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These are from the early flathead V12 versions used in the E type and the Series 1 and 2 saloons. They require, as someone explained above, different cams and even more importantly, heads, to work properly. In my view carbs are not a bolt on proposition for the HE engine with its high compression ratio and odd combustion chamber shape.
I quite understand the attraction of carbs, although our V12 HE engines have far more trouble with their ignition systems than their fuel injection which is quite separate. It is just that I do not believe a carbed HE engine will run at all well, if even driveable at all, and Daim will end up with a dreadful car he will not want to drive that uses huge amounts of fuel.
Greg
That of course is something I don't want to happen... So I'll chuck the carb idea and head back to the wiring diagrammes for the fuel injection... Instead I'll see if I can move the air con compressor somewhere else. Replace it with a smaller unit and move it say to the right hand side of the engine, to allow more air into the V.
That of course is something I don't want to happen... So I'll chuck the carb idea and head back to the wiring diagrammes for the fuel injection... Instead I'll see if I can move the air con compressor somewhere else. Replace it with a smaller unit and move it say to the right hand side of the engine, to allow more air into the V.
Daim. there is a guy in the UK who for under 200 quid will put proper louvres into the bonnet as many as you want each side: Sports Car Metalwork: Bonnet Louvres | Sports Car Metal Works
That, together with moving the horns out of the airflow, removing non-contacting bits of the rubber trim seal along the rear bonnet shutline, adding an external tranny cooler and bypassing the trans cooler out of the rad completely, and converting to an huge electric fan and replacing the aux fan with a more modern type, even if you do not want to go the whole hog and cut an airflow hole in the front bumper, will fix your under bonnet temps for good.
I have done all of the above except the louvres, and when pocket money allows and a trip to the UK calls, I am going to go for the louvres. Actually, I do not really need them to control coolant temps, but the under hood heat on a hot day is just staggering and louvres will fix that for good. My friend who works for a well known car mag has a Jensen Interceptor, and he says the models with louves in the bonnet are much better both for cooling and under bonnet temps.
We got the 4500 dollar conversion on 1 of 2 XJ-S's. It came to us like this. Boss bought it. Probably, way more then he should of. Had not been run in 5 years. They got it started to ship it. Didn't buy anything new. Just got it started. Runs good above 2500 but will not idle. Replaced both filters they had on it. Pressure reg is leaking so that's next. Gotta pull a plug so I can figure out what plugs it has. It's kin of a POS. But, will see what we can do. Has the 6 pack of Weber carbs. Probably need rebuilt. Body kit etc. Rusted floors.
Although, I would never give up the advantages of fuel injection for carbs, and this might be a totally stupid idea, but what could be a cool improvement to the engine bay would be to replace the current throttle bodies and airboxes with something that featured the multi-trumpet look of a set of side-draft Webers. Have the air cleaner hidden in the altered throttle bodies, and the trumpets as intake.
Does anyone here has a hands-on experience with swapping Holley 4160 to 4150?
I did exactly that for my 5,3L PreHE engine. With 2 x 4160 (390 CFM), it worked great. However, I tried to use the jets and bleeders sizing from 4160 as a starting point for 4150, and it does not seem to work well. Thus, the initial tunning is quite difficult.
Any tips for that?
As for my original question, I managed to find out that the problem was actually with the ignition system (There was a small crack, probably from material fatigue, not easily visible. Beyond 2000 rpm it was causing a loose contact, efectively behaving as rev limiter.)
After fixing this, the Holley 4150 require pretty much the same settings as 4160. Unsurprisingly they are a bit aggressive and better in higher revs. Here are two videos for comparison:
Typhoon 100% right, Daim. The HE engine is not that suitable for carbs and will give you catastrophic fuel consumption on Webers, if you ever get them even roughly tuned.
Your best option if you want carbs is to change the heads/engine for the pre HE saloon or E Type factory carbed setup. But can you explain your aversion to the EFI system? Once the loom bits in the engine bay are sorted (if they need it) it's a pretty reliable system I have found.
Greg
To swap heads to the pre HE you have to also swap pistons. Pre HE has no combustion chamber, it’s in the pistons. 99% of all pistons are 7.8-1 compression which really hurts fuel mileage.
Which engine type do you have in your carb'd XJS, Lawrence?
The factory V12 in E type form and on the series I and II saloons had factory carburation. This is the pre HE engine, mind. This setup will fit under the bonnet of an XJS.
