Craigorypeck
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| posted on 14/8/12 at 10:27 PM |
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High CR and boosting, how much?
I built my YB to run fast road NA, has approx 11.8:1 CR but I stuck an eaton on for the craic, pushes 5psi and the timing has been retarded way back
from na setting to 18 degrees from 4500 to 7500 rpm to avoid pinking, but it seems to boil coolant every time i give it some prolonged beans,
especially in higher gears .. can potter about with no probs but any hard right foot and its a jacuzzi under the bonnet. My guess is the timing being
that retarded is causing hot spots around exhaust valves and boiling coolant?? or am I getting the wrong idea all together!? pointers please. Ta
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coyoteboy
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| posted on 14/8/12 at 10:49 PM |
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Might not help being too retarded. Also, if you push 5psi you're pushing 1/3 extra power so you have 1/3 extra heat to remove. TBH I just
wouldn't bother boosting a high CR engine because they're generally very hard to get right on a budget due to the very high dynamic CR.
That said, good luck!
[Edited on 14/8/12 by coyoteboy]
[Edited on 14/8/12 by coyoteboy]
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Oddified
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| posted on 15/8/12 at 07:21 AM |
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Are you sure it's not just the head gasket that's gone and the extra power/boost from the super charger has finished it off? (or making it
obvious).
18deg timing isn't that low to cause any issues.
Ian
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Craigorypeck
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| posted on 15/8/12 at 07:49 AM |
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You may be right but I checked with a rad pressure tester and its holding its pressure..? tested on hot and cold engine. I might get the lend of a CO2
sniffer test aswell, will do a compression test too.
would my head gasket be under a lot of strain with upped CR and a 5psi of boost?? more so than a standard YB cosworth with low CR pistons but more
boost??
[Edited on 15/8/12 by Craigorypeck]
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Oddified
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| posted on 15/8/12 at 02:17 PM |
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Not really more strain, but if the gasket was a bit marginal before fitting the supercharger, then the extra cylinder pressures would make it worse.
Quite often a gasket that's only just started to go will only really leak when under maximum pressure/load (ie, giving the car some stick) and
when driven normaly will seem fine. Over time the problem gets worse and water being blown out happens on less throttle.
Which head gasket is fitted now?.
Ian
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Craigorypeck
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| posted on 15/8/12 at 04:09 PM |
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Hi, there's a reinz standard yb one In, from buttons I think, looked like decent item with metal between the bores.
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Oddified
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| posted on 15/8/12 at 04:49 PM |
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I know the one, as it's what i used to use on mine.
Absolutely fine until you start hitting it with some extra power, in my case nitrous (over 100bhp extra). When it had gone, it would be fine running
around normaly, use nitrous and it would empty the water out on the floor. I found they'd last 2 or 3 rwyb meetings and then start blead
pressure into the water under full load. I always found that they'd not blow as such with a chunk missing, but there would be spider legs (for
want of a better description!) from the cylinders leading to the water jackets.
I've now been using a Cometic mls gasket for a few a years now, with no coolant issues at all since.
Ian
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Craigorypeck
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| posted on 15/8/12 at 09:02 PM |
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oh dear, you could be right enough, also getting what I'd call more than enough vapour from the crank case breather too. Are you using nut and
stud head bolts??
also are those cometic ones the 5 layer metal jobs??
[Edited on 16/8/12 by Craigorypeck]
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Oddified
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| posted on 16/8/12 at 07:37 AM |
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quote:
Originally posted by Craigorypeck
Are you using nut and stud head bolts??
Yes i use an ARP stud kit on mine. I tried those first to help the head gasket but the only thing that stopped it was a cometic mls.
If your running 11.8 comp, then i guess you'll probably have forged pistons fitted (Accralite or similar) which means the piston-bore clearance
is greater. Any of the more modern weasel pi$$ engine oils breath a lot/leak, i found that Valvoline VR1 20/50 works very very well in these
engines.
Ian
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Craigorypeck
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| posted on 16/8/12 at 04:59 PM |
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yes accralite pistons and I'm using halfords 15-40 semi synthetic, i was under the impression their oil was as good as any others because of
strict consumer protection?
do the multi layer steel ones need a particular finish on the mating surfaces?? ie could i just whip off the head give it a clean and thro a multi
layer in and it will work as should??
