SleeperZ31 Posted May 22, 2008 Share Posted May 22, 2008 Just had a quick question involving compression ratio's on the vg30(e) since im planning on making all N/A power i figured increasing the compression ratio within a reasonable limit would be a great addition to the isky cams (which im still frickin' waiting on) along with the in-progress plenum, and it brought me back to my '94 z28 days when i had its heads shaved enough to correct the slight warpage it had which in turn increased compression slightly.. How much do you think the vg30(e) heads could be shaved without causing valve-piston clearance issues and how much would this change the comp. ratio, AND would it be a worthwhile venture? I know that thinner head gaskets and high-dome pistons achieve the same effect, but pistons would require my car being down for some time (and its my only ride so thats a no-go) and thinner head gaskets pose the risk of leaking and usually have a shorter life expectancy so i figured having the heads shaved might be the way to go for more N/A H.P., what do you guys think? Quote Link to comment Share on other sites More sharing options...
Careless Posted May 27, 2008 Share Posted May 27, 2008 shaving the head will be better in theory compared to a thinner or thicker headgasket because you might get a better quench area depending on how the combustion chamber is tapered from factory. I think pistons and rod bolts are the way to go. Nissan rods are generally well built from what I've seen them being put through. Can't say for sure with the VG's. Take into account that any detonation will severly pound your factory pistons. VG Turbo engines have a dog-low compression ratio, especially the 87 turbos. So that makes you do more math to get where you want. Are you using an N/A engine to start? Have you considered VG30DE pistons? they feature an 11cc dome for JE Forgies, which are off the shelf. Are the pin offsets and compression height the same for the DE and E heads? Are pistons interchangeable? The best way to obtain a suitable compression ratio through semi-accurate calculation would be to use an excel spreadsheet built for purpose, or Dyno 2003 engine simulation software. Input the HG thickness, HG ID, cylinder ID, Piston Deck clearance and Dome volume, and find out the factory combustion chamber volume. I'm sure there are more variables, like the ring-zone where the piston and cylinder don't meet, but air can get into in order to push the piston ring out towards the wall under load. But you get the idea, right? Then take your shaved value and your cylinder ID, and do some math to figure out how much Combustion Chamber volume you've removed. THEN you can calc your compression ratio. Anyone who builds engines will tell you that the head makes the power. The bottom end just deals with it as best it can. A lot of people have opinions on quench but I believe that with a vacuum oriented engine (N/A are relying on vacuum to draw in air across the entire rev-range), you will need a properly calculated quench zone to homogenize the mixture of air/fuel before burning. Something that the turbo-charged engines do with swirl in the combustion chamber due to high pressure and cylinder filling... but they benefit from quench too at certain power levels... just something to think about before you gung-ho and head rebuild. it costs money. time does too, but i think time is better spent Quote Link to comment Share on other sites More sharing options...
SleeperZ31 Posted May 28, 2008 Author Share Posted May 28, 2008 Great info, thanks! some of the testing that would be required to accurately measure the increase in compression from having the heads shaved are a bit out of reach (theres no dyno's anywhere near me..*sigh*..) but oddly enough plenty of experienced machine shops (doesnt make sense, does it?) but yes, it is a N/A to start with and will be for some time, definently hear you on watching out for detonation, hate to destroy the mill from too much compression but i doubt that having the heads shaved would increase it that much, and the combustion chambers being polished so theres less chance of localized hotspots from excess casting so maybe i will have 'em shaved, just gotta get the $$$ Quote Link to comment Share on other sites More sharing options...
Careless Posted May 28, 2008 Share Posted May 28, 2008 Great info, thanks! some of the testing that would be required to accurately measure the increase in compression from having the heads shaved are a bit out of reach (theres no dyno's anywhere near me..*sigh*..) but oddly enough plenty of experienced machine shops (doesnt make sense, does it?) but yes, it is a N/A to start with and will be for some time, definently hear you on watching out for detonation, hate to destroy the mill from too much compression but i doubt that having the heads shaved would increase it that much, and the combustion chambers being polished so theres less chance of localized hotspots from excess casting so maybe i will have 'em shaved, just gotta get the $$$ all you need to test for compression ratio is a 100cc buret and stand, some masking tape, an inside micrometer, a depth guage (usually a feature of vernier calipers), some deionized water, plexiglass and lithium grease if I remember correctly. polishing your combustion chamber might yield a 1 or 2cc increase in combustion chamber volume, and you can play with headgasket variables for thickness. pm me if you'd like a trial version of dyno2003... I'm sure you would find it useful in experimenting. It's mainly for US domestic engines, but It'll give you a good idea of what to expect from an N/A 3 Litre. Machinists rely on past experience and customer's wallets to find out how much horsepower one engine or another makes... I can see why though... Not many machinists/builders will supply complete engine packages for Nissan motors, so they have no reason to buddy up with an engine dyno outfit or something along those lines. Adding to all this, I'm starting to find the minute details of engine blue-printing to be the most interesting part of the car... I'm trying to acquire all the tools I can and buddy up with a reputable machinist to cross-examine my findings to see that I'm doing everything right. Of course my project will be the first complete build by myself... *crosses fingers* What kind of power do you expect, just for thread-info sake. Quote Link to comment Share on other sites More sharing options...
SleeperZ31 Posted May 29, 2008 Author Share Posted May 29, 2008 personally all i want is to be at the 200hp mark, alot to ask i know considering the turbo vg30e was just able to make that much stock, but even if its below the 200hp mark just something thats fun to drive and nice sounding, the only reason im really doing cams is because a bolt broke off flush into the current heads with my header installation and no machine shop would be able to extract it with the heads in place(its my only ride and i couldnt have it down long enought to take the heads off and have the bolt removed, and im afraid to push it past 3,500rpm for fear of blowing an exhaust gasket) and i figured if im gonna throw a new set of (or should i say new-ish) heads i might as well take the time to improve them a bit my big dream is to do a supercharged vg30(e) using the supercharger and manifold from an xterra and use the internals and engine managment from a turbo vg30, ive got the engine stand and tools and located a turbo motor but no luck finding a supercharger or (even harder) the lower intake plenum...oh well, i can still dream... so far for mods ive got the msa headers, no a/c, electric fan and CAI, along with better wires and plugs, pending cams, P/P heads and a engloids plenum...think i can hit 200hp?....oh and i dont know if it counts for much but royal purple full synthetic oil too..lol Quote Link to comment Share on other sites More sharing options...
Careless Posted May 30, 2008 Share Posted May 30, 2008 It's a 3.0 litre. possibly 2.9 or so when you're done. sure it's possible, infact I'd be quite dissappointed if it was less than 190 range. but I would just use the VG30DE as a base. 222hp off the bat, you can make 260bhp with an 11:1, cams, exhaust and some head work, i'm sure. Might cost even less to do, aswell. might be something to think about. pick one up and do it on the side yourself. I reckon you can find a VG30DE for about 500 bucks. Quote Link to comment Share on other sites More sharing options...
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