Guest Anonymous Posted April 28, 2002 Share Posted April 28, 2002 I've been on Zcar.com for quite a while but it seems most of the real minds/experience have migrated to this site. So, here I am with a couple questions for the inline Gods. I'll post them one at a time so's it don't get confusing. Todays question. I've recently transplanted a '82 280ZX n/a engine into my '78 convertible (really proud of convertible that I made). SOMEDAY, I'm sure that it will have a V8 in it. In the meantime, I'd like to get a little more smile on my face when I punch the gas. I could get more compression by swapping the old N47 head onto the flattop L28 or I could do the shave/shim job that Bryan Little describes on his site. But, will it be worth the effort? Will this really give me a definate and noticable power upgrade? Will the higher CR wear out my engine faster? Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted April 28, 2002 Share Posted April 28, 2002 Dresbachz, Yes, you WILL get a noticeable increase in power. the Stock CR is only 8.3:1, quite low IMO. You can still maintain reasonable pumpgassability ( ) with 9:1, and as you may have read, SU Norm tried his at 11.3:1 on 93 Well, in case you want a dummie explaination on how this increases power I can give you one.. during the compression stroke, when the piston compresses the air/fuel it displaces a certain cylinder volume to combustion chamber volumes, increasing the first, or deceasing the latter results in more tightly packed air/fuel mixture, and more powerful combustion (when sparked) However, there is a horrible, horrible downside, which we all know as Detonation, pinging, knock, etc. When the mixture becomes compressed and everthing is just a little bit hotter in there due to upped compression, pre-ignition tempuratures become hot enough to make the mixture EXPLOAD- untimingly. This is called autoignition, it sounds like a good thing by name, but its not.. hehe Higher octanes will have higher autoignition tempuratures, so how much you want to raise the CR depends on the availability of high(er) octane fuels, and leaving a margin of safety so you don't get knock. In other words, how high can you raise it to run on 92/93 In case you don't have the numbers for the math, here's the formula CR= (cylinder+chamber volume)/chamber volume Remember that for the chamber volume you HAVE to add in the exact amount of cc's for the headgasket too, this is very touchy, note that people slightly alter a headgasket for a significan't increase/decrease in CR. For practical purposes, use this formula to find the right head: chamber CC volume= cyl volume/(CR-1.0) then refer to here: http://www.zhome.com/ZCMnL/tech/128combo.html My recommendation if you're really looking for power would be an E31/E88 with large intake/exhaust valves, you can crunch the numbers yourself. HKS makes a 2mm and 1mm 91mm-bore headgasket.. you can plot around those two, or use stock hg cc's to mess around with that. I don't think you should have to mill the head, just find a different one, and use the right headgasket. Good luck with your street machine. -980mak Quote Link to comment Share on other sites More sharing options...
DAW Posted April 29, 2002 Share Posted April 29, 2002 Bang for the buck in performance gain, increase your compression. The question facing you is how to do it. Put on your old N47 head onto the F54 shortblock and you'll have about 10:1 cr and a big boost in performance. The problem is that this combination tends to ping. A lot. You can add octane boosters, etc but that's kind of a pain. One way to go would be to get an N47 head from an L24 Maxima, install the intake valves from your N47 L28 head (44 vs 42mm), this head will boost cr even higher than the L28 N47 head would, but it has the benefit of the high-quench closed (peanut-shaped) combustion chambers and you may get around the ping problem. You might have to run two head gaskets to pull this off. If that didn't work, then the P79 shave/shim/N47 valve trick is what's left. DAW Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted April 29, 2002 Share Posted April 29, 2002 you could always up the cam in the 280 range with that type of compression and run it with regular unleaded. I have dome pistons in my chevy with a compression of 10.2:1 and a 284 extreme energy and I run regular fuel for faster times all the way to 40 degree total advance and still no ping even at 7000 rpm. cams for inliners aren't expensive specialy if you go get it ground. don't go to much or you'll suffer the low-end blues. don't forget that you need to change spring, lashpads and rockers, Im going to do an experiment I bought a 280 cam off of ebay for a L16-L20b Im going to see if I can get some 1200 grit paper and clean the rockers so I don't have to spend so much on them. who knows but good luck I have another z with a 280z block (dished pistons)and a early 240 head and su'z and it rocks I like it better then my v-8 z for drivability 20 mpg instead of 6-8 mpg o well price to pay to get in the 11's good luck Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted May 27, 2003 Share Posted May 27, 2003 If you want to know your EXACT comp. ratio, there's a little more math involved than explained above. Starting with the hardest, the head volume.(really not hard at all) The simplest way to do so is to use a beacker; fill it to 1 litre, pour it into one of the chambers untill the water reaches the top, measure what's left in the beacker and subtract it from 1 liter... that's your head volume.(repeat these steps for the piston, if it's dished) Note: this is not a very accurate method; better to get actual specs from manufacturure (thanks, Dan). next hardest--ringland displacement. measure the diameter of the bore of the block, cut that in half and you have the radius. Multiply that by itself, then by the ring land height of the piston, then by 3.14. set that number aside. measure the radius of the piston, square it, multiply that by the ringland height, then multiply that by 3.14. Subtract that number from the one you just set aside. You now have your ringland displacement. gasket displacement. multiply the thickness of the gasket by the the radius of the bore squared, by 3.14. that's your gasket displacement bottom dead center displacement. Measure the distance at BDC to the top of the deck from the top of the piston, then multiply by the radius of the bore squared, then by 3.14 add all the numbers above together and you have the displacement of your combustion chamber. Now, measure the cylinder volume at top dead center, add the head volume, gasket displacement, and ringland displacement. when you've finnished, divide BDC displacement by TDC displacement and you will get your compression ratio. I'm sure that most everyone knows this, but I would hate for a newbe to be browsing through the posts and think it's as simple as stated a few posts up... And, since it's an old thread, chances are no one will read this anyways. Quote Link to comment Share on other sites More sharing options...