I believe The HE engine is not really suitable for carbs, as the high compression and poor combustion chamber shape will always give combustion problems and cylinder air/fuel mix problems at several points over the rev range, even if by a miracle you manage to get decent running at some revs. Then add in detonation at high revs that cannot easily be offset by the ECU telling the system to go full rich, catastrophic fuel consumption (maybe 8 on webers) and it looks guastly.
So it is pre HE engine or forget it, I believe. I can always be wrong, of course but undoubtedly there would be a mountain of problems to solve carbing an HE.
Greg
Realize the pre HE engine uses a different distributor. Then the later HE and accordingly the ignition timing is nearly impossible to get right.
The trouble is the distributor on a V12 can only be physically advanced or retarded about 2-3 degrees. And that requires darn near total dismantling of the distributor.
Then the timing mark is on the bottom of the engine which makes it really hard to check and see what your timing is.
I had over 4 dozen distributors and an actual Sunnen distributor machine to use. Working with the advance weights and springs I eventually got the timing working properly but that required all sorts of spring and weight combinations. I welded weight onto the Jaguar weights and used a variety of Ford, Chevy, Dodge springs.
I had nearly countless hours doing it.
I used a computer Engine analyzer program to calculate how much timing was required at what sort of RPM.
I’m going to use a mega squirt and eliminate the distributor for my race car. Rather than go through that again. A few Key strokes on my lap top and timing is set.
I’ll be using a set of Weber IDA’s and using E85 Yes they are seriously too tall to fit under the hood. But The hood is Fiberglass so it’ll be easy to cut holes in it.
The ethanol in E85 makes 105+ octane which allows more ignition timing. And tolerate right and lean much easier. ( plus the engine runs cleaner without the build up of deposits on the valves that has produces). Finally the extra oxygen molecules in ethanol allows more fuel to burn and thus make more power.
As I can't really be arsed to fiddle around with the injection system on the V12, I was wondering: were there any "common" carb conversions in XJ-S models?
Not saying conversion like V12 out, V8 in. But in the sense of using say 12 single carbs or 6 Weber doubles and co?
Reason being: there is a way here for me to legally get a historic plate even though the engine is "modded". That requires knowing what was a common conversion. And if I then do that conversion, the car will get the tax bonus and valuation gains I intend it to get...
Any ideas?
To use carbs you will need the distributor from a pre 1975 car ( XKE or XJ12 ) plus the cylinder head and custom made pistons. 10.1 compression would be ideal For the street. Oh, and manifolds and carbs.
WBER 40 IDF CARBS will work with the 6 cylinder hood/bonnet. No room for an Air filter though if you want power.
PS. Webers don’t come properly jetted. And the stuff you need, jets, air correction meters chokes etc. will cost more than the carbs.
You can use the Jaguar factory manifold but you’ll have to use the 7.8-1 pistons unless you have Joe Cureto rejet those Strombergs. There is more power using 4 SU carbs(2 inch HD8’s) but that’s not a bolt on.
Agreed and the stock early Bosch/ Lucas systems are ridiculously simple to repair and diagnose. I'd much rather sort it out than balancing multiple carburettor throats, synchronizing throttle blade openings, playing around with emulsion tubes/ power valves/ transition orifices/ automatic chokes/ secondary throttle opening etc to try and get something resembling half decent driveability out of carbs.
Even with an exact starting point for a set of carbs to just "bolt on" there will be countless hours of tuning.
As a guy who has spent a life tuning and adjusting carbs. I couldn’t agree with you more. The factory system takes a little reading and understanding. But it’s so much simpler. Mostly plug and play once things are right
The forum has a good “book” on the system.
These are from the early flathead V12 versions used in the E type and the Series 1 and 2 saloons. They require, as someone explained above, different cams and even more importantly, heads, to work properly. In my view carbs are not a bolt on proposition for the HE engine with its high compression ratio and odd combustion chamber shape.
I quite understand the attraction of carbs, although our V12 HE engines have far more trouble with their ignition systems than their fuel injection which is quite separate. It is just that I do not believe a carbed HE engine will run at all well, if even driveable at all, and Daim will end up with a dreadful car he will not want to drive that uses huge amounts of fuel.
Greg
The problem isn’t the carbs, cams, or combustion chamber. It’s the distributor.
The closest distributor to what you need is the 1980 only sold in England with 10-1 compression engine.
The later HE distributor has too much retard and the Early PreHE engine has too much advance.
You can only “adjust” about 2-3 degrees without modification. Even then the timing weights and springs aren’t exactly right.
To do that properly you’ll need to spend a couple of hundred dollars on a chassis Dyno. With a good selection of weights and springs. Be prepared to weld on weight and grind a different curve.
09-06-2015 | 11:22 AM
