How much total timing for Aluminum head 509??
 

I am getting ready to fire my engine by the end of the week and was wondering how much total timing to use? I am thinking about 34 degrees and was looking to see what other similar combos have used? Here are my engine details:

.030 over 502 forged GM 4" crank scat h-beams with probe mid-dome forged pistons.

Pro-Comp aluminum heads with good valve job, chamber work, and rocker geometry issues corrected. Extensive deep port matching to FP 1275 gasket so 320CC intake volume was increased.

496 exhaust Aluminum and ceramic coated. turbulators removed as well as all baffles/mufflers. Corsa Captain Call with new diverters and flappers on the back.

RPM Air Gap intake also deeply port matched to FP 1275 gasket with Mighty Demon 850 with 1" open spacer.

Cam is .611int/.595ex 228/[email protected] 114LSA 18726543 LS style firing order. Comp SS 1.7 rockers

Thunderbolt IV Ignition with 22* module if I can find a pigtail to plug it in?

Fuel will be 93 from the gas station as I am looking at 10-1 CR ..........................

Donzi 26ZX with Bravo 1 26P prop looking for 52-5400RPM max. 90% of the time cruising at 37-3800rpm

So there is my question, how much timing with aluminum heads running 93 octane? There will be times I will have to put some 89 octane in on the water but if that happens, I will be proactive and leave at least a 50/50 mix hopefully!
I will be running closed cooling as well with cool engine temps but it gets hot here in Tampa.

So, is 34 a pretty safe number? I figure initial will be around 12* with the 22* advance module....... I dont want to get into any detonation as I dont think these procomp heads will take much abuse......TIA TBF

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34 is safe. it may like 36

Are you running it on a dyno first where you can see what it does ?

If not I would also stick with 34

OK thanks... this is my first dunk into the go-fast pool and I don't want to eff this up for being stupid! I am not out for every last possible bit of power but if I can get this thing to go 70MPH reliably than I am happy. I do have a wide band exhaust plate on the top of each manifold for a data logging LM-1 and I am installing a wide band gauge as well so I can tune this properly from actual conditions on the water...........

10:1 CR. running 36 degrees on 89 octane, I would have some concerns with that.
I would recommend spending the money on the dyno. Looks like you have spent some money and time. Without dyno testing you maybe leaving power on the table, let alone break-in under a controlled test. You will have unknown A/F #s and stepping your timing not exactly knowing, what the engine wants. If you had a stock engine rebuild, might be a different story.

Sounds like a great project I have a similar 509 in our Pachanga (SeaRay) take a look under the SeaRay area on this site, it's running on the dyno....34 is safe but leaves alot on the table 36 made 40 more HP.

Man I did not want to hear that! 40 HP is significant...... 10HP or so is not such a big deal. I did have the engine in line for dyno testing but I could not wait any longer..... My engine guy has a lot of real exotic stuff going right now so I understand how that goes........ As far as fuel, 93 pretty much all the time but I am sure I will have to buy on the water on occasion, if so I would maintain a minimum 50/50 mix between 93 and 89 so 91 would be more likely the min....... with the data logging LM-1 and wide band gauge as well I can keep a pretty close grip on AF ratios. I built this motor at 10-1 knowing this was about the most you can use running aluminum heads......

What kind of cranking psi are you getting on a compression gauge?

with out any knock control 32-34 max,i usually build my motors 9.2 -9.4 with aluminum heads 34 total timing

I agree. The risk isn't worth the reward. In a street car , or strip car, the compression is nice. In a boat, the extra 15-25hp gained, isn't worth having to run on the verge of detonation, 93 octane mandatory, for the extra mph or two gained. I'd rather gain power from head flow, cam selection, prop work, etc.

I'd be conservative on timing in hot humid florida sea level air with 10:1 and a relativly mild low rpm camshaft.

Not yet......I will have the engine on a run stand tomorrow or Thursday....... I will pre-oil and get the compression tester on it when I can crank it.....

Every N/A BBC (with traditional heads) I've dyno'd runs best between 34-36 degrees total timing. Running less than 34 starts dropping power fast. Generally speaking, if you need less than 34 degrees of timing to stay out of detonation there's something wrong with the combination or fuel quality. I personally wouldn't run a 10:1 engine hard on less than 91 octane, even with aluminum heads.

Bob Lloyd
Full Throttle Marine

Rod length and stroke have alot to do with what timing to run. The longer the piston dwells at top dead center the less timing you need... Your setup 32-36 degrees will be fine I doubt you would be able to notice 4 degrees of timing difference in a boat. Barely notice a 50 hp increase.

I did go with the longer 6.385 rods as I had a choice as I needed to get new pistons and rods...... Also the shorter piston made the weight a little less which can't hurt but I did not know about dwell time.... I will read up on that... Thanks.... I should have some compression numbers tomorrow....

In MildThunder's thread about detonation and preignition, I touched briefly on the issue of timing with the more efficient "fast burn" combustion chambers that are common on modern heads. I think someone chimed in (Haxby?) saying that a fast burn chamber should make good power with less timing advance than what is needed on the 40-year old chamber designs on the stock heads. Not sure what kind of chambers your heads have - might be worth consulting them to see if they say anything about timing advance.

Like MER said, the dyno is the best way to determine optimal timing, but even that could change when it is in the boat, under a different load in different conditions. Good luck, I'll be crossing the same bridge soon with my 489.

That was an excellent read about detonation and pre-ignition..... I saved it for my archives!
I have the pro-comp heads and the chambers look like just about any other BBC so nothing
Special there...... I will run the engine for a while on the stand and set the timing at 32-34 degrees for my ride home. Marine shop is in St. Pete and I am over in Tampa so I will go pretty easy on the way Back.....3000rpm at the most and I will vary that for a good break in..... I have a protected lagoon I can use for tuning and dialing in the jetting using the wide band once I get the boat back on the dock.......

tpabayflyer ,

I have the same boat with a HP500 (carbed) I run 34* total seems to work well (less compression and use 93 octane). I'm able to get 71 mph out of a stock 24p bravo and 73 mph with a labbed 26p both at 5200RPM bravo and my drive is an XZ. I think you expectations are realistic.

Michael

Michael you should save some money and run 89 octane. No need in the hp500 for 93.
As far as the op I think 34 will be fine. 36 may make a slight bit more but 36, 10:1 and nothing special chambers may not be worth it.

Hp500 only need 87 octane any more and it will make less power.

i would not sweat it at 35* of timing,,your going to be running in water which rund cooler,,you can shave 1 point of compression when using aluminum cylinder heads..in other words it will act like a 9:1 motor..cast iron heads build and hold more heat which will detonate faster..the only thing i forsee you having issues with is the procomp heads,,they dont like salt water or any water and dont seal too well..