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Discussion Starter · #1 ·
is it just me or is 7.4:1 compression *****. Now Top End Performance posted that 8.5:1…8.1:1 is the best compressions for the 280zxt's so why don't any of us use the the non turbo rings that would help in the compression and make it 8.3:1, thats right in the middle and correct me if I'm wrong but the added compression should increase torque so you would get more off the line in a race. Tha would deffienty help before the turbo kicks in. Please post me back about this I would like to get so insight on this from all of you.




tbs
 

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what the? IS RIGHT.

last i heard (i could be totally wrong on this) rings have no effect on compression ratio. if you change your pistons you could change your compression ratio. just a thought.
 

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Its alot safer to run lower compression on a turbo motor, Thats why its like that from the factory. Higher compression will make it ping easier, than a low compreesion motor set at the same boost level so you cant really run as much boost. I'm not sure if the higher compression makes up for the lower boost.(I'm no expert, thats just my understanding of it. so dont take my information as the absolute truth, I'd do some research to make sure its right if I was you)

If you wanna raise you compression you can put in flat top pistons, shave your head, or install a NA dished piston head(I think, not 100%sure).


Justin T
'80 280ZX
'77 280Z(comming in about 15 hours wahoo!)
 

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Rememeber Datsun/Nissan designed it around a non intercooled application also running on cheep gas. 7.4 to 1 is week but also served its purpose. Now Top End Performance (We Wont go there with these guys) My Previous engine was running somewere like 9 to 1 so i ended up droping down to 8.5 to 1 ratio for less problems with the lowered pump gas octane now a days. As For rings they dont drop or raise compression ratios.. Well let me correct this if the rings were worn the would drop compression.... If you wanted contact SCE gaskets and get a thinner then factory head gasket this would help out on compression ratio. just a little though...
Good luck with your search
Ron240zxt
 

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The NA head and the P90's both have the same combustion chanber volume.

Compression difference is due to NA using flat-top pistaons and Turbos use dished. Turbo pistons also use a thinner compression ring - it will give instead of breaking under a little detonation - at tleast that is what the engineers have reported.

If I were to build my engine, 8.5 would be what I would use, large intercooler and limit boost to 15-20 lbs w/aftermarket computer.
 

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yeah im using sds' stand alone and it works fine, itll run 22 psi daily with no detonation. But you really have to set up the maps good. I think ill up the compression a bit once i get the car painted and the engine out of the bay. Hello 400 rwhp (hopefully) :)
 

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Discussion Starter · #8 ·
hey thats great but can you use the flat top pistons with the turbo rings, that would give you 8.3 compression of the engine and with an intercooler you wouldn't detonate as long as if you don't over do it so can you or not? Also zpeedrazer could you help me with setting up my fuel maps, I putting in a 300zxt ecu and going to get it upgraded rather then buy a stand alone like you but need to know about the fuel pump, damper, enjectors, fuel rail, and regulator so I can run high boost with my conquest intercooler.



tbs
 

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sure ill help as much as i can. But im telling ya dude, if you can save up enough i STRONGLY encourage you to get a stand alone. Im running a electronic paxton pump running under my fuel cell, rc engineering 550cc injectors, and a cartech fuel pressure regulator. The fuel rail is just a custom piece of aluminum with the a line feeding it, and the injectors connected to the bottom.
 

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Discussion Starter · #10 ·
thanks man and do you know what kind of hp the injectors will support? I want to upgrade my fuel maps, ecu and then get a t3/t4 turbo for it.



Thanks again

tbs
 

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Until you really know what your doing with fuel maps and such you really should limit compression and your psi. Don't forget that 13 psi with a t3 and 13 psi with a big t4/t3 is totally different. Also the conquest intercooler is way better than stock but, does not flow enough air for big power #'s. I guess it depends on your buget and goal.
Also the rings are not going to effect your compression. The only way to raise your compression is to lower your volume in the combustion chamber. Rings do not do this they seal against the side of the block. They have other uses such as helping to transfer heat to the block as well. I am by no means an engine builder but, I suggest you do some more reading before you open the check book. I'm not tring to be rude but, tring to save you some money and trouble along with alot of frustration.
If I were you I would do the intercooler with some good manderal bent pipes and start learning about the engine as a whole not just the turbo parts. A modest boost increase will give you some good results. Try about 9 psi and see how the car reacts. Remember to increase the boost a little at a time and pay attention. Most of the ZX's will do 9 psi without any fuel problems. Anything over that and you need to address the fuel system.

Cody 82 ZXT
 

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Pesky 10Sec Hondas' Run...

10:1, so whay not that?
Combustion chamber design, that's why.
All the above posts were right, the 7.4 is in-line with what most manufacturers were doing at the time. Remember, when this motor was built, Nissan had been pumping out L-Blocks for over 20years in one form or another. They KNEW how long the block would hold up, and woah be to the set of pistons that didn't go AT LEAST 200,000 miles, instead of the normal 100,000. There is LARGE margin built into the engines, and the 7.4:1 C.R. is just one of those margins.
All points about higher compression are correct, though, it will help torque, and 8.5 is generally considered ideal...
 

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Discussion Starter · #13 ·
OK can I get some help with fuel maps then.

I would like to know just about every thing there is to konw about the fuel maps and what Tony D and Cody 82zxt have done to theres, I want to do everything excpect the stand alone since I'm hooking up the 300zxt ecu





tbs
 

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Re: OK can I get some help with fuel maps then.

Are you refuring to the Jim Wolf 300ZX computer conversions? If so then most of the work is done for you. As I under stand it if you set everything up as they tell you the car will run real good but, a touch rich. I'm sure they program it to run rich because they aren't tunning each car they are send the units out to. Different cars do different things. I've thought about going that route but, havn't really had the money to do it just yet. My car needs so much that I can't spend all my time and money on going fast. I'm doing ok as it is. I've never lost to another Z and have beatten some healthy competion.
If you want I'll going to what I've done. My is actually very simple but, Works very well.

Later,
Cody 82 ZXT
 

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The higher the comp the greater the chance of detonation at the same timing. You can make alot more power with lower compression and alot of boost than running 9:1 with 10 psi. Yes your thermal effiency is lower and off boost torque is a little lower with low comp. but not much, and how often are you needing max torque at an rpm lower than you produce boost. If I'm get in it awn, I've got my rpm's at atleats 3000-3500, after that hang awn. To the question about fuel maps. Getting the fuel right is good, but the timming, I think is more important especially with stock pistons. Too much timing, regardless of how much fuel and you will detonate.
 

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10Sec Hondas' Run...8:1

No 10 second turbo Honda runs a stock compression ratio. They put custom pistons in to drop CR. They run 8.5:1 or so and with 25psi boost, they still need to run race gas.
 

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I paid total of $200

to hook up my 300ZXT ECU and MAF. Try to do a standalone for that.
 

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Lower boost makes more power!!!

Read Corky Bell's book Maximum Boost. It explains in easy to understand terms how you can make more power with low static compression ratios. If you really need off-boost throttle response, lots of street turbo cars run 8.0:1 to 8.5:1 compression, but on pump gas you can run more boost without detonation.

Stock L28ET motors rule!!!!
 

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Re: I paid total of $200

Hey Sleeper,

What are you doing for fuel and timing? Did I read right? 300ZX with the Maf and not a flapper door assembly. How hard was to do? I'd love to get rid of the Flapper door what a huge resrtiction.

Cody 82 ZXT
 
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