Motor Help

[USMC1812]

I just bought a jetboat with a Chevy Mark V 502. From what the guy has told me, the heads have been ported and polished, springs upgraded to 180 lb, and a 670 lift cam. It is running a 850 Holley and from what I can tell a stock aluminum manifold. First, he thought that with this it was running between 650 and 700 H.P., what do you guys think? Second, I would like dress up the motor a little starting with the carb and manifold. This in mind I was thinking of tunnel rams, trying to add some height to the motor, however , the guys in the jet section said that these were best for higher revving engines. My motor as is redlines according to the tac at about 5600. One guy suggested an Edelbrock air gap, which I know nothing about. What do you guys think? What I am going for here is better looks and at the same time better performance. If was your boat and you had about $2,000.00 to play with what would you do?
Thanks,
Doug

[USMC1812]

What would be a good NOS system for this boat and where should i get it?

[Hotcrusader76]

NOS is nice!
Fogger kit is the best engineered from what I can gather...stay tuned for HotCrusaders boat... Bottle fed? Hmmmm maybe....
Tunnel Rams are nice...I rev to 5600 on occasion and run a 468 with dual 660's. No problems starting or running...all day long..... Guzzles gas like no tomorrow....But crusies at 3-3500 RPM with no problems. That's normal for jets anyhow, I believe.

[Bahner tunnel]

It is my opinion that a tunnel ram with a nice set of double pumpers is the best dollar per h.p. increase (besides nitrous of course.)A friend of mine has a ripe 496 BBC in a 19" Ultra jet which ran 82 m.p.h. on a handheld g.p.s. with a Team "G" and a single Holley 850 d.p. He then borrowed my Holley Pro Dominator tunnel ram with a pair of Holley 660's and ran 87.8 m.p.h and gained 2000 rpm with no other modifications to the motor besides the induction package . An almost 6 m.p.h. increase for around $500-$700 if the items were picked up used . Besides the increase in top end speed , the mid-range was acceleration noticably stronger .

[Bahner tunnel]

Sorry , I got a little excited with the zero's . I wish that a pair of carb's could help you gain "2000 r.p.m " It was actually 200 r.p.m. His motor turned 6100 r.p.m at full throttle . Also I have a .680" lift solid roller cam and was told by Greg Shoemacher at G.S. Marine that the "rule of thumb" was 220 lbs. seat pressure (BBC). This is supposed to be a safe pressure to around 6500 rpm. with that lift . Good luck with your new toy .

[USMC1812]

Bahner tunnel:
It is my opinion that a tunnel ram with a nice set of double pumpers is the best dollar per h.p. increase (besides nitrous of course.)A friend of mine has a ripe 496 BBC in a 19" Ultra jet which ran 82 m.p.h. on a handheld g.p.s. with a Team "G" and a single Holley 850 d.p. He then borrowed my Holley Pro Dominator tunnel ram with a pair of Holley 660's and ran 87.8 m.p.h and gained 2000 rpm with no other modifications to the motor besides the induction package . An almost 6 m.p.h. increase for around $500-$700 if the items were picked up used . Besides the increase in top end speed , the mid-range was acceleration noticably stronger .Great, now the next question, will will my motor handle 200 more RPMs? If not, what do I need to do. Second, how hard is dialing in the carbs and how often do you have to mess with them? what impeller was he running?

[Bahner tunnel]

It is my understanding that all 502's are 4-bolt mains and have 7/16" rod bolts along with a steel crank so I would not think that the extra 200 rpm would be a problem . The only thing I'm not sure of is if they come with forged pistons but I beleive they do . As for the carbs , we ended up with the best response/speed with size 82 jets in each carb with 7 psi of fuel . (note: 660's only have one set of jets in thier stock form with non-jettable secondary metering plates). Your motor is almost identical in size and cam specs. so this jetting would probably be a good starting point if you went with 660's. (This depends on your elevation of course , we are at sea level with this combo) As for his pump , it is a Dominator with a "B" cut impellor, droop , diverter ,ride plate ect. From the sounds of your motor h.p. and rpm at full throttle , I would say that you have a "AB" or "B" cut as well . As for staying in tune , I don't feel this is a major concern with a quality linkage set-up and water free gas.

