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Greetings All.

I was just wondering...What are the effects of raising the compression in a N/A donk? Would it effect fuel ecconomy or power??
Also...what effect does compressin have on forced induction...? Anyone??

Cheers,
--Tonba
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Higher compression will in theory result in more power with increased heat. Bumping up compression is a good way to going power N/A however the higher the compression the higher octang of fuel you will need. So if you were to say bump up compression to 10.5:1 you would probobly have to say goodbye to regular unleaded petrol and use premium.

With forced induction high compression is dangerous as it results in detonation. Thats why when people want to bump up the boost they will use a decompression plate (head gasket) or replace pistons with a lower compression items.

Im no expert but in a nutshell for N/A bump up compression slightly. Turbo drop compression slighty.

Well, the Ralliart increased from 9.1:1 to 9.4:1. It still uses RULP. Going to 10:1 probably may require PULP depending on what heat's generated. I'd be concerned about doing it now and it's on edge and then discovering in the middle of summer when it's hot hot you're kocking the engine about.

Higher compression will in theory result in more power with increased heat. Bumping up compression is a good way to going power N/A however the higher the compression the higher octang of fuel you will need. So if you were to say bump up compression to 10.5:1 you would probobly have to say goodbye to regular unleaded petrol and use premium.

With forced induction high compression is dangerous as it results in detonation. Thats why when people want to bump up the boost they will use a decompression plate (head gasket) or replace pistons with a lower compression items.

Im no expert but in a nutshell for N/A bump up compression slightly. Turbo drop compression slighty.

Basically this is correct. Compression and fuel type is dependant on many factors. Combustion chamber design/ piston design/ valve overlap etc. I'd say 11:1 static compression would be as high as you wanted to go on the street in a Magna.

high revving NA engines = raise compression

big boost FI engines = lower compression

but it is possible to raise comp. slightly and still lightly boost it.

eg: NISMO High Comp. RB25DET w slight tuning and stock turbo = 260kw atw

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Greetings All.

You wouldent exactly say the magna is a high revving car...would you?

Why wouldent you go higher then 11:1 on a street magna?

Chhers,
--Tonba
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there are old 350 donks with 13:1 compresson running super and some octain booster.... timing my friend, timing.


Higher compression doesn't effect power much at all... its all torque baby. ever wondered why diesel's have such high torque, try 16:1 compression. sometimes upto 60psi of boost aswell.. for a wopping 170kw, yet 1000nm.

increasing comp is one of the better mods for a NA car but always involves dissasembly of the cylinder head.

before going turbo, my NA had 14.1;1 using PULP with booster.

we got to around 240hp @ the threads before going turbo. we are now 8.1;1 (comb of pistions and de.comp head gaskets) @ 14psi and about 335hp at the treads with more to come.

i found with the NA engine at 14.1;1 comp is a absoloute biach to drive at low rpm. drive it hard or drive it home. there is no other way to drive such a high comp 3L.. lol.. seriously, its a pain to drive in stop start stop start traffic, and it drove me nuts :nuts: !!

turbos are the way, as you still have very good low rpm drivability, and you have a potentially very quick revving car too!!! :badgrin:


BOoya

Booya, why was it hard? I mean, what would it do that was difficult?

Ben I think your twin throttle body was the result of poor driving below 2000rpm, not the compression itself.

Ben I think your twin throttle body was the result of poor driving below 2000rpm, not the compression itself.


indeed... that i never factored... however i cant then really just comment on the compression on its own, as the comp + twin tb were installed at the same time, and as a result, i got "funny" engine response below 2000rpm... mainly with idle (idled like a hardcore V8 with major cam work sounded heaps cool tho :cool: )

but yer, your right blake, thats prolly what made it a bit unfriendly under 2000. not so much the comp ratio on its own...

but at least i can say ive been there, done that, and it works a treat :badgrin:

All i can say bud, it that car sounded UNREAL!!! Was truely awesome, and as allways you have to go one step further... TURBO :thumbups:

All i can say bud, it that car sounded UNREAL!!! Was truely awesome, and as allways you have to go one step further... TURBO :thumbups:


yer, i miss that hardcore thump thump thump sound :badgrin:

seriously, this girl was BADASS when sitting there on idle... it was horney as hell!! :badgrin:

Would bumping it up a little increase much? Like im willing to use BP Ultimate all the time for the increased performance..

