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Fixed timing on a blower motor?

Shlbyntro

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So i will honestly say I've seen it both ways but am just plain not a fan of fixed timing on any motor. For blower applications, I like setting the engine up with 14° base timing and a quick advance up to 34° at 2250rpm

What say the brain trust as to pros and cons of both?
 

monkeyswrench

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I'm going to ask a few questions before I jump in here...what motor, what blower, what fuel?

The big question...Set to kill, or run around all weekend on pump?
 

Shlbyntro

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Good point, application means everything I suppose....

For sake of argument, let's call it a "family performance boat" with regular Havasu type usage: 50-70% wide open running with 30-50% cove/channel trawling.

Let's call it a basic BBC blower build as well. 502 with forged internals, 9.75:1 compression. Whipple up top making 5lbs and a big ass single quad as the bow on top
 

monkeyswrench

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I'm not a boat engine guy, so let me state that first:rolleyes: For something like this, I'd equate it to a "streetable" setup. I've always felt locking the timing gives you consistency, and ease of setup, but at a price. Obviously, all you'll get is a compromise, in terms of a motor that is not a one trick pony. The timing numbers you posted I would think would be really good for the given application. The total advance may be a little conservative, but for a larger type boat may be perfect. I guess it also depends on if it's your boat, or one for someone else. I always seem to pull a few degrees for something going in someone else's ride. Just kind of a little padding, and not knowing if the owner stays true to fuel requirements.

Hopefully other, smarter people chime in today. I'd like to know what boat guys say:)
 

BoostPower

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Maybe @BoostPower will chime in on this.
Usually a 15 degree swing gives you a better less surging idle on most setups. Depending on the static compression locking out at 29-30 is ok but if you use the lightest silver springs and biggest bushing limiting idle timing that works well. The other way is lock it get it running see what idle timing it likes, make not then calculate distributor bushing size based on idle timing and max advance and set the dizzy up that way. Also you may want to tack weld if you lock out so there is less play


Sent from my Efi Beacon!
 

BoostPower

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So basically what I'm reading is both ways are acceptable. Which do you prefer @BoostPower and why?
I prefer a curve on a mild pump gas because you can’t crank warm well with locked out beyond 30 degrees on most common setups.

I like to run 34-36 degrees but can’t crank there so you can get a crank retard msd box type to Overcome that or put a curve in a distributor as an option.

If it’s a twin turbo motor or any not to exceed 30 degrees I prefer locked as long as the setup cranks without that slow advanced restricted sound

On efi it’s a different world




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92 cole

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If this a single engine boat I believe in locked at 34 (for Pump gas) total with a mag kill switch it's easy to start and hit the mag switch to light the engine. This gets rid of the lugging at cranking and saves starters. Much more timing will detonate an engine to death with out bumping up the fuel. There are alot of variables in this. What ignition and blower drive on engine set-up, are we under driving or over driving. the list goes on and on. M
 

Shlbyntro

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Theoretical in this case. I've had an influx of big power come my way recently and for some reason just started making mental notes on what I was seeing on a bunch of them. Was seeing about 50/50.

My favorite was the fountain that was running like ass and had one motor with fixed timing and the other with an advance curve via an ignition module. I ultimately convinced the owner to let me install mechanical advances in the distributors and do away with the ignition module on the one.

This last one being the one that prompted the question


Oh also the cams had ls firing orders and the distributors were wired standard. It was just a big ol' clusterfuck lol
 

BoostPower

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So basically what I'm reading is both ways are acceptable. Which do you prefer @BoostPower and why?
Just depends on drivability. Ignition box retard or not and the dynamics of the cam. Few others but you don’t want to crank with too much lead advance. Remember. Often timing marks at zero may not be accurate so be a bit conservative unless verified.


Sent from my Efi Beacon!
 

Blackmagic94

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My setup I’m building now

Jet botë
468 gen v motor with 088 heads
8.75:1 compression
Unknown hydro roller cam
Littlefield 6-71 gonna under drive to 15% to try and get 4.5-5.0 psi
91 octane AZ fuel



Where would you lock the timing. 30-32?
 

monkeyswrench

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My setup I’m building now

Jet botë
468 gen v motor with 088 heads
8.75:1 compression
Unknown hydro roller cam
Littlefield 6-71 gonna under drive to 15% to try and get 4.5-5.0 psi
91 octane AZ fuel



Where would you lock the timing. 30-32?
I'd start real conservative with the cam profile being an unknown. May be worth it to either profile it, or swap if you're just hanging the head now.
 

Blackmagic94

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So what is Low and I’m aware to low makes a marine engine run hot
 

obnoxious001

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My setup I’m building now

Jet botë
468 gen v motor with 088 heads
8.75:1 compression
Unknown hydro roller cam
Littlefield 6-71 gonna under drive to 15% to try and get 4.5-5.0 psi
91 octane AZ fuel

Where would you lock the timing. 30-32?
As Monkeywrench stated, if you are currently building the engine, take the time to find out exactly what the cam is.

Do you know for sure that your TDC mark is correct? I rebuilt one once that the builder had missed TDC by 6 degrees, so the Whipple engine was running 40 degrees instead of 34,, you can guess the result.
 

Blackmagic94

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All I’m doing is installing a blower on an installed engine in the boat.
 

monkeyswrench

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With it being a done runner, and adding the huffer, I'd start it back at 28-30. It may be real lazy, but you'll know real quick. The cam profile can change the dynamic compression, so your 8.75 can either act like 8:1, or 9.25:1. As far as boats, I don't know a whole lot about how the load characteristics will effect things either.
On cars, I usually try to do a leakdown test on all cylinders. A huffer will "accentuate" a little blowby, or worn guides. Nothing worse than blowing a whole weekend to do it again next weekend.
 

Blackmagic94

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With it being a done runner, and adding the huffer, I'd start it back at 28-30. It may be real lazy, but you'll know real quick. The cam profile can change the dynamic compression, so your 8.75 can either act like 8:1, or 9.25:1. As far as boats, I don't know a whole lot about how the load characteristics will effect things either.
On cars, I usually try to do a leakdown test on all cylinders. A huffer will "accentuate" a little blowby, or worn guides. Nothing worse than blowing a whole weekend to do it again next weekend.
Could mix a bit of vp to be safe for the first test
 

monkeyswrench

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That will give you a cushion, but may also give you false results. I'd run as close to "real life" as you intend to run it.
 

namba860

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Sounds a lot like the engine in my boat and how I use it. I set mine @34 Deg. total @ 3500 rpm and the initial usually ends up around 12 Deg. @ idle
 
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