Application:Offshore race/pleasure boat,BBC,800-1300HP @6-7000 RPM,engines are well built w/details available.
Problem:As these engines are used for pleasure, 92-93 octane is used. Due to lack of preferred inner cooler design,no inner cooler is used and engines are over engineered in other areas to control detination.However,throttle settings are constantly changed which is beleived to add heat,flex rotors and encourage detination.
 Solution:Find method of installing pressure relief as throttle plates are closing/closed, w/o destroying distribution. Method considered is either going through the burst panel or finding best location in plenum tent, plumbing from tent to bored hole next to distributor to bypass valving to throttle body base plate, using 1.25" tubing.
Suggestions for the Newbee ?

Where are the throttles, upstream or downstream of the supercharger?

Detonation will not occur by changing the throttle quickly or by closing the throttle.

Detonation will occur if you have to much advance, a slightly lean mixture or at wide throttle openings with high compression ratio.   

Pat, Dual 4150's or dual 4500's set upstream, on top of a 1"+/- base plate which sets on top of the supercharger case. The carbs are turned 90* to the blower case for closer spacing. CL between the two carbs is adjusted from front to back, subject to case design and size, to enhance distribution.

While constant throttle plate changes don't create heat, there is concern the billet rotors are flexing. The gears also see back lash. The combination is thought to create some degree of heat soak, effecting A/F ratio change. Further, we are concerned, as heat soak builds, puddling increases and distribution is effected. The dyno A/F target is 12.4. Also,hydraulic,is a factor.

The safest method seems to be, oversized case, under driven 8 to 25 %. The boost curve flattens just after peak torque.

Every roots blower manifold I have seen has a blow of valve(Bellow Seal Valves) or burst panel venting to atmosphere if there is excessive pressure from a backfire. No bypass is required nor even desirable with throttle plates on the blower inlet side.

For a moment I forgot this is a boat application and is probably always at sea level in relatively dense humid air.

The use of magnesium blower, aluminium head and iron block in this case is quite alarming re galvanic corrosion.

If I was sticking with roots blowers I would use aluminium cases and billet rotors.

8.4:1 and 7.5# boost from a roots blower and no intercooler on 93 octane is also a bit scary on carbies and I presume a mechanical ignition system timing device.

I Have never seen a 16:71. If I was going bigger than a 14, I would be inclined to try to source the twin 6s that John Force developed. It is a long blower with a centre bulkhead and takes two sets of 6:71 rotors. That fixes reotor flex problems in the blink of an eye.

Are you running salt water through the engine for cooling.

Are you running an intercooler.

When does the inlet valve close

$20,000 sounds like daylight robbery for a freshen up and casts serious doubts on the suitability of the parts being used.

For off shore I would be more inclined to run turbos and salt water to air intercoolers. I would think more like 7:1 CR and 9# boost if intercooled.

I would be using Iron heads and raw water cooling or all aluminium motor and fresh water cooling via a salt to fresh water heat exchanger.

I would ensure extremely good ventilation of the carbys and inlet air ducts and probably the blower housing. If the blower gets hot, I would consider running a thick insulating plate and heat shields under the carby. Make absolutely sure the fuel in the float chamber never boils and starts to perculate through the bowel vents.

If heat shields and insulation plates are still inadequate you could make a water cooled spacer plate and run dead cold raw water through it. Make absolutely sure it cannot possibly leak water into the inlet air tract and will be made of corrosion resistant materials.

I would not run as cold as possible, quite to the contrary, I would try to tune a raw water cooling system so the discharge water is about 80 deg C at sustained high load.

This can be tuned by scoop position, design and placement and water pump size and drive speed. I normally run the pump to keep engine at 60 to 70 deg C discharge temp and install a pump bypass with a non return valve in the bypass.

At the power levels you are looking at I would be running roller cams with over 0.700 lift and 270 to 290deg duration and something like 400# on the seat.

I would be using something like Carrilo rods and real good steel cranks.

I would be using forged pistons.

I would be using something like Ferrara extreme duty valves.

I would be inclined to use a Vertex or Supermag magneto tuned to continuous duty usage. I can put you in contact with a man to do the Maggys. A marine grade MSD is another possibility.

I have no idea what you mean by density altitude in the manifold. Do you mean boost pressure or do you mean inlet manifold air temperature or something extrapolated from both.

MORE NEWS