camerondownunder88 Posted July 6, 2006 Report Share Posted July 6, 2006 Hi All, I am looking at modifying a 4K motor to put in to a KE30. But I see when people put the 3K head on the 4K motor it goes to 10:1 CR. With this do you guys have to use high octain fuel or do you use the standard pump fuel? Also in morris minors they had a water mist injection to stop detonation. If we use a CR of 10:1 could we use this set up so we only need to use standard fuel if we don't want to or can't afford high octain unleaded at 98? Cameron Quote Link to comment Share on other sites More sharing options...
ToDa30/4 Posted July 6, 2006 Report Share Posted July 6, 2006 If your carby jetting is right you wont have a problem Detonation can be caused by lower octane fuel... but it can also be caused by your engine running too lean (not enough fuel) Leave the 3K heads on the 3Ks There is nothing wrong with 4K heads... old corollas on toymods .reckons its agood thing to swap heads,i was planning to do that .comp ratio around 9.8 to1. 4K heads with flat pistons give around 9.5 to 1 correct. ive been running 91 oct. fuel in the stock 3K-H could i run 95 or ?. interesting topic for me at the moment .cheers Dave Quote Link to comment Share on other sites More sharing options...
Felix Posted July 6, 2006 Report Share Posted July 6, 2006 i don't necessarily agree with oldcorollas ideas on engine building.... 4k's with flat top pistons have 9.0:1 CR standard (autos 8.5:1). the only ones with 9.5:1 are the dished piston variety. it only costs around $50 or so to skim a 4k head to up the compression. my advice is don't bother putting a 3k head on a 4k. Quote Link to comment Share on other sites More sharing options...
Robert Posted July 6, 2006 Report Share Posted July 6, 2006 4k's with flat top pistons have 9.0:1 CR standard (autos 8.5:1). why do autos have lower compression? Quote Link to comment Share on other sites More sharing options...
ToDa30/4 Posted July 6, 2006 Report Share Posted July 6, 2006 the motor i have is a 4K-C auto . so 8.5 .1 correct. thats good for s/c later but not n/a i reckon ,i want to fit single 40 dcoe weber ,elec dizzy ,extractors & system , tighe #113 cam & cb4 springs into the 3K-H, will that set up work ok ?. until i build the 4K-C to suit s/c'ing with extra cb4a inner springs & efi or at a pinch reuse the weber suck thru.would new stock 4K pistons 8.5 .1's be ok at 6 psi boost.? Quote Link to comment Share on other sites More sharing options...
Felix Posted July 6, 2006 Report Share Posted July 6, 2006 pinging is more prevalent at low throttle light load conditions. i guess with an auto when it is slotted into drive you instantly put a light load on the engine. lower compression and/or less ignition advance helps. if you are putting together an engine, work out the compression yourself. a piece of clear perspex and a syringe are all you need. you will also need to take into account head gasket volume. you never know if a head has been skimmed in the past due to overheating. ToDa30/4 what sort of power range do you want from your 3k? how do you drive it? are you going to drop the diff ratio? do you want torque, revs or a mixture of both? i'd look at a tighe 112 for a 3k myself. stock valve springs with shimming are good for 8 grand (or more) in my experience. stock 3k and 4k pistons are all the same (except for dished 4k), flat tops. any compression ratio difference between 4k's would be in the heads combustion chamber volume. 4k pistons should be fine at 6psi. Quote Link to comment Share on other sites More sharing options...
Jono Posted July 6, 2006 Report Share Posted July 6, 2006 does anyone use that valve protection stuff? Quote Link to comment Share on other sites More sharing options...
ToDa30/4 Posted July 6, 2006 Report Share Posted July 6, 2006 (edited) cheers for that ,u kno the #112 would suit the 3K better ,buying the #113 to suit the 4K but figured on slotting in the 3K for some extra ponies till i get the 4K built,will be keeping the stock diff for the mo.figure on picking up torque & reving to 6500 on the 3K ,more on the 4K with the square bore/stroke maybe 7500 ish :dance:i use the uppercylinder stuff in the 3K on 91 oct. fked if it makes any diff tho Edited July 6, 2006 by ToDa30/4 Quote Link to comment Share on other sites More sharing options...
madrolla68 Posted July 6, 2006 Report Share Posted July 6, 2006 the motor i have is a 4K-C auto . so 8.5 .1 correct. thats good for s/c later but not n/a i reckon ,i want to fit single 40 dcoe weber ,elec dizzy ,extractors & system , tighe #113 cam & cb4 springs into the 3K-H, will that set up work ok ?. until i build the 4K-C to suit s/c'ing with extra cb4a inner springs & efi or at a pinch reuse the weber suck thru.would new stock 4K pistons 8.5 .1's be ok at 6 psi boost.? The valve springs you are referring to what are they and where can i get some Quote Link to comment Share on other sites More sharing options...