[USMC1812]

[QUOTE]Originally posted by Bahner tunnel:
It is my understanding that all 502's are 4-bolt mains and have 7/16" rod bolts along with a steel crank so I would not think that the extra 200 rpm would be a problem . The only thing I'm not sure of is if they come with forged pistons but I beleive they do . As for the carbs , we ended up with the best response/speed with size 82 jets in each carb with 7 psi of fuel . (note: 660's only have one set of jets in thier stock form with non-jettable secondary metering plates). Your motor is almost identical in size and cam specs. so this jetting would probably be a good starting point if you went with 660's. (This depends on your elevation of course , we are at sea level with this combo) As for his pump , it is a Dominator with a "B" cut impellor, droop , diverter ,ride plate ect. From the sounds of your motor h.p. and rpm at full throttle , I would say that you have a "AB" or "B" cut as well . As for staying in tune , I don't feel this is a major concern with a quality linkage set-up and water free gas.[/QUO
You hit the nail on the head it is an AB. Is this a good impeller or is there somethimg that would woork better for me. The guy I got the boat from used to drag it. The motor is strong. I would sure like to put a tunnel ram on it but am a little weary of the dual- carb setup as i do not know that much about them. Ideally what I would like to do is take the carb that i have now and just bolt it to a new manifold. But, again if there is something better than I would like to know. I am trying to avoid looking back and wishing that I had done something different! What would you do?
Thanks for your help!
Doug

[USMC1812]

What about NOS, what system and what are the drawbacks?

[565edge]

If you want something simple and would be a lot easier to tune i would buy a team g,or victor jr,4500 top(dominator flange)buy a single dominator 1050,then buy a nos cheater kit,make sure you have a good fuel system,and a good ignition,for a cam i would call john partridge at bullet cams,they know there shit,is your motor a hydraulic roller cam 502?dont bother with 660's,single dominator and a plate system easy to tune and good bottom end,I have a dart tunnel ram with dual carb shop 1150's on my motor but it has 15:1 comp and its a 565,if you going to buy a tunnel ram go with a victor ram or the dart,and put either dual 600's to no bigger than 750's on it,good luck.

[Bahner tunnel]

I beleive the "AB" is a good "all around" choice although getting it cut to "B" specs. would put your motor slightly up in the rpms at full throttle where it could possibly be making more power depending on your cam . Do you know your cam's duration at .050" valve lift ? This would determine where it is going to make it's peak power and if the extra rpm would be helpful in your situation or not . For example if your motor makes peak h.p. at 5600 rpm , then turning 6000rpm would be a waste of time and fuel economy .( on average each "cut" is an increase in 400 rpm. From A to AB to B ect...) My friends cam is .640" lift with 262 degrees at.050" lift . This combo makes his 496 ci peak at around 6000 rpm , which with his "B" impellor allowed his motor to turn . As for the tunnel ram question , Maybe the best bet would be to run you single 850 with a new "single plane " intake such as a Team G or a Victor Jr. ect. This will give you a performance increase over the dual plane that you currently have with out the possible tuning hassles of dual carbs . This will also get better mileage when compared to the duals . My friend ran 80 jets in all four corners with 30cc pumps in both front and rear when he ran the single 850 with the Team "G"(a good starting point)This combo gave neck snaping throttle response with zero hesitation . This was the first jet that I rode in that made me a beleiver . I used to think outboards were the hot set-up . I have talked to the Edelbrock Tech guys about which intakes to run on my new 496 and they mentioned that the Performer RPM stop making power at 5500 rpm with a motor of that displacement . Even though they claim a power range from 1500 to 6500 rpm . This dosen't seem like the hot set up for a boat motor that lives at 3000+ rpm even at cruise speeds . As for the nitrous question , it is pretty trick to set up properly and demands your total attention . If carb jetting is a little scary , I would avoid the "fast gas" until you are more comfortable with the entire tune of your motor such as jetting,timing,plug heat range,fuel system ect. You are only a bad batch of gas away from total meltdown . You would also need a good ignition system as well as a stout fuel delivery to match. I have heard good and bad with nitrous in jet boats . Besides all of the scary stories , If your motor can take it , it will be faster. If everything was dailed in , you could run a 150 h.p. set up with out a problem . Anything higher would require at the least some bitchen rod bolts . The main reason I feel that motors don't live with nitrous is they are under built for the "ultimate" power they will see on nitrous . For instance , you are making around 650 h.p. and go with a fairly mild 150 h.p. nitrous set-up,while "on the bottle" your internal components are seeing the stress of approx. 800 h.p. Not to mention your jet drive as well. If they are not up to par for the increased strain they will be subjected to they will eventually fail . On the other hand if your bottom end is truely bullet proof , then nitrous is hard to beat . Does this help .