subtle_driver Posted September 17, 2006 Share Posted September 17, 2006 Hi, I have a stock 73 240z L24/E88. I want to raise the compression to approximately 10:1. What is the required amount to shave from the head (e88) to get near to this compression. My E88 head is used, and it has been shaved before[unknown specs]. I need the stock/unshaved "thickness" measurement from the top to bottom (head gasket surface, to the valve cover). And I need the thickness required top attain apporoximatly 10:1 ratio. THANKS!!!!!! The machinist needs to know how much he needs to take off. Quote Link to comment Share on other sites More sharing options...
Administrators BRAAP Posted September 19, 2006 Administrators Share Posted September 19, 2006 So you “need” 10:1 comp ratio in your L-series eh? You are planning to run at least AV gas or race fuel right? Off the top of my head, I don’t know how much material needs to be shaved from the E-88 for a flat top piston L-24 to achieve that comp ratio, but if it ends up retaining its open chamber design, it will rattle like a Dodge Cummins even with 92 Octane premium. If you are planning to run race gas, then why not take full advantage of the fuels detonation resistance and run 12-13:1? If you are planning to run pump gas, do yourself a HUGE favor. What “little” power gain would be had by raising the comp ratio to 10.1, will be lost and even more power lost due to the amount of ignition timing you will have to back out to keep it from rattling. If the E-88 head is your only option with pump gas, leave the comp ratio alone where it is and spend your money on chamber reshaping, mild port work, mild cam, free flowing exhaust, lightened flywheel, quality ignition parts, etc. The Datsun L-series with open chamber heads or dished piston does NOT like even 9.5:1 on pump gas. Good luck, Paul Ruschman Quote Link to comment Share on other sites More sharing options...
madkaw Posted September 19, 2006 Share Posted September 19, 2006 Paul , sounds like i am at the limit then. Good thing my machinist talked me out of 10 to 1. He figured right at 9.55 to 1 on my head. The chambers cc'd at 41.5 but the bore is notched for my big valves that has reduced the CR . I don't want to run on AVGAS!! Quote Link to comment Share on other sites More sharing options...
subtle_driver Posted September 19, 2006 Author Share Posted September 19, 2006 here is some more info, The head is ported, and I am running a schnieder stage 3 cam with springs, and free flowing exaust with headers, SM needles on my SUs, high volume electric fuel pump, turbo oil pump, no fan clutch, no smog, electronic ignition, 5 speed, lightened flywheel, underdrive pulley.... just bolt ons.. mostly stock. I was just advised to raise it to 9:5 or 10:1 at least when installing the cam. The head is off, and I want to do it. I just need some machining specs. It doesn have to be perfect, at least somewhere between 9:5 and 10:1. I am going to use a Felpro gasket. I will tune it to run richer, and adjust cam, and ign. timing accordingly. And I am going to use 91 gas. please advise..... Quote Link to comment Share on other sites More sharing options...
subtle_driver Posted September 19, 2006 Author Share Posted September 19, 2006 sounds like 9:5 would be desireable. Now I just need the specs for the machinist.... Quote Link to comment Share on other sites More sharing options...
subtle_driver Posted September 19, 2006 Author Share Posted September 19, 2006 I measured the head thickness, it is 4.5 inches exactly[for my used e88]. Quote Link to comment Share on other sites More sharing options...
