Proper timing for a mild blower sbc?

355, 6-71, alcohol, Dart 230 steel heads, 10.5 static, MSD 7AL3, 1.76 Glide, 5500 stall, shift 7650 rpm, 4:11 gear, 33.5 tire, Enderle cube - 85 pill, .062 hi-speed @ 62 PSI, 1800 lb RED, runs 7.18->7.22 @ 177-179 mph, timing 35 degrees. 60 fts 1.04 consistent, 1/8th 4.5 & change, plugs like good...Most 7.20'ish dragsters are running 184/185 mph, car doesn't seem to be pulling hard in hi gear...should I pull some timing out - to about 32?...I don't really care about mph, but I feel the car should be performing better than 179 mph...I have played with with pill# and hi-speed pressures, but those items don't seem to make any large difference. Comments? Thanks ITA

 

How big a pump, how much boost?

 

whats your rpm in the lights?

 

Are you over driving your blower?

How do your plugs look?

 

between 22 to 24 lbs boost, Enderle 600 9.2 gpm pump, plugs look perfect all around, running 26% overdrive, fuel pressure anywhere between 190 to 202 psi thru the lights at 7600 rpm. Maybe I need to bump up the traps rpm?....maybe 7800?

 

That is pretty close to the combination I had in the day. I had a PRO Mag 12, and Brodix track 1 heads (same flow).

If it is not a stripped blower, (I ran a very tight phased and clearance, retro plated non stripped blower...alky only!), I would expect you are not getting anymore boost no matter how fast you spin it. ET would go up because the boost was coming in quicker.

Your fuel is almost spot on to what we ran.

We ran a 3.90 gear, and a light weight tall growth tire. Went +190 mph every pass, but had it set up for a consistent 1.17 launch. Never pushed past 32 degrees...and would then would take fuel out of it with the high speed, until it picked up.

Leave the fuel in at the hit! it seems like it is working. The problem we ran into was the motor is spinning so quick, to the high speed, when we launch at 5000 and shift at 7500. ...when is the high speed opening? It is right now!! I am guessing that is why you are not seeing much change, without adjusting the main. That is one of the reasons we changed to a tall gear and a lower stall. 3500. We made the blower work down low, with LOTS of fuel, and could then map out the higher rpm range, high speed.

We stopped there because we were index racing at 7.60's ...and nobody in their hemi's and big blocks were ever expecting a small block to go by at the lights going 194 mph! They would lift every time, as they were so far ahead!! Soft launch made the consistency, and pick it up by 330. We were going 165 to 167 at the 1/8th.


I eventually...bought an SSI blower. Put the whole pump into the motor, and then brought the blower into the fuel....hello 6.90's !!!


Sound anything like what you are seeing?

 

What are your nozzles sizes and quantities?

Here is a LINK to a tool I made for my car, you can play what-if scenarios.

 

Yeah, it does....I'm running a 3 day race deal this weekend - leaving early in the morning, so about all I can do at this point is move the timing back a bit to about 32 degrees, and adjust the crack pressure on the high speed. Like I said, it's coming in at 62 psi. I spoke to Spud Miller and he suggested that I move that up to about 80 psi so she'll be fat on the launch and stay fatter longer in high gear before the fuel starts going away. Maybe that will help with the lack of "pull from the 1/8 mi & on. I agree that the unstripped blower is producing all it can and any more spin is a waste of time, and that a 3.90 gear is probably optimum, but at the end of the day, it's bracket racing so we dial to what it runs. However, I think there's some high 7 ohs hiding inside her. At 7.20 @ 179, the plugs are perfect so maybe that's just her happy place. I'll let you know on Monday about the changes and the results. Thank you!....Also, the jetting is 50/48/46/44 front to back - hat only no ports

 

9 gal pump is alot of fuel volume for what you are doing and the cubic inches--- I'd say it's fat at the end of the track ----- you don't give many details on your supercharger either . If you don't do anything else try a bigger main jet , and keep creeping up to a larger dia till it shows improvement ---

I don't see how fattening it up down low and taking timing out of it will solve anything listed in your first post ---- ?????

 

I agree with Mark....kind of what I was getting at. Pull the fuel out at the big end till it shows heat into the second thread on the plug. At 32 degrees you should see heat before detonation. Problem is...it seems to like fuel at the hit (those are good numbers) and not sure with such a tight launch, that you can separate top end from bottom end.

I only ran the whole pump...when we got into 35 lbs of boost (32 at the hit) port nozzles, and turning it up o 8800 rpm. Still stayed at 32 degrees!!

Timing could work, but try fuel first. Work on the top end...watch the Launch effect....Who knows, it might go even faster.

Good luck this weekend. Keep us posted!

 

Looks like we got a lot of things sorted out on the weekend. Left the timing alone @ 35 and concentrated on fuel delivery. Decided to start adding fuel till it didn't want any more. Car used to run in the mid '20's with the occasional dip into the teens...Pulled out the 85 main jet - went to 75, and changed the high speed to .050 # 55lbs. Went 7.12 @ 182 - 1.019 60'. Then went to a 65 main, same high speed - went 7.01, - 1.00 60' @184.25. Ran out of t&t time, the plugs tell me that we can still add more fuel back into it..So, looks like we're going in the right direction. Thanks for all the help & suggestions.
Never heard of a blown sbc wanting a 60 to 65 main jet...

 

Awesome news!

Like I said...my car loved LOTS of fuel at the hit...and then work on taking it out, at the big end!

Are you getting an even burn in each cylinder? I eventually went to port nozzles, but only put less than half of the fuel through them. It allowed me to even up the cylinders, but not take away from sealing the blower up, and keeping it cool, with lots of fuel.

For your combination with a 1800 lb car...your numbers are pretty impressive!!!!

Keep us posted!

 

Right now - no port nozzles....just in the hat. Ports are a winter deal so, as you say, we can tune each cylinder more effectively. #1 and #2 are burning hotter than the rest so that's where port nozzles will help - I was blown away (no pun intended) by the ET response when we started to fatten her up. I've ordered a bunch of smaller jets - 59->64 and we'll keep dropping sizes until it doesn't want any more. I also have an MSD 8972 timing retard box kickin' around the house which I might have a look at. But for our next outing on Labour Day weekend, we're just going to do the fuel thing and see what happens...I think there may be another half a tenth in her. As for the motor, I'm amazed. It's not a radical piece by any means...unstripped 6-71, steel heads and rods, reasonable cam and a 7AL3,,,that's about it