high comp or low comp........
09-05-2006, 07:24 PM
#1
high comp or low comp........
Im looking at building up a long studded 200 block which comes with standard pistons and trying to decide what to do!!!
For starters it'll prob just be a stage 3 jobby standard cams greens etc but...... as its being built from scratch i wanna leave scope for later mods which on advice will prob end up being greys and a bd14 inlet together with an MSD closed loop and dizzyless conversion!!!
So now trying to decide whether i get the standard pistons that come with it pocketed and run standard comp as i know alot of it is down 2 mapping and you can still get good power with standard comp, or whether to get a set of low comp pocketed pistons and use those as i know alot of ppl use low comp.......
Any help/advice is apreciated
For starters it'll prob just be a stage 3 jobby standard cams greens etc but...... as its being built from scratch i wanna leave scope for later mods which on advice will prob end up being greys and a bd14 inlet together with an MSD closed loop and dizzyless conversion!!!
So now trying to decide whether i get the standard pistons that come with it pocketed and run standard comp as i know alot of it is down 2 mapping and you can still get good power with standard comp, or whether to get a set of low comp pocketed pistons and use those as i know alot of ppl use low comp.......
Any help/advice is apreciated
09-05-2006, 07:35 PM
#2
I've found that life I needed.. It's HERE!!
Join Date: Sep 2003
Location: Gloucester
Posts: 1,080
Likes: 0
Received 0 Likes
on
0 Posts
I used to be a big fan of high compression. Not any more. I may get involved later on if this thread gets interesting!
For reliability I'd probably go 7.5:1 - that gives scope for 400-500bhp in the future.
For reliability I'd probably go 7.5:1 - that gives scope for 400-500bhp in the future.
09-05-2006, 07:59 PM
#4
10K+ Poster!!
sorry to thread hijack Toe Knee but im in the same boat although its zetec turbo not cosworth, i'll give my spec to get the ball rolling and stu's opinion, hopefully you wont mind 
zetec engine, steel rods, forged pistons, headwork, larger valves, aftermarket cams, cosworth management, t34 and 2 bar boost, i'd like to see around the 400bhp from the engine, or close to it, but would prefer the car to be very driveable and not quite make the power figure if you know what i mean.
would you be happy mappnig that with 8.2:1 stu? or would i need lower comp?
Originally Posted by Stu @ M Developments
Whats your maximum expected power output for this engine Tony?
would you be happy mappnig that with 8.2:1 stu? or would i need lower comp?
09-05-2006, 08:11 PM
#5
PassionFord Post Whore!!
Join Date: Jul 2004
Location: Wiltshire, Bath, chippenham area!
Posts: 7,428
Likes: 0
Received 4 Likes
on
4 Posts
Originally Posted by Ian@Racetek
I used to be a big fan of high compression. Not any more. I may get involved later on if this thread gets interesting!
For reliability I'd probably go 7.5:1 - that gives scope for 400-500bhp in the future.
For reliability I'd probably go 7.5:1 - that gives scope for 400-500bhp in the future.
In the real world, what are the upsides? and downsides?reliability of parts?
i'd be interested to know!!
09-05-2006, 08:11 PM
#6
Originally Posted by Stu @ M Developments
Whats your maximum expected power output for this engine Tony?
Probably better i ring you really mate as i wanted 2 talk 2 u on waiting times for getting the dizzyless conversion and closed loop before i bother with greys etc
Cheers ian, was looking thru stu's webshop and saw the 7.5.1 pistons on there aswell!
09-05-2006, 08:19 PM
#7
I've found that life I needed.. It's HERE!!
Join Date: Sep 2003
Location: Gloucester
Posts: 1,080
Likes: 0
Received 0 Likes
on
0 Posts
Pee Vee
Tell me about it. Well component wise, downside is excess cylinder pressure - so has to be studded with wrc gasket etc.
And a good mapper (Stu/Harvey/Karl etc) can make a low comp engine as enjoyable as a high comp one if its specced ad set up properly. And it'll last longer.
Remember, most high comp engines are rebuilt regularly as they are mostly used in competition. Though I'm sure there are a few who will disagree.
Tell me about it. Well component wise, downside is excess cylinder pressure - so has to be studded with wrc gasket etc.
And a good mapper (Stu/Harvey/Karl etc) can make a low comp engine as enjoyable as a high comp one if its specced ad set up properly. And it'll last longer.