How much would this sort of job cost? My uncles a mechanic but he hates modifying unless he thinks it will do something..

Always been curious about this topic, please shed some more light on it!

Its a must do mod for a NA build up.

Ask tm_se_red about how it makes a difference.

How about the beloved falcon with raised compression and cam running a 15.4... auto. not even you manual boys get that consistantly.

IMHO its 30% of a NA build up. without it the engine lacks.

BOOYA for sale. $38,000NEG and this one off show stunner is yours:
Sale information
266kw/~500nm@wheels dyno proven
ffs you dont have 500nm or torque :nuts:

ffs you dont have 500nm or torque :nuts:


off topic for a second for this tool;

http://www.booyamotorsport.com/v2/sep_pics/dyno/dyno.htm

thank you very much.

Ben.

Engines running forced induction need a low compression design becuase as boost raises so does the compression. If you tried to turbocharge a high compression engine the final compression reading would be sky high.

Thats why drag cars running really high boost (example 20psi) have really low compression. As a result of turbo lag (large turbo) and low compression, it takes them a long time to build boost. :D

Engines running forced induction need a low compression design becuase as boost raises so does the compression. If you tried to turbocharge a high compression engine the final compression reading would be sky high.
Hey... the CR stays static. There is research into varying CR engines though. Lower CR allows more mass of air for the same pressure than high CR. More mass of air is what the engine's need to produce more power, not volume.

Well, the Ralliart increased from 9.1:1 to 9.4:1. It still uses RULP. Going to 10:1 probably may require PULP depending on what heat's generated. I'd be concerned about doing it now and it's on edge and then discovering in the middle of summer when it's hot hot you're kocking the engine about.


Yeah, this is right. Mitsu only went to 9.4:1 with the Ralliart because going higher would neccesitate going to PULP.

I think increasing bore to 3.8 and increasing compression at the same time allowing the car to be tuned for PULP, would have to be one of the best bang for your buck mods you could do. I know it's on my wish list :D


.

Its a must do mod for a NA build up.

Ask tm_se_red about how it makes a difference.

How about the beloved falcon with raised compression and cam running a 15.4... auto. not even you manual boys get that consistantly.

IMHO its 30% of a NA build up. without it the engine lacks.

I agree! i dont believe u need to change the pistons to get a good higher comp result, and 9.4:1 is the maximum for standard unleaded anyway. but i can tell you exactly what difference it makes as the ONLY mod on otherwise stock cars.
a few times i have worked on cars that have needed new headgasket and tidy up head after being overheated etc, and ive had the head shaved at the same time to bump up compression. This was on older cars that ran leaded.
The difference is always that the car will take corners in 4th that previously needed to change down to 3rd, and will take corners in 3rd that previously needed to change down to 2nd. so a lot more low end torque. And better fuel economy as well.
The only downside, if it really is one, is that if u put your foot down too much at low revs it will shudder and knock wheras a stock engine will just be sluggish until revs build. Anyway that is really only a problem for hopeless drivers, and only affects manuals.

well ive driven my car with higher compression, a cam and carb. it FLEW! it was a beast and we only skimmed 10 thou off the head, which wouldn't have increased compression all that much. as soon as i got a new head put on (stock one, so stock CR) i saw a worse fuel economy and less torque for sure. i miss my higher compression :cry:

skimming the head is cheap aswell! i got the head skimmed 10 thou which costed me $60. all they do is cut abit off, easy, but effective. the worse part of the whole process was taking everything apart and putting it all back 2gether.

altera98: yuo can run 13:1 on pump fuel quite easy
boy-ya: my car can make 700nm of torque... on a dyno, do a first gear run see how much you have then :bowrofl:

altera98: yuo can run 13:1 on pump fuel quite easy
boy-ya: my car can make 700nm of torque... on a dyno, do a first gear run see how much you have then :bowrofl:


if your smart, you'd do a dyno run in 4th gear so the gear ratio is 1:1 with the engine so you dont get stupid amounts of torque. this dyno run was done as it would of been done in a dyno dynamics shoot out mode used in competitions such as Summernats horsepower hero's etc etc. i have no doubts that what ever i can put on this dyno i can match on any other dyno dynamics in the country. actually, might even be better providing that the dyno shop in a capital city is at sea level, and not +1700m above the sea :nuts:

then again, i guess you dont believe that the rpw tt doensnt make 600odd nm of torque either.. :nuts:

im amazed how much some people show their stupidity on a public forum.

