Problem is? Engine/drive x/gear
05-02-2002, 08:56 PM
#21
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Turbojack - Are you getting into the secondaries at 4200? Have you marked the position of the throttle stick where the secondaries begin to open? What are your pressure readings in the box and the manifold at different RPM?
I'm assuming that you have no power valve on the secondary side so need to be 6 jet sizes up from primary to begin with. That would be 74s. Because the carb doesn't understand boost you have to go richer than that to get enough fuel when at full boost. You have 83s. That's a lot richer. Unfortunately that means as the secondaries begin to open at medium boost, they are way too rich. If you jet it down and start to see more RPM above 4200, you will prove this theory, but watch out at full boost!
Good luck!
I'm assuming that you have no power valve on the secondary side so need to be 6 jet sizes up from primary to begin with. That would be 74s. Because the carb doesn't understand boost you have to go richer than that to get enough fuel when at full boost. You have 83s. That's a lot richer. Unfortunately that means as the secondaries begin to open at medium boost, they are way too rich. If you jet it down and start to see more RPM above 4200, you will prove this theory, but watch out at full boost!
Good luck!
05-02-2002, 09:20 PM
#22
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Tomcat
"So the face velocity is almost 1500 fpm"
Can you put this is laymans terms?? A bigger number is better? From what I am reading I think that if the procharger
Last weekend I did not see if I could still get the 4200 at part throttle. I had marked the throttle as to where the secondarys start to open. I will check & see what rpm this is equal to this weekend.
Power valve only in primarys, these carbs do not have the option for them in the secondarys. Thinking while typing, power valves in the secondars might be good. I will try to get numbers this weekend at different rpm, boost pressure in box, & pressure in manifold. This way we could see where they would open based on the difference & what power valve would be used. I would say the power valve is good for max 6 steps. I have read the last couple of weeks, anywhere from 4-10 sizes. I have not checked the size of the hole in the carb block but it is small compared to the one in the 850 cfm carb I have. I also am needing to see exactly where(rpm) the power valve opens up. With 6.5 I would need a difference less than 3.25 psi. Procharge in last call last week said I needed 80's in secondarys & 4.5 power valve. Jspeedemon I think told me last year that he had a 2PSI difference between box & manifold. With a 4.5 PV almost would not open in that case.
In trying all these different jets I learned that a 2 step difference, 72 to 74 in primarys I could not get enought power to plane out boat.
Only check of difference I made last weekend was at 2200 rpms had 3 psi box, 5" vacuum in manifold & at 1000 rms in gear 10" vacuum & 1+ psi in box.
"So the face velocity is almost 1500 fpm"
Can you put this is laymans terms?? A bigger number is better? From what I am reading I think that if the procharger
Last weekend I did not see if I could still get the 4200 at part throttle. I had marked the throttle as to where the secondarys start to open. I will check & see what rpm this is equal to this weekend.
Power valve only in primarys, these carbs do not have the option for them in the secondarys. Thinking while typing, power valves in the secondars might be good. I will try to get numbers this weekend at different rpm, boost pressure in box, & pressure in manifold. This way we could see where they would open based on the difference & what power valve would be used. I would say the power valve is good for max 6 steps. I have read the last couple of weeks, anywhere from 4-10 sizes. I have not checked the size of the hole in the carb block but it is small compared to the one in the 850 cfm carb I have. I also am needing to see exactly where(rpm) the power valve opens up. With 6.5 I would need a difference less than 3.25 psi. Procharge in last call last week said I needed 80's in secondarys & 4.5 power valve. Jspeedemon I think told me last year that he had a 2PSI difference between box & manifold. With a 4.5 PV almost would not open in that case.
In trying all these different jets I learned that a 2 step difference, 72 to 74 in primarys I could not get enought power to plane out boat.
Only check of difference I made last weekend was at 2200 rpms had 3 psi box, 5" vacuum in manifold & at 1000 rms in gear 10" vacuum & 1+ psi in box.
Last edited by Turbojack; 05-02-2002 at 09:24 PM.
05-03-2002, 04:20 PM
#23
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Sorry Turbojack, I wasn't clear. Air velocity of 1500 feet per minute (~17 mph) through the fins of the core will surely be turbulent within the core, a good thing for heat transfer. I don't know what the best air velocity is for these cores, enough to get a good scrubbing of air against the fins, but too much and the resistance to flow becomes a problem. If you look at Spearco's data you can see that as you put more air through a given size of core, you do remove more units of heat, but the percentage of heat removed, vs. total heat in the air, goes down. Since we have to work with what the manufacturers sell us this is pretty much besides the point.
When I said 74 jets I meant in the secondary side. Those jets would flow as much as the 68 jets plus power valve holes on the primary side for "square jetting". You need more than that to add enough fuel for the higher density air under boost, but 83 jets may be too big, hence Procharger telling you 80 jets. I'm thinking that when you note the position of the throttle you will find the overly rich secondaries are causing you to bog down at 4200 RPM. Nothing wrong with starting on the safe side. Do you have a pyrometer?
