zeiss150 Posted April 14, 2005 Share Posted April 14, 2005 Hey Z people What is the highest CR that a turbo engine can have? mind you im not tring to build a monster turbo just a moderate 250 RWHP. I'm looking to build a turbo with between 8.07:1 and 8.6:1. it would be an F54 short block with flat top pistons and a P90 head. Has anyone ever done this or heard of this. Question #2 ... Are performance cams a good idea on turbo motors? I have a schnider 460 lift 273 duration cam setup... would the Turbo ECU freek out? Thanks for the info. Rock on Z People Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted April 14, 2005 Share Posted April 14, 2005 from all the info I've absorbed here and elsewhere, the highest CR commonly used on turbo L6's is right around what you're planning on, 8.5:1 area. I think I've seen some guys do motors that were low 9:1 area with turbos, and a few guys have had problems at these compression levels but most have not. This is real gray area stuff I mean no one really seems to know for sure what is too much CR to turbo or how much is too much boost to run with a given CR with these motors. It's gonna depend more on your EFI setup and ignition timing, as well as what octane of fuel you use. There was a story in a magazine a while back where they turbocharged a Toyota Matrix which had like 11:1 compression, running mild boost I THINK either 7 or 10psi, with fully programmable EFI/ignition. I think the stock Lancer Evolution runs around 9.5:1 compression stock and high teen or 20psi boost. It can be done, just dont plan on doing it with stock L28ET efi and ignition control. Another advantage those motors have is much more modern and efficient head design, which plays a huge role in detonation control. But run it rich enough, high enough octane, and enough timing retard on boost and you should still be able to run good boost numbers and make great power with no problems. I say 8.5:1 area you'll be fine and have a much more responsive motor off boost. Quote Link to comment Share on other sites More sharing options...
Drax240z Posted April 14, 2005 Share Posted April 14, 2005 I've got a buddy running 9psi boost on an 11.2:1 K20... Awesome street car. Not to be tried on an L-series... Quote Link to comment Share on other sites More sharing options...
zeiss150 Posted April 14, 2005 Author Share Posted April 14, 2005 anyone got cam info for turbos? Quote Link to comment Share on other sites More sharing options...
cheftrd Posted April 14, 2005 Share Posted April 14, 2005 anyone got cam info for turbos? Same as what you'd run for NA, but with less overlap. Quote Link to comment Share on other sites More sharing options...
technicalninja Posted April 14, 2005 Share Posted April 14, 2005 Max preformance turbo cam has substaintially different valve event timing than max preformance N/A cam. Turbo cam requires smaller valve overlap to reduce exhaust backflow when both valves are open. Pressure in exhaust manifold is usually much higher than boost pressure in intake. (ie 10 psi boost=15 to 20 psi exhaust backpressure (before turbo). In your case the 260 Schnider cam is mild enough that it will work fine. Flattop F54 with stock P90 head and stock headgasket = 8.8/1 comp ratio. This will work as long as proper attention is paid to heat control (ie intercooling and proper compressor selection), ignition timing, and fuel enrichment. Compression can be lowered easily two ways. Increase thickness of head gasket-this can effect the squelch caricturistics and create more problems than it fixes. Better to unshroud valves and remove material in combustion chamber. Do not remove material at outer edges of combustion chamber- this can effect squelch as well. If you use a thinner head gasket or the head has ever been milled this will increase compression. Almost all L series heads have been milled at sometime in their life. Check closely. Any changes in engine output (increased power=increased flow=increased fuel needs) will require addressing fuel delievery. The stock EFI with all stock settings is limited as to how much fuel it can deliever. There are post apon post that address this. Spend some time reading these. The stock EFI brain has no idea what cam is in the motor. It has mapping for the stock engine and does not have the ability to re-learn as many of the newer F.I.s can. Your cam installed in a stock system should not create major issues as it is fairly mild anyways. Your cam, increased compression ratio, increased boost,stock turbo, stock EFI system is probably a recipe for problems. Before spending any $ on parts buy a couple turbo books- Corky Bell's book Maximum Boost is a good choice. Reading will save more than any other thing you do. Educate yourself. Good information is available. Although he is not usually associated with turbocharging, David Vizard has written many books dealing with engine preformance and his explaination of cam dynamics is one of the easiest to understand. Nitrous cams and turbo cams share many of the same needs. Hope this helps Rick Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted April 14, 2005 Share Posted April 14, 2005 techninja you're still around!! man I haven't seen a post from you in forever... maybe just not looking in the right places?! Hey thanks again for the tips you gave back when I was doing the main bearings on my motor... really helped me out a lot! Well she's still running... I have to admit for a while I didn't know what to expect and had NO confidence in my ability to pull off a job like that w/o something major going wrong. But so far so good it's been a few thousand miles at least. I haven't rechecked the thrust play again... kinda don't want to afraid what you said is probably true and it's already out of spec again.... but what can I do? Can't afford a rebuild and I'm not gonna replace main bearings again NO WAY... 10 hours under the car was just no fun. I'll run it til it breaks and go from there, probably just get another engine by that point. Quote Link to comment Share on other sites More sharing options...
