inline6 Posted March 4, 2011 Share Posted March 4, 2011 I was reading this thread about running high compression with quench without detonation... http://forums.hybridz.org/index.php/topic/40328-heads/page__hl__%2B1fastz+%2Bcompression__st__40 I plan to set my engine with .022-.024" piston to head clearance per 1fastz's info, however my head is a late style E88... Other pertinent info: I am in VA and we have good 93 octane gas... I am building a long rod 3.0 liter stroker l28. It uses the stock crank, offset ground to accomodate a Toyota 3SGTE (Celica) rod (~138mm length). Crank will have slightly less than an 81mm stroke after it is offset ground. The rods are aftermarket (they are lighter - around 565g instead of 711g? stock)... The pistons will be custom, forged, and also lighter than stock... I'm trying to decide what compression ratio to set my motor at for 93 octane pump gas and because building L series motors isn't my full time job, I don't have the experience to know what the approximate number is. I want to nail down a number before I order the pistons because it may change whether I run flat top or a slight dome. Right now, playing with a spreadsheet I built, if I plug in flat top pistons and run a 1 mm head gasket, the pistons need to be .016" above the deck. With that setup and depending on exact valve relief size, I am at about 10.7 to 1. Obviously, the E88, unlike the MN47 head, is an open chamber design (my chambers were cc'd at 45.6 cc's give or take a couple of tenths). But, it does still have some area (all around the outside) of the combustion chamber which is flat. In this particular engine, since I will be running an 89 mm bore, the area that is flat is greater than stock. The cam is a Sunbelt grind with lots of overlap... intake at .050" duration of 290º (seat duration 320º) and exhaust at .050" duration of 274.8º (seat duration 315º). I will be running carbureted initially -- tripple 44 mikunis on long cannon manifold with 50mm tall air horns and a cold air box... I have a TWM 45mm thottle body setup, injectors, and an Electromotive TEC IV which will go on a little later. I want to see what the horsepower/torque and drivability is with the carbs first. I plan to utilize the Electromotive Tec IV FI for ignition with both setups... Do you experienced L series engine builders think I can run 11:1 or more even with "full" advance (which is what, 35-36º?) without detonation issues? I don't want to order custom pistons and later find out that I should have gone higher on compression ratio. I can mill the head some more to get a little more compression if need be, but the valve reliefs will have to go deeper if I go that route. And again, with pistons in hand at that point, I'm looking at more machine shop costs (which are unnecessarily incurred) to take the reliefs deeper. Of course, I also don't want to have an engine that requires me to run retard the timing to combat detonation... Undoubtedly, there is a point with this combo where the compression will be too high for 93 octane. What I am asking is, what is that point likely to be? What point would you recommend? Also, I will be running a BHJ street damper and 10.5 lb Fidanza flywheel... I was thinking of having the crank lightened and knife-edged while it is at the crank shop being offset ground. They can probably remove atleast 3 and maybe more pounds. Any thoughts there? I have heard that, with it not being a fully counterbalanced crank, it might become less stable with lightening - introduce dynamic balance issues which may cause more flexing of the crank. Oh yeah, the car is a hot track car, but not a competition race car... It sees multiple track events a year and some autocrosses, but I drive it to and back from the track. And, I hope (maybe this will only happen when the fuel injection is put on) that the engine will be tolerable enough to drive around on the street once in a blue moon. Quote Link to comment Share on other sites More sharing options...
30 ounce Posted March 4, 2011 Share Posted March 4, 2011 (edited) My motor is very similar to what you want to build. I used a Rebello 3.0 kit for the bottom end in an F54 block. My head is/was an E88 but if it wasn't for the casting # no one would recognize it. I welded the combustion chambers up to create a quench area that looks like the one in the "Custom Cylinder Head Building...Whats involved" link above. (Although I didn't see that until a year after I did it.) I had the head ported by Bowers Racing (they also did the chamber welding)and put steel seats in. I'm using an Isky 490 lift 290 duration cam and called them to find out what compression ratio to run. They recommended 11.5-1 partly because I'm at 5280 ft. above sea level and can get 93 octane close by. I have run 91 octane with just a hint of pre ignition on a hot day. I think if you are willing to weld the chambers up you can run more compression than the open chambers will allow. I,m using the NISMO .6mm metal head gasket and my pistons are flush (0.0) with the deck. Edited March 4, 2011 by 30 ounce Quote Link to comment Share on other sites More sharing options...
z-ya Posted March 4, 2011 Share Posted March 4, 2011 (edited) For 93 octane, I would keep the CR below 11:1. I would use a piston that gets you the CR your looking for with a stock head gasket. I have a Bob Sharp prepared C production crank going in my race motor build. There is no knife edging, no lightening, all standard dimensions. They basically deburred the casting, drilled out the plugs and tapped them NPT, and tuftriding. Then they verified straightness, balance, and an ultra polish to the journals. They never had any problems with L28 cranks. IMO, you will be spending a lot on machining for little to no gain. I just got the bill from my machinist: $2100. Basic boring, balancing, checking, polishing, mainline hone, rod sizing, cleaning, head and block resurface, etc. etc. But nothing like you are talking about. It's going to cost a lot for all the machining for what, 50cc displacement? If you are getting custom pistons anyway: L28 crank and rods, E88, 89mm custom flat top pistons, 1mm big bore head gasket = 2949cc @ 10.63:1 CR. Or if you want a better rod to stroke ratio use 9mm L24 rods and adjust the piston compression height to get the right deck clearance and CR. Pete Edited March 4, 2011 by z-ya Quote Link to comment Share on other sites More sharing options...
Leon Posted March 4, 2011 Share Posted March 4, 2011 As an aside, those of you who have drastically altered combustion chamber shape have to keep in mind that MBT (max best torque) timing will change. I'm sure if one has spent the money for head altering that dyno time will be in order, so remember that a faster burning chamber will require less timing advance to get best performance. Quote Link to comment Share on other sites More sharing options...
inline6 Posted March 5, 2011 Author Share Posted March 5, 2011 It's going to cost a lot for all the machining for what, 50cc displacement? If you are getting custom pistons anyway: L28 crank and rods, E88, 89mm custom flat top pistons, 1mm big bore head gasket = 2949cc @ 10.63:1 CR. Or if you want a better rod to stroke ratio use 9mm L24 rods and adjust the piston compression height to get the right deck clearance and CR. Pete You are probably right Pete. I really don't have any experience with building motors. I have had a couple of heads done and put them on myself, but that is about it. I've been wanting to build a really nice L series motor since I was 18... So, I have arrived at this combo after spending a bunch of time in the forum and am basing it on other's comments. The motor is going to cost a bag of money, no doubt. But, the rods are in hand, and the crank is at the crank grinder... I guess I will start a motor build thread soon and will follow it all the way through to dyno sessions to see what all this extra effort is worth (or how little it is worth). Quote Link to comment Share on other sites More sharing options...
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