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Detuning Nb Race Engine – Tech heads help needed!
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Author:  kuzzy [ Tue Jul 22, 2008 9:08 am ]
Post subject:  Detuning Nb Race Engine – Tech heads help needed!
I have an Nb race engine about to go into my historic resisted mini. I was going to race it as an Nb race car, but my plans have changed and I’ll use it for hill climbs and sprints – and the occasional trip to pick up the Sunday’s paper.

Once my bank account recovers, I would like to detune the engine to run on Premium Unleaded and some sort of octane booster etc. It currently has about 13:1 compression and a wild cam 4,500-8,000 RMP power zone. I like the fact that it is a beast to drive and don’t want to change that but, I don’t want to pay for Avgas over the long term and hence will need to reduce compression - which will stuff the Cam as it needs high compression to work etc. The car also has a 45 weber and long manifold with instrument cluster modified to suit, Longman large valve head, straight cut drop gears close ratio straight cut gears in the box with a LSD.

So, what is the highest compression I can run and a suitable wild cam to match (knowing that a big cam will bleed off some cylinder pressure). Any suggestions?
Author:  Tspeed Jem [ Tue Jul 22, 2008 6:45 pm ]
Post subject: 
Have you tried running it on high octane unleaded with booster? Seems a shame to de-tune it. As you say, the duration of your cam will effect what compression ratio you can get away with (longer duration will lower your dynamic compression ratio). My friend's (Austin 850) engine is 12.5 to 1 compression, and yes it did use to ping a little at lower revs under load but this was on 'Super' with no booster and a mild cam.
If it were me I would try it and see if it pings or not. Not only do you get better power from higher compression you also get better fuel economy according to Vizard.
I'm sure someone else will have better first hand knowledge on this though.
Author:  drmini in aust [ Tue Jul 22, 2008 8:07 pm ]
Post subject: 
My Mini had an S ex-race motor in when I got it- it had flat top pistons and was running about 12.5:1, and would ping its head off on Super fuel.
I put 2 BK450 head gaskets on it for a couple of years, then eventually I removed the head and enlarged the chambers heaps, got it down to 10.8:1 with 1 gasket, still using flat tops. It ran fine on 98 unleaded.

For a sporty road cam I fitted a Camtech VP3 and 1.5:1 rockers, it went hard :P for about 40,000 miles until most of the lobes wore off.. :shock: I blame the oil I was using at the time, and the pointy lobes of this cam.
Russell Engineering's RE13 cam is similar specs to the VP3 but I find it has more midrange, also the lobes are nicely radiused so will last longer.
Author:  Lindsay_Palmer [ Tue Jul 22, 2008 11:37 pm ]
Post subject: 
Drmini, just a it of trivia you might be interested in. MG people in the states have had heaps to trouble with cam lob wear in new/rebuilt motors. The problem was found to be some brands of oil now have greatly reduced levels of zinc. Zinc normally coats the freshly ground metal, if you could get a powerful enough microscope you could see the zinc forms what looks like small hairs on the metal protecting it from wear during running in of the motor . No zinc means you are relying solely on the shear resistance of the oil, which is enough once motors have worn in but not for new motors. I also know of friends with XU-1 toranas having the same problem but that is due to the cam manufacturers not spraying the metal at the cam at the right temperature.
Author:  drmini in aust [ Wed Jul 23, 2008 6:59 am ]
Post subject: 
I'm aware of that ZDDP problem Lindsay, from the MM forum, the funny thing is some lobes on this cam were fine, some were so worn the lift had dropped from .470" to .270" :shock:
I was using a well-known grade of oil, starting with the letter P. I change oil every 1500 miles.

Since then I've used Graham Russell's RE13 and RE282 cams, I've had them in and out of a few engines and not seen any problems.
I now only use either Castrol Edge Sport 25W/50, or KMart's KMX 20W/50.
Author:  kuzzy [ Wed Jul 23, 2008 8:25 am ]
Post subject:  Nb Race Engine
Maybe I'll should try a mix of Avgas and high octain unleaded stuff when I get it on the road (last 20L dum of Avgas cost me $50! and I would hate to think what it is going to cost in the future).

Anyone tried that?
Author:  TheMiniMan [ Wed Jul 23, 2008 10:12 am ]
Post subject: 
Kuzzy, you are going to have to rip the head off & open the chambers up if you want to run it on the road ... it`s as simple as that,,, drop out the big cam & relieve some of the valve spring tension while you`re there

otherwise ,,, well,,, need i say???

It`s nothing new,,, there`s no special magic substance that allows anyone to run high compression & massive cams & sooper strong valve springs on the road

It`s one or the other,,, the compromise is still just as bad as the full race,
Author:  simon k [ Wed Jul 23, 2008 10:32 am ]
Post subject: 
Doogie told me about one of his motors (called the Grunter) that had 13:1 compression and needed avgas, he sold it to a bloke and explained that it couldn't run on anything less. The guy said "yeah yeah, no problem", and promptly ignored him.... he was back a few weeks later with a fooked motor

I reckon you should find a standard head and open it up, put in an RE13, and keep your 'race' bits on the shelf for when you want to put it on the track proper
Author:  kuzzy [ Wed Jul 23, 2008 10:49 am ]
Post subject:  Nb Engine
OK, RE13 cam (or simular) and drop compression / fit new head.... What is the working rev range for a RE13 cam and how high can I go with the compression with this type of cam on the street?

It is a pitty as I already have another Nb mini that I have started to race but it is big bore / short stroke and the head can't be used as a spare for it.
Author:  simon k [ Wed Jul 23, 2008 10:53 am ]
Post subject:  Re: Nb Engine
kuzzy wrote:
What is the working rev range for a RE13 cam and how high can I go with the compression with this type of cam on the street?


2.5K to 7.5K

I don't think you'd want any more than 10:1
Author:  TheMiniMan [ Wed Jul 23, 2008 11:29 am ]
Post subject: 
Image

:-)
Author:  Timbo [ Wed Jul 23, 2008 12:10 pm ]
Post subject:  Re: Nb Race Engine
kuzzy wrote:
Maybe I'll should try a mix of Avgas and high octain unleaded stuff when I get it on the road (last 20L dum of Avgas cost me $50! and I would hate to think what it is going to cost in the future).

Anyone tried that?


Can you still buy avgas if you don't own a cessna? I was under the impression that its illegal to use in cars as it contains lead?

Tim
Author:  TK [ Wed Jul 23, 2008 12:11 pm ]
Post subject: 
also illegal to run avgas on the road. the government doesn't get enough tax from it.
Author:  TheMiniMan [ Wed Jul 23, 2008 2:36 pm ]
Post subject: 
with a race car fuel log book you can buy it,,, but as Ty said, it is illegal to use on the road
Author:  slinkey inc [ Wed Jul 23, 2008 2:40 pm ]
Post subject: 
I know where you can buy it, I've only ever seen people pumping into jerry cans or drums - never a car. :wink:
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