As for the power valves, you said that switching from an 8.5 to a 6.5 solved the rich condition between 2100-2500. You delayed the opening of the power valve holes. In your last post you said that you saw 3 psi (~6" Hg) in the box and 5" Hg vacuum for a total of 11 " Hg at 2200 RPM. You would think that would be enough differential pressure across an 8.5" power valve to hold it shut, but switching to the 6.5" power valve solved the rich condition so I'm not going to argue.
Procharger's recommendation to go with a 4.5" valve will delay the power valve opening even more, I'm assuming that means until the throttles are opened a bit more. This would also reduce the richness the engine is dealing with just before the secondaries begin to open. Sounds like a fine balancing act is required to get through this transition period and still have enough jet in the secondaries to support full boost density. Remember when we beat that topic to death?
It sounds like you're headed in the right direction. Good luck, and be careful!
Oh yeah, you have 1 psi at idle?! How fast are you spinning that compressor? What are you expecting as full boost?
When I said 74 jets I meant in the secondary side. Those jets would flow as much as the 68 jets plus power valve holes on the primary side for "square jetting". You need more than that to add enough fuel for the higher density air under boost, but 83 jets may be too big, hence Procharger telling you 80 jets. I'm thinking that when you note the position of the throttle you will find the overly rich secondaries are causing you to bog down at 4200 RPM. Nothing wrong with starting on the safe side. Do you have a pyrometer?
As for the power valves, you said that switching from an 8.5 to a 6.5 solved the rich condition between 2100-2500. You delayed the opening of the power valve holes. In your last post you said that you saw 3 psi (~6" Hg) in the box and 5" Hg vacuum for a total of 11 " Hg at 2200 RPM. You would think that would be enough differential pressure across an 8.5" power valve to hold it shut, but switching to the 6.5" power valve solved the rich condition so I'm not going to argue.
Procharger's recommendation to go with a 4.5" valve will delay the power valve opening even more, I'm assuming that means until the throttles are opened a bit more. This would also reduce the richness the engine is dealing with just before the secondaries begin to open. Sounds like a fine balancing act is required to get through this transition period and still have enough jet in the secondaries to support full boost density. Remember when we beat that topic to death?
It sounds like you're headed in the right direction. Good luck, and be careful!
Oh yeah, you have 1 psi at idle?! How fast are you spinning that compressor? What are you expecting as full boost?
05-03-2002, 07:00 PM
#24
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crank pulley is 8.5" blower pulley is now 5" was 5.5" gear change is 4.41-1 so at 800 rpms impeller is turning 5998 rpms & at 5600 where is hope get to some day is 41,983
I stoped today & picked up new coil, dist. cap & rotor. Going to try this stuff first. If that does not do it I am going to see what prop change will do. It might work with smaller prop & will be able to get RPM's up to do plug reading at high RPM If rich I wll lean down more.
I thing I understand the air velocity thing now.
I am out of here to head to lake tonight.
I stoped today & picked up new coil, dist. cap & rotor. Going to try this stuff first. If that does not do it I am going to see what prop change will do. It might work with smaller prop & will be able to get RPM's up to do plug reading at high RPM If rich I wll lean down more.
I thing I understand the air velocity thing now.
I am out of here to head to lake tonight.
05-05-2002, 08:32 PM
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And the problem was MSD digital box!! Replaced with old MSD 6 analog box & turned 104 @ 5600rpm's, 6 lbs of boost. Speed was still climbing but I chickened out. The MSD box I used did not have a rev control & was worried if I blew a drive, I did not want to take motor along with it. Just was glad to find problem. Next time to lake will be Memorial weekend & I will test to see what max is. & try different props.
TC I made list of Rpms, box & manifold pressures but do not know what I did with it.
RPM right where secondarys open was 3800, I think it was 0 psi in manifold & 6 in box at that RPM. When I find paper I will list.
TC I made list of Rpms, box & manifold pressures but do not know what I did with it.
RPM right where secondarys open was 3800, I think it was 0 psi in manifold & 6 in box at that RPM. When I find paper I will list.
05-05-2002, 09:11 PM
#26
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That's great news! With 6 psi (12" Hg) across power valve it is shut right? So if you cruise just below this throttle setting your plug readings tested OK with the 68 jets. How does the engine respond when you open the secondaries?
05-05-2002, 10:54 PM
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Plugs look just a little lean at this point. Knock sensor is not showing any knock. Probem I see is in trying to come on plane with not much boost & throttle in secondarys. Motor wants to stumble just a little bit. Power valve is open, secondarys open, & my guess motor has too much fuel. I did not do a high speed plug reading after I made my one high rpm pass.
When throttle is open past primarys after cruise it hesitates for split second then it starts climbing fast.
Forgot to add humidity was at about 80-90%, temp was about 85 when we were doing the tests.
When throttle is open past primarys after cruise it hesitates for split second then it starts climbing fast.
Forgot to add humidity was at about 80-90%, temp was about 85 when we were doing the tests.
Last edited by Turbojack; 05-05-2002 at 10:59 PM.
05-06-2002, 04:22 PM
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I am sure glad that you have gotten the setup close as you have to this point. Sounds like that thing is going to deliver what you wanted for power and speed. What prop did you have on it to get that speed and rpm?
