James,
One of my concerns when building an MGB GT V8 was to ensure that the engine
did not overheat. I had heard so many comments on V8s running hot because
of the cramped engine bay. So I got Australian headers that went through
the wheel arch, D & D Fabrication "heavy duty" radiator and I squeezed in a
14 inch 2,950 cfm Perma-cool puller electric rad fan. The latter achieved
by a special 3" water pump instead of the standard 4". But in my travels I
think I heard that wheel wells were low pressure so that engine air would
be sucked out through the holes for the exhaust header. This seems
reasonable as the "hole" is at right angles to the air flow. In other
words the air travels over the hole not into it. This would then cause a
decrease in pressure in the wheel arch? If you watch cars in the rain
does not the water spray out of the wheel arch not into it? Also if the
wheel arches were high pressure then the rain and dirt would be blown into
the engine through the wheel arch holes and this would be very obvious to a
runner of a V8.
Maybe someone can check the theory?
At 01:32 AM 8/20/2003 -0400, James Nazarian wrote:
>Paul, I was rereading your post and I have another question for the list.
>It occurred to me at some point that I have plenty of air coming into the
>engine bay but I don't think that I have much going out. Obviously the
>radiator opening is all inflow, and as I understand it the wheelwells are
>high pressure areas so the header cutouts should also be contributing to
>inflo. With the size and fitment of the V8 it does not leave a lot of space
>around the engine and transmission for outflow.
>
>One common solution seems to be to lift the rear of the bonnet, but as you
>pointed out, at speed that would be an area of inflow as the high pressure
>area in front of the windscreen can reach as far as 1.5 windscreen heights
>forward thus causing much of the bonnet to be in a high pressure area. This
>seems to be supported by my observations of the bonnet being pushed down and
>relieving tension on my hood pins, allowing them to shift.
>
>This would also rule out any form of louvering the bonnet as it will nearly
>all be in high pressure air. So I wonder what modifications can be
>performed to increase the outflow of air from the engine bay? I have read
>that changing to a ST airdam will do this by channeling frontal air around
>the car and lowering the pressure under it but because I have already
>lowered the car 1" I don't care to do that for this or for aesthetic
>reasons.
>
>I have considered the possibility of louvering the front fenders in front of
>the doors but I do not care to modify the body in such a way, partially
>because of the cost of repainting, but mostly, again, for aesthetic reasons.
>This leaves me wanting for another method of increased outflow.
>
>I don't think that it is that big a problem especially since I plan to
>reconfigure my airbox to include the carb body, as I detailed earlier, but
>it is a curiosity that I would be interested in hearing thoughts about.
>
>James Nazarian
>71 MGB Tourer
>71 MGBGT V8
>85 Dodge Ram
>----- Original Message -----
>From: "Telewest (PH)" <paul.hunt1@blueyonder.co.uk>
>To: "James Nazarian" <jhn3@uakron.edu>; "v8" <mgb-v8@autox.team.net>
>Sent: Monday, August 18, 2003 8:34 AM
>Subject: Re: timing
>
>
> > IMHO points bounce will cause the misfire and the high tach reading, but
> > they should go above 6k before bouncing. Dunno your engine but the Rover
>V8
> > is remarkably tolerant to both retarded and advanced ignition, much more
>so
> > than the 4-cylinder. But with two different distributors it is difficult
>to
> > believe it is points/timing/advance related. The factory V8 curve should
>be
> > 26 degrees at 2600 rpm, so your stock dizzie isn't that far out. Doing
>some
> > warm weather tests the other day I recorded 65C/149F near the carbs with
> > 31C/88F ambient. I increased the ambient coming in at the grill to
>41C/106F
> > and the idle speed did start to drop a little, unfortunately I didn't
>record
> > the temp near the carbs under those conditions. Are you saying you have
> > 180F/82C near the carbs? That is much hotter than I recorded, and
>probably
> > significantly more than it was during the hotter ambient. Can you run it
> > with the bonnet off? Or with the rear jacked up? I know at speed the air
> > might be going *in* at the back of the bonnet rather than out but at least
> > the carbs might be getting more 'fresh' air that way.
> >
> > ----- Original Message -----
> > From: "James Nazarian" <jhn3@uakron.edu>
> > To: "v8" <mgb-v8@autox.team.net>
> > Sent: Saturday, August 16, 2003 5:27 AM
> > Subject: timing
> >
> >
> > > For the sake of consuming bandwidth here is that 'other' email. I have
> > some
> > > drivability problems that I just can't shake.
> > > ...
>
Regards
Barrie
Barrie Robinson
barrier@bconnex.net
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