Engine Guru's - I Need Help
 

Hi, I'm hoping someone on here may be able to offer some help.
My car has the L98 6 litre (Australia) with 6 speed manual.
Over the years I have been slowly modifying the vehicle to achieve
my goal of an 11 second 1/4 - which I achieved last month.

My mods were X-Force Extractors, free flow cats, magnaflow 2 1/2 cat back,
VCM otr & VCM Cam.
Cam specs:-
"The VCM-11 camshaft is a heavily split duration camshaft designed with performance street use in mind with strong mid range and high rpm power.

Cam Specs:
Cam Profile: 225˚ 232˚ .580" .590" 112.5˚"

I had the car tuned & put out a healthy 425 rwhp.
So, after the last drag meeting, I thought the next step would be heads.
So, I removed the heads & sent them to CHI & got them cc'd, ported, machined, valve grind etc.
Whilst apart & got some Lunati tie bar lifters.
Measure lifter lash & bought correct length pushrods & put it all together.
I then took the car & got muffler delete rear mufflers fitted to it.
At the tuner today & first run it made 405 at the wheels - it was running lean
though. So he gave it more fuel, tried some more timing etc & have now got it to 430 at the wheels.
We're clutching at straws, so put the rear mufflers back on - no difference.

We're thinking now does it need more header or inlet manifold ??

Any one have any suggestions????

Read this thorough comparison on intake manifolds:
http://www.hotrod.com/features/1507-...ifolds-tested/

The week it came out (early August) I bought the FAST LSXR and it made a nice improvement.

I have read several tests of cat-back systems showing no improvement at all.
However, installing long tube headers and no cats will make a big difference.
Just my opinions - no facts to back them up.

If you've changed your compression, which it sounds you have, did knock retard get logged?

Same dyno/tuner? Similar weather conditions?

If yes, I'd look at the graph and see of you are getting any valve instability and of course looking for knock retard.

If no then I'd look at the graph and compare the two. Take it to the track and see what it does. If the dyno