:D your forgetting the essence of dyno torque, its not ENGINE torque, its amplified by gears.

there are old 350 donks with 13:1 compresson running super and some octain booster.... timing my friend, timing.

I'll pay that one. However looking at the Magna's combustion chamber design (Astron) and the fact that pump fuel varies so much I'd hate to be driving something with very high comp on the street.

Also consider the older (early 90's) NASCAR's that ran anywhere between 18:1 to 24:1 compression. They would idle through the pits and occasionally blow the lid off a piston due to fuel starvation. Magna heads aren't gunna flow at low rev's and pop goes the weasel.

How can I get this done to my Verada :(

tighten the head bolts by 800f/p of torque :)

tighten the head bolts by 800f/p of torque :)

Aren't we a comedian today..

:D your forgetting the essence of dyno torque, its not ENGINE torque, its amplified by gears.
Well I guess thats kinda what Booya was getting at when he said:


if your smart, you'd do a dyno run in 4th gear so the gear ratio is 1:1 with the engine so you dont get stupid amounts of torque.

SOOOO, being that in 4th, the gear ratio is 1:1, that means THERE IS NO "AMPLIFICATION"! :nuts: There's actually gonna be losses through the drive line... & after all, who gives a F#*K about engine power figures.. ATW is the only way to compare, espeacially when you start talking Manual/Auto or FWD/RWD/AWD.

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Greetings All.

TC, your just gunna have to realise that booya DOES have a V6 turbo. If a XR6 can put out around 400nm of torque (just a guess), then why cant booya's heavyly modifed turbo put out 500nm+ of torque??

Ok guys, back on topic.

Why do you guys think that a higher compression ratio of say ... 12:1 on a V6 magna wouldent be good for the street?? Also, booya, what was ya fuel consumption like with the high CR??

Cheers,
--Tonba
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Yeah i think i'd be interested in doing some work on my heads now that the car has done quite a few Km's so i'm in Sydney who knows anyone who can do a good job either higher comp head gaskets or shaving the heads slightly by ten thou.
If anyone could let me know that would be great. A:flame:

Yeah i think i'd be interested in doing some work on my heads now that the car has done quite a few Km's so i'm in Sydney who knows anyone who can do a good job either higher comp head gaskets or shaving the heads slightly by ten thou.
If anyone could let me know that would be great. A:flame:
I think you'll need pistons, not gaskets.

altera98: yuo can run 13:1 on pump fuel quite easy
boy-ya: my car can make 700nm of torque... on a dyno, do a first gear run see how much you have then :bowrofl:

"pump fuel" thats including 95,98 ron PULP and LRP, i meant only regular 91 ron ULP.

with the V6's, shaving 10 thou to bump it up up to around 9.4:1 would be about all you could do without mismatching the inlet ports too much anyway. this small amount would be ok to do a little home porting with dremel or drill bit attachement and emery paper to slightly "lip" the bottom of the inlet manifold and the top of the inlet port on head to perfectly rematch.
for the 4cyls they could go a bit more, depending on whether the cars have dished or flat topped pistons and how much lift their cam is running. but as TM SE red found, decking 10 thou off is just sweet.
its best if u can wait until your timing belt is due for replacing to do any headwork on any OHC engines, so u can save a fair bit off the labour.

Whoops you can change the compression down by changing the head gaskets ( steel ) or can you get it higher??

You can increase static compression by shaving the head and using a thinner head gasket.

I would first check with an expirenced machine shop to see if this effects clearences etc.

