What Powerband Should Have?

[lahondal 17]

Hi!

 

I have a 298º cam mounted on a 1.6GTi with bike carbs and many other bits. Stock head.

 

It revs quickly from around 5300k to 7k, but from there becomes much more difficult.

 

It have:

 

-298º cam

-Flat pistons, 11.6 CR.

-Stock head.

-Stock exhaust manifold.

-Lightened flywheel.

-Megajolt management, and 33º advance.

 

This is the powerband should have? Or maybe the stock 1.9head is restricting the revs?

 

Thanks!

[Tom Fenton 1,542]

I would say the head and exhaust manifold is strangling it. There is no use putting a 300 deg cam in an engine with otherwise standard bits, it needs a flowed head and decent exhaust manifold to get the best from it.

[lahondal 17]

I had readed that the stock exhaust manifold is better than all people say, so I kept it on the car and spend money in other bits like the megajolt management.

 

It have a custom exhaust system, 50mm, and only 1 backbox, same diameter.

 

Is there in UK a good tuner who can work the head? I know the theory in porting heads, but is so difficult doing it well.

 

Thanks!

[alexcrosse 124]

I don't think they're happy to rev past 7000 anyway on a standard bottom end..

[petert 589]

Yep, stock head. The poor old valve springs have probably laid down and died well and truly by now.

[lahondal 17]

The pistons are lightened and balanced, and the rods too.

 

Flywheel is stock. Acording some calcs i did, with 73mm stroke the pistons will reach the piston speed limit (20m/s) at 8200rpm. The TU 1.6 engines with 82mm stroke revs happily to 8000 with no problem...

 

Well, I post full spec now:

 

-298º Cam, double catcams springs, titanium retainers, vernier pulley.

-Lightened 405SRi flat pistons, 1.6 GTi rods, all balanced to the tenth of a gram. Stock flywheel.

-Stock 1.9 Head (the bigger valves). Light polish on inlet to match manifold. Skimmed to adjust the CR.

-Mi16 flywheel, pretty lightened.

-ZX9R bike carbs, 40mm throats. Custom inox manifold. Facet fuel pump. 165mains, air corrector holes blocked off.

-Megajolt ignition management.

-Stock exh. manifold, 2" system, only 1 backbox.

 

What is your opinion of shenpar motorsport?

[lahondal 17]

Hi again.

 

Im thinking in theory I have the correct cam timing, but if I had a mistake, can this reduce the powerband enough for not be able to reach 8k mark?

 

I can play with the vernier pulley, but I dont have RR at the moment....

 

Best regards, David.

[petert 589]

Possibly. What inlet lift does it have at TDC?

[lahondal 17]

It have 4.30mm at TDC.

 

Anyway, I checked it yesterday, and was 5 degree retarded. I did the timing using de maximum lift method, and it seems this is not the best way...

 

Need to take it for a round...

Edited April 16, 2013 by lahondal