Remember, most high comp engines are rebuilt regularly as they are mostly used in competition. Though I'm sure there are a few who will disagree.
Trending Topics
09-05-2006, 08:23 PM
#8
Std comp upto 550bhp is SAFE ..Over that you needs to lower to like 7.6-1 unless constantly on race fuel.
This is words from PRO'S and i deal with alot ..Thats why i ditched the GT35 as my comp could realistically only run 550bhp MAX on road fuel....and my 500bhp is lovely like this...get Karl to map it
..Over that you needs to lower to like 7.6-1 unless constantly on race fuel.This is words from PRO'S and i deal with alot
..Thats why i ditched the GT35 as my comp could realistically only run 550bhp MAX on road fuel....and my 500bhp is lovely like this...get Karl to map it
09-05-2006, 09:46 PM
#11
Does Karl do dizzyless and closed loop setups then Phil?!
Tbh thou i got superb service when i came up to Stu's i know i will again if i go up there (despite it being millions of miles away
) that chances are that's where im gonna end up again!! Althou this time would be for the weekend not brighton to blackpool and back in the same day cos i was fooked for ages after that and im sure the mrs will love 2 go to blackpool 2!!
Tbh thou i got superb service when i came up to Stu's i know i will again if i go up there (despite it being millions of miles away
) that chances are that's where im gonna end up again!! Althou this time would be for the weekend not brighton to blackpool and back in the same day cos i was fooked for ages after that and im sure the mrs will love 2 go to blackpool 2!!
10-05-2006, 06:34 PM
#13
BANNED
BANNED
Join Date: Jul 2003
Location: Surrey BUT IF UR A FIT WOMEN
Posts: 4,185
Likes: 0
Received 0 Likes
on
0 Posts
[quote="Ian@Racetek"]
And a good mapper (Stu/AHMED DOES HARVEY'S MAPPING !!!!/Karl etc) can make a low comp engine as enjoyable as a high comp one if its specced ad set up properly. And it'll last longer.
Though I'm sure there are a few who will disagreeMY HAVEY BUILT ENGINE LAST 100 WITH A GASKET FAULT THEN ONLY 2000 MILES AFTER THAT !!!!!!!!!!!!.[/quote]
And a good mapper (Stu/AHMED DOES HARVEY'S MAPPING !!!!/Karl etc) can make a low comp engine as enjoyable as a high comp one if its specced ad set up properly. And it'll last longer.
Though I'm sure there are a few who will disagreeMY HAVEY BUILT ENGINE LAST 100 WITH A GASKET FAULT THEN ONLY 2000 MILES AFTER THAT !!!!!!!!!!!!.[/quote]
10-05-2006, 06:35 PM
#14
20K+ Super Poster.
iTrader: (1)
Dont think Karl does closed loop.........but dont take my word, i might be wrong 
he as done all my work, and all i can say is he is awesome at his job but i know Stu does awesome work aswell
he as done all my work, and all i can say is he is awesome at his job but i know Stu does awesome work aswell
11-05-2006, 11:16 PM
#18
Ok not high comp as in higher meant standard compression 
Will get round to ringing stu for his suggestions seeing as im prob gonna get him 2 map/tune it this is just to get a general idea on opinions on whether its worth going low comp or not.
If i stick to standard then the pistons are gonna need pocketing anyway just in case i decide to stick a bd14 in there later on hence wondering if it was just worth buying another set of low comps already pocketed or not
Will get round to ringing stu for his suggestions seeing as im prob gonna get him 2 map/tune it this is just to get a general idea on opinions on whether its worth going low comp or not.
If i stick to standard then the pistons are gonna need pocketing anyway just in case i decide to stick a bd14 in there later on hence wondering if it was just worth buying another set of low comps already pocketed or not
12-05-2006, 07:09 AM
#19
PassionFord Post Troll
Join Date: Jun 2003
Posts: 2,725
Likes: 0
Received 0 Likes
on
0 Posts
Hello Mate, as ive said you will need to pocket your pistons anyway , even a std engine always touches valves when you buzz it or miss a gear , if you want any sort of power and reliabiltiy take engine to whichever engineer ( and your cheque book ) and let them get on with it .
Dont buy mis matched components and then expect the builder to make a good job of it , a good engineer will spec the comp ratio and machine the pistons all at once for you . Sounds like you'll use a T34 for about 400bhp , if thats true dont lower the comp as you'll have poor drive off boost .