Guest shane280z Posted May 27, 2003 Share Posted May 27, 2003 Dresbachz. My 02 is to get a supercharger. Easist bolt on for the L-2.8 there is. The Buick Grand National charger is still available and selling under 200dollars at sites like EBay. You must build a bracket on the sparkplug side of the engine but that is easy to do. And since you have a NA zx engine you can get away with using the ColdStart injector as a working 7th injector for the increase in blower power of fuel. You NEVER hook up a injector directly into a supercharger remember because it carries air compressed ... and very clean.... into your existing AFM and should you have a backfire will not therefore blow yourself right up! The difficulty is how much boost you want the supercharger to be able to go at. For the Grand National I think 6pounds is adequate and a given redline of 6200 is recommended. The other difficulty and main problem with how to work this particular supercharger is just how you are going to Pulse-Fire that 7th injector. I have some schematics on how to do this but... I would have to scan them into digital format and send 'em to you as a email attachment, And this 'pulsation problem' is only so because the GrandNational Buick superchrger was not electrically designed for your Z 's electrical wring specks. But it is a easy build and affordable . Plus its got a WONDERFUL sound as the revs come up. later. Quote Link to comment Share on other sites More sharing options...
J Taylor Posted May 27, 2003 Share Posted May 27, 2003 Not to be an ass but the Grand National never came with a supercharger. They were all turbocharged. Also pretty sure a Grand National is not going to redline at 6200. That's a setup that makes as$loads of torque downlow but doesn't like to rev very high. JT Quote Link to comment Share on other sites More sharing options...
Dan Baldwin Posted May 27, 2003 Share Posted May 27, 2003 Before I rant, I'll address the original post. Dresbach, What your proposing is an excellent idea. Easy swap, and your compression will go up about 1.5, from ~8.5:1 to ~10:1 assuming neither head is shaved. You might want to check the cc volume to see if it has been. Stock cc on an N47 is 44.7cc. Now for the ranting and raving (tune out if you don't have the stomach for it): Whoa, this is getting scary! Datsun-Dude, your volume equations are incorrect. The volume of a cylinder is pi*r^2*h. NOT pi*D*h (unless you have square "cylinders")! Also, a 1 liter beaker isn't going to give you nearly the accuracy you want. We're talking about chamber volumes in the 40cc range. 1cc accuracy is essential, and you'd really like to be in the tenths. ARRRRGGGGGGHHHHHH! Shane, you do know that the Grand National was turbocharged, not supercharged, right? As has been gone over before numerous times on this and other sites, the supercharged L28 is a pretty poor idea compared to a turbo as far as practicality and performance are concerned. Besides, all this guy wants to do is increase his compression DAW, as has also been beaten to a bloody pulp on this site, an open chamber N42 has been used on MANY highish compression L28 without any undue detonation issues. OK, Norm broke some ringlands at 11.6:1. I have had no issues at 10.5 and 10.8:1. NONE. On 93 pump. N42s and N47s have been plopped on many a flat-top bottom end with no problems. Just because the open chamber heads *theoretically* should have detonation problems doesn't mean they do. Based on my and others experience, what the poster is proposing does NOT pose a detonation risk. PEOPLE, if you do NOT have the technical or practical expertise on a subject to offer helpful feedback, DO NOT POST. I'm not trying to be mean, but what I've seen in this thread is NOT up to the standards of HybridZ. Not by a long shot. If this reply is too insensitive for HybridZ, may the moderators remove me now. Quote Link to comment Share on other sites More sharing options...
