How much is the efficient horsepower or boost on 93 pump gas?

If you add boost you add heat and stress.. but to what point is it enough boost/HP for pump gas without having to remove too much timing to make it run correctly?

I mean.. if by runing 14psi from 10psi you gain 25hp.. I think I'd leave it at 10psi... wont you agree?

 

I fooled with High Lam's OBDII s-trim/aftercooler 396 on a Mustang dyno. On CA 91 octane gas it made 600rwhp at (IIRC) 11 psi.

I haven't had my car on the rollers yet, but my butt-dyno tells me it makes a bunch more than that on CA 91 and ~15 psi. Max timing on street gas is in the low-to-mid 20's. I agree that there has to be some limit on the power you can make with a given displacement on pump gas, but I don't think I'm anywhere near it.

 

And don't confuse timing advance with power. Advance is what you need to light the fuel off to ensure a complete burn of the fuel. Different octanes, combustion chambers, piston tops, etc. all need different amounts of timing lead. The higher compression goes, the more the timing differs, depending on fuel type. Just because you only need 20 degrees advance doesn't necessarily mean you are making less power, just that the motor is wanting less timing to get complete combustion.
Old style motors liked 38-40 total timing, the LT1 liked 34-36 due to a more efficient head design. The trick is to pull enough timing to keep it out of detonation, since the knock sensor will over-compensate drastically when it senses knock. It might take only 2 deg. to keep it out of knock, where as the sensor might take 10 deg. out.

 

Yes, but my point with timing is tunning...

My point is: what is the limit of pump gas on say a 383?

If you have 10psi and make 600rwhp on 93 pump octane... and you raise boost to 14psi and you only gain 35rwhp... You would need a lot less timing with it to avoid detonation, aren't you reaching the pump gas HP limit?? If you put some C16 or other higher octane you could probably bump up a bit the timing and net higher results and performance.. thats my real questions...

What is the sweetest spot?

 

The answer would be "depends"

Every motor will be different. Depends on how it was built, and tuned.

Example 1 383 LT1 with stock compression, good blower specific cam, in a normal weight 4th gen. I have seen 12-14 psi reported, on pump gas, but on the other hand I have seen 10 psi needing race gas or octane booster. Would have to get specific info to see what the differences were

Example 2 383 LT1 with 9.5 compression, good cam, in a 3000 lbs. car with a high stall or manual trans. 14-16 psi on pump gas (maybe) since the motor doesn't get loaded as hard at lower revs.

You usually don't have as much trouble with detonation at higher revs, unless the fuel delivery is a problem.

My car. Stock LT1 with insta melt hypercraptic pistons. 3010 w/ driver, 3400 stall, 12 psi boost on 93 octane. Running rich, and pulling 1 deg of timing per lbs of boost. I don't load the motor that hard at low revs, and I have zero signs of detonation so far.
If I had better pistons I wouldn't be afraid to go higher onthe boost, as it is I will probably pull it back just to be "safe".

It is kind of like naawwzz.. every motor has a point of "saturation", where more spray doesn't go any faster, you just cannot physically burn it, or it will start to hydraulic the motor and break something. It all "depends" on each combination, and there is no hard fast rule.

Kinda like "turbos off a diesel will never work".. Yep, sure nuff they don't!

 

For example.. almost everyone I know running over 620rwhp is using race gas...

That was my point to it maybe...

If i am already at the 600 mark with 10psi is it adviseable to go over that and run 93 octane or the stress would be too much or too much heat to much everything for the power gained???

 

Stress? Maybe.. "depends" (theres that word again! ) on the combo in the motor. Only way to know is to sneak up on it, using measurable ways to check it.
If you go up two psi, and it starts melting plugs and overheating, might be too much!

Sorry, but for every combo it is a toss up. On a stock motor, the accepted point of no return is 6-7 psi. Of course, you can run 10-12 psi.. maybe it'll live, maybe not. Problem with boost or naawwz is that the darn stuff is addictive, and too much is never enough!

I guess in your case, if it is happy at 10 psi, showing no knock retard, and the plugs are clean, then try 12 and watch it real close. And if it still happy, go again! If you do it carefully and in a controlled manner, you should know when you reach the point of no return. Then you add race gas and see if it is actually octane limited, or something else.

I wouldn't recommend that experiment on stock slugs tho!

 

You guys talk over my head a little bit, but I do know that the ATI nova made over 1200 hp and runs 8.90's in the quarter mile with a 427 big block and ATI blower on 92 pump gas weighing in at 3500 lbs.

 

Dont forget, although timing may differ for a more efficient combustion, you also have to note where your highest BEMP will result, the sooner you spark the closer the highest BEMP will result to TDC, the closer it is to TDC the more power you make aswell. This highly depends on compression & octane fuel, I doubt it has anything to do with how effiecient the heads are, sure more effcient heads will give you higher pressure in the chamber but they will not affect the latency of your highest pressure, the sooner you spark, the sooner the highest pressure will result, if its just after TDC you'll make more power, until you get to a point where your starting to push the cylinder down a bit too soon & you detonate & or start to looser power cuz most of your combustion is before TDC & even gets to a point where your highest BEMP is before TDC, thats bad