articfriends

Kanookstar,i understand what your saying --but,crockett's flowed my injectors (they are the mini? ones used in 2000 502's) I guess there were several different ones that were used on efi merc's (from what crockett's say's) and he said mine flowed 46 or 48 lb's per hour,the p/w was at about 90 % and my base pressure regulator keeps presure at 52 -55 psi under vacum,my variable rate regulator (the second one) raises pressure to about 70-75 psi at 9 psi boost,if they will only support 537 hp then why were we able to get a a/f ratio (meausured w exhaust probes on his dyno) of 11.5-11.8 under boost?I know what your math say's but now i'm real confused,i put 4 deg more timing and went from 5-6 psi boost to 9-10 psi boost after making 637 hp on dyno at 5-6 psi and picked up 7-9 mph (60 hrs ago of run time),shouldn't the motor have melted down by now? My plugs are still a little sooty and black also,thanks for your input,after hearing from tomcat i'm seriously thinking about a carb and new intercooler,maybe there's another 5 mph in my set-up!!Thanks again,Smitty

Kanookstr

You have to realize that on a dyno you are only pulling those high RPM numbers for a couple seconds. The only way to be sure of your plugs, is to do a 10+ second WOT run and turn off the key. (do not come down to an idle. Just turn off the key and leave the throttle at WOT) then check your plugs after the boat comes to a stop. I think you will be surprized how white they are. I wish you luck, I just wanted you to be aware of a possible melt down, or broken pistons.

articfriends

kanookstr,thanks,i'm seriously thinking a carb and regular manifold are in my future,Smitty

Kanookstr

EFI is real nice when set up right.

I run the 502 EFI system on my procharged engine, But with 50 lb injectors 2 bar MAP sensor AFR cnc aluminum Heads, 731 crane cam, and a proven Ecu recal from a AZSM. I run a constant 50 psi fuel pressure. But with an Aeromotive 1000 fuel pump, High flow Fram fuel/water filter. I also run a 5/8" line suppling the pump, then 1/2" lines going to the fuel rail, I got rid of the Merc 1/4" line that fed the rail, and opened it up for 1/2". I then come out the front of the rail with 3/8" return to the Aeromitive Reg, then to the tank.

jspeeddemon

I have to agree with MCollins that your cam is kinda small for the peak power to be up in the high 5000's RPM range, as well as that exhaust flow on those heads is very weak. On a blown application you could get by with a weak intake number, becasue the blower will overcome that poor flow, but you gotta have a good exhaust and 202 at .600 lift is downright piss poor. My heads flow high 260's at .600 lift. That poor exhaust flow is like building the Hoover dam inside your airflow path. Tomcat can tell you better than I about airflow theory and relationships, I just know the application numbers from experience. Hell they did an article about a 454 Mag in Popular Hot Rodding they put a Vortech supercharger on and I believe with 8 lbs of boost and made 750 hp without an intercooler. It's all about keeping the balance in the motor, if one part doesn't match you'll have a turd on your hands. Your I/E ratio is way off because of that exhaust flow. You should be at @ 75-80%, you are at less than 65%. I know of a drag boat that ran in the 10 second class that ran virtually same time with 250 or 500 Nitrous jets in the motor, because of the same issue, having poor exhaust flow and great intake flow numbers. The motor could not expell but so much exhaust, so the extra nitrous had little to no effect. He was using stock rectangular chevy heads that had been worked extensively, both intake and exhaust. However, without raising the exhaust port, like aftermarket heads, you can't get the flow numbers in the upper 200's. Guess what, your merlin heads have the exhaust ports in the stock location. I hope you understand this is all in the effort of constructiveness trying to get your hp where you want it, not trying to badmouth your motor. It would be the same effect as building a killer motor and then using the stock Mercruiser manifolds, just in your case the restriction is the head itself.

jspeeddemon

I have to agree with MCollins that your cam is kinda small for the peak power to be up in the high 5000's RPM range, as well as that exhaust flow on those heads is very weak. On a blown application you could get by with a weak intake number, because the blower will overcome that poor flow, but you gotta have a good exhaust and 202 at .600 lift is downright piss poor. My heads flow high 260's at .600 lift. That poor exhaust flow is like building the Hoover dam inside your airflow path. Tomcat can tell you better than I about airflow theory and relationships, I just know the application numbers from experience. Hell they did an article about a 454 Mag in Popular Hot Rodding they put a Vortech supercharger on and I believe with 8 lbs of boost and made 750 hp without an intercooler. It's all about keeping the balance in the motor, if one part doesn't match you'll have a turd on your hands. Your I/E ratio is way off because of that exhaust flow. You should be at @ 75-80%, you are at less than 65%. I know of a drag boat that ran in the 10 second class that ran virtually same time with 250 or 500 Nitrous jets in the motor, because of the same issue, having poor exhaust flow and great intake flow numbers. The motor could not expell but so much exhaust, so the extra nitrous had little to no effect. He was using stock rectangular chevy heads that had been worked extensively, both intake and exhaust. However, without raising the exhaust port, like aftermarket heads, you can't get the flow numbers in the upper 200's. Guess what, your merlin heads have the exhaust ports in the stock location. I hope you understand this is all in the effort of constructiveness trying to get your hp where you want it, not trying to badmouth your motor. It would be the same effect as building a killer motor and then using the stock Mercruiser manifolds, just in your case the restriction is the head itself.[/QUOTE]

