how much timing to run w small roots blower?

[Frankshaft]

Actually, I have a couple questions. I calculated about 9.5:1, +or- a little. 4vr Pistons have about 8 cc worth of area. Rpm heads are 70cc. If the block is 0 decked, and a .040 gasket, that's roughly 9.45:1, not including the crevice volume. That's the area between the top of the Piston and above top ring, between the cylinder bore. It can be more volume than you think, effectively reducing compression more. If the block isn't 0 decked, that can account for as much another .25 of a point. If the heads are milled, it takes about .006/cc with those. So, it takes a fair amount to really alter compression with milling them. I am going out on a limb and saying you really aren't at a true 10:1.

[Frankshaft]

Camshaft is apparently the Edelbrock perf rpm camshaft #7102
234/244 @ .050, .488/.510 on a 112. Sounds decent enough for the intended usage.

It must be an old lazy slow grind.......lol. The advertised duration is 308/318. I read that it is exactly the same cam as the elgin #1067P...not sure if thats true.

Yes, that is true. Summit has a version, Erson, melling, jegs, and about 20 others. It's not a crazy cam but they do work. And it will be good with that. You essentially have a performer rpm package with a small blower for an intake.

[Scotthatch]

Ok, Im going to use his old msd distributor (with locked out mechanical), eliminate the vac. advance totally. Add the msd 6btm box, which has the dial w the 4 settings. The octane after the fuel mix should be about 97. Static compression is still 10.04-1. So at this point should I start with say.....33 degrees of timing, and use setting number one on the dial, for 1 degree of timing out for each lb. of boost........giving me 27 total with the full 6 lbs? Sound reasonable with the new octane?

When you lock out the vacuum can on the distributor do so in the middle of the can travel the worry is always rotor phasing .... yes 33 on timing but start with 2 on the dial ... the number on the knob is not always accurate we tend to calibrate them by testing ... keep reading the plug and adjust as needed and I know it's is loud on boost but keep a ear out for knock ... also once running try 3 after a run at 2 and see if power drops a lot ..idea is to see if the engine is real sensitive to timing

[Scotthatch]

Also mount the knob where you can't bump it or add a loknob to it to be safe

[F-BIRD'88]

How are you arriving at "6 psi boost" What is the blower pulleys driver ratio?

Using the vacuum advance with a locked out ( mechanical curve locked)
allows you to do the same thing as a BTM retard box does.
Now you got the money to buy the Water /Methanol injection system.
Water methanol 50-50 is cheaper than buying race gas, which will get old in a hurry.

Race gas does not COOL the Blower nor cool the discharge air.
Water methanol gives you a cooled blower and cooler more dense discharge air.
More powerful, hot soak resistant. eliminates detonation,

Common blue winter formula windshield washer fluid ( non detegent)
is about 35% methanol. It is effective too.

Mixing race gas is not the way to go. It will get old fast.
With 10:1cr and significant boost you will need more than a 2:1 mix

Do it right either lowr the engine cr or use water methanol injection.

[Scotthatch]

How are you arriving at "6 psi boost" What is the blower pulleys driver ratio?

Using the vacuum advance with a locked out ( mechanical curve locked)
allows you to do the same thing as a BTM retard box does.
Now you got the money to buy the Water /Methanol injection system.
Water methanol 50-50 is cheaper than buying race gas, which will get old in a hurry.

Race gas does not COOL the Blower nor cool the discharge air.
Water methanol gives you a cooled blower and cooler more dense discharge air.
More powerful, hot soak resistant. eliminates detonation,

Common blue winter formula windshield washer fluid ( non detegent)
is about 35% methanol. It is effective too.

Mixing race gas is not the way to go. It will get old fast.
With 10:1cr and significant boost you will need more than a 2:1 mix

Do it right either lowr the engine cr or use water methanol injection.

The vacuum can deal is not the same as boost retard .....

And i would guess once the tune is done it will run fine on premium pump gas ..... we have done this lots here .. the only reason I am starting causes is because it's harder to help over the internet ...

[rewguy]

Actually, I have a couple questions. I calculated about 9.5:1, +or- a little. 4vr Pistons have about 8 cc worth of area. Rpm heads are 70cc. If the block is 0 decked, and a .040 gasket, that's roughly 9.45:1, not including the crevice volume. That's the area between the top of the Piston and above top ring, between the cylinder bore. It can be more volume than you think, effectively reducing compression more. If the block isn't 0 decked, that can account for as much another .25 of a point. If the heads are milled, it takes about .006/cc with those. So, it takes a fair amount to really alter compression with milling them. I am going out on a limb and saying you really aren't at a true 10:1.

I found a sealed power ad for the same pistons that labeled them -6.1cc, pistons are .011 in the hole, 64cc head, 4.100 bore gasket that is .039 thick.
Pipemax said 10.04-1 Although I'm sure there's enough fudge factor there to call the area above the top ring maybe .15 or so......hard to say and probably not that important.

[Scotthatch]

Got this one running a few months back ... way more motor and blower ...9.5 to 1 ... boost retard .. 8 lbs of boost right now and runs on premium pump gas


https://youtu.be/idwLsvxPOYE

[F-BIRD'88]

The boost you can run and the timing when under boost will be very limited.. thus the perf will be very limited.

vrry lacking in repeatabiliy too (blower hot soak)

do not equat with a different 9.5:1 cr motor with a different blower
or you will be soon doing this all over again.

[Scotthatch]

The boost you can run and the timing when under boost will be very limited.. thus the perf will be very limited.

vrry lacking in repeatabiliy too (blower hot soak)

Really?? Not that I have seen .... charge temperature on a mini blower at normal boost and speed is only like 160 degrees sometimes even lower .... and everything I do is street driven .... I have done what you are talking about but it was on a 12.5 to 1 motor with 7 lbs of boost and did nos on top just for fun .... my first blower motor with a 144 b&m I did in 1990 for my bother in law and it still runs today untouched ... it was 8.5 to 1.... 6 lbs of boost running a small pulley and runs on crap gas from any pump ....

[Scotthatch]

15233745643110.jpg

I do mini blowers all the time ....

[Scotthatch]

15233805177111.jpg

Like I said at the beginning of the thread if you up the charge density in the cylinder you would be surprised how little timing you need to make Peak power as the blower is making a homogeneous mix