I know that at higher revs the valves on a standard engine start to kiss the pistons. I've currently got the soft cut rev limiter set to 6800 but the power is still climbing steeply, so what needs doing to raise the limit up further?

Is it a case of solid tappets and stiffer valve springs or are valve cutouts in the pistons needed as well? The bottom end has had a full dynamic ballance so AIUI that should be good to at least 8k rpm and the head has had a good fettle so there's every reason to believe that there's plenty of top end there for the taking.

 

It depends on cams and boost how much you can rev it.I had reached the limit of my standard springs at 1,5 bar and over 7000rpm(around 360bhp). Then we put in an inner spring from Audi which fits perfect inside the standard one, and now i run 2,2 bar boost and rev to 7800rpm max. cheap and functional! This on BD 14 cams, around 450 bhp.

 

I'm on standard cams and don't really see any great reason to change.

Are you suggesting that the boost level affects the valvetrain with respect to interference or am I misunderstanding you? FWIW hitting the limiter at 6800 we were getting 370bhp at just 16.5psi.

I note that burton and ggr are both doing "'soft duplex spring" kits for around a tenner a spring. If that's all that's needed to raise the limit then it seems like a no brainer to do it next time I have the heads off any of my engines.

 

If you are on the limit of the spring and then put high boost on aswell, it can start to fluctuate. Not uncommon. I don,t think that you will need to change for 370 bhp, and why rev it more with standard cams?They don,t have a massive lift and don,t accelerate the valves that much either.

 

And you don,t need solid lifters if you don,t exceed 8000 rpm. Standard works to 8k!

 

mines revs to 8k no worries..
have valve cut outs and isky springs, tons of boost and lumpy cams

 

Mr 19", Got it now, thinking it through the inlets that flutter as the springs try to close the valve against the boost rushing in against the valve. As to why rev it more, well because I can, the engine is so short stroked as standard that it's a crime not to let it rev like it want to.

I may be running standard short duration, low lift cams but power is still climbing rapidly and from the torque curve it looks like it's going to be worth going to 7300 soft limit 7500 hard. If that is the case then we can twiddle with the boost map to give around 400bhp all the way from 6000 to the 7300 redline, to give a monstrously grunty and flexible top end without compromising driveability.

If I were going to fit bigger cams then I'd also get the valve seats recut for bigger valves, the porting that I've already done is going to be fine up to 8500 but at 8k the standard valves will start to be a limiting factor.

So what we're saying is that standard rods, bolts, tappets etc are all good to 8k, it's just the springs that need swapping. Superb, thanks chaps.

 

No probs! Have you changed the stroke or is it standard? You have the opportunity to adjust the cams for higher revs with adj. cam pulleys too! Increase the overlap a bit. Good luck! Johnny.

 

Stroke is standard. One of the things that I've been trying to do with this engine is to get the maximum out of it with the minimum of changes to the internals. Other than having everything balanced the bottom end is as it left the factory (actually that's not quite true as I use a shortened 2wd big wing sump on a 4x4 enginge so the oil sump has been shortened as well), top end the only changes are my custom plenum, the extra set of injectors and the porting that I've done. What that means in practice is that if I break something I can just swap the head and ancillaries onto a different bottom end, or once I finish porting another head to put on my spare engine then I can have a decent spare engine with minimal investment.

I do wonder about verniers but I hear so many tales of them wandering around that I'm not mad keen on them.

 

I have no problems with mine. From Collins. Good luck with your plans!