390SE wont pull at over 5KRPM. Any thoughts?

[ed_crouch]

As above, when doing some testing, I noticed that the grunt really, really, subsides above 5K. I am told that the 390SE engine is supposed to be "well grunty" al the way to the redline.

How does everyone elses do at high RPM??

I guess it might be fuelling problems...

Maybe they're all like it.

Ed.

[numbnuts]

Assuming everything else is in good condition and the car is set up correctly, it could be a worn camshaft, there is a wealth of rv8 knowledge on here so i am sure there will be some more ideas along in a minute.

[matt-man]

I didnt think it was a good idea to take the V8 engines past 5K???

I used to drive it to about 5.5K if really going for it but now always change at 5, or maybe 5.2 if im distracted!

[l33]

matt-man said:

I didnt think it was a good idea to take the V8 engines past 5K???

Me neither, I thought that generally, V8's didn't like high revs and thats why they have so much low down grunt. I rarely take mine above 5k revs.

[wedginald]

I had a 350i that really stuttered above about 4000... Turned out one cam lobe was completely worn off! Spent ages looking for fuelling probs before finding the real cause. Hope this isn't your problem but don't discount it.


Richard

[andy390se]

above 5000rpm slow down man!!!
how are you looking at the dial when pushing 5000rpm through the gears?
are you warming it up for goodwood on sunday?

[number 7]

Peak power on the 390's and above was quoted at 5.5K, although you don't really need to go much above that.

7.

[danny hoffman]

If it's a very worn cam the flapper in the AFM will start to bounce, both at high revs and full throttle lower down the rev range. This will cause the engine to hesitate.

Ian had a similar prob which turned out to be the pickup in the dizzy.

[ed_crouch]

Thanks for your help peeps.

Looks like the concensus between my 2 threads is that that I may have some fuelling issues... I do have a cheap pressure gauge, but will seek to calibrate it against something reassuringly expensive (and borrowed!!). Theres no real hesitation, it just runs out of puff...

I'll have a look into the fuel presure, and promise to keep it below 5.5K...

Incidentally, the 5.5KRPM was doing 0-60 on a N.S.L. A road, and I couldnt get below 7 seconds. Is this slow for a 390??

Ed.

[adam quantrill]

Well slow. 350i is 6.1 seconds, and that involves a short period in third because of the gearing.

[ed_crouch]

Well, fuel pressure turned out to be 39 PSI with the engine off, and the fuel pump running (opened the AFM flap to close the fuel pump contacts).

This is about 260kPa, which would appear to be normal...

Jchase, Is the way I did the test correct?? i.e. without the engine running?? I guess maybe some injector flow might drop the pressure a little...

Also, when the pump stopped, the pressure immediately dropped to 32PSI (210kPa), and held steady at that pressure (so I've not got leaky injectors then!).

Is this normal??

Ed.

[ed_crouch]

When i did the valley gasket, I did have a good look at the cam, and the lobes looked pristine...

Hmmm.....

I wonder whats doing it...

Ed.

[adam quantrill]

Ok so you have good pressure, but what about flow?

Try taking the fuel line off the engine (depressurise first) and time it into a graduated container to see how much it flows. Maybe there is fuel starvation at the top end?

What about the ignition? Have you checked the timing and advance? When I got my grey 350i the dizzy had no mechanical advance, it was locked up, and the people before me had set it to about 12 degrees BTDC. So it didn't rev too well about 4,500. When that was sorted it was much better.

As for gunnning it, yes you should be able to take it to 6k, and it should be pulling hard at 5,500, which is when you start to think about changing up. By the time you declutch you'll be at 5,700. And dump the clutch into the next gear, with a nice cheeky squeak of wheelspin!

[jchase]

Hi Ed,

Sounds like the fuel pressure is fine, as Adam says next thing is fuel flow at that pressure, then you will have tested the fuel pump and pressure regulator at least.

-Jim

[ed_crouch]

Thanks, fellas. Will keep searching.

The car is going into Autocraft for a rolliung road diagnostic session. This will shake the demons out!

Ed.

[thomas7037]

Justan Idea but I remember reading that over 5k and the hydrulic lifters begin to tail of and'froth'the oil not lifting the valves as much and so sort of self limiting the engine. Am sure it was on a link posted on here not long ago. will try to find it. Sounds beliveable but don't know if its true

[ed_crouch]

Yep, ive heard that too. Will get the motor set up properly, then if it still does it, Rhoades solid lifters might be an idea!

Trouble with them is that you have to do the tappets often...

Also might need different pushrods, as the hydraulic ones arent adjustable IIRC.

Ed.

[wedg1e]

My 390 revs way past 6000... not that I do it very often. The limiter is set for about 6200 but any more than about 5800 is just torturing the poor bugger.
Hydraulic followers too...

[rev-erend]

ed_crouch said:

Thanks, fellas. Will keep searching.

The car is going into Autocraft for a rolliung road diagnostic session. This will shake the demons out!

Ed.

I'm sure the RR route will show where the problem is.. it's a good move.