Making the most of a High compression ratio

[nova_rally]

Now that I have a high compression ratio, what can I do to make the most of it? At the moment my car's not too happy about it, and I'm having a lot of difficulty setting the timing up properly. So what can I add that would make a difference?

Alan

[Dan]

how high is it, i'm not sure what mine is but on a dry compression test in the past i got 235psi in each bore which is poss around 11.5-1 or a touch more. what other mods u got with it also or are you pretty standard apart from this.

[nova_rally]

No idea what the figure is on it, flaming high though! only mods are a 1300 (13S) head using 14NV inlet and carb, and the 14NV cam. Peco Back box as well not that that actually means anything!

Looking at getting a new Cam and a Vernier Pulley to try and get it sorted.

Alan

[Stuart]

what kind of problems is it exhibiting? pinking etc, adjusted the dizzy for the timing (with a gun) ??

[Snowface]

my bad idling could be down to my high c/r then?

I got a bored out 1300 bottom end (1324) which has had the face skimmed and am running a 1.2 head on that.

[Stuart]

now now kids on need to start worrying about your compression ratios


if you had a high CR eg Dan, CP etc then you could have a possible reason to worry, but they dont do they, nooooooooo as they have the fuelling and ignition setup right. get that sorted first then go finding other problems.

[m.d.]

i was told by my local engine tuner that if i raise the compression ill have to use a vernier pully as the timing will be impossible to set up otherwise

[Dan]

lol i have used a vernier in the past when using different cams, but after all that it turns out that mine now is set to the same position as a standard one as its not needed

[m.d.]

lol i have used a vernier in the past when using different cams, but after all that it turns out that mine now is set to the same position as a standard one as its not needed
yeah so is mine lol

[nova_rally]

Diesling and pinking (but I think I've sorted the pinking). A high copression ratio in itself doesn't mean anything in terms of performance, so I just wanna know what will make use of it?

Alan

[beghy]

Now that I have a high compression ratio, what can I do to make the most of it? At the moment my car's not too happy about it, and I'm having a lot of difficulty setting the timing up properly. So what can I add that would make a difference?

Alan


DUDE

had the same problem last year with mine 1400 running 1300 head and all it needed was to retard the ignition. why the hell are you using the 1400 inlet still, you wana get rid of that for a 1300 item it might be the cause you never know?

as for high C/R its good just as long its under 11.5 or u'll have to use high octane fuel or retard the igition

[nova_rally]

Retarding the ignition only makes it run s**t, have no power, diesel worse, heat up more, bogs down on hard acceleration and occasionally will misfire and seriously misfires and pops when letting the throttle out and it won't start cold.

Running 1400 manifold because theres nothing wrong with it.

Alan

[Snowface]

if ur happy running a more restictive manifold thats fine.

1300 is def better though.

[CP]

A couple of points - could be just bollox but it might help:

1. I dont know but it maybe that you wont have taken the compression ratio that far up with your conversion. The real killer is a 1.4 head on a 1.6 which is over 13:1. I could only just get mine to run and then when I did (on twin 40's) it wouldnt stop even with the plug leads removed!!

2. High CR = much more liklihood of detonation/pre-ignition. This damages the valves, the compression chamber, the plugs and the pistons - bit like blow torching the internals

3. To avoid this you need to A. retard ignition B. use high octane fuel (100+). This will release the extra power potential and save your engine from melt down. (High octane fuels are more difficult to get to burn and less likely to ignite under higher pressures)

what you describe sounds like timing and fuelling issues. you are prob running way lean and too advanced = too hot, back firing.

you should:
get some compression readings from your engine - see dans comments to get some idea of whether yur cr is way high or not

check your plugs - see back of haynes for too lean etc indication or buy special fuel mixture indicator plugs

get it timed right

get it fuelled right

get an appropriate fuel - if need over 98 RON then get an additive or ask in the motorsport/aeronautical world for the green 100+ RON petrol.

If you are up in the high 12's CR then you will be advised to watch how you drive - its been found that motorway drving can kill high CR engines by burning the valves out. I could be wrong but I get the impression that high CR engines like to be driven motorsport stylee - not really suited to normal road use

[SKoob]

is a CR of 11-1 gonna be a problem :?

[Cheese]

is a CR of 11-1 gonna be a problem :?

Should be fine mate :D

[nova_rally]

I'm gonna pop down the motorsport place in a minute and have a go with some of that Octane Booster stuff, see if that helps any. It has been running fine so far (3 days since I last messed with the timing) and hasn't dieseled on me despite doing everything that usually cuases it to, and it hasn't been making any nasty pinking noises.

You know on the cam carrier there is a cast mark by the dizzy - is there supposed to be a coreesponding mark on the dizzy, coz mine aint got one! the only mark I can find on the dizzy is about 30degrees advanced of where I have it....

Alan

[Cheese]

Dizzy should have a small raised triangle on it, this 'should' be lined up with the mark on the cam carrier. If the dizzy has been painted this would make it difficult to see..

[nova_rally]

That might explain why the timing's all wrong then! lol! whereabouts is this triangle? on mine so far I've found (from front to back of engine bay) An arrow pointing towards the front of the car, then a number stamped in, then a random line. I'll go and have a proper look in a minute, but I doubt I'll find it. :lol:

Alan