Guest the_dj Posted June 19, 2003 Share Posted June 19, 2003 I have a pop off valve that I can put on my car if I need to for hardware overboost protection, but I have an idea that may be more failsafe: Can I take my car's computer, and for every manifold air pressure above what I decide is the safe value, set the fuel injector pulse width to zero. As far as I can tell, this can make my car 100% detonation proof in the event of an over boost situation. With this precaution, is there any need at all to use a pop off valve? Boost pressures are low (5psi), so I know it's not needed to keep the turbo spooled. Opinions? Quote Link to comment Share on other sites More sharing options...
SleeperZ Posted June 19, 2003 Share Posted June 19, 2003 The computer has no idea what manifold pressure is (I'm assuming factory ECU?) And fuel cut is extremely dangerous, especially at high boost - you could get instant detonation if an injector does not cut off cleanly - killing ignition is safer. If you really feel uncomfortable with your boost controller, modify the popoff valve. I added a 200SX spring inside my existing popoff, and got a full flow popoff at 12 psi. Quote Link to comment Share on other sites More sharing options...
Guest the_dj Posted June 19, 2003 Share Posted June 19, 2003 The computer has no idea what manifold pressure is (I'm assuming factory ECU?) And fuel cut is extremely dangerous, especially at high boost - you could get instant detonation if an injector does not cut off cleanly - killing ignition is safer. If you really feel uncomfortable with your boost controller, modify the popoff valve. I added a 200SX spring inside my existing popoff, and got a full flow popoff at 12 psi. Holley Commander 950, manifold air pressure system, Bosch 42lb injectors on a small block chevy. I know the injectors will do exactly as I tell them. I'm also only looking for 6-7psi for now. Quote Link to comment Share on other sites More sharing options...
Guest Zcarsmakemyheadhurt Posted June 19, 2003 Share Posted June 19, 2003 Use a VPC from HKS and proper waste gate ventalation. You can also use the BOV to vent "on boost". But at 6psi I don't see a need and if your turbo is sized correctly over boosting shouldn't be too big a deal uless your small on the exhaust side. What size is the blower? Alex C Quote Link to comment Share on other sites More sharing options...
Guest the_dj Posted June 19, 2003 Share Posted June 19, 2003 Use a VPC from HKS and proper waste gate ventalation. You can also use the BOV to vent "on boost". But at 6psi I don't see a need and if your turbo is sized correctly over boosting shouldn't be too big a deal uless your small on the exhaust side. What size is the blower? Alex C It's a pair of stock T3's from the 280ZXT. Quote Link to comment Share on other sites More sharing options...
Guest Zcarsmakemyheadhurt Posted June 19, 2003 Share Posted June 19, 2003 T3's on a SBC....you may have a problem. T3 on a Ford 302 but a 350 is going to spin the hell out of those units. I don't want to bash your combination but that engine is capable of making more horsepower than those turbos can support. Good luck, I hope it works out but I would say up size on the units. Quote Link to comment Share on other sites More sharing options...
Guest the_dj Posted June 19, 2003 Share Posted June 19, 2003 Careful about getting off topic (though I answered you below). I'm simply asking if a fuel shutoff at my boost limit is truely an effective means to detonation-proof my engine in the event of an overboost due to wastegate failure or some other goof-up. T3's on a SBC....you may have a problem. T3 on a Ford 302 but a 350 is going to spin the hell out of those units. I don't want to bash your combination but that engine is capable of making more horsepower than those turbos can support. Good luck, I hope it works out but I would say up size on the units. T3's with a .63/.60 a/r are the recommended size for a twin turbo setup on a "reasonable" small block, up to a little past 10psi. T25s are also used effectively. It's twice the engine of a 280zx (204% displacement) and twice the amount of air available to move (2 of the turbos). Those turbos are good for 15psi intercooled on a 280zx so I'm not really worried about 6 psi. Quote Link to comment Share on other sites More sharing options...
SleeperZ Posted June 19, 2003 Share Posted June 19, 2003 It sounds like you have the right equipment to do what you need to do. I think you can probably implement what you are proposing without a lot of trouble. I would still be cautious about using a fuel cut, and would look into cutting ignition as well, like a Nissan ECCS. I highly doubt you will overspeed those turbos - single T3, yes, twins, no way - it sounds like a good match. Quote Link to comment Share on other sites More sharing options...
Guest the_dj Posted June 19, 2003 Share Posted June 19, 2003 It sounds like you have the right equipment to do what you need to do. I think you can probably implement what you are proposing without a lot of trouble. I would still be cautious about using a fuel cut' date=' and would look into cutting ignition as well, like a Nissan ECCS. I highly doubt you will overspeed those turbos - single T3, yes, twins, no way - it sounds like a good match.[/quote'] With the equipment I have (read: free ) I don't know about a spark cut, but I can set it to only spark at TDC. Would that work as well? Hard to detonate with no advance I'd think. Quote Link to comment Share on other sites More sharing options...
TimZ Posted June 19, 2003 Share Posted June 19, 2003 As long as you are simply cutting the injector pulses off clean (i.e., not in the middle of the pulse), the fuel cut should work fine. This is what Vishnu generally does on their TECII - controlled Subie setups. Fuel and spark would be even better, but I would be leery of spark cut by itself. You would be dumping alot of unburned fuel and oxygen out the exhaust port. Just sounds like asking for big fireballs. Quote Link to comment Share on other sites More sharing options...
Guest Zcarsmakemyheadhurt Posted June 19, 2003 Share Posted June 19, 2003 Ya, but did you see fast and the furious??? What heads on this engine? Quote Link to comment Share on other sites More sharing options...
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