Help me decide

[TooneySonic]

Hi guys

As afew of you know i have an issue with my car with low compression, and i am down on power compared to similar cars with the same mods (roughly 12bhp)

Any how the compression test showed up at 175 across all four cylinders, not good. However a following leakdown test showed everything to be fine, so i cant determine the cause of the low comp. The only option is to take the thing apart > ££££

So where do i go from here?

1) live with it and accept it? to be honest the car runs perfectly fine. its just i hate the thought of having paid so much money and the car not fulfilling its potential, its bugging me

2) have my head rebuilt? i've had a drive in drive out quote which includes a rebuild and mild headwork (might aswell since its out) for £860, but thats assuming the valves etc are okay

3) buy a secondhand head and fit that? considering two at the moment... one has spared no expense headwork and has had a rebuild 5k ago with new valves, the other a standard unit.

Baring in mind that soon the car will be benefitting from either a s/c or itb's, your thoughts would be appraciated guys

Craig

 

[sideways danny]

175? you told me 150 the other day :S 175 is a bit low but not "that" bad. Any idea if there was any hot and cold difference on the compression test?

 

[BenR]

It was 150.

 

[BenR]

Leakdown was between 5-7% across all 4.

TBH, for the cost you'd spend chasing that last 10bhp, I dont think its worth it. But I said that at the time.

 

[Russ_16v]

i was going to say thats not too bad lol, my first valver i had 140 over all cylinders lol

to be fair it was on 170,000 very hard miles

 

[geesus69]

surely this is a no brainer if you are getting s/c or itb's? :S

get the work done at the same time (or use the one thats already had work done) to compliment whichever induction route you choose?!

 

[W17GLE]

whats i go like against other cups? if its still faster i'd be happy if it was only the same after all that work i'd be gutted

 

[Russ_16v]

i'd look at it this way, were you happy with it before you knew about it? it must go well enough otherwise you wouldnt have bought it

id forget about it until you decide if your sticking with n/a or going with f/i as going with the latter i would imagine the head will be coming off, then tackle it then

 

[TooneySonic]

Leakdown was between 5-7% across all 4.

TBH, for the cost you'd spend chasing that last 10bhp, I dont think its worth it. But I said that at the time.

yeah i know thanks again ben but its bugging me lol and i came across this s/h head so thought i throw up the post

 

[TooneySonic]

175? you told me 150 the other day :S 175 is a bit low but not "that" bad. Any idea if there was any hot and cold difference on the compression test?

sorry got my wires crossed between 25psi and 25%, Ben is correct the result was 150

 

[TooneySonic]

whats i go like against other cups? if its still faster i'd be happy if it was only the same after all that work i'd be gutted

couldnt pull against drunkenmonkey's 182 last week, though both cars were still cold so we didn't strecth them properly

nothing wrong with the mods which have done the trick, just got me a slow one tbh

 

[W17GLE]

couldnt pull against drunkenmonkey's 182 last week, though both cars were still cold so we didn't strecth them properly

nothing wrong with the mods which have done the trick, just got me a slow one tbh

oh thats not good if its only as quick as nicks i'd of expected it to pull quite easily

 

[TooneySonic]

yeah and nick weighs more than i do hehehe

 

[W17GLE]

He's always got that slight disadvantage lol. i don't think the traction control helps him either as i always dick him of the lights and thats with both my ph1s

 

[TooneySonic]

He's always got that slight disadvantage lol. i don't think the traction control helps him either as i always dick him of the lights and thats with both my ph1s

pmsl

was a rolling start, he did get his foot down first i reckon though

 

[BenR]

yeah i know thanks again ben but its bugging me lol and i came across this s/h head so thought i throw up the post

The heads not the issue, leakdown tests were very good with virtually zero loss.

Also like I said at the time, you can expect a loss in cranking compression when you fit wilder cams......however due to the resting cam position and schricks cam data being uselessly vague, I cant form an educated guess without physically checking.

Combine that with great leakdown results and poor comp results = weirdness.

 

[fossie]

What should the compression be on a 172 engine, my mate did his tonight and got 205 across all 4

 

[TooneySonic]

What should the compression be on a 172 engine, my mate did his tonight and got 205 across all 4

good result that i believe from what Ben has told me (iirc) that 200 is the magic number

 

[fossie]

Phew ill let him know then, his time slipped 2 teeth on a rr the other day........... seems everythings ok now tho

 

[BenR]

quality comp gauge is important though as you can get massive deviation betweeng gauges.