Guest bastaad525 Posted May 10, 2005 Share Posted May 10, 2005 Just wanted to mention this as a point of interest. There's an article in this months SCC magazine covering an aftermarket-tuned, turbocharged '05 Lotus Elise. 11.5:1 compression ratio, running 7psi of boost safely on 91 octane. Up to 8000 RPM, at that! Since the question get's asked here all the time about how much boost and how much CR is safe. Just goes to show that with the right tuning and a good engine design (obviously the design of the Toyota motor in that Elise is light years ahead of our aging L28ET's) you CAN run boost even on a very high compression motor safely. Now if only someone could say what all would need to be done in the case of an L28 to get away with boost on that high of a CR, or if it could be done at all. I would think it's just a matter of the design of the combustion chambers? Quote Link to comment Share on other sites More sharing options...
getZ Posted May 10, 2005 Share Posted May 10, 2005 You didn't mention anything about intercooling. There are supercharger kits for the LS series small block chevys with around 11:1 compression running 6-7lbs of boost as well. The way around dealing with the high compression is intercooling. If you are building a dedicated supercharged or turbo charged engine you'll make more power raising the boost rather than raising the final compression ratio. Quote Link to comment Share on other sites More sharing options...
EZ-E Posted May 11, 2005 Share Posted May 11, 2005 Well on that note I would have to say that actually running more boost as I see isnt getting you there as it is if you are running a higher compression engine and lower boost and keeping the turbo in its sweet spot as to running more boost and possibly hitting the surge limit. With a slightly higher compression motor built and tuned properly, with 8:1 or 8.5:1 compression ratio and proper tune you could make more power at less boost and not pushing the turbo harder then needed. Sure with a lower compression motor you could run more boost but off boost performance truely suffers, as well as offline performance. One day Ill be running a 8.5:1 turbo motor. I dont think you can go wrong. As for the aritcle I did read it as well and it was a great read and an awesome machine. The Lotus is such a gorgeous car. Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted May 11, 2005 Share Posted May 11, 2005 oddly enough they covered the EXACT same car in this months issue of Motor Trend as well. I know it's running an intercooler of course, not sure what kind, but it's not like water or alchy injection or anything, just a regular intercooler. Anyways I just wanted to show an example, that there ARE guys running boost on very high compression motors. I mean, to me, 11:1 CR is like the limit for a NATURALLY aspirated motor, so it blows me away to see them boosting it. I agree with EZ-E's outlook as well. With this motor, a small displacement, high revving motor, they used a small turbo (T28) tuned to low boost (7psi) so it's barely working at all, and has a GREAT powerband w/o even breaking a sweat, pulling hard from 2000 RPM all the way to like 8000. And it put down 246 hp to the wheels.... that's more than my 2.8 liter running about twice as much boost... it can be done both ways. I'm sure his is MUCH more responsive OFF boost though. Quote Link to comment Share on other sites More sharing options...
JSM Posted February 17, 2009 Share Posted February 17, 2009 Thanks for this. For a NA high compression motor 10.5 what would be the highest boost you would run If I were to mess w/ something like this? Quote Link to comment Share on other sites More sharing options...
