6-71 blower dizzy help

[Blackmagic94]

Locked out timing or Mech Advanced.

468 bbc
6-71
-17% under driven

 

[jetboatperformance]

What distributor ? what fuel ?

 

[ltbaney1]

need more info. application, fuel type, distributor type? have you considered a magneto?

 

[Bigbore500r]

You lost me when you called the distributor "dizzy". Good luck!

 

[oldschool]

Yes

 

[ramos45]

I have blowershop 250's on a 460 and 468 with Merc TBIV distributors and V6-14 ignition modules. These modules on a v8 give around 7-8 total advance and all in by 2500rpm. My Idle is at 28 degrees and all in with 35 degrees.

Same size motor with different blower size but i'm pretty sure this would work with yours too if you find yourself going this route.

 

[guest hs]

I have blowershop 250's on a 460 and 468 with Merc TBIV distributors and V6-14 ignition modules. These modules on a v8 give around 7-8 total advance and all in by 2500rpm. My Idle is at 28 degrees and all in with 35 degrees.

Same size motor with different blower size but i'm pretty sure this would work with yours too if you find yourself going this route.

Do you have a hard start condition when the engine is hot with that much initial in it?

 

[ramos45]

Do you have a hard start condition when the engine is hot with that much initial in it?

not at all, engines hot or sitting at cove all day, turn the key and they fire right up. Now sitting for a few days is a different story but that's a fuel topic not timing.

 

[liquid addiction]

I am confused. Are you looking to buy one, need help with one, need recommendations ?

 

[Blackmagic94]

JegS billet mechical advance with 4 curves or locked out
Msd marine 3 digital
Msd coil

9.2;1 compression
91 octane
Dual 650xp Holles
Hydro roller cam unknown

the jet boat is what this is going on.

 

[Blackmagic94]

No im asking if I keep it as a Mech advance or lock it out at 30-32 degs


The msd can also pulley 10 or 20 deg for locked timing start retard as well

 

[oldschool]

Not a blown engine, but my TT engine is locked at 30 degrees. That is per Alexi @ Boostpower.

 

[Rayson1971]

I had msd on my 572 with 8-71. MOTOR guy told me lock it out. Ran great at 30- 32 degrees timing. No more to keep on pump gas.

 

[Teague_JR]

You're going to run a roots blower with no intercooler, iron heads, and 9.2:1 compression on california pump fuel? I dont think there is a safe setting I can recommend to be honest. Keep it to 4 PSI boost and 30 degrees. Just lock it out at that point, or run the shortest/fastest curve you can, whatever is easier.

JT

 

[Blackmagic94]

You're going to run a roots blower with no intercooler, iron heads, and 9.2:1 compression on california pump fuel? I dont think there is a safe setting I can recommend to be honest. Keep it to 4 PSI boost and 30 degrees. Just lock it out at that point, or run the shortest/fastest curve you can, whatever is easier.

JT

Who said California pump gas.

The math says 2.75 psi of boost but who knows. Worse case I will swap the pulleys and run some leaded fuel if need be at 6-8 psi especially if that low of boost doesn’t hit my goal.

 

[Blackmagic94]

You're going to run a roots blower with no intercooler, iron heads, and 9.2:1 compression on california pump fuel? I dont think there is a safe setting I can recommend to be honest. Keep it to 4 PSI boost and 30 degrees. Just lock it out at that point, or run the shortest/fastest curve you can, whatever is easier.

JT

Curve options if not locked out.

 

[guest hs]

You're going to run a roots blower with no intercooler, iron heads, and 9.2:1 compression on california pump fuel? I dont think there is a safe setting I can recommend to be honest. Keep it to 4 PSI boost and 30 degrees. Just lock it out at that point, or run the shortest/fastest curve you can, whatever is easier.

JT

Definitely needs an intercooler

 

[scottchbrite]

Lock that bitch down, get a MSD boost retard, put it on E85-no intercooler needed, and send it.

Pussies can’t be heroes......

 

[BUSTI]

Leave the advance in the distributor. Use the black bushing (largest in size least amount of advance) and the lightest springs. you want full advance as soon as you can with teh roots blower. Set the total timing at 32* - 34* total timing. Locked out Distributors IMO put unnecessary wear on the starter.

 

[BUSTI]

Definitely needs an intercooler

I agree. spend a few bucks on the intercooler and put more boost to it. 9.4:1 is a little high for my liking with no intercooler.

 

[Blackmagic94]

9.25 not 9.4

 

[Blackmagic94]

Leave the advance in the distributor. Use the black bushing (largest in size least amount of advance) and the lightest springs. you want full advance as soon as you can with teh roots blower. Set the total timing at 32* - 34* total timing. Locked out Distributors IMO put unnecessary wear on the starter.

Black p
Bushing is in it already. Would it be safer to start at 30 total or is that gonna build more EGTs

 

[Teague_JR]

View attachment 839854


Curve options if not locked out.

Black bushing and light blue springs.

I mean "california" as in 91 with 10% ethanol, not good 93 or non ethanol stuff you can get elsewhere...

I would SERIOUSLY recommend an intercooler, regardless of fuel. plumbing off the jet pump is super easy, unlimited cold water pressure.

JT

 

[Blackmagic94]

11.1 effective compression. Still below the threshold of pump and that is at 3.0 not 2.75 psi

 

[BUSTI]

Black p
Bushing is in it already. Would it be safer to start at 30 total or is that gonna build more EGTs

At that high of a compression ratio 30* of timing is safer for sure. I've never checked the EGT's just read plugs for aluminum deposits from detonation

 

[Blackmagic94]

I’ve read that to far retarded makes it run hotter.

