sb tuning problems

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ap6street

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Jan 7, 2016
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Location
australia
360/408 sbm
360-1indy heads unported
10.28 comp
Solid roller 245/245 612/612 108 102.75
34 total timing i think around 14 initial from memory
Was around 10" vacuum at idle 850 -900rpm
1050 quickfuel raceq
Using bcpr6ey-11 bgk plugs
Msd ignition .

Although i like to open up the throttle a bit. The car does see a lot of cruising rpm 1500-3000 and idle time.

Problem being after driving for 20-30minutes the engine wont idle rpm slowly drops down to 500rpm and then will stall at lights.
By this stage the plugs are fairly black.

Questions ? Comments ??
 
I think with that combo, you need at least 24 degrees initial...and maybe your idle should be 1100 or so in neutral.
 
Yep try 20 initial, idle it at 950 to 1,000 at idle in park, also with msd open plug gap to .045. Carb seems more of a race setup, CFM might be fine but you will probably have to change jets, IAB & IFB. Also check the float level when engine is cold and after a long drive.
 
Ok cool yeah the carb is big . The roller dyno shop suggested changing it out from a 850.

Also with 20 or 24 initial seems i can only get 18 minmum springs from msd meaning 38 or 42 total . Bit high ???
 
Buy a 10 or 14* bushing. I have 14*, no more 10* bushings. They are available from a few vendors.
 
that,would,be,awesome,if,not,could,you,let,me,know,where,you,got,them,from,????

somewhere,in,the,states,im,guessing????
 
You may already have the primary butterflies opened up into the idle transfer slots and dumping way more fuel then you need at idle and low speeds. If this is indeed the case you need to crack open the secondaries 1/4 - 1/2 turn so that you can close down the primaries.

You will need to reset your idle mixture screws if you open the secondaries. I would also look at add some more initial timing, but more like 16-18 degrees for initial timing.
 
Primaries are openened ansolute minimum.
I emailed mancini racing to see if they will offer the fbo cnc'd bushing 10 and 14 stops.

If i was to get these i wwould probably try 18 0r 20 initial with the 14 .

When my car left the dyno tune . They had total set on 32 not sure on initial but im guessing 14 .
 
If you take it to the track, the dyno tune may not be the best tune up for the car. Seen this a bunch of times. Advance the timing 2* and see if MPH picks up. I fit does, the dyno tune is off because it didn't load the engine the same as the car.

MSD does not provide a bushing with less than 18* advance. That's why I made 14 and 10 * units. If you want to straight up hillbilly engineer a bushing, get a piece of .500 stock with a, IIRC, .187 hole in it. Jig it up in a drill and use a file to reduce it to about .405 od. Cut it off, flatten two spots on either side with same file... done.

IMHO, you can set the timing wherever you want, it won't run best with anything under 20 initial.

Simple test. DO NOT DRIVE THE CAR AFTER DOING THIS!!!
Start car, get it warmed up. Twist distributor a little CCW, if it picks up RPM it WANTS the timing. Reset idle and do it again. You may actually be able to get the carb under control doing this. Shut it off and try to restart, if it drags the starter badly, turn distributor clockwise a bit, try to start again. You want to find the point that the engine has as much initial timing as the engine wants or the starter can handle when hot. Any less and the engine isn''t as happy as it could be.

Do the math with your current 32* total number and that's the bushing you want. You have to work within the mechanical parameters of the distributor and bushings available. Once you get the correct bushing in there, then go drive the car.

I wouldn't waste my time with a 14* bushing! Get a 10*.

Timing FIRST, then mess with the carb settings. I wouldn't touch anything regarding the secondary plate opening until you have the idle timing sorted out. It will run entirely different once you give the engine the initial timing it wants!
 
I bumped it up to about 22 24 last night and the idle sits nice at around 1200.
So u rekon maybe 22 and a 10 stop
 
You are on the right track, I believe. Ya know you COULD just lock out the distrib at 32, 34 whatever. I did, but I run a 4:10 gear. No 1500 RPM cruising with my set up. I run mostly street driving... and 33 degrees locked out. No detonation, no problems. Some guys don't like the idea, but for me and a lot of other guys, it works great.
 
could go 1 step hotter on spark plugs, I would aim for 34* total, that should idle at 1000. what did she make on the chassis dyno-470hp?
 
Lol 350 on the chassis dyno.
Dyno dynamics.
But i was bit concerned when i got the car back the foot pedal was only opening throttle half way and no secondaries.
They changed the carb there
 
Idling too high today , but could be the advance kicking in . 20 initial and starting at 1200 creeping tho
 
11 heat range(NGK scale) is way to cold for this engine and compression without boost or NoX. I would run a 7-8, and do all the time with engines like this. If you want a good steady reliable idle, you also have to keep the mechanical advance from kicking is until 1500 or higher.
 
I think if U are around 20* initial and 35* total it is good. .043" gap is good (1.1mm) mike got a little confused on ngk heat, probably only runs ngk in his jap dirt bike like me, but 6 is 1 step too cold! cruising a lot 1500-3000 do not go bigger cam. here ngk is not worth the extra $, I run autolite and champion
 
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