Boost and timing

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chargd72

chargd72

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Those with blowers or turbos. I'm running a magnum 360/408 at 9.1:1 compression with a Novi 2000. I'm guessing I will be around 12-15 psi when I get the car back on the road (first pull I hit 10 psi my stock 904 blew up as expected, but that's a whole different story). Right now I have timing locked out at 34* and I'm pulling 1.4* per psi until I get my air/fuel readings and adjusted properly. What is your target total timing for those running at full boost?
 
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I am running a 340 with 8.2 to 1 compression with a 6/71 (6 lbs boost) and I have my timing locked at 31 degrees. I'm not pulling any timing. When I go to 10 lbs boost I run a water/meth injection system coming on at 5 lbs boost and the timing stays at 31 degrees.

Jack
 
Coyote Jack said:
I am running a 340 with 8.2 to 1 compression with a 6/71 (6 lbs boost) and I have my timing locked at 31 degrees. I'm not pulling any timing. When I go to 10 lbs boost I run a water/meth injection system coming on at 5 lbs boost and the timing stays at 31 degrees.

Jack
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That's probably pretty much right where you want to be with your compression. Is your bottom end built? My goal is to pull 1.0-0.9* of timing per psi. So at 15psi that will put me right about 20* total when all in on 93 octane. I'm just trying to confirm that's a safe target. Once I get that dialed in, I would like to run alky so I can put in more timing.
 
My bottom end is a stock forged crank, Eagle H-beam rods and TRW forged pistons. They are heavy which in my opinion helps in a boosted engine. My only advice on the timing is to start conservative and then sneak up on it a little at a time. Every engine is different, especially when it comes to boost. The last thing you want to do is figure you have it nailed and set it at what you think is an optimum setting. Chances are that you will not like the results.
I am thinking about going to EFI controlled with a Megasquirt ecu. That should allow me to play with the air/fuel and timing a lot easier. Right now just looking into it, but it looks doable on a budget.

Jack
 
Sounds like you have a pretty stout bottom end. I run a stock 318 mag, EQ roller heads, 62-1 turbo @ 13 lbs on E85. I have megasquirt II and I start pulling timing at about 4 lbs at a rate of 1.5 a lb. my total is 36 under load. On pump gas, I pulled 2 psi per lb. starting at 0
 
T56MaxTorq said:
Sounds like you have a pretty stout bottom end. I run a stock 318 mag, EQ roller heads, 62-1 turbo @ 13 lbs on E85. I have megasquirt II and I start pulling timing at about 4 lbs at a rate of 1.5 a lb. my total is 36 under load. On pump gas, I pulled 2 psi per lb. starting at 0
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Your total timing is 36* at full boost?? Or is it locked at 36* before you start pulling?
 
My total is 36 before I start pulling the timing back.
 
T56MaxTorq said:
My total is 36 before I start pulling the timing back.
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Gotchya. I was about to say you must be a tuning wizard if you were at 36* on boost. So on e85 at 13 psi you are at about 23* timing all in. That's sounds about right for a stock 318. I'm hoping to get around 26* with meth at full boost. I have a half filled block, ARP main studs with a girdle. I hope it'll hold.
 
It'll probably hold with that block, those studs and girdle. Depends on how hard you push the boost. Stay conservative to your goals and don't trust meth to the point where you ultimately rely on it to cool temps down. Tuning is a big factor. The best forged piston will grenade if you go lean and detonate. Anyone can run stock oem parts on boost like I am, it's all in the tuning, for me the limit is my parts integrity to the stress of boost, meanwhile you have the upper hand. You're running big inches and it won't take much boost to reach 600hp easily.
 
Yup. detonation is the key and the first thing that feels it is the pistons. For the most part unless you are really producing some big ponies the rods and crank can take a lot of punishment. It is the pistons that usually die first and it doesn't really seem to matter that much if they are forged or cast. The forged can take a lot more in normal situations but when you introduce boost and detonation, forged pistons don't last much more than a second longer than cast pistons.

Jack
 
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