dr_hunt Posted February 17, 2009 Share Posted February 17, 2009 Anthony Dickson who had a HP turbo systems turbocharged mustang went 8.15 @ 176+mph in Albuquerque while standing the car on it's back end and leaving fiberglass bumper pieces all over the track. Truly it was impressive. The car has since gone in the 7's with another owner. The engine in that car at the time was a culmination of a learning curve. He had been through several engines, piston combinations etc before getting something that would hold together. The engine builder and machinist IIRC was Tod Budlong of Budlong motorsports in Albuquerque, NM. He indicated to me that that particular engine was a 10:1 engine running like 30lb of boost using a water/air intercooler. Granted he runs race gas and all but the concept of boost and high compression is certainly there and can make big big HP if the tune is correct as indicated by the 176mph on the other end in a 3200lb mustang. Here in NM the altitude is 4500 to 5000 feet and the density air is typically 7000 to 8000 feet. Getting a low compression turbo engine to start and idle here is extremely difficult. The age old premise of lower compression and more boost certainly holds true but at this altitude drivablility suffers to a great deal. I have been having issues with my 7.2:1 TT SBC in the Monte. Consequently for the z build I am doing a 10:1 engine on the advice of Tod Budlong. Mild hydraulic roller 228 duration at .050 and about .600 lift with a 114LSA. Of course the z will have a huge jgs precision intercooler also. As octane increases so can dynamic compression. On alky engines and Nitro engines it is not uncommon to supercharge a 10 to 14:1 engine with great results. An 10:1 350 sbc with Dart Sportsman II iron heads, aluminum rods, nothing radical and a 6-71 blower running 15lb boost made 1250 corrected HP here in Alb. on the dyno at Edwards Engines and powered Joe Saavedra's rail dragster to 7.00 at 178mph. It has gone in the 6's at 185mph with just more timing. Another 8.5:1 350 sbc with a 8-71 blower fairly radical combo made over 1000 corrected HP on pump gas! Quote Link to comment Share on other sites More sharing options...
JSM Posted February 17, 2009 Share Posted February 17, 2009 I looking to add a simple, stock, 280zxt system to my car and be happy w/ the results even at 5-7 PSI. I'm doing this to keep the cost low. I would add an intercooler though. My current setup is an N42 block, slightly bored w/ flat top pistons and a fairly massaged E31 head with a pretty big lift and duration cam. Rats, I just realized I don't have the injector releifs in the head. Quote Link to comment Share on other sites More sharing options...
roger280zx Posted February 18, 2009 Share Posted February 18, 2009 There was a guy on here a while ago running compression in the 9's with a stock zxt setup at 7psi. Don't know his name but you can search and find pictures of his pistons in a threat where he said the thing spooled fully at 1200rpm. Quote Link to comment Share on other sites More sharing options...
Pyro Posted February 20, 2009 Share Posted February 20, 2009 it all has to do with flame travel speed and how far the flame needs to go. Modern engines are designed to have a very fast flame speed and they try to keep the piston diameter to a minimum (less distance to travel). Why? a fast flame speed and a short distance to travel means an engine needs less ignition timing advance (less head start) to complete the burn. So, instead of needing 35 degrees of timing advance (an old z engine), new modern engines can get by with 20. And less ignition advance means high compression can be used with the same octane fuel. 81 to 83 L28 engines have faster flame speed as compared to the 75 to 80 L28 engines. Flat tops and a bigger quench area makes a faster flame. Quote Link to comment Share on other sites More sharing options...
Scottie-GNZ Posted February 21, 2009 Share Posted February 21, 2009 You guys are also forgetting the high-tech, modern day computer technology in the engine management system. The ZXT system is an abacus in comparison. Quote Link to comment Share on other sites More sharing options...
GrayZee Posted February 21, 2009 Share Posted February 21, 2009 The ZXT system is an abacus in comparison. Ha ha ha... that is funny... very true as well. Quote Link to comment Share on other sites More sharing options...
HowlerMonkey Posted February 26, 2009 Share Posted February 26, 2009 I've been running a 1984 L24e with stock compression ratio and 280zx turbo hardware on it with the stock injectors, stock 1982 280zx non-turbo ecu and air flow meter, and stock boost for the last 50,000 miles with no troubles............but I have to run 93 octane. With an intercooler and the 280zx turbo or 300zx turbo management system, you could probably run up to 10psi on 93 octane on a non-turbo compression ratio. Keep in mind what kind of fuel you intend to run when deciding on compresion ratio. Quote Link to comment Share on other sites More sharing options...