Dan Baldwin Posted May 27, 2003 Share Posted May 27, 2003 Oh yeah, Dresbach, I don't think the higher compression will wear out your engine faster, as long as there are no detonation issues, and there shouldn't be assuming the ignition timing is set properly. It's better to burn out than fade away anyway, right? A properly tuned L28 with 9.8:1 CR should last practically forever. These engines are very strong and reliable. Oh yeah, the handy Lengine calculator gives 8.5:1 for the dished piston motor, and 9.8:1 (not quite 10) with the N47 head, so the gain, stock vs. stock, is more like 1.3. I do think you will notice the power gain. Beauty is that torque is increased EVERYwhere, from idle to redline. If you're stock cammed, you might try to aim for maybe 10.2:1. I did run around 10.5:1 for a while with the stock cam without issues, but that's with a different bore/stroke, and might have been right on the edge. The only times I got detonation was when I stupidly set the timing to 18 degrees at idle, with the stock mechanical advance, which gave me something like 43 degrees advance at rpm, and when I lost an advance spring and was getting ~25 degrees or so at idle. Quote Link to comment Share on other sites More sharing options...
yo2001 Posted May 27, 2003 Share Posted May 27, 2003 wasn't there a topic about static and dynamic compression on this forum? That'll be good read. Over 10:1 on a stock cam is going to be almost pushing the limit. 9.8:1 sounds good to me. Norm told me to keep the motor under 215-220psi under compression test. (I was running about that much on my N/A setup) With stock pistons at least. And Norm is running N42 with alot of material shaved from the bottom of head. He said his head chamber isn't open any more. It's like E31 head, semi-hemi chamber. Good strong flame front should help under high compression motor from pinging. FYI Quote Link to comment Share on other sites More sharing options...
Dan Baldwin Posted May 27, 2003 Share Posted May 27, 2003 In my first post I implied that D_D gave us the equation for the volume of a square "cylinder". The equation pi*D*h (height times bore times 3.14) is actually for the surface area of a cylinder. Quote Link to comment Share on other sites More sharing options...
Dan Baldwin Posted May 27, 2003 Share Posted May 27, 2003 Norm is running N42 with alot of material shaved from the bottom of head. He said his head chamber isn't open any more. It's like E31 head True enough. Mine, after some shaving, is still an open-chamber head, though. As I stated above, I've run over 10:1 with the stock cam without any real detonation issues. I'm at 10.8:1 (from actual volume measurements) now, but of course I do have a pretty big cam. Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted May 27, 2003 Share Posted May 27, 2003 Yeah, radius squared, that's what I meant. Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted May 27, 2003 Share Posted May 27, 2003 I know it's a little ironic or even idiotic that I would take the time to explain the the right way to get your C/R, or displacement, then get it wrong.... And I do appriciate your correcting me, but try not to be so insensitive... I'm fragil -- Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted May 27, 2003 Share Posted May 27, 2003 I've went ahead and corrected the furmula I wrote earlier so it should be right, now. Again, my bad... Quote Link to comment Share on other sites More sharing options...
DAW Posted May 27, 2003 Share Posted May 27, 2003 Guys, re comments above, I am speaking from experience re ping tendency on open vs closed-chamber heads. I've put Nissan L series motors together both ways and it's been my experience that the closed chamber has an edge re ping tendency (both with the same stock cams and c.r.) the closed-chamber had slightly smaller bore & stroke but both had similar rod/stroke. With a cam, there might be no ping with either head but with stock cam I think it tends to isolate detonation problems. so I'm not talking theory, just practical experience. Those who have "shaved their heads" may not be doing a true comparison as they may have transformed toward closed-chamber configuration. Maybe more interesting is what I observed between two 2.8L l6s I use. Both have the same stock L28 cams and both have high compression one is 9.8:1 and the other is just over 10:1. Both have unshaved open-chamber N42 heads. Two different stock flat-top shortblocks, the F54 has triple side-drafts; the LD28 has stock/modified EFI with analog/non-O2 sensor ECU; both have headers. The LD28/N42 doesn't ping...ever, and it's the one with the higher c.r. (cranking pressure is 209-215). The F54/N42 cranks at 198-205. I can set initial advance at 12 on the engine with the higher c.r. but only at 8 on the other due to pinging. So why does one ping and not the other? (I don't know; I'm asking) Could it be the f.i. provides a more consistent stoichiometry than the side-draft carbs? (Accelerator pumps are working fine and jetting should be rich enough). I assumed the LD28 was more resistant due to the thick piston crowns and 46.5mm of comp.ht. but now I'm wondering if the rod/stroke could be the main factor (130.4/79 vs 140/83) with the TDC dwell duration providing a more even burn, or whatever. What do you think? DAW Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted May 28, 2003 Share Posted May 28, 2003 Which rod ratio is which? Quote Link to comment Share on other sites More sharing options...
DAW Posted May 28, 2003 Share Posted May 28, 2003 The 130.4/79mm is the F54; the 140/83 is the LD28. DAW Quote Link to comment Share on other sites More sharing options...
yo2001 Posted May 28, 2003 Share Posted May 28, 2003 But if the two set (between closed and open chamber) are exactly same set up, would you not need more timing on open chamber to get the optimal power? Just a question Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted May 28, 2003 Share Posted May 28, 2003 The ratios are actually pretty close, the LD motor being slightly longer. Given this, as well as the higher comp. ratio, and all other things remaining equal, the LD motor would be more likely to ping, if this was the cause of it. Weird... Quote Link to comment Share on other sites More sharing options...
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