SKiddell Posted October 29, 2006 Share Posted October 29, 2006 BRAAP Please don't take this as in any way offensive or aggressive but I am a little confused. Else where in the world, certainly in the UK, Z compression ratios of 10:1 are fairly common place and I know that in Japan where there has been more L series development than anywhere in the rest of the world put together, on serious L series engines, high compression is defacto. Personally, I run 11:1 on an 2.8 litre using standard 95 RON fuel with 34+ degrees of advance and making almost 260Hp at the fly....is it about to fall apart into a knock induced early grave? well some 60 or so 1/4 mile passes (15 of which were under 13.5) and nearly 10,000 miles of road use says no. Further more, in a classic race series in the UK (HSCC) there are 4 240's running, along with at least 2 hill climb cars in other events... all of them have 11:1 or greater ratios, one 240 has just placed 3rd in the Spa 6 hour endurance race (see http://www.zclub.net/forum/showthread.php?t=7564&highlight=spa) which was certainly running greater than 11:1 .....and significant advance. I know this to be true as either the owners or the engine builders are members of our club. Now I agree that more often than not they are running as high an octane rating as possible (97 or so) but if you work it out, this is the equivalent to your 92 AKI rating (different systems of octane ratings RON vs. Average RON+MON etc) So that goes someway towards factoring differences in octane rating out. You also mention What “little” power gain would be had by raising the comp ratio to 10.1 Compression is known to be a tried and tested method of increasing power output, particularly on the L series. Once, without thinking I swapped a 1mm 89mm dia head gasket for a 91mm HKS steel, (inadvertently dropping the compression by 0.4 of a point) on the dyno the engine showed a 15hp power drop off, we tore the engine down and as matter of course replaced the gasket, using what we had left which happened to be a Felpro 1mm @ 89mm, we then re-dyno'd it and hey presto normal service was resumed.... You could write this off "shade tree" mechanics but to give UK engine development a little more credence, in January I know of at least 2 all steel 3 litre engines being built, using a custom designed 83mm stroke steel billet cranks [/url] lightweight Carrillo rods and custom forged, short skirt pistons http://www.zclub.net/forum/attachment.php?attachmentid=2430&thumb=1&d=1161459548. One will run triple side draughts and the other individual throttle bodies. Both these will be running in excess of 11:1 on 97 Ron fuel (approx 92 AKI) We even have one guy seriously looking to have aluminium L series blocks cast. Yes I agree that excessive compression can be extremely damaging but if spark and mixture are controlled, quality components and machining used, then why not run 10:1? many factory models are in excess of that.... now if we want to start talking dynamic compression well that's another thing all together. Quote Link to comment Share on other sites More sharing options...
Guest 280ZForce Posted October 29, 2006 Share Posted October 29, 2006 BRAAP Please don't take this as in any way offensive or aggressive but I am a little confused. I believe BRAAP is concerned with the guy seeking advice is trying to run pump gas. Here in CA (where the gentleman is from), at the pump we can only get as high as 91 octance and it aint nothing special. So I believe the concern is detonation with that low of octane with that compression. Gas here and gas in the UK are on different levels IIRC. Quote Link to comment Share on other sites More sharing options...
Administrators BRAAP Posted October 29, 2006 Administrators Share Posted October 29, 2006 Skiddell, I’m glad that you are able to run 11:1 compression ratio and apparently have no engine damage. I’m sorry we can’t do the same here in the US with our Pump gas, though we do run 12:1 and higher with AV gas and Race fuel quite regularly, (I’ve built more than few L-series heads for high compression L-series engines for people on this forum). I personally am running close to 12:1 in my L-28 powered 240-Z race car with 100LL Av Gas, and a very aggressive ignition advance, 42 degrees total timing, and it runs GREAT! (I’d probably be better off with around 38 degrees as it is a high quench MN-47 head). Ok, now as for your Octane comparison between the US and the UK, None of your math formulas are going to dispel the plain fact, (and well documented fact on this and other forums), that here in the US, the L-6 engine using the open chamber heads, i.e. E-88, N-42, N-47, WILL and DO detonate AUDIBLY, not just lightly or silently, but LOUDLY, with 91-92 octane Premium pump gas in the US and that is with only 9.5:1 compression ratio! I do agree that running as much compression ratio as you can, would be ideal. As a professional engine builder, my belief is that you should always build in as much static compression ratio as your fuel will allow, WITHOUT having to back out any ignition timing from the ideal timing that engine combination prefers. I strongly believe that if you sacrifice ignition timing just to acquire a small increase in static compression ratio that you are going backwards in regards to power output. For a street engine, even if you sacrifice a little static compression, so be it. You wouldn’t be able to feel that small loss in the seat of the pants any way. Custom pistons for the L-6 are very expensive and for most street applications/budgets, a small sacrifice in ideal compression ratio is usually a compromise most budgets are willing to live with. At some point, you have ask yourself is 5-10 HP worth a set of $800 pistons? (US dollars). At $80 per HP at best, that is hard to justify. For US Pump Gas L-6 applications, I stand firmly 100% in my original post in this thread. Quote Link to comment Share on other sites More sharing options...