Nismo280zEd Posted March 3, 2009 Share Posted March 3, 2009 As octane increases so can dynamic compression. On alky engines and Nitro engines it is not uncommon to supercharge a 10 to 14:1 engine with great results. An 10:1 350 sbc with Dart Sportsman II iron heads, aluminum rods, nothing radical and a 6-71 blower running 15lb boost made 1250 corrected HP here in Alb. on the dyno at Edwards Engines and powered Joe Saavedra's rail dragster to 7.00 at 178mph. It has gone in the 6's at 185mph with just more timing. Another 8.5:1 350 sbc with a 8-71 blower fairly radical combo made over 1000 corrected HP on pump gas! I apologize if my question is rather newbish, but I'm trying take in as much knowledge as I can for my turbo build. I just recently picked up a stock T3 turbo from a zx and intend to install in my 280z. I like running E85 and live close enough to a station that I can justify the drive to fill up with it. So what I take from your post... is If I run stock L28E compression 78 280z internals, running E85, and the stock T3 turbo... I can actually run say 10-12psi safely with a good tune in megasquirt?!? I was under the impression the highest I could go was 5-7psi on stock compression so adding the ethanol I could up my psi without risk? I should also mention I will be running an intercooler and eventually meth injection. So does this mean you can run a highlift cam on a turbo motor also? -Ed Quote Link to comment Share on other sites More sharing options...
cockerstar Posted March 3, 2009 Share Posted March 3, 2009 I think you guys are being rather conservative with the amount of boost you're looking to run. Everything I know comes solely from reading here rather than from first hand experience, so take what I have to say with a grain of salt. I've always been under the impression that with a properly tuned MS system and stock turbo hardware plus an intercooler it's safe to push around 10-11psi. After that you maxed out your injectors and needed to upgrade there. Stock n/a compression is still relatively low and isn't too much higher than turbo compression (for a lot of head/piston combo's) and still well within the realm of what is safe to boost. The compression bump is going to result in being able to run slightly less boost overall, but it is also going to help with off boost driving and is arguably favorable for a daily driver. Quote Link to comment Share on other sites More sharing options...
jc052685 Posted March 3, 2009 Share Posted March 3, 2009 I think you guys are being rather conservative with the amount of boost you're looking to run. Everything I know comes solely from reading here rather than from first hand experience, so take what I have to say with a grain of salt. I've always been under the impression that with a properly tuned MS system and stock turbo hardware plus an intercooler it's safe to push around 10-11psi. After that you maxed out your injectors and needed to upgrade there. Stock n/a compression is still relatively low and isn't too much higher than turbo compression (for a lot of head/piston combo's) and still well within the realm of what is safe to boost. The compression bump is going to result in being able to run slightly less boost overall, but it is also going to help with off boost driving and is arguably favorable for a daily driver. Your injectors are maxed out when your AFR and duty cycle say so. Not by any preset PSI. Personally I was running around 15psi with stock injectors. Quote Link to comment Share on other sites More sharing options...
cockerstar Posted March 3, 2009 Share Posted March 3, 2009 I know that it isn't a set psi, but the amount of boost plays a very significant role. More boost = more air = more fuel = larger injectors. Great to hear that you were in the 15psi range with stock injectors! I always thought they generally maxed out a bit before that, but the later the better! Quote Link to comment Share on other sites More sharing options...
dr_hunt Posted March 3, 2009 Share Posted March 3, 2009 I apologize if my question is rather newbish, but I'm trying take in as much knowledge as I can for my turbo build. I just recently picked up a stock T3 turbo from a zx and intend to install in my 280z. I like running E85 and live close enough to a station that I can justify the drive to fill up with it. So what I take from your post... is If I run stock L28E compression 78 280z internals, running E85, and the stock T3 turbo... I can actually run say 10-12psi safely with a good tune in megasquirt?!? I was under the impression the highest I could go was 5-7psi on stock compression so adding the ethanol I could up my psi without risk? I should also mention I will be running an intercooler and eventually meth injection. So does this mean you can run a highlift cam on a turbo motor also? -Ed There is alot that governs what boost you can run on a compression motor and how much hp it will make. High lift cam has nothing to do with the equation as it is all about seat timing and head flow. I am running afr heads which flow very well over .600 lift. If I was running some other head I probably would not run that much lift. Intercooled and meth injection I would imagine 12 psi being pretty safe depending on whether or not the intercooler was properly sized and the tune was good. It is all about design and engine management IMO. Quote Link to comment Share on other sites More sharing options...
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