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Old 06-02-2013, 11:36 AM
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Timing Roots Blown SBC

Hi everyone,
I'm new here, i'm hoping to gain some insight and help on my latest project!

The Build: 388ci sbc, 9.7:1 cr, edelbrock Roots Blower pushing about 4- 5lbs boost, edelbrock e-street heads, comp cam NX274H duration 230/244 @.05 113 Lobe.

Ok, the plan is to make this a wild street car on 93 pump gas. The car will be lucky to be driven once a week.

Now I would like your opionions on..... wait for it.... Timing!! I have a msd digital-6 plus ignition box & msd billet distributor #85551. I would like to run an initial timing of 22 & be all in at 28 @ 3000rpm. However the springs & bushings are preventing me from doing this. The other option was to just lock-out the timing at 28 and take advantage of the start retard the digital-6 box offers.

Your opionions please......

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Old 06-02-2013, 11:50 AM
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fbird88 likes this type of engine combination,hold tight.
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Old 06-02-2013, 12:30 PM
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Yeah I was trying to avoid installing a BTM, is it absolutly essential?

Is locked-out timing at 28 no good for my application?

I'v currently got my engine out, I had cracked the ring-lands on 4 of the pistons running too much boost (7lbs), too much timing (40) & a small cam (214/214 @ .05). We Live & We Learn!!

Is the BTM the best way of avoiding Detonation without compramising HP?
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Old 06-02-2013, 01:21 PM
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Has anyone had any experience driving a street car with locked-out timing with a simmilar setup to mine; sbc 388ci Roots mini Blower 9.7:1cr??
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Old 06-02-2013, 01:45 PM
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I run an 8.4:1, 8-71 383 on the street with a BTM and injection system. The one time I sent my BTM to El Paso for repair, bought a 6AL for the weekend test and tune, before the inj system, with fixed timing at 34*, I melted 7 pistons, an expensive lesson, I couldn't hear it detonating, but sure felt it lay down on the third run at 1,000 feet.
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Old 06-02-2013, 08:51 PM
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Ok, I guess I'll get the msd boost timing master, I do not want to strip the engine down a second time to replace pistons!

So the accepted timing is 26 initial with 36 total (10 of mech advance) & have a boost retard of approx -2 per lb boost (I will be running about 4lbs boost retarding the timing from 36 back to 28).

At what rpm do I want to be all in? 36 advance @ 3000?

Oh and one other thing.... Recomended Spark plugs for these heads are champion RC12YC are these appropriate for a blown engine @9.7:1 scr running 4lbs boost?
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Old 06-02-2013, 09:12 PM
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You probably know a roots blower makes power right off idle, I'd have timing all in by 2500. Four pounds of boost is a cake walk but keep it low due to your high SCR, 9.7.
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Old 06-02-2013, 09:52 PM
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Thanks for the input 68Nova

Any thoughts on use of advance springs to get 2500 all in? Going off the charts & using a 10 advance stop bushing with initial set at 26 im guessing the stock heavy silver springs should fitt the bill.

Any ides on thoes spark plugs?
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Old 06-02-2013, 10:15 PM
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Ok, I guess I'll get the msd boost timing master, I do not want to strip the engine down a second time to replace pistons!

So the accepted timing is 26 initial with 36 total (10 of mech advance) & have a boost retard of approx -2 per lb boost (I will be running about 4lbs boost retarding the timing from 36 back to 28).

At what rpm do I want to be all in? 36 advance @ 3000?

Oh and one other thing.... Recomended Spark plugs for these heads are champion RC12YC are these appropriate for a blown engine @9.7:1 scr running 4lbs boost?
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Old 06-03-2013, 07:45 AM
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I ran a simmilar combo before that rocked;

Same 388ci sbc, same shortblock, but running a 214/214 duration cam @.05, running the stock 3.6inch top pulley (pushing 3lbs boost), SCR was the same @9.7:1 The car hauled ***!!

This setup worked well! but of course I was looking for more....

Switching to a smaller 2.8inch pulley, gave me 7lbs boost, but cracked my pistons.
Running initial timing of 22 & all in at 40 didn't help either!

Anyways "the re-build" my local Comp Cam rep recommended me this cam; NX274H. I'm going to switch to a 3.2inch pulley (a more safe 4 or 5lbs boost) & sort out my Timing!

Now you tell me its all messed up?!?
The 2200 converter & 3.08 rear gears are a little small (but it is being used as a street car 95% of the time).

Where is the happy-medium?!?

Will the cam mess this build up that much?

Last edited by blowme77; 06-03-2013 at 07:56 AM.
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Old 06-03-2013, 08:27 AM
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Quote:
Originally Posted by blowme77 View Post
Ok, I guess I'll get the msd boost timing master, I do not want to strip the engine down a second time to replace pistons!

So the accepted timing is 26 initial with 36 total (10 of mech advance) & have a boost retard of approx -2 per lb boost (I will be running about 4lbs boost retarding the timing from 36 back to 28).

At what rpm do I want to be all in? 36 advance @ 3000?

Oh and one other thing.... Recomended Spark plugs for these heads are champion RC12YC are these appropriate for a blown engine @9.7:1 scr running 4lbs boost?
Have you looked at MSD's programmable 6AL-2. It has boost retard. Build all the timing settings you want. Easy to use and change the timing in just a few minutes.
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Old 06-03-2013, 08:36 AM
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The edelbrock mini roots blower I got was advertised to provide 5lbs boost on a 350 sbc & run with cr's up to 9.5:1. Thats why I bought it, I thought it would be a good match for my 9.7:1 388.

I took off my Peformer RPM & 650 carb & installed the blower & 800 carb.

The blower ran great with a quick tune, but only pushed out 3lbs boost. No signs of detonation, at this stage i was running my timing 22 initial 40 all in. There was a huge increse in power & wheel-spin.... grin factor 9/10.

The blower came with a 3.6inch top pulley & 7.5inch bottom pulley in the kit. So far the only inconvience is the top press fit pulley.

From what I understand the blower has mp122 internals.

Again..... are you sure the cam (recommended by the comp cam guys, not me) will not benifet my setup?
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Old 06-03-2013, 08:46 AM
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Cheers Fang,

Does the 6al -2 have the 20deg start retard like the digital 6 plus??
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Old 06-03-2013, 09:39 AM
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Originally Posted by blowme77 View Post
Cheers Fang,

Does the 6al -2 have the 20deg start retard like the digital 6 plus??
I don't think so, as you can design any cruve you want. I'd call MSD and ask them. I put one on my n/a 355 and like it. Had a MSD 6AL before. Here's a pick of my Drag racing timing along with the boost retard pic. Being n/a I don't run any boost retard but will when I get my blown 360 finished. You'll have to lock out the dist at 36 degrees before setting up the 6AL-2 progamable. Note: There is a 6AL-2 and a 6AL-2 programable. Also a laptop is real handy as the computer. Such as, drive to the strip, plug in laptop, change to drag cruve and have fun!
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Old 06-03-2013, 10:59 AM
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Although I don't have the same set-up as you, I do highly reccomend the BTM. I pull out 2* per pound of boost. I run my timing locked out at 34*. Get the MSD Pro-billet mag pickup dist. There is another way to get the start retard without buying a new CDI. You can install a toggle switch to the ignition, as you turn the engine over and get her spinning, flip the switch.

Do you have a CDI?
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