Xander Posted April 14, 2005 Share Posted April 14, 2005 It is possible that I win the title for highest compression on a turbo engine here on Hybridz. I am currently at aproximately 1:9,7. I have a F54 block, slightly shaved P90 head. flattop pistons with a 2 cc squish pad on top. The pistons are .5 mm above the deck. Here's a picture of the pistons installed: at first it assembled the lot with some crappy headgasket. This blew out within a week. So I installed another crappy headgasket . 2 days later I blew that one. Installed a felpro. When torqueing the head something was stuck in between the head and the gasket. That destroyed the felpro. So I am now at headgasket No 4. I am now driving around with a new nissan headgasket and ARP studs. The boost is limited to 7 psi. The drivability is great. I can quite easilly drive of in 3rd gear. and it picks up nicely from 1200 rpm. But I will probably never reach my 300 hp goal. the good part about all this is that I can now swap a head gasket within 2 hours . Quote Link to comment Share on other sites More sharing options...
Tony D Posted April 14, 2005 Share Posted April 14, 2005 For Turbo Cam Information, read Racer Brown's Technical Article, and talk to Ron at Iskendarian Cams. Ron did the R&D for all those Nissan Grinds everyone seems to be using "L4, L6, L7, L9..." Ron was deeply involved with Electramotive in the camshaft development for their racing program in the early 80's. If he ground the cam on the #83 Turbo car, which made 580HP at 7500rpm on 20.6# of boost, and made 520ft-lbs of torque at 5600rpm I think he's got a real bead drawn on what can and can't be done on a Nissan Turbo Cam! Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted April 14, 2005 Share Posted April 14, 2005 There you go... Xanders setup is a good benchmark for "this much is maybe TOO much". I do think 9.7:1 CR is the highest I've heard of on a turbo L6. The fact that he's blowing gaskets even with programmable EFI and spark is pretty interesting. I think it will be MORE interesting to see how well it holds up with the Nissan gasket and ARP studs. An HKS metal gasket would hold up even better... I bet this does end up working for him at some point though. Quote Link to comment Share on other sites More sharing options...
Xander Posted April 14, 2005 Share Posted April 14, 2005 I think the problem with high compression turbos is the fact that no one has enough self control to NOT up the boost. Because of the higher CR there is a lot less room for error. I am now at 7 psi and the car drives good, but I already have the feeling that it is slower than yesterday. You get used to speed so easily. To help me resist the urge to up the boost I have now removed my HKS EVC boost controler. and another point is that the first 2 headgaskets were of a poor quality. One was a Rolls brand and the other a Rock brand. I was warned that I should not use these headgaskets on a turbo, but I installed them anyway. Lesson learned I guess. I'm now in the proccess of building my own Dyno. I already have a wideband oxygen sensor so when Get it all running I can do the real tuning of this thing. I'll let you guys know how much horses it will produce. (or if I blow another headgasket). Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted April 15, 2005 Share Posted April 15, 2005 with proper fuel and spark tuning, the nissan gasket and arp studs, I think you should be able to do at least a little more boost than stock safely... maybe 10psi? considering 10psi on bone stock setup is good for about 200rwhp I'm thinking on your setup might get 220-250 maybe? it's gonna feel like a rocket from the moment you touch the pedal.... Quote Link to comment Share on other sites More sharing options...
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