Dont buy mis matched components and then expect the builder to make a good job of it , a good engineer will spec the comp ratio and machine the pistons all at once for you . Sounds like you'll use a T34 for about 400bhp , if thats true dont lower the comp as you'll have poor drive off boost .
12-05-2006, 08:53 AM
#20
As Tony says POOR OFF BOOST DRIVE......my car on 8-1 drives mint but get to 4000rpm and 32psi from a T4 and WARP DRIVE ...I had various comps and on a road car it HAS to be std comp..forget the T4 though as its way too mental 
...I had various comps and on a road car it HAS to be std comp..forget the T4 though as its way too mental
12-05-2006, 09:03 AM
#21
Originally Posted by Bosch-Man
Std comp upto 550bhp is SAFE ..Over that you needs to lower to like 7.6-1 unless constantly on race fuel.
This is words from PRO'S and i deal with alot ..Thats why i ditched the GT35 as my comp could realistically only run 550bhp MAX on road fuel....and my 500bhp is lovely like this...get Karl to map it
..Over that you needs to lower to like 7.6-1 unless constantly on race fuel.This is words from PRO'S and i deal with alot
..Thats why i ditched the GT35 as my comp could realistically only run 550bhp MAX on road fuel....and my 500bhp is lovely like this...get Karl to map it . 1. I don't know anyone with 550bhp on standard compression that has fully loaded their car in fifth gear (on pump fuel) - do YOU?
. If they did, it would be 550bhp for 5s followed by zero bhp . And don't give me any crap about switching to race fuel - WTF is the point in having a car mapped for high comp that you have to switch fuels before being able to max it 
. You would be better off lowering the compression for reliability, enabling you to max it out when-ever you like and THEN running a special high ignition map for race fuel, which has the benefit of giving you 40-50bhp extra .2. YOU haven't even loaded your car fully in THIRD gear, let alone forth or fifth
, and if your car has 500bhp, I'm a space man .
12-05-2006, 09:06 AM
#22
Originally Posted by Bosch-Man
As Tony says POOR OFF BOOST DRIVE......my car on 8-1 drives mint but get to 4000rpm and 32psi from a T4 and WARP DRIVE ...I had various comps and on a road car it HAS to be std comp..forget the T4 though as its way too mental
...I had various comps and on a road car it HAS to be std comp..forget the T4 though as its way too mental Drive any low comp car that has been specced / live mapped by a PRO and it would blow your "off-the-shelf" chip / DIY engine into the weeds
. Get Karl to set your car up properly (i.e. a live map) and you wouldn't dare come out of first gear, let alone second .KEEP IT REAL
.
12-05-2006, 09:41 AM
#26
DEYTUKURJERBS
Originally Posted by Mike Rainbird
Originally Posted by Itsmeagain
Mike, careful, Markk might have a few pints and then come on saying you should run 9.5:1 and that we all wankers
, but for a high geared road car, computer says NO . Geezer the other week was asking about what compression for a 2litre zetec running 2bar held boost and about 400bhp (on pump gas, obv).
I said roughly 7.5:1 id go for (depending on a lot of things of course, but at 2bar thats a decent ballpark number).
And then Markk came on kicking right off
No explanation, barring hes right and we all dont know shit
12-05-2006, 09:44 AM
#27
Tony, its all a case of application really.
As mike says if you run high compression and big boost then you are going to have MASSIVELY retarded ignition, and thats going to lead to an excess of heat in the exhaust side of the head and manifold and turbo, not good for reliability obvioulsy.
The upside to high comp is that it will be marginally more economical and slightly more powerful off boost, but who the hell drives a cossie around much while its in vacuum anyway?
For a high milage road car on normal road fuel, i would go std comp or lower, i wouldnt even consider high comp personally in your circumstances, those 7.5:1 pistons you mention are probably a good bet
Talk to stu though, if he is the one mapping it its his opinion that really counts.
As mike says if you run high compression and big boost then you are going to have MASSIVELY retarded ignition, and thats going to lead to an excess of heat in the exhaust side of the head and manifold and turbo, not good for reliability obvioulsy.
The upside to high comp is that it will be marginally more economical and slightly more powerful off boost, but who the hell drives a cossie around much while its in vacuum anyway?
For a high milage road car on normal road fuel, i would go std comp or lower, i wouldnt even consider high comp personally in your circumstances, those 7.5:1 pistons you mention are probably a good bet
Talk to stu though, if he is the one mapping it its his opinion that really counts.