Just a question. If your in fourth gear then isn't your final ratio your diff ratio. Hence torque increases?

There's a guy in SA that does Twin Turbo 3L Magna V6 motors that puts out 700kw at the fly on a engine dyno on PULP! So turboing seems to be the best bet for the V6 if all you want is to effectively increase out put.

Well I guess thats kinda what Booya was getting at when he said:



SOOOO, being that in 4th, the gear ratio is 1:1, that means THERE IS NO "AMPLIFICATION"! :nuts: There's actually gonna be losses through the drive line... & after all, who gives a F#*K about engine power figures.. ATW is the only way to compare, espeacially when you start talking Manual/Auto or FWD/RWD/AWD.


pssst, there are more than just the gearbox gears in a drive train...

let it go, we arnt going to agree.

20 thou off a head shouldnt effect clearences, but i would ask a mitsu dealer for specs before i went and did it! 13:1 is probably too high for a factory ecu to handle without retarding the timing nearly off the scale of the dizzy. 20 thou would up it maybe by .5-.7 so i assume a set of new pistons would be the only way to get it really high :(

Whoops you can change the compression down by changing the head gaskets ( steel ) or can you get it higher??

nah the steel plate is not a gasket, only a decompression plate ie decreases compression. you can use double head gaskets to lower compression as well, provided u arnt going over about 1 bar boost. I doubt anyone makes a thinner head gasket for magnas?? to try raise comp, the effect would be small anyway.

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Greetings All.

You can get a set of pistons what will raise your CR up to 10.5:1.
In addition to these all you would need is a piggy back computer (such as unichip or greddy), and tune to PULP. Will set you back around $650 for the pistons.

Cheers,
--Tonba
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how much would u be lookin at to get the pistons put in though

new rings and bearings would be about 300 for a kit, maybe more. can do it with the head on and the engine in if your proficient enough with a spanner (in some cars.. ive never rebuild a 6cyl magna)

including labour costs around another 600-800 and it would be "rebuilt" aswell. but they would take the head off but not recon it.

You can get a set of pistons what will raise your CR up to 10.5:1.
Yeah, but who makes and supplies them?

++++
Greetings All.

You can get a set of pistons what will raise your CR up to 10.5:1.
In addition to these all you would need is a piggy back computer (such as unichip or greddy), and tune to PULP. Will set you back around $650 for the pistons.

Cheers,
--Tonba
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thats a bit of a ripoff isnt it? are these forged hypereutectic and fully balanced pistons or what? :shock:

new rings and bearings would be about 300 for a kit, maybe more. can do it with the head on and the engine in if your proficient enough with a spanner (in some cars.. ive never rebuild a 6cyl magna)

including labour costs around another 600-800 and it would be "rebuilt" aswell. but they would take the head off but not recon it.

i rebuilt the bottom end of a camira like that once (no honing the bores). yeh if theres no crossmembers and steering arms etc in the way u can do it all from underneath lying on your back, unless u have access to a hoist lol

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Greetings All.


thats a bit of a ripoff isnt it? are these forged hypereutectic and fully balanced pistons or what? :shock:
Two words, RPW & Hypereutectic. Id consider it if I was in the position to do so...

Cheers,
--Tonba
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++++
Greetings All.


Two words, RPW & Hypereutectic. Id consider it if I was in the position to do so...

Cheers,
--Tonba
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ahh fair enough then. come on Tonba spoil yourself, if anyone deserves the gruntiest ever n/a magna you do... :D

I didn't realise that Hypereutectic were the brand. I thought they were a design of piston. My bad :confused:

I didn't realise that Hypereutectic were the brand. I thought they were a design of piston. My bad :confused:

think u were right the first time:confused:

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Greetings All.


ahh fair enough then. come on Tonba spoil yourself, if anyone deserves the gruntiest ever n/a magna you do... :D
LOL...I wish...Ive got no money...:doubt: :cry:
But when i do get a solid income...BRING ON THE MODS!!
LOL!!

Cheers Mate!!
-Tonba
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pssst, there are more than just the gearbox gears in a drive train...

let it go, we arnt going to agree.

I agree.... HAHAAH! Got ya. lol