jspeeddemon

I have to agree with MCollins that your cam is kinda small for the peak power to be up in the high 5000's RPM range, as well as that exhaust flow on those heads is very weak. On a blown application you could get by with a weak intake number, because the blower will overcome that poor flow, but you gotta have a good exhaust and 202 at .600 lift is downright piss poor. My heads flow high 260's at .600 lift. That poor exhaust flow is like building the Hoover dam inside your airflow path. Tomcat can tell you better than I about airflow theory and relationships, I just know the application numbers from experience. Hell they did an article about a 454 Mag in Popular Hot Rodding they put a Vortech supercharger on and I believe with 8 lbs of boost and made 750 hp without an intercooler. It's all about keeping the balance in the motor, if one part doesn't match you'll have a turd on your hands. Your I/E ratio is way off because of that exhaust flow. You should be at @ 75-80%, you are at less than 65%. I know of a drag boat that ran in the 10 second class that ran virtually same time with 250 or 500 Nitrous jets in the motor, because of the same issue, having poor exhaust flow and great intake flow numbers. The motor could not expell but so much exhaust, so the extra nitrous had little to no effect. He was using stock rectangular chevy heads that had been worked extensively, both intake and exhaust. However, without raising the exhaust port, like aftermarket heads, you can't get the flow numbers in the upper 200's. Guess what, your merlin heads have the exhaust ports in the stock location. I hope you understand this is all in the effort of constructiveness trying to get your hp where you want it, not trying to badmouth your motor. It would be the same effect as building a killer motor and then using the stock Mercruiser manifolds, just in your case the restriction is the head itself.

articfriends

thanks for your input jspeedemon,When i freshen the engine this winter i'm going to take a hard look at what heads i run next year,i went with the cam on tyler crocketts reccommendation(the fact the motor has to work with the efi and have a strong enough signal for the map sensor). I am running -10 an hose from tank to BIG essex E.F.I. fuel pump (procharger JUNK would not make much pressure above 50 psi with injectors opened up). I am running twin -8 hoses to efi rail also,and a 2-bar map sensor too. The head flow #'s i posted were from what i deciphered off merlin products head's site,they do have the exhaust ports d-shaped and raised .400 from stock. Kanookstar,were the 50 lb injectors you got from azsm drop in's for your stock ones,and what year was your original efi system? azsm told me to send them my whole intake and fuel rail 2 years ago when i talked to them about changing injectors,IN case it needed to be machined (i didn't feel real confident that they couldn't tell me from the year and #'s off my stock injectors what mine were and if theirs would drop in place). Doe's anyone out there know what years or #'s injectors flowed what? Crockett is the efi expert west of the mississipi and he say's these smaller mini or micro injectors merc used in the newer e.f.i.'s flowed more than early ones,he flowed mine and put hi flow screens in them but never provided actual documentation as to what they really flowed (he told me at one point 48 lbs per hour and later 42 lb's per hr? You guys are great,thanks for all your input,Smitty

mcollinstn

You're running a centrif supercharger. It builds boost with rpm.

You ran a tall prop which is good, but when it brought your revs down, you lost boost. This is normal.

You gotta PULLEY it to get your boost where you want it. If you want, say, 9 pounds of boost, you gotta choose your RPM (I say 5200 with that cam, and will say it again and again), then play with props and pulleys. If you consider yourself to have "restraint" then you can put a "too big" crank pulley on and then just make sure you don't throttle above your "desired boost level". Once you find the prop that gives you 5200rpm at 9 pounds (I'm still using that as an arbitrary number, you can choose your desired boost number yourself), then if you got throttle left, you need a smaller crank pulley. Takes playing with to get there.

I still say you are LOSING power with revs over 5200, if you compare equivalent boost numbers.

tomcat

502Procharger: thanks for the thumbs up; tell Dave to send me some pictures!

mcollinstn: You're a fountain of knowledge as usual, but somehow "restraint" and "desired boost level" don't seem compatible.