 

[ramos45]

I’ve read that to far retarded makes it run hotter.

Yep, unburned fuel leaving through exhaust valve. Sounds counterintuitive but it is what it is

 

[vstdispatch]

View attachment 839843 JegS billet mechical advance with 4 curves or locked out
Msd marine 3 digital
Msd coil


Lock it out

9.2;1 compression
91 octane
Dual 650xp Holles
Hydro roller cam unknown

the jet boat is what this is going on.

 

[Teague_JR]

I’ve read that to far retarded makes it run hotter.

Correct. You'll see horsepower go down and EGTs go up.

 

[Blackmagic94]

Any suggestions on jets to start with. I was gonna do 10.5 power valves

 

[HALLETT BOY]

Calling a distributor a dizzy is like using the word prolly instead of probably ...

 

[motormonkey]

Also drop the spark plug heat range and mix some 110 or a gas. Black bushing and light springs. Intercooler a plus or make a boost bottle for it .

 

[Blackmagic94]

Boost bottle?

 

[Instigator]

Boost bottle?

No!
Iron heads, definitely an intercooler. Otherwise you will never get to utilize the blower that you spent all that money on. Aluminum heads and intercooler would be best but you can always run aluminum heads without an intercooler on a stern drive which I have done but on a jet boat I wouldn't run iron heads under a blower without an intercooler for sure. Cooler will be cheaper than heads at this point.
An lock the timing either way. 30 degrees max without intercooler and maybe be able to bump it to 34 or 36 degrees with intercooler and better fuel even if it is a av gas blended with 91.
Just my 2 cents.
Keep egts under 1350 if you can and you'll be fine.

 

[Rayson1971]

So you got 34 different answers and opinions. Call a reputable motor builder and ask the people that do it all day everyday. Teague jr. comes to mind. That'll be your best answer.

 

[braindead]

So you got 34 different answers and opinions. Call a reputable motor builder and ask the people that do it all day everyday. Teague jr. comes to mind. That'll be your best answer.

Then what's the point of this website?

 

[Blackmagic94]

I’ve received a lot of great info and feedback from here.

 

[bonesfab]

Do you want power or do you want it to live?

 

[outboardrick]

If it were me, from what you have said of the motor, I'd lock it out and set it at 30 degrees. Just make sure you have it at 30, don't trust a dial back timing light. Ever.

 

[oldschool]

If that MSD has start retarding, lock out at 30 and retard 10 degrees.

 

[Blackmagic94]

Do you want power or do you want it to live?

2.75 psi of boost answers that question which way Lol

 

[motormonkey]

The amount of boost you say your going to run, your fine. Bad gas will get you first. I have run blowers for years without a chiller at 5 pounds to 8 pounds boost and open cooling. Alot of people have. It's when gas or too much timing, a bad tune, standing on it for 3 miles bad things will happen.Run cooler plugs.
No doubt a chiller is the way to go, but they are not without problems either with a open cooling system. Run safe timing and good gas.
It's a jet boat. Have fun with it.

 

[Bigbore500r]

My 2 cents - worth 2 cents USD

Always start total timing conservative (low) and work up. To retarded, and it will raise EGT and kill power, but too much and you'll just murder the pistons in quick order. 28-30 is probably safe as a starting point

Jetting - Start rich and work your way back, reading plugs. (wide band 02 is best if you can somehow set that up for tuning purposes, but probably unlikely your gonna do that...)

Make sure you verify actual boost once it's running. Head and Cam selection affects boost, as well as RPM, you can end up with more (or less....) than you thought depending on your cam timing and your head flow. Dont just assume "its only 2.75 lbs" because a chart told you it is.

Roots blowers are great space heaters, combined with no intercooler and iron heads it's gonna be more show than go, but should still be fun,. Keep it mellow if you want to live. You mentioned "11.1 effective CR" from the chart, but remember it isn't so much about static compression + blower displacement, as it is about dynamic compression and cylinder pressure which are directly effected by cam selection. That chart is a very vague guideline, that does not take into account IAT, coolant temps, blower discharge temps, etc. Treat that as a ballpark guide. Start safe and work your way up

 

[Blackmagic94]

I am very well versed in tuning turbo mustangs. But a carb blower is my first rodeo.

 

[Blackmagic94]

I was going to buy new headers and modify them to fit my wideband and have them dump the water near the end of tail pipes and eliminate the dumb header nozzles at the beginning of the primaries

 

[Blackmagic94]

Boost gauge
Electro fuel pressure gauge
Ngk plugs 1-2 steps colder at 0.35 gap from what I was running
Start at 28 total and adjust from there


Still need help on base jetting and such

 

[Nordie]

Boost gauge
Electro fuel pressure gauge
Ngk plugs 1-2 steps colder at 0.35 gap from what I was running
Start at 28 total and adjust from there


Still need help on base jetting and such

If you're that determined to run a low boost blower and looking for carb setups this is what I would do. I would call fuel curve west, and tell then your exact setup and what you're trying to achieve. The more you can tell them the better off you're going to be. You really should know what cam you have in that motor, pistons, ring gap, everything. If I was in your shoes (former boat owner/jet boater) I would sideline the blower and slowly collect parts, and when it's time to build the proper setup/tune you'll be much happier.

 

[Tank]

Reading through this whole thread one thing seems to be consistent. Get a cooler. They look bad ass anyway

 

[oldschool]

If your familiar with turbos why not go that route?

 

[Bigbore500r]

If your familiar with turbos why not go that route?

Cause slapping a roots on top of an existing bote motor is easy