SKiddell Posted October 30, 2006 Share Posted October 30, 2006 Please don’t mistake these posts of mine for anything other than inquisitive banter, I am only seeking to understand the reasons why...not seeking to prove people wrong. at the pump we can only get as high as 91 octance and it aint nothing special. But in my previous post and according to the octane rating methods used in both countries, 91 octane is equivalent to the 95 or so that we get here (standard) and 10:1 compression ratios on 95 RON happens all day every day. I believe BRAAP is concerned with the guy seeking advice is trying to run pump gas. I fully understand that, but the guy "could" have be from anywhere in the world so the advice may have been technically incorrect, as it happens he wasn’t. My point being that people all over the world read these forums and take advice from them. 11:1 compression ratio and apparently have no engine damage no "apparently" about it, its a fact but certainly no big deal. I hear what you are saying and I cannot deny that you have the advantage of living eating and breathing the American Z tuning scene so ultimately will have 100% more knowledge about what works and what doesn’t......in the US, but take for example the cylinder head you worked on recently for a fellow club member (beautiful port work), this is destined for the UK and according to your specification has a 55cc chamber volume (more or less stock size for a P90) in the UK we use the P90 and the first order of the day is to shave the snot out of it, then shim the towers (I prefer the Kameari tensioner myself ) just to get the compression up, hey you did agree that if possible, compression is a good thing I do agree that running as much compression ratio as you can, would be ideal I am curios as to why you retained the large CC when it will be used solely in the UK, in an environment where higher compression ratios can be achieved. Like I say I am not seeking to flame or dis anyone, maybe you have found ideal cams to suit lower ratios, producing good dynamic ratios, maybe you have found compromises in the valve size and geometry or exhaust systems that overcome some of these issues, in the UK we only have 200 240Z's so development is done by only 1 or 2 people where as you guys were fortunate enough to have 1000's of the darn things. Quote Link to comment Share on other sites More sharing options...
subtle_driver Posted October 30, 2006 Author Share Posted October 30, 2006 dang people, I just want to know how much i need to shave off to get about a point gain or slightly more on my e88.... I am just starting out in the world of work, so i don;t make much money, so ya, shaving is a good option for me. I'll back off the timing and richen it up to keep it from pinging. LOL!!! Quote Link to comment Share on other sites More sharing options...
z-ya Posted October 30, 2006 Share Posted October 30, 2006 Using the LEngine calculator I did the following: L24 -> E88 head -> STD gasket = 8.76:1 STD gasket = 7.1 cc volume 1mm gasket = 5.7cc volume So if you subtract 5.7 from 7.1, you get 1.4. This approximates machining 1mm from the head, and using a stock head gasket. If you enter 1.4cc in the LEngine "Gasket CCs" box (hit return key), the CR changes to 9.73:1. If you use a 1mm gasket (enter 0 in the LEngine "Gasket CCs" box ), the CR ends up being 10.0:1. Paul, what are standard cam tower shim thicknesses? Do they make 1mm shims? If so, I would machine 1mm off, and use 1mm cam tower shims. Then you can run a stock head gasket and end up with a 9.73:1 CR. If you don't have any detonation problems, you can always run a metal 1mm gasket and have a 10:1 CR. I ran a 10:1 CR L28 (flat top, N47) in my track car for years running 93 octane northeast USA pump gas. Running a stock cam, I could only run 26 deg of advance. With a performance cam, I could have probably run quite a bit more timing. I was runnnig Megasquirt fuel injection too. Depending on how well the carburetor fuel curve matches the required fuel curve of the engine will determine how much advance you can run. With carbs, your kind of stuck, unlike EFI where you can tune those leans spots out. Quote Link to comment Share on other sites More sharing options...
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