I think I am finally nearing a dyno visit to put some fine tuning on my 451. You guys out there with turbo'd big blocks, what kind of ignition timing should I expect to see under boost? The combination that I have is a 451 with ported Eddy heads and 9.5 C.R., SMPI (Autronic SM2), wasted spark ignition (M&W Pro-drag 4 firing eight coils), and a water-to-air intercooler. I am hoping to run 10lbs or better on 91 octane. If I can't make 10lbs, then whatever it will safely run wil be my limit. Turbo's (2ea) are T3/T4's with 60-1 compressors. If there is any pertinent info I have forgotten, let me know and I will add it. What I am mainly after is what those of you who have your cars sorted out are running. Thanks for any info!

Each engine is different. My engine was a 440 with 8.7:1 compression, Eddy heads, and a turbo specific cam. No intercooler was used.
I had no problems running 12 psi on pump gas. If it wasn't extremely hot outside I could run 17 psi but normally shot some rubbing alcohol in the intake to cool it down.
My turbos are hybrids too. T4 60-1 compressors and T3 Stage III turbines with Stage III wheels. Those are perfect for street engines but the turbine outlets will prevent big boost levels. They're simply too small to get lots of exhaust out.
If I was making more of a drag/street car I'd use T4 P-trim turbines.

I know each engine will want its own tune. I am just trying to get an idea of where the timing should be so I have an idea of what a conservative place to start will be. The dyno's in this area have never seen a twin turbo big block Dodge (no surprise there really). While I will be there and hope to be involved in the process, I also have no experience with anything like this. I would like to go into the tuning session with a clue of what to expect. Or at least be able look at the values on the map and know if they are way too much.
You metioned the cam in your response Kevin, and you are right. I forgot to mention that. Mine also is a custom grind (from Hughes). Ultimately I am not expecting hard fast numbers, just examples of what others are running so that I may get a ballpark estimate. This project has alot of time, monetary, and not the least of which emotional investment. I really don't want to destroy it on the dyno.
Thanks for the feedback!!

Randy

I run around 32 degrees at upto 10 lbs and bring it down closer to 29 to 30 at 13-15 lbs on pump gas.
9.3:1 572 with victor heads here.

I would start at around 26 degrees total and see how it reacts.

Sure hope hughes didnt give you a reverse split cam...

383 with 10 lbs. boost,water/air cooler 8:1 compression,Eddy heads, 91 octane pump gas. I run 12deg. initial and 25deg. total and on a 95 degree day last summer it would very briefly clatter on the 1-2 & 2-3 shift.I'm talking about 2 audible knocks in about 1/10 of a second. That's probably about all the detonation the cast pistons can stand.

Thank you both for the responses! I really appreciate it. EFIdart, I don't remember the cam specs off hand. I would have to go look at them. What would the problem with a reverse split cam?
Thanks again everyone.

Randy

Any dyno tuner should be able to help you with the timing. Tune for best torque to make the engine live. Don't add timing to make HP, add boost. Always tune for best torque at any positive load points. Don't limit yourself with a pre-determined boost number. You will kill a motor faster with timing than with boost.

I run 8 psi boost and 30* timing on 91 octane fuel. 400, aluminum heads 9.1: compression. 224/230 hyd roller cam. I run 20* at idle 38* at zero boost and take away 1* per lb of boost. I run a small water meth for insurance but I am parinoid. I will be turning it up to 12 psi and will try about 28* timing. Runs well but havn't tried this current combo at the track. Oh and EDIS-8 waste spark ign.

Our starting point was 40 degrees initial and 20 degrees off at 30 psi. That worked fine, but in the dyno we were able to use even more advance under boost and that did help the power.

Thank you all! I really do appreciate the info. Trendz, I don't plan on limiting anything to a certain boost level. However there will be a limit due to the self imposed requirement to run 91 octane. The car is a street car, and I want it to be able to go anywhere on readily available pump gas. I am not against alcohol injection, but as I prepare to go to the dyno, I don't have an injection system.

Randy

I'm not suggesting retarded timing. Peak torque is the indicator that you have a very safe timing curve that will keep an engine alive. If you tune an engine to peak torque, than add timing, you will make more hp at that load point, at the cost of torque and engine longevity. Peak torque indicates a timing curve that is using the energy of flame front to roll the crankshaft forward. If the dyno is showing torque falling off, but hp going up... It tells me that the flame front is happening a bit to soon, creating opposing forces on everything from the headgasket to the main caps and everything in between. Hp goes up with advanced timing because the torque lost to advanced timing gets "stored" in tdc dwell time(high cylinder pressure), and releases in the instant there is any rod/crank angularity after tdc. No problem if you have real strong components...but a very fine line to walk with stock based parts.
Lets say you want a stock based 900hp engine. For discussions sake, say the engine is on the dyno and at 15pounds of boost it's making 875hp at peak tq. You could bump in another 3 or so degrees and get real close to your 900hp goal at the same boost level, OR you could give it a touch more boost and re-tune to peak tq timing.
The first scenario gets you your 900hp with added internal stresses and less tq, with a more fuel efficient engine.
The second scenario gets you the 900hp, added tq and lower internal stresses, with a less fuel efficient engine.

Trendz, I agree with what you just said, timing is everything. The Problem is 9 out of 10 guys reading the posts on here will interpret less timing into starting at 20 degrees at 10 lbs for example when they should realistically be at 25. We aren't running LS1's or other engines that perform well with low timing, let’s face it 440 Wedge based engine combustion chambers aren't near as efficient..

I do like jyrki's ignition slope, which is an aggressive and safe place to start.

That stock blocked destroked 440 I used to run was very sensitive to timing, 3 degrees too little timing was 130rwhp difference.. (Going from 20-23 degrees.. when in hind sight should have been more like 25..).

Well I saw Randy's (wrenchinrandy) car run on the chassis dyno today (Hi Randy!) and I was very impressed. It's such a nice docile every day driver type car yet cranks out 730 hp at the wheels. Figure that's close to 860 hp flywheel and thats at only 5500 rpm. If I remember correctly this was done with only 19 degrees of advance and 15 psi of boost. The tuner tried adding a few more degrees but for some reason it didn't seem to like the additional timing. Anyways, very impressive car. Great job Randy.

my junk is not like yours, but 500" b1 106mm on the dyno we locked it at 30 degrees all the way to 30lbs and it liked it just fine on e85

Yes I love turbos for the drivability. My cam is only 224*@.050" and I made 581 to the tires at 5000 RPM because the turbo was choked on the turbine. When it flashed the converter it would jump to 700 ft lbs of torque. With the EFI the drivability is something else. Oh and the truck only need 3.23 gears to run in the 11s. Turbos rock.