eyefi Posted August 12, 2004 Share Posted August 12, 2004 can the stock motor really take 30psi of boost, assuming tuning and octane? i dont want to get into detonation or pre-ignition debates, assuming no det or pre-ign and good compression numbers. Quote Link to comment Share on other sites More sharing options...
Alex Posted August 12, 2004 Share Posted August 12, 2004 Probably - but for how long is the question....the more you stress the engine the shorter it's life - but I don't think you can just use an equation to work out a finite answer. Quote Link to comment Share on other sites More sharing options...
TLicense Posted August 12, 2004 Share Posted August 12, 2004 Has anyone managed to crack the ring lands yet? Usually one of the first things to go aren't they? Quote Link to comment Share on other sites More sharing options...
eyefi Posted August 12, 2004 Author Share Posted August 12, 2004 Originally posted by Alex Holdroyd Probably - but for how long is the question....the more you stress the engine the shorter it's life i think thats taken as read Originally posted by Alex Holdroyd but I don't think you can just use an equation to work out a finite answer. im not looking for an equation, im looking for experience or solid theory. EDIT - spelling Quote Link to comment Share on other sites More sharing options...
eyefi Posted August 12, 2004 Author Share Posted August 12, 2004 Originally posted by TLicense Has anyone managed to crack the ring lands yet? Usually one of the first things to go aren't they? ive never heard of it. pretty much all the short block failures ive seen (or heard of) have been pre-ignition, det or over revved failures. Quote Link to comment Share on other sites More sharing options...
Adam W Posted August 12, 2004 Share Posted August 12, 2004 I would say . . . yeeeessss, but only for drag racing/dyno pulls where the heat doesn't build up in the engine too much. And you wouldn't expect 150,000 miles out of it either! You could quite easily blow up an engine hewn out of forged kryptonite at 10psi if you had rampant detonation; although a stock bottom end isn't going to be as strong as a built one, that strength difference is less important than the way it is tuned. Lots of octane, maybe water injection to try and keep the temperatures down, and a well tuned ignition map would be key. You will reach a certain point where the stock rods can't handle the horsepower, ie the compressive loads on them at each power stroke will be too great and they'll bend. That's not really a boost-related issue though, its to do with peak cylinder pressures, ie torque/horsepower. Quote Link to comment Share on other sites More sharing options...
Barry Posted August 12, 2004 Share Posted August 12, 2004 As Adam says, its not the pressure that blows the engines, it the heat build up and det. As long as you have the charge cooling measures in place! Quote Link to comment Share on other sites More sharing options...
Syed Shah Posted August 12, 2004 Share Posted August 12, 2004 The engine can take loads of pure power, as proven in the US. As longs as the AFRs and ignition maps are ok, with fuel good enough to stop and det, it will take 30psi. However, for reliablities sake, certain things need doing. After the basic needs are met, cooling is crucial for the engine and turbos. It is possible, but if you want it to last, it needs doing carefully and thoughly. Quote Link to comment Share on other sites More sharing options...
eyefi Posted August 12, 2004 Author Share Posted August 12, 2004 there is no det. it's a specific question that does not involve any det whatsoever, at all, never ever ever ever, forever and ever amen. so head bolts and gasket r fine? stock pistons and rings r fine (if in good condition)? stock ignition is fine? Quote Link to comment Share on other sites More sharing options...
Alex Posted August 12, 2004 Share Posted August 12, 2004 In the perfect world which didn't involve going round corners and potentially any momentary oil starvation due to G loading then yes it would survive...but it would show up any weakness in your oil circulation/pressure and your cooling systems. Only problem I can see is gaskets and the valves...the valves when first pushed open would be under a lot of stress. Quote Link to comment Share on other sites More sharing options...
Adam W Posted August 12, 2004 Share Posted August 12, 2004 What are you planing on *doing* at 30psi? The loads imposed by a ten second dragstrip blast or a 4th gear dyno run are way less than a track day or a full-boost top speed pull. What turbo are you running? That sort of boost on gasoline (even race fuel) is like running a blowtorch over your pistons, they get hotter and hotter until something gives (or you lift off). Detonation is a lot more dramatic, like hitting them really hard with a hammer, but both can cause problems. Not sure about the head lifting off, but peoples experience in the states suggest that it won't be a problem. Quote Link to comment Share on other sites More sharing options...
Digsy Posted August 12, 2004 Share Posted August 12, 2004 Originally posted by Adam W What are you planing on *doing* at 30psi? The loads imposed by a ten second dragstrip blast or a 4th gear dyno run are way less than a track day or a full-boost top speed pull. What turbo are you running? ...and that is the crux of the matter. There are 700hp inline four engines in the US running 50PSI + N2O based largely on "cooking engine" stock internals, but after 50 1/4 mile runs the whole engine is fooked. As I've said before, statements like "the stock engine is good for 700bhp" (or whatever) have to be backed up with some kind of assumptions about usage to put them into perspective. Quote Link to comment Share on other sites More sharing options...
dandan Posted August 12, 2004 Share Posted August 12, 2004 30 psi as compared to 15psi (taken completely literally) will cause no problems. An extra 15psi added onto the combustion pressure becomes almost a drop in the ocean. In pure pressure terms I don't think it's a problem. You'd need to specify what turbo (and hence airflow) was being used to force the air through all the restrictions (in the engine/intake system) to cause this pressure rise. If you are talking about a big T78 or similar then the airflow will be huge. So by that arguement, once fuelling is correct, you're talking an awful lot of power for a stock engine. I have no personal experience of 600bhp+ 2JZ's so can't comment. US "experience" suggests the motor will hang together but it's a potential time bomb. Stock gasket is about the best around I believe, not sure on head screw specifications so can't say. I don't think you're asking this in the literal sense though, you are talking about the engine being capable of withstanding the loads generated from what would be an extremely high specific power output. Revs are the killer, stock bottom end certainly isn't a rev machine that's for sure. What sort of revs would you be talking about holding that boost to - stock rev limit wouldn't cut it with the necessary turbo and cams for that boost from a big turbo. I think the pistons would be "ok" (assuming no det, nice chilly charge temps and adequate octane and afr). My major concern would be the conrods and the rod bolts - serious imposed loads there! My 2p Quote Link to comment Share on other sites More sharing options...
