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a few boost and detonation questions

the poi

the poi

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Joined
Jan 5, 2003
Location
Pasadena, CA
alright, stock 87 760ti with a 85 b230ft, just a cone intake w/ heatshield. I'm going to be splicing in my grainger valve this weekend, what kind of boost should be reasonable to expect on 91 octane? I'd also like to know more about the fuel system and the engine control...I've heard in a couple places about a knock sensor, but I had thoguht that there wasn't a knock sensor nor a way for the ecu to reatrd timing in any way. I thought there was just a 13.5psi overboost protection and that was it...
And as for timing advance/retard, any pointers on what I should do?
What's really thrown me is a person i read here with advanced timing, 89 octane and 15 or 20psi of boost, with no det, while I know another guy who has to run 97 or so octane to be able to get up to 15psi with eveyrhting else stock...
 
Every engine is different, it depends on how well maintained it was, milage, and overall condition.
 
i ran 93 octane and 15 psi with no detonation and stock timing. it really just depends. turn it up slow, and make sure you have a gauge. there is no way for your engine to retard timing, but there is a 15 psi fuel cutout.

Michael
 
without trouble u can raise boost to 13 psi......

for a while i actually ran 14 psi with 87 octane.....it would detonate for a split second and then my timing would get pulled back......
 
red_liner, the timing got "pulled back"? maybe im missing something, but mike and red's psots seem contradictory... which cars did have a knock sensor and retard?
 
The 240's have a mechanical boost retard that pulls the timing back 5 or 6 degrees at a couple of pounds of boost. The 740's have a knock sensor, the ecu uses information from the knock sensor to keep the engine right on the edge of detonation, 240's had no knock sensor, running right on the edge of detonation gives you the most power and best MPG. Some 740's have a turbo plus option, thes cars run 12 psi stock, I think the turbo plus is an ignition system with more retard capability, or extra fuel capacity, or both. to run more boost you need more timing retardation and you will eventually run into detonation again with enough aditional boost, then you need to richen up the fuel mixture.
As for a guy running advanced ignition timing and 15 to 20 psi on 89 octane, his engine no longer runs or he is full of sh!t, if he severley RETARDED ignition timing he could mabye pull it off.
I have a 245 runnuig 15 psi, but I am at altitude so I can run a little more boost than at sea level. To do this my car runs a little rich at idle and I have done the terminal 11 trick to get extra fuel above 12 psi. without the extra fuel this would not be possible. You can get a rising rate fuel pressure regulator for your 740 engine from MVP then you can raise the boost substantially more.

-Jack
 
jackbombay said:
The 240's have a mechanical boost retard that pulls the timing back 5 or 6 degrees at a couple of pounds of boost. The 740's have a knock sensor, the ecu uses information from the knock sensor to keep the engine right on the edge of detonation, 240's had no knock sensor, running right on the edge of detonation gives you the most power and best MPG. Some 740's have a turbo plus option, thes cars run 12 psi stock, I think the turbo plus is an ignition system with more retard capability, or extra fuel capacity, or both. to run more boost you need more timing retardation and you will eventually run into detonation again with enough aditional boost, then you need to richen up the fuel mixture.
As for a guy running advanced ignition timing and 15 to 20 psi on 89 octane, his engine no longer runs or he is full of sh!t, if he severley RETARDED ignition timing he could mabye pull it off.
I have a 245 runnuig 15 psi, but I am at altitude so I can run a little more boost than at sea level. To do this my car runs a little rich at idle and I have done the terminal 11 trick to get extra fuel above 12 psi. without the extra fuel this would not be possible. You can get a rising rate fuel pressure regulator for your 740 engine from MVP then you can raise the boost substantially more.

-Jack
Click to expand...
thanks, that really helps a lot!
 
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