Thanks
[Edited on 16/8/12 by Craigorypeck]
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coyoteboy
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| posted on 16/8/12 at 06:55 PM |
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Halfords oil to the correct spec is perfectly fine, but if you're over-stressing the engine comparend to standard operation you might want to
consider a better rated oil, and maybe change of weight profile etc. If you're regularly seeing higher running temps than in normal operation
your oil could be losing too much viscosity, a higher weight on the top end should help, but bear in mind that oils with a big weight range tend to
die faster (the polymers used to ensure the large viscosity range degrade with heat and age).
As for MLS - they're less forgiving than normal gaskets - you want the surface CLEAN and you want to ensure the mating surfaces are true to the
spec suggested by the gasket manufacturer, not the engine manufacturer.
[Edited on 16/8/12 by coyoteboy]
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Craigorypeck
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| posted on 16/8/12 at 08:18 PM |
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Ok, thanks for that, will get on it soon. 
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BaileyPerformance
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| posted on 20/8/12 at 10:11 AM |
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I would say 18deg is still alittle bit too much timing, i know your not running much boost but the high static CR will bring on the det quickly which
you cant always hear in a noisy car.
As stated before i wouldn't think the retarded timing is effecting the cooling system, i have seen 550bhp ybs at 4-6deg timing without
overheating. (but with big ally rad)
If the engine has been run with mild det it could have damaged the head gasket causing your problem, from past experience the stock yb gasket (we only
used Ford ones) is good for 25PSI but at standard CR. Ignition timing was around 8 deg at max boost. 16deg at idle.
Does the car seem slower at less timing?
What is your AFR at full throttle?
What is the engine temp when it starts to boil?.....do the hoses seem hard?
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Craigorypeck
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| posted on 20/8/12 at 11:19 PM |
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Hi there, The temp gauge goes up but not a lot, i do have the temp sender at the rear of the engine where the coolant comes in after the heater box,
not the best place for it tbh as is not a real indication? hoses are hard after a run.
Afr at full throttle is around 12:1 never leaner.
I did tune the timing myself whilst driving and there was some pinking but never sustained, always backed off and lowered, but still it did receive
some pinking time in the process.
I think its defo a gasket issue
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Craigorypeck
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| posted on 25/8/12 at 09:05 PM |
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Block is cracked in 2 places, water is getting to oil.
Wanted 205 block!
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mcerd1
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| posted on 26/8/12 at 03:55 PM |
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maybe this is the time to upgrade to one of those fancy motorsport or alloy blocks that burtons sell 
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Craigorypeck
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| posted on 26/8/12 at 05:21 PM |
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Aaaaaaaaahahahahaha! with the amount i can spend it might get a standard 2.0 non 205 block @ >£50
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mcerd1
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| posted on 27/8/12 at 12:00 PM |
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quote:
Originally posted by Craigorypeck
Aaaaaaaaahahahahaha! with the amount i can spend it might get a standard 2.0 non 205 block @ >£50
I've got a couple of them with pistons stuck in them you could have for nowt
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laptoprob
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| posted on 24/11/12 at 09:09 AM |
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I know the post is a few months old but nobody really answered the question origianlly.
Any of you tech gurus have the definitive naswer.....can you boost a high comp engine,say 12 or 13:1?
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bi22le
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| posted on 24/11/12 at 10:19 AM |
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Its seems that potentially yes but the risks and chances of failure are high.
Track days ARE the best thing since sliced bread, until I get a supercharger that is!
Please read my ring story:
http://www.locostbuilders.co.uk/forum/13/viewthread.php?tid=139152&page=1
Me doing a sub 56sec lap around Brands Indy. I need a geo set up! http://www.youtube.com/watch?v=EHksfvIGB3I
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jeffw
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| posted on 24/11/12 at 10:44 AM |
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I'm running 11.5:1 with 15psi at the redline. Zetec with a Rotrex
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BaileyPerformance
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| posted on 24/11/12 at 11:46 AM |
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quote:
Originally posted by laptoprob
I know the post is a few months old but nobody really answered the question origianlly.
Any of you tech gurus have the definitive naswer.....can you boost a high comp engine,say 12 or 13:1?
Depends on the cam profile and engine design, its not just static CR and boost pressure that's important is the effective CR. The effective CR
(the actual pressure inside the cylinder) and the shape of the combustion chamber decides how much an engine will take before it detonates.
If you have and engine thats running 15PSI of boost it does not mean all that boost if finding its way into the cylinders, most of it will get in
there at low RPM (assuming you can make boost a low RPM that is) but as the RPM rises the boost pressure in the cylinder will reduce. This is due to
inlet/head/cam restricting airflow.
Decent engine such as a cosworth YB the head design is very good as standard, so the engine will make good power at low boost pressures, as the boost
pressure is increased (in the hope of gaining more power) the law of diminishing returns comes in, for example a stock YB will make around 270BHP at
15PSI but it will not make 540BHP at 30PSI (without further breathing mods) so it is clear not all the boost is finding its way into the cylinders.
Ultimately its detonation thats the overriding factor when chasing big power, a simple way to keep the engine out of det is lower the static CR, this
slows down the flame front and reducing combustion temps helping to reduce det. The negative effect of a low CR is the fact it reduces the
engine's efficacy by not making the "best use" of the the fuel, the EGT is much higher on a low CR engine than on a high CR engine
as there is more wasted energy on the low CR engine.
If its massive BHP your after (500BHP+) then a CR or around 9/1 is as high as you can go on pump fuel, but 300-400BHP on a zetec or YB is best
achieved with a high CR as this makes the engine better on fuel and gives much better throttle response.
It is possible to run very high CR's on a turbo/SC engine if the right cams are used and timing in to suit, normally an engine is most likely to
knock at peak torque, the effective CR can be reduced by selecting a cam with quite high overlap, this bleeds some boost down the exhaust reducing the
pressure in the cylinder - but when the high RPM is used a cam like this will come into its own and really make the engine breath making much more
power than a standard short duration cam. We have used full race NA cams in turbo engine and made some big numbers on the dyno, but be warned the
ignition timing and fuelling MUST BE SPOT ON AT ALL TIMES otherwise you will end up with bits of engine on the floor!!
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jeffw
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| posted on 24/11/12 at 12:50 PM |
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I should say that 15psi comes out of the Rotrex but only 9psi arrives at the plenum as 6psi is eaten by the intercooler (which is rubbish I know).
The car makes 300HP/250 ft lb at the wheels.
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MRLuke
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| posted on 24/11/12 at 04:00 PM |
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quote:
Originally posted by BaileyPerformance
Decent engine such as a cosworth YB the head design is very good as standard, so the engine will make good power at low boost pressures, as the boost
pressure is increased (in the hope of gaining more power) the law of diminishing returns comes in, for example a stock YB will make around 270BHP at
15PSI but it will not make 540BHP at 30PSI (without further breathing mods) so it is clear not all the boost is finding its way into the cylinders.
Do you not have to consider that 15psi is actually 15psi above atmospheric (as at 0psi boost engine will still make power) Therefore you are going
from circa 30psi total to 45psi total. Gives power of about 400bhp which probably isnt far off what a cossie makes on 2bar?
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BaileyPerformance
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| posted on 24/11/12 at 09:26 PM |
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quote:
Originally posted by MRLuke
quote:
Originally posted by BaileyPerformance
Decent engine such as a cosworth YB the head design is very good as standard, so the engine will make good power at low boost pressures, as the boost
pressure is increased (in the hope of gaining more power) the law of diminishing returns comes in, for example a stock YB will make around 270BHP at
15PSI but it will not make 540BHP at 30PSI (without further breathing mods) so it is clear not all the boost is finding its way into the cylinders.
Do you not have to consider that 15psi is actually 15psi above atmospheric (as at 0psi boost engine will still make power) Therefore you are going
from circa 30psi total to 45psi total. Gives power of about 400bhp which probably isnt far off what a cossie makes on 2bar?
Your probably right, a cossy would make 400BHP ish at 2bar, but that's what i said - 30PSI (2bar) it would not make twice the power it did at
15PSI (1bar).
The term "boost" infers extra air over an above what the engine can pull in on its own "naturally aspirated". I good race
engine will achieve a VE of 95%, F1 maybe over 100% due to cleaver ram effect, average production car engine probably around 80%. The higher the VE
the higher the effective compression and more power. So its not true to say 15PSI of boost is actually 30PSI as that would suggest the engine has a VE
of 100% before you turbo charge it, which is not likely.
Boost is always quoted gauge not absolute - but the engine management measures absolute (MAP) as it needs to read vacuum for load purposes when off
boost as well as on boost.
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