TLicense Posted August 12, 2004 Share Posted August 12, 2004 In my old GT4 days guys were cracking the ring lands due to high compression. I would have thought the pistons would have been designed with a similar philosphy, and hence why I would have thought they would be the first to go... Quote Link to comment Share on other sites More sharing options...
eyefi Posted August 12, 2004 Author Share Posted August 12, 2004 suppose we had 2 engines, each produce 600hp. one uses a small turbo at 30 psi to make this power and the other uses a huge turbo at 20psi to make this power. now the crank and drivetrain see the same stresses, this im not interested in. what i am interested in r the differences imposed by the high intake pressure situation. now to my simple reckoning if u have the octane and tuning in order, no det, then the piston or cylinder really shouldnt give a shit about the boost cos it sees much much higher pressures during the power stroke. but the intake valves will have a much harder job staying closed against the boost, infact can they close against that sort of pressure? the fuel system will have to work quite a bit harder, a much higher rail pressure would have to b achieved and can injectors still spray effectively under that pressure? does 600 hp @ 20psi generate more heat in the piston than 600hp @ 30 psi? get my drift, its not the power output that i want to bash its the way u get there that i wanted to look at. i didnt mean to b vague in the first post but that nails down what i meant. some people r running 30psi with 60mm turbo's on 112 octane leaded race fuel, engines still intact (3 yrs later), monitored for knock and timing retard (stock ecu based). compression the same as day 1. now u will never know how they where used, but i dont think they've sat in a garage for 360 days a year, nor will u know if they have had 6 new shortblocks. Quote Link to comment Share on other sites More sharing options...
eyefi Posted August 12, 2004 Author Share Posted August 12, 2004 Originally posted by dandan I don't think you're asking this in the literal sense though, you are talking about the engine being capable of withstanding the loads generated from what would be an extremely high specific power output. cheers dan, i had u in the first bit but i think i lost u in this bit though yr post wasnt there when i started to reply. Quote Link to comment Share on other sites More sharing options...
dude Posted August 13, 2004 Share Posted August 13, 2004 Originally posted by dandan I think the pistons would be "ok" (assuming no det, nice chilly charge temps and adequate octane and afr). My major concern would be the conrods and the rod bolts - serious imposed loads there! My 2p :thumbs: :thumbs: Dude:flame Dev Quote Link to comment Share on other sites More sharing options...
Adam W Posted August 13, 2004 Share Posted August 13, 2004 Originally posted by eyefi suppose we had 2 engines, each produce 600hp. one uses a small turbo at 30 psi to make this power and the other uses a huge turbo at 20psi to make this power. now the crank and drivetrain see the same stresses, this im not interested in. what i am interested in r the differences imposed by the high intake pressure situation. now to my simple reckoning if u have the octane and tuning in order, no det, then the piston or cylinder really shouldnt give a shit about the boost cos it sees much much higher pressures during the power stroke. but the intake valves will have a much harder job staying closed against the boost, infact can they close against that sort of pressure? the fuel system will have to work quite a bit harder, a much higher rail pressure would have to b achieved and can injectors still spray effectively under that pressure? does 600 hp @ 20psi generate more heat in the piston than 600hp @ 30 psi? get my drift, its not the power output that i want to bash its the way u get there that i wanted to look at. i didnt mean to b vague in the first post but that nails down what i meant. some people r running 30psi with 60mm turbo's on 112 octane leaded race fuel, engines still intact (3 yrs later), monitored for knock and timing retard (stock ecu based). compression the same as day 1. now u will never know how they where used, but i dont think they've sat in a garage for 360 days a year, nor will u know if they have had 6 new shortblocks. Interesting question! I don't think you need to worry about the valves closing, I thought about upgrading the valve springs on mine but when you look at the surface area of the valves and the standard spring pressures, it became a non-issue in my case as I am keeping the standard rev limit. Whoever said that revs kill engines much quicker than boost was dead right, I think the real issue is the heat build up. The peak cylinder pressure will (I think . . .) be pretty much the same in your examples, although they will occur at different points in the rev range. I think peak cylinder pressure is directly related to torque, which obviously gives you your horsepower figure through a factor of rpm. If you ran the 30psi engine on higher octane fuel than the 20psi engine you could conceivably use a very similar amount of ignition advance for both both boost levels, so it's possible you wouldn't have too much of a problem with high EGT's. The air going into the cylinder would start off hotter in the high boost engine though. A smaller compressor wheel making 30psi will generate more heat that a biggun at 20psi, even though they're flowing the smae amount of air. With good intercooling this effect is obviously going to get less pronounced, I don't know how significant it would be to the overall picture. Back pressure could also be a variable as well if the turbos have different sized exhaust housing or turbine wheels. So the short answer is "umm, I dunno". Quote Link to comment Share on other sites More sharing options...
Paul Whiffin Posted August 13, 2004 Share Posted August 13, 2004 I used to run 2 bar boost on my standard engine, 1.5 bar for track days with no probs what so ever. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.