12-05-2006, 09:50 AM
#28
Mike.....i remember you drove my lo comp T4 8 injector car off boost and YOU said it felt similar to YOUR own Saff 
Now that was 7-1 comp...you drive mine now and youd be stunned at the off and on boost performance compared to your old saff..remember i have driven your Escos too and off boost is NOTHING like this...maybe yours is poorly mapped?
PS yes i have held it flat in 3rd and got to 6000rpm in 4th flat the roads are not long enuff!!!!..Currently running 2.3bar spike dropping to 2bar.
Now that was 7-1 comp...you drive mine now and youd be stunned at the off and on boost performance compared to your old saff..remember i have driven your Escos too and off boost is NOTHING like this...maybe yours is poorly mapped? PS yes i have held it flat in 3rd and got to 6000rpm in 4th flat the roads are not long enuff!!!!..Currently running 2.3bar spike dropping to 2bar.
12-05-2006, 10:01 AM
#32
Originally Posted by Bosch-Man
Mike.....i remember you drove my lo comp T4 8 injector car off boost and YOU said it felt similar to YOUR own Saff Now that was 7-1 comp...you drive mine now and youd be stunned at the off and on boost performance compared to your old saff..remember i have driven your Escos too and off boost is NOTHING like this...maybe yours is poorly mapped?
PS yes i have held it flat in 3rd and got to 6000rpm in 4th flat the roads are not long enuff!!!!..Currently running 2.3bar spike dropping to 2bar.
Now that was 7-1 comp...you drive mine now and youd be stunned at the off and on boost performance compared to your old saff..remember i have driven your Escos too and off boost is NOTHING like this...maybe yours is poorly mapped? PS yes i have held it flat in 3rd and got to 6000rpm in 4th flat the roads are not long enuff!!!!..Currently running 2.3bar spike dropping to 2bar.
You have selective memory
1. I drove your car 2 miles up the road and didn't go above 4500rpm as you were running it in, so of COURSE it was going to feel similar to any other T4 car poodling around
.2. You have NEVER driven my car with it's current conversion
. The only time you drove it was when it had the T34 / 0.55 a/r and light blues . As it is, it runs rings around even that turbo .3. So you have done 8k in 3rd?
12-05-2006, 10:15 AM
#33
Mike...as i am only talking about off boost then you are backing up side If you drove this car upto 4500rpm youd be shocked at how much nicer and faster it feels...fruity would be the apt word in your case ...lo comp and std comp off boost driving is chalk and cheese and i have experience of that
In 3rd i have hit the 8200rpm limiter yes many times and its fooking ace 4th gear you are travelling too fast
If you drove this car upto 4500rpm youd be shocked at how much nicer and faster it feels...fruity would be the apt word in your case ...lo comp and std comp off boost driving is chalk and cheese and i have experience of that In 3rd i have hit the 8200rpm limiter yes many times and its fooking ace
4th gear you are travelling too fast
to go on track or to Brunters
12-05-2006, 12:54 PM
#35
i ran 7.56:1 on a .63 t34 and noticed little if any difference from stg1 2wd saff cossie on anything other than on boost (obviously!),round town the only major difference was the clutch,the turbo came in within 500rpm of the std t3 as well. so i reckon 7.5 is a good bet really from my own experiences
oh,and yes it could be held flat out in ALL gears! was a harvey gibbs engine.
oh,and yes it could be held flat out in ALL gears! was a harvey gibbs engine.
12-05-2006, 05:56 PM
#36
Cheers for the replies thats a bit better
Hummm as much as it pains me to pay someone else 2 do a build u might be right there Tony to save any long term probs and i cant afford for this 1 to go pop aswell power wise thou as i said will just be stage3ish for now but wanna leave scope for future mods later on when i can afford/stu can do the closed loop/dizzyless conversion, will have to discuss it and see.........
Chip didnt mean it as in higher comp than 8:1 meant standard or low comp slight miss type!!!!
Hummm as much as it pains me to pay someone else 2 do a build u might be right there Tony to save any long term probs and i cant afford for this 1 to go pop aswell
power wise thou as i said will just be stage3ish for now but wanna leave scope for future mods later on when i can afford/stu can do the closed loop/dizzyless conversion, will have to discuss it and see.........Chip didnt mean it as in higher comp than 8:1 meant standard or low comp slight miss type!!!!
