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Hi,I just acquired my first boat and I've always wanted a retro/nostalgia drag boat. Since I'm a muscle car freak and have ended up with a collection of Mopar cars & parts I thought something Mopar powered would be appropriate.I'm interested in any info on the Mantra hull (history) and of course making more speed with my 383/BerkeleyJG. The engine appears to be a fresh rebuild (.060 over) and has a aggressive hydr. cam (533 lift),single plane,Predator carb,dual elec.pumps. The first time out it ran well but didn't pull to the rev limit (6K). Is this due to drag on the hull or limited HP? I haven't got a tach wired in yet but I know 6K rpm in my 69 Roadrunner (383).Also interest to hear from any other Mopar powered Jetboat owners. Thanks
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If I remember well your boat is probably an 18foot bubbledeck model from the seventies{I'll try to go trough my old mags to find some info}.The hull makes no difference on your RPM but the impeller size does.The 383 wouldn't turn 6000 rpm with an A impeller.First you need a good tachometer to take the guesswork out.To achieve 6000 you would have to turn the impeller down to a b size at least may be even a c .Around 5400-5600 rpm would be my preference to find.I remember the 340 engine in my 72 challenger was happiest at around 5000.Boats need a lot of torque to get on plane and your 383's torque lower than the BB chevys and Fords.My friend's 68 Charger was flying w/383 but that car was very light.Check your hull's buttom for hooks at the end part.
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Originally posted by MoJetBoPar:
Hi,I just acquired my first boat and I've always wanted a retro/nostalgia drag boat. Since I'm a muscle car freak and have ended up with a collection of Mopar cars & parts I thought something Mopar powered would be appropriate.I'm interested in any info on the Mantra hull (history) and of course making more speed with my 383/BerkeleyJG. The engine appears to be a fresh rebuild (.060 over) and has a aggressive hydr. cam (533 lift),single plane,Predator carb,dual elec.pumps. The first time out it ran well but didn't pull to the rev limit (6K). Is this due to drag on the hull or limited HP? I haven't got a tach wired in yet but I know 6K rpm in my 69 Roadrunner (383).Also interest to hear from any other Mopar powered Jetboat owners. ThanksThanks for the impeller info. From what I've heard the impeller is tuned to your torque band similar to a torque converter in a car. The 383 does lack torque at low end compared to a 454BBC/460BBF. I do have a 600 Holley and Edelbrock dual plane intake to try out. This could tune the torque band to the impeller I currently have.I'm more interested in top-end speed though so I'll have to save for the new impeller. The Mantra I have is a 1977,18ft(Tahiti style),no bubbledeck. That would have been preferred along w/through transom exh. but it was hard enough to find something Mopar powered. Anybody know where I might find some water injected exh. manifolds? Thanks again.
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Hi MO,If your carburator/manifold won't work out,try to go little bigger carb even so Holley recommends 600's for up to 400cubic inch.Also I would use Edelbrock or weiand single plane manifolds.The BBF[460]we could notice more top end going from 780 to 830 carb.If you more interested in top end try retard your cam by 6 degrees that puts your power band in the upper RPM.As I earlier mentioned we tried different timing set ups and the 6 degrees gave us best top speed.
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I would ditch the Predator in favor of a 800 Holley.
Is this Mantra a tunnel?
[This message has been edited by dropkeel (edited September 30, 2000).]
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I am building a 547 Mopar jet boat. My first idea is you need to try out a vacuum gauge to see if you are pulling vacuum at wide open throttle. I think any big block buzzing along at 5000 RPMs is going to be consuming more the 600CFM, I think 700-800 would work alot better. If you decide to try a Holley, check the vacuum at idle and make sure the power valve is set for the engine vacuum, the number on the power valve should be half of them manifold vacuum is at idle. I have never used a Predator, but they are supposed to work since it is a variable venturi carb. I am using a Jacuzzi jet (eek) with my motor, I will be using a stainless A impeller
if I can get one, if not American Turbine makes parts to change it to use different impellers. We'll see. Pictures of my boat can be seen on my profile. Brian
