The V8 Owners Forum -

Yes I am surprised, and the car has really come alive. Already ripped my engine steady out so will need to beef things up a bit.
One problem that concerns me is a backfire under acceleration about 5500rpm. It was doing it before I changed to ECU and throttlebodies.
Look at this clip of last Monday you can hear it backfire on the straights although it is intermittent.
It happened once on the rolling road and apparently is not fuelling or ignition.!!!! need to get to the bottom of it. Happens at 3mins 58 in and 4mins 34 in.


cheers Mark

Exhaust or intake backfire? If exhaust could be fuel puddling somewhere in the system getting lit by another charge, you wouldn't notice a one off non fire but you will hear it light in the pipes. If intake backfire then it is hanging an intake open, more serious but most likely a slightly soft valve spring losing control of the valve movement.

Alan

Nice result

Would be fun to know how much the porting helped and how much is because of the new induction. How about sticking the trusty carb back ?

As it is a solid lifter cam I suppose it could be valve clearances.
Spec says 22thou Hot but I find it impossible to do hot. Set Exhaust to 12 thou and inlet to 10 thou. maybe I should try increasing these?
What are other people doing?
Cheers
Mark

Sneak up on it, 2 thou at a time, when the backfire disappears try closing back up a thou, if back fire returns go back up one and you are done, if it doesn't return you are done anyway.

Alan

Jukka
Already sold the Huffaker intake & carb.
I think the porting works better with the downdraught manifolds as where the infilled corners were becomes the outside radius entering the head.
I am very surprised at the result.

mark

My engine will make also +40hp more with ITB`s vs plenum..

Those valve clearance´s must be adjust in cold engine, not hot. I ask this when i bought my cam. I will run 0.5mm clearance in/ex when engine is cold..
I have got also specs sheet, but not any word how to adjust clearance..
V8 developments/real steel say cold engine.

So my valve clearances must be much too tight. will try 0.5mm.

Hi
If it is of any help I run a mechanical roller cam, I run stainless valves in ally heads, I set 20 thou inlet 22 thou exhaust set cold. I can't see how I would set mine hot, it would take a week with keeping having to warm the engine through every 2 or 3 cylinders. I would be happy to close mine down to 15 thou inlet and 18 exhaust, but I don't think I would tighten them more than that.
Best regards
Mike

Thanks for the info. I am thinking that it must be clearances as the complete induction and ignition system has been changed.
The extra torque has ripped out my engine steady so I will beef it up and probably fit a second one on the other side of the engine.
Also going to strengthen my anti tramp bars to be on the safe side.
Hoping my R380 gearbox can cope. Will also have to keep an eye on halfshafts.

mgbloke wrote:As it is a solid lifter cam I suppose it could be valve clearances.
Spec says 22thou Hot but I find it impossible to do hot. Set Exhaust to 12 thou and inlet to 10 thou. maybe I should try increasing these?
What are other people doing?
Cheers
Mark

Doesn't tapped clearance get less when hot?

DaveEFI wrote:

mgbloke wrote:As it is a solid lifter cam I suppose it could be valve clearances.
Spec says 22thou Hot but I find it impossible to do hot. Set Exhaust to 12 thou and inlet to 10 thou. maybe I should try increasing these?
What are other people doing?
Cheers
Mark

Doesn't tapped clearance get less when hot?

Yes you would think so. I went with 12 thou after reading that the Ally block and heads expand more than the steel valvegear. Cant remember where I read it. Obviously a bad thing to do.
It is all making much more sense now. I couldn't think why Nos 1 and 3 sparkplugs were dark compared to the others. Obviously exhaust valve not closing properly when it gets to a certain temp/rpm.
Thanks everyone.

Hi
My heads are ally over a steel block with chrome molly push rods, stainless steel valves.
As the pivot of the rockers is mounted on the ally heads and ally expands a bit more than twice the rate of steel it moves away from the cam at about twice the rate as the push rods expand to close things up, and although the stainless valves will be a lot hotter than the head the lash gap will still open up as every thing gets hotter. It is always safe to set lash gap cold, just prone to be a bit rattly.
Best regards
Mike

Found this interesting

"Compensating for a Cold Engine When Adjusting the Valve Lash
When installing a new camshaft, your engine will obviously be cold. The problem is that the provided lash specifications are for an engine that has been running long enough to be at normal operating temperatures. What are you to do? There is a standard correction factor that can be used to get you close to the required settings. You must now consider the material alloys of the engine parts, because the thermal expansion of these components affect the valve lash in different ways. Therefore the correction factor used for your lash setting will depend upon whether the cylinder heads and block are made out of cast iron or aluminum.

Take the "hot" setting provided to you in the cam manufacturer's catalog or from the cam card that came with your camshaft. Use the figures below to alter the original lash specifications to get a "cold" lash setting.
Using iron block and iron heads, add .002"
Using iron block and aluminum heads, subtract .006"
Using both aluminum block and heads, subtract .012"
Remember this correction adjustment is only approximation, and it is only meant to get you close for the initial start up of your engine After the engine has been properly warmed up to normal operating temperatures you must go back and reset all the valves to the specified "hot" valve lash settings."

I opened the valve clearances slightly and it seems to have worked.

On the negative side I have just discovered that the Merlin heads are again leaking coolant into the oil. This is a long standing problem that I have had. real steel say it is a porous casting and not a crack but Both heads have been affected. First off RS had them back and sent them for laser welding but they leaked again.What a shame as apart from this problem I have been more than happy with them.
Seriously thinking about ordering some TA heads but again there is very little information and I cant find anyone that it using them.

Mark