camerondownunder88 Posted July 6, 2006 Author Report Share Posted July 6, 2006 Hi, All of a sudden people are now saying not to use a 3K head on a 4K motor? Why? As if you increase your compression you get more power on the cheap. And at the rate a 3K head can be collected at the wreckers why not do it? As what are the down falls of using one? Also one of you said if you jet your carby right you will not get detonation. But at a 10:1 ration a 3K head will give you on a 4K motor if I'm right the air in the cylinder will be so hot the fuel will be burning before the piston is TDC. So giving you car more fuel is this cooling the air more so it isn't detonating the fuel? Or is this to run it rich so the stoichiometric ration is to high and it can't burn easy? As if any of these options are right I would thing you are losing valuable kilowatts when we all ready only have a hand full. So my point was to try and make a water injection system like used on the old morris minor and then run up the compression. This will enable us to jet our carby's to the closest we can get to the perfect stoichiometric ratio of 15:1 and stop the detonation. The water mist will also just up compression more so if we went this way we could get maximum power out of a 4K with increased compression instead of trying to suppress detonation and losing power in the process. And then what is the point of using a 3K head? Also does anyone have any in depth info on water injection? Cameron P.S. Just so some of you know we can't burn fuel at the perfect stoichiometric ratio in a motor as it would burn so hot it would melt every metal we could make a motor out of. I know as I build jet engines and well we can burn it close but not spot (even in jets) lol Quote Link to comment Share on other sites More sharing options...
ToDa30/4 Posted July 6, 2006 Report Share Posted July 6, 2006 (edited) The valve springs you are referring to what are they and where can i get some performancesprings Edited July 6, 2006 by ToDa30/4 Quote Link to comment Share on other sites More sharing options...
Robert Posted July 6, 2006 Report Share Posted July 6, 2006 Hi, All of a sudden people are now saying not to use a 3K head on a 4K motor? Why? As if you increase your compression you get more power on the cheap. And at the rate a 3K head can be collected at the wreckers why not do it? As what are the down falls of using one? Also one of you said if you jet your carby right you will not get detonation. But at a 10:1 ration a 3K head will give you on a 4K motor if I'm right the air in the cylinder will be so hot the fuel will be burning before the piston is TDC. So giving you car more fuel is this cooling the air more so it isn't detonating the fuel? Or is this to run it rich so the stoichiometric ration is to high and it can't burn easy? As if any of these options are right I would thing you are losing valuable kilowatts when we all ready only have a hand full. So my point was to try and make a water injection system like used on the old morris minor and then run up the compression. This will enable us to jet our carby's to the closest we can get to the perfect stoichiometric ratio of 15:1 and stop the detonation. The water mist will also just up compression more so if we went this way we could get maximum power out of a 4K with increased compression instead of trying to suppress detonation and losing power in the process. And then what is the point of using a 3K head? Also does anyone have any in depth info on water injection? Cameron P.S. Just so some of you know we can't burn fuel at the perfect stoichiometric ratio in a motor as it would burn so hot it would melt every metal we could make a motor out of. I know as I build jet engines and well we can burn it close but not spot (even in jets) lol stoichiometric ratio is 14.5:1 and water injection is a waste of time Quote Link to comment Share on other sites More sharing options...
Felix Posted July 6, 2006 Report Share Posted July 6, 2006 (edited) does anyone use that valve protection stuff? no. when i recently rebuilt my 4k head the valves and seats weren't that bad at all. the engine had seen 3 1/2 years service and had only minor pitting on the exhaust seats. in fact the engine ran a tighe 113 (at 9.8:1 CR) during that time period. went hard in the 4k making peak power around 7500 with shimmed stock valve springs. my 5k has a solid lifter conversion with holden blue motor double valve springs. it has seen 8500. camerondownunder88 the average 3k head you find is exactly the same casting as a normal 4k head. the 3k one just has more of the deck face skimmed off. not hard to do the same thing to a 4k head at a machine shop. at least then you know it is straight and not possibly warped. running 10:1 CR shouldn't provide to many problems. if it pings back off the timing (although backing off the timing makes an engine run flatter). you don't run stoich under full load conditions (more like 12-13:1 A/F), stoich is more for cruise. with 10:1 CR you should be running at least 95 octane premium. cam overlap effects dynamic compression, which is what you should really be thinking about.... :dance: Edited July 6, 2006 by Felix 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.