low comp engine [Archive]

J$£5GTT

06-02-2009, 13:03

ok later rather than sooner im gonna build up my spare engine,
after i get all the bits etc together,what are folks thoughts on
low compression engines?,is this the way to go...t25,cam....
im know 5 tech head far from it just need some advice as to the
basis of my starting point...the block an pistons.
cheers
:)

Markey Mark (BD)

06-02-2009, 14:13

I would stick with standard compression mate, wouldn't bother with low comp its not really the way to go.

TNT Tricky Nicky

06-02-2009, 14:21

My understanding of it is you can run more boost on a low comp engine and achieve the same power output as a standard comp engine with less boost so I don't really get the point of it, maybe it's a case people are fitting turbos that are too big for the engine and want the most out of the turbo and adjjusting the comp ratio is the only way of doing it?

Rob@Backyardracing

06-02-2009, 17:30

Depends what your building and if your able to gain the power back from what you lose with the compression... i beleave that one of the most powerfull GTs in this club runs 6.x:1 :)

Russgt5

06-02-2009, 17:48

I wish i had been a member and benefited from some of the advice here before giving BBPT the money for thier new work unit in exchange for a low comp engine.......im now starting to think i've wasted even more money than i first thought i had :crap:

Penfold aka The Dealer

06-02-2009, 17:51

I wouldnt worry to much Russ,

one of my 5's is low comp, cant say i notice the difference to much :D

Adam 005

06-02-2009, 21:17

I myself have skimed the top of my o.e pistons to lower comp a little as i do run high boost at times.but i can't say i notice much differance between my old o.e comp motor and the lower comp motor.

Skiming pistons is done some times to compensate for a head that has been skimed a few times.
If you are thinking of running the boost we were talking about then i would stick with o.e comps.i can see it causing any problems aslong as fueling and charge temps are correct.:agree:

J$£5GTT

07-02-2009, 13:30

J$£5GTT

07-02-2009, 20:20

so then id say the club has a fair few members so how many of you
are running a low comp unit and what are your opinions?

sphinX

08-02-2009, 00:16

Im runnin low comp, cars had no problems since iv had it and power wise..lets just say im happy :D

Scoff

08-02-2009, 00:27

so then id say the club has a fair few members so how many of you
are running a low comp unit and what are your opinions?

if you won't be running more than say 20psi boost then you definately do not want to go low compression, you will throw power away and increase fuel consumption while your at it.

J$£5GTT

08-02-2009, 10:23

if you won't be running more than say 20psi boost then you definately do not want to go low compression, you will throw power away and increase fuel consumption while your at it.

ok so maybe alright for a weekend car then with more psi etc,but i use my car
so dont want even more fuel consumption,im going to stick with standard comp
i think
:)

Mudslinger

08-02-2009, 11:30

im sure im running as low as 6.*:1 compression using custom je pistons , obviously the reason behind going low comp when building the engine is purely to take out the limiting factors , using standard compression is ok in low boost set up as whats being said , but what happens when you hit that det threshold which will be pretty soon for most peeps , water injection ?? does anyone actually use water injection these days ? i have heard so many debates over the years about wi working , but really wouldnt it be better to just use low comp pistons and then take away that limiting factor without trying to burn water ?

Frix

08-02-2009, 13:30

im also running low comp, with about 20psi, and very happy to say the least!!:D

Adam 005

08-02-2009, 13:45

i would say that i do use more fuel with the low comp motor

Frix

08-02-2009, 13:51

i would say that i do use more fuel with the low comp motor

:agree:

Mudslinger

08-02-2009, 15:10

i would say that i do use more fuel with the low comp motor

its kinda hard for me to comment on fuel consumption on mine just yet , but i cant say i ever noticed any difference on the my previous low comp engine , although it did run a grp a carb and probably did run a tad rich .

is it not just the case that your running more boost for the rise in fuel consumption rather than the comp ratio ? a mean how much more fuel are we talking here ? i doubt its a massive diff ?

Adam 005

08-02-2009, 16:44

its kinda hard for me to comment on fuel consumption on mine just yet , but i cant say i ever noticed any difference on the my previous low comp engine , although it did run a grp a carb and probably did run a tad rich .

is it not just the case that your running more boost for the rise in fuel consumption rather than the comp ratio ? a mean how much more fuel are we talking here ? i doubt its a massive diff ?

i think my motor might be running a little ritch off boost but it only does 24 mpg.it always seems to need a lot of thottle off boost:confused:

Big Jim

08-02-2009, 19:00

Scoff's right, don't go low comp. Only reason to do it is to run monster boost on normal fuels. I usually raise the CR, you just need to mod the chamber shape to get some decent turbulence.

Alternatively get some Sunoco Maxnos in the tank and you could run 2bar+ on 11:1!!!

sphinX

08-02-2009, 21:27

Well thats strange, with low comp on my car im still getting 30+mpg if i drive sensibly? I don't know maybe im just a granny at times lol

Adam 005

08-02-2009, 22:25

Well thats strange, with low comp on my car im still getting 30+mpg if i drive sensibly? I don't know maybe im just a granny at times lol

yeah i'm thinking i might need to fiddle with the set up on my carb.I am a little usure which way to go with it. i over fuels at low boost but tends to lean out a little over 20psi:confused:

Nayls

08-02-2009, 22:30

yeah i'm thinking i might need to fiddle with the set up on my carb.I am a little usure which way to go with it. i over fuels at low boost but tends to lean out a little over 20psi:confused:

if you play with a 25mm carb instead of a ****ty group A carb you'l be fine :)

Adam 005

08-02-2009, 22:36

if you play with a 25mm carb instead of a ****ty group A carb you'l be fine :)

i was thinking along those lines my self i just need to get a new venturi as i only have a 27mm

Nayls

08-02-2009, 22:43

i was thinking along those lines my self i just need to get a new venturi as i only have a 27mm

i've got a couple of carbs in bit's,i'l see if i have a 25mm in there for you.