (forgot to mention that). These are the best pictures I have at the moment. Carbs are the 4776 double pumper mechanical secondaries.



 

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If you have flame arrestors inside that scoop, that could be your choke point, I would try running it with them removed. Also have your verified the float levels are correct? Check when the boat is at the same angle as when it's floating.
 

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1 boat's never enough
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Discussion Starter · #9 ·
Are you tanks vented? what fuel pump do you have? Are your fill caps vented? Whats the pressure at wot?

I'm using the Holley blue electric with an external regulator set to around 7 lbs. It's between 5-6 at WOT best I can tell. I believe either the tanks are vented or the caps. I set the float levels on the trailer (level) so will check them on the water. This has been very helpful and gives me at least some things to consider and try out. Thanks!!!
 

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There are several design issues I see.

The deadhead regulator for one feeding 2 carbs.

But !!! a lot of times you have to jet way up on a tunnel ram because the vacuum signal is poor.

Make sure it is just not running out of gas (which it is) due to fuel system design. Many things mentioned already to check plus mine. :)
 

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Fuel Volume!!

Some good information and points presented. I'd like to point out an often ignored issue.....Fuel Volume. You are currently running all of your fuel to feed this motor thru only one small Holley regulator. Attached is a pic of one opened up, showing the small 7/32" (less than 1/4") orifice that the check ball seats on. Even though this motor is not huge (450 HP ?), this is not adequate. Fuel volume is actually more important than fuel pressure.
Just .02 Jocko
 

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JOCKO may be on to something, on my deal I have a #10 line from the pump to a Magnafuel 4 port regulator, then a #6 to each bowl. I'm still leaning to the flame arrestors being the choke point though, could very well be a combination of both, and I would correct both before many more WOT's.
 

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Discussion Starter · #13 ·
Some good information and points presented. I'd like to point out an often ignored issue.....Fuel Volume. You are currently running all of your fuel to feed this motor thru only one small Holley regulator. Attached is a pic of one opened up, showing the small 7/32" (less than 1/4") orifice that the check ball seats on. Even though this motor is not huge (450 HP ?), this is not adequate. Fuel volume is actually more important than fuel pressure.
Just .02 Jocko
Interesting. another point is that the carbs I'm running had shorter bowls installed in order to be able to stack them end to end (9.25" center spacing). Could this also have an effect on flow? i.e. if the reg is restricting flow and the reserve in the bowls are smaller than normal, the short time it takes to get up to max rpm could run them dry? Maybe I'm chasing a bigger problem.
 

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the volume in those bowls really isn't that much smaller than the dual feed bowls. Those bowls are used on Carson Brummett's turbo set up and those things make better than 1200 HP. If you what to run a 2 port reg, you will probably have to can that 3/8 little reg and step up to a larger 2 port.
http://www.jegs.com/i/Holley/510/12-704/10002/-1. But I would pull the flame arresters and jet that thing up about 4 sizes first. While you have the bowls off, check to see if they have power valves on the primaries. How does your fuel pump get its power? Is it thru a relay, or a key switch?



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Bigger regulator

GN7 is right on with that larger Holley regulator. That model has a substantially larger inner orifice.....7/16" vs the smaller 7/32". I also completely agree with his jetting recommendation as well as ditching those flame arrestors! Jocko
 

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I ran a tunnel ram setup w/ 2 holley 600. Would top out at 3800. Changed 140 stat to 180* and eng ran well beyond 6 grand. Might look into that.
 

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I ran a tunnel ram setup w/ 2 holley 600. Would top out at 3800. Changed 140 stat to 180* and eng ran well beyond 6 grand. Might look into that.
Im willing to bet that has nothing to do with it. It's in a jet boat and most jet boats don't run A thermostat.
 

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Discussion Starter · #18 ·
the volume in those bowls really isn't that much smaller than the dual feed bowls. Those bowls are used on Carson Brummett's turbo set up and those things make better than 1200 HP. If you what to run a 2 port reg, you will probably have to can that 3/8 little reg and step up to a larger 2 port.
http://www.jegs.com/i/Holley/510/12-704/10002/-1. But I would pull the flame arresters and jet that thing up about 4 sizes first. While you have the bowls off, check to see if they have power valves on the primaries. How does your fuel pump get its power? Is it thru a relay, or a key switch?
That's where I'm going to start. I'll take it out without flame arrestors and see what happens. I already ordered the jet kits and will start playing with that. The power to the pump is through the switch. Is that a voltage drop question? A relay sounds like the right way to go, just didn't think of it. sounds like a busy weekend at the river (but fun!!!!). Thanks for all the help, I'll post the results Monday but if there's any other suggestions, please go for it.
 

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1 boat's never enough
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Discussion Starter · #19 ·
the volume in those bowls really isn't that much smaller than the dual feed bowls. Those bowls are used on Carson Brummett's turbo set up and those things make better than 1200 HP. If you what to run a 2 port reg, you will probably have to can that 3/8 little reg and step up to a larger 2 port.
http://www.jegs.com/i/Holley/510/12-704/10002/-1. But I would pull the flame arresters and jet that thing up about 4 sizes first. While you have the bowls off, check to see if they have power valves on the primaries. How does your fuel pump get its power? Is it thru a relay, or a key switch?
Update; I wasn't able to swap out jets this past weekend since we had flooding issues at the house (but what an amazing weekend in Havasu!!). I brought the carbs home and openned them up. 66 on the primary side, 73 on the secondary side. Primary power vavle is in place but no secondary power valve. Any suggestions? I ran it without the flame arrestors and it didn't make much difference. Still seems to be lean though.
 

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That's where I'm going to start. I'll take it out without flame arrestors and see what happens. I already ordered the jet kits and will start playing with that. The power to the pump is through the switch. Is that a voltage drop question? A relay sounds like the right way to go, just didn't think of it. sounds like a busy weekend at the river (but fun!!!!). Thanks for all the help, I'll post the results Monday but if there's any other suggestions, please go for it.
Mercury makes a power realy kit for a outboard trim circuit, uses the marine bosch relay in a water tight plug connection.trouble free!
 
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