How many lost horses
Discussion
So here’s a question, my X308 XJR is listed as coming out of the factory circa 370 bhp.
I had an upper pulley upgrade completed a few years ago and in the very near future will be upgrading the lower crank pulley, The crank pulley replacement is due to the existing being potentially faulty, so I may as well upgrade it.
Today, I did a Dyno power run and the car produced 343 bhp.Torques are still as per original spec. I will do a rerun after the crank pulley upgrade.
My question is what can I do to try and get some of those original horses back ? I dont want to spend any more on upgrades, maybe just replacement standard parts, or will a major service be productive ?
Any thoughts please ?
I had an upper pulley upgrade completed a few years ago and in the very near future will be upgrading the lower crank pulley, The crank pulley replacement is due to the existing being potentially faulty, so I may as well upgrade it.
Today, I did a Dyno power run and the car produced 343 bhp.Torques are still as per original spec. I will do a rerun after the crank pulley upgrade.
My question is what can I do to try and get some of those original horses back ? I dont want to spend any more on upgrades, maybe just replacement standard parts, or will a major service be productive ?
Any thoughts please ?
The BHP figures they quote are always subject to interpretation. The only figure that should be allowed is a measure of what actually comes out of the back wheels, since you can't use the horses the engine makes which are subsequently lost. But even this is fraught with difficulties.
All sort of things will affect the power measured on the day. Temperature, humidity, air pressure.
The number you get given will have some number randomly added to the measurements to compensate for losses through the rest of the car etc.
All sort of things will affect the power measured on the day. Temperature, humidity, air pressure.
The number you get given will have some number randomly added to the measurements to compensate for losses through the rest of the car etc.
Yes I would never trust those readings
Bear in mind the biggest power sap on any supercharged Jag is heat soak and intake temperatures. No XJR6 will ever pull 325hp and I have never seen any standard X308 XJR pull 370 hp. You will always notice that they go much better when you stab the pedal after being kind to it, if you push it over and over the intake temps rise and the car starts to feel a lot less punchy. Also so many dynos give false readings, and often don't accurately account for transmission loss etc.
I've got both XJR 6 car standard and modified and XJR8 cars standard and modified, and pound for pound the best adaptation is to introduce additional cooling to the intake, or as we did on our XJR6, run additional water pumps to circulate the water faster.
Talk to Swallows Jaguar in Bristol, they are doing loads with both engines and are learning through actual experience.
Bear in mind the biggest power sap on any supercharged Jag is heat soak and intake temperatures. No XJR6 will ever pull 325hp and I have never seen any standard X308 XJR pull 370 hp. You will always notice that they go much better when you stab the pedal after being kind to it, if you push it over and over the intake temps rise and the car starts to feel a lot less punchy. Also so many dynos give false readings, and often don't accurately account for transmission loss etc.
I've got both XJR 6 car standard and modified and XJR8 cars standard and modified, and pound for pound the best adaptation is to introduce additional cooling to the intake, or as we did on our XJR6, run additional water pumps to circulate the water faster.
Talk to Swallows Jaguar in Bristol, they are doing loads with both engines and are learning through actual experience.
I am still not happy.....
If I have a well serviced car and an upper pulley upgrade surely I shouldn’t be so far down on power ?
If the upper pulley gives, say, 30 bhp and I am getting 343, that is nearly 60 bhp missing somewhere.
Thats a fair amount to lose despite the cars age....where do Ineed to start looking for them ?
If I have a well serviced car and an upper pulley upgrade surely I shouldn’t be so far down on power ?
If the upper pulley gives, say, 30 bhp and I am getting 343, that is nearly 60 bhp missing somewhere.
Thats a fair amount to lose despite the cars age....where do Ineed to start looking for them ?
The only way to measure what you're getting at the flywheel is to take the engine out and bolt it to a test rig.
So the dyno is measuring the rear wheel figures and guessing from there.
The most useful way of using the measurements is to look at before and after making some changes. Do a test run, replace a pulley and then do another test run and see whether the new results are better than the old ones. Even here the numbers are only comparable if the intake air temperature and pressure are the same for both runs.
So the dyno is measuring the rear wheel figures and guessing from there.
The most useful way of using the measurements is to look at before and after making some changes. Do a test run, replace a pulley and then do another test run and see whether the new results are better than the old ones. Even here the numbers are only comparable if the intake air temperature and pressure are the same for both runs.
People live and die by these dyno readings. I agree the crank HP is only a computerised guess but it's worked out with the same percentage for all cars, plus WHP is what the car is putting down, every dyno is a little different at reading this but all within the same 10/15bhp WHP of eachother.
I think I had the same problem as you with my XJR I had for 7 years, in the end I put sports cats and full exhaust on it and still got beaten racing things that shouldn't have beaten me. As said heat soak is a massive problem with the supercharger on these, maybe this is the issue, I've never seen one with big power, perhaps 400bhp with 1000's spent on it.
I think I had the same problem as you with my XJR I had for 7 years, in the end I put sports cats and full exhaust on it and still got beaten racing things that shouldn't have beaten me. As said heat soak is a massive problem with the supercharger on these, maybe this is the issue, I've never seen one with big power, perhaps 400bhp with 1000's spent on it.
If it was me I would get it back to stock power and some (as you have one pulley to start with) before you starting tuning the engine more. It doesn't make sense to do it the other way round, then you might end up with stock power when you should have over 400bhp, so still in the same position.
Have you checked your fuel trims to make sure your not running the wrong mixture due to a O2 or lambda sensor, this will cause you to be down on power.
Has it had recent spark plugs, are the emissions correct? perhaps flush out the whole injector system.
Have you checked your fuel trims to make sure your not running the wrong mixture due to a O2 or lambda sensor, this will cause you to be down on power.
Has it had recent spark plugs, are the emissions correct? perhaps flush out the whole injector system.
Zippyworld said:
The car is going for a crankshaft pulley upgrade, that should give 60bhp ish.
The cooling system is also being upgraded to cope.
Once its done I’ll get it on the dyno and report back next month.
Thankyou for the input so far....
Pulley upgrade does not give you 60hpThe cooling system is also being upgraded to cope.
Once its done I’ll get it on the dyno and report back next month.
Thankyou for the input so far....
We have a 40000 mile XJR with the crank pulley, exhaust, larger intercooler, improved intake and at that stage it made 414hp
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