XJR SC Poor performance when requested

[J44EAG]

Oil bake!

Dare I suggest oven cleaner?! I`ve not yet had to use it but on the basis that the chemical shifts oven carbon off teflon oven surfaces, I see no reason why you might not get a result on the throttle body and throttle plate. If the carbonisation can be removed, then so much the better. Make sure the throttle plate edges are as clean as possible. You may have to live with the gunk on the throttle throat. One thing is sure. You have less gunk on it than you had before you stripped it all down!

If you place a new gasket on the charger elbow, you will notice about a 1/8 ring of metal sticking out inside the internal gasket diameter. This is highly disruptive to inlet charge air flow and also allows more crank case gas gunk to accumulate. If you have some metal cutting burrs and a spare quarter of an hour, remove all that excess metal outside of the gasket area. That will help significantly to de restriction of this engine. There will be no negative aspects of doing this simple modification.

Ensure that the trench on which the MAF sensor sits, is also clear of gunk. The internal surfaces of the elbow are best cleaned with rotary aluminium brushes (NOT carbonated mild steel brushes) to remove gunk build up. If you are feeling ambitious, embark on some elbow gas flowing with burrs and sanding rolls. See my tuning thread for details.

Mike

[Lordgaz]

Thanks again Mike.
I decided against oven cleaner (I did not have any to hand, and was unsure of any side effects having had a google) , and instead cleaned as best I could with carb cleaner and acetone - as you said, any cleaning would be an improvement.
I gave the elbow a reasonable porting - (not mirror finish by any stretch due to time), but removed the seams and imperfections - I did not have a gasket to hand, so left out the grinding of the inlet for now.
Time to put everything back together.

[J44EAG]

On the charger inlet and the elbow outlet, together with the re-usable steel, rubber coated gasket, there is room for an easy improvement which is a real performance winner.

If you machine about 6mm from the lower edge of the gasket, then scribe that shape onto the faces of the charger and elbow, you can then lower the floor of the charger and the elbow as ramps. There is plenty of metal that can be cut away and can result in opening that area up by about 20%. This really helps de-constrict a big bottle neck in the inlet side of the V8R. You will find the car picks up better and there is no loss of tractability. Lawson advised me on this mod. Time taken with an air die grinder and cutting burs, about two hours. Two golden rules. "Think like air and look for steps, ridges and constrictions". Second rule, "Think before cutting. Think twice, cut once". Don`t over thin a casting and stick the grinder burr through the metal! Tuning mods don`t always need to cost much except for time and effort.

Mike

[Lordgaz]

I will take a look tomorrow. (Most of the car is half a mile away at a garage). May I check you mean to grind away approx in the area of the red line?

[J44EAG]

That`s it.

Do the gasket first. Then scribe around it. Then cut ramps in the elbow and inlet to the charger lobes. Look in towards the back of the charger case. Note the odd shap of the right hand rotor inlet. Compare with the left hand one! It is hugely different. Cut away the blockage in that right hand area first, then open up and gas flow around that inlet area generally. I`ve a post in the engine section which shows what I did to my charger. Its not difficult. Just a bit time consuming. I did the whole gas flow job in a day refusing to talk to any one who turned up to see what I was doing. Only at the end of the job and with a suitably polishing compound stained black face, would I let anyone into my working area.

Jagcare in Portsmouth refitted my charger as my sciatic condition stopped me ripping the job apart myself. Driven out of the workshop once I had worked my bench magic absolutely astounded John, the owner. His eyebrows had shot up when I took him the charger back for re-fitting. He shook his head in dis-belief when he subsequently drove the car. "So this is how it should run, eh? What a difference."

If you do this porting mod, I can then advise on sorting out the breathing in the pressure plate area and the cow-horn manifold.

Tom Lentall also knows my car and has also been very complimentary about the improvements that were made.

I recently drove a standard car. It felt as if someone had stolen half the engine.....

Mike

[Lordgaz]

I have re-read your post on the porting mods.. it’s a lot more relevant now I have these parts off the car.. just wondering what method you employed to cut the gasket between elbow and SC

[J44EAG]

Best to use hand tools. I recall I used as 1" medium cut file, placing the gasket between two pieces of ali sheet in a vice. The gasket is very resilient having an inner core of mild steel. You might get rid of the surrounding rubber using a Stanly knife and a steel straight edge before carefully filing down the encapsulated steel shim gasket. Go easy with the filing and try not to buckle or distort the steel shim in the process. Use a round file to get the corner radius at both ends.

Cutting burrs in a powerful drill or compressed air driven windy tool are useful to remove the bulk of ali within the elbow and the charger. Expect to spend an hour creating each ramp within the elbow and rear of the charger case. The ridge in the elbow below the throttle body gasket can also receive attention as can the radius below the gasket on the 90 degree turn. There is a considerable amount of metal that can be removed from the elbow and air flow can be greatly improved by considering its path, seeing air turbulence points and the general air journey through the elbow. Be careful not to cut metal away without considering elbow wall thickness. Keep that in mind at all times and avoid your mind wandering as you work the parts. Some of the work is mind numbingly boring so you need to mentally lock into the job and avoid any distractions. Finish the whole job off with various grades of sanding rolls and polish the whole job if you still have the enthusiasm towards the conclusion! Every obstruction you remove gains a little extra grunt. It is very accumulative.

As previously said, I can talk you through gas flowing the pressure area of the charger and also the cow-horn manifold. Results are in direct proportion to the care and attention you give to each individual component. Get it right and you will be astonished at what you can achieve.

I`d suggest you might also fit a 6% reduced size pulley which does not require machining of the drive shaft snout casing or up-rating of the tensioner and belt system. Lawsons` up-rated and strengthened coupling is worth considering but the drive gears do chatter with one fitted. Perhaps best just to ensure you get a new standard coupling. Don`t re-use the old unit. They get brittle with age.......

Mike