Agriv8
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| posted on 17/10/06 at 07:27 PM |
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Rover v8 CR sugested optimum/maximum
Right the new v8 is comming togeter apart from the piston incident  (would put myself up for numpty of the month but its two embarasing so i cant
even type it ) DJE are sending me some second hand ones at reasnoble cost.
I have calculted my CR (Compresion Ratio ) and its comming out at 9.5 - 9.6 to 1 , If i use my tin gasget can lower as i have a set of coposite
one's on the way
Now allowing for crap measuring lets say this could be .3 each way (used my veriers for everything apart from the combustion chambers / piston dish CC
) wife has commented that kitchen work surfaces arn't for car stuff and thats what I have a garage for !!!!!
what would people sugest the maximum CR for a v8 running electric dizzi.
upgrade planned for later winter to move to programable fuel and spark but for the moment going to stick with the rover v8 Hotwire EFI.
I suppose its a case of what CR is pinking going to to be an issue...
will be using std un-leaded
will post similar question on V-8 forum just wanted to gauge peoples thoughts on here.
Many thanks
Agriv8
Taller than your average Guy !
Management is like a tree of monkeys. - Those at the top look down and see a tree full of smiling faces. BUT Those at the bottom look up and see a
tree full of a*seholes .............
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mark chandler
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| posted on 17/10/06 at 07:46 PM |
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Depends on the cam, a hot cam can support a higher comp ratio as in reality with valve overlap its actually less.
I never had a problem with 9.35:1 engines, as you are using the composite gasket its worth getting the heads skimmed, in the ideal world you should be
getting the block done to suit.
When I ran a turbo toyota using optimax I could run 1/2 bar more pressure with optimax so your choice of fuel also affects things.
I would not worry, just try and get everything even so measure pistons and rods and swap around to achieve the most level playing field possible.
Regards Mark
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craig1410
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| posted on 17/10/06 at 08:13 PM |
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Hi,
According to Des Hammill in his book, "How To Power Tune Rover V8 Engines" (ISBN: 1-903706-17-3) on page 69 he says:
quote:
As a guide, 9.25:1 compression ratio is the maximum possible for use with 91-93 RON octane fuel, 9.75:1 is the maximum possible for use with 95
RON octane fuel and 10.5:1 is the maximum possible with 98+ RON octane fuel (a super unleaded fuel such as Shell Optimax in the UK). Racing engines
will usually stand 12.5:1 compression ratio using 98+ RON octance super unleaded fuel with or without as additive such as YetraBoost, but this is the
limit.
I strongly recommend this book to anyone who is working with the RV8 as it is a very well written and has sections dealing with every area of the
engine you could think of. Very practical advice such as the above too.
I hope this helps,
Craig.
ps. FWIW, I will be running my RV8 on Shell Optimax (or V-Power as it is now) and will be advancing the ignition as recommended in the above book to
maximise mid range power. Apparently you simply advance it until it starts to pink then bring it back a few degrees. Also, be aware that crank pulley
timing marks have been known to be way out as supplied by the factory so don't assume they are correct. Check them first.
[Edited on 17/10/2006 by craig1410]
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froggy
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| posted on 17/10/06 at 08:16 PM |
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if you can get some s/hand 9.75 vitesse pistons and take 20thou off the heads using the comp gaskets will give you back the 9.75 c/r . i ran that in
my last 3.5 on flap efi without problems . ask dave ellis as he does my engine work and is a decent chap . the v8 forum is the font of all knowledge
for these engines 
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clutch_kick
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| posted on 17/10/06 at 10:51 PM |
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Hmmm .... if you get the combustion chamber worked on by somebody who's good, you can eliminate potential hotspot areas, that lead to
pre-ignition.
I usually always suggest using the best fuel you can afford, You guys are lucky to have the Optimax in the UK, we have crappy 95 octane, but I add
MethylBenzine to it (121 octane), and corrct the fuel to about 98-100 octane.
get the cams times nicely, and make sure (this is probably the most important bit) that you are sucking in COLD AIR!! a cold air intake is
imperative!! You can even fit a water injection setup for N/A engines to drop the intake temps.
if your ECU has knock retard, or if it is Programmable ... you'd probably get away with about 9.7-10:1 CR
just to give you an idea ... the Toyota 4A-GE 20v Blacktop runs a CR of 12:1 and pumps out 165ps. The 3S-GTE (GT-Four engine) produced 255ps, with
0.85Bar boost and stock CR of 9:1 (turbo engine).
[Edited on 17/10/06 by clutch_kick]
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Agriv8
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| posted on 18/10/06 at 06:49 AM |
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Thanks Chaps,
yes I should sit down and read one of the V8 bibles, It was more a post to see what people thoughts were.
TVR ran arround 9.75 I belive ( though as with all things rover v8 related I suspect the actuall CR could be lower that this ) so that is what I have
aimed to get for this build.
The Cold Air is as cold as I can get in the confines of 7 ( cool air sucked from outside ) Though the issue of Heat soak into the plenum is 'one
still to do'.
Froggy you got them Blowers bolted on yet ? yep posted a copy post on v-8 owners
I belive Tesco's are now selling 101 RON ( alegadly )
regards
Agriv8
Taller than your average Guy !
Management is like a tree of monkeys. - Those at the top look down and see a tree full of smiling faces. BUT Those at the bottom look up and see a
tree full of a*seholes .............
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02GF74
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| posted on 18/10/06 at 07:43 AM |
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quote:
Originally posted by Agriv8
TVR ran arround 9.75 I belive ( though as with all things rover v8 related I suspect the actuall CR could be lower that this ) so that is what I have
aimed to get for this build.
10.5 was the factory maximum on the rover P5/P6 back in the day of 5 star.
Otherwise it was 9.75.
TVR ran between 9.50 and 10.0.
I'd probably say stick to about 10.0 with composite; try it with tin and if it has issues, then you can go down a bit.
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craig1410
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| posted on 18/10/06 at 07:52 AM |
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quote:
Originally posted by Agriv8
I belive Tesco's are now selling 101 RON ( alegadly )
I know they do "Tesco 99" in some parts of the country but haven't heard of 101. Shell V-Power is also 99 RON and I would take it
over any Tesco fuel any day regardless of what RON Tesco might claim to be producing. I run a Leon Cupra R 225 on a daily basis and stick to Shell
Optimax/V-Power religiously as do most Cupra owners. It really does make a difference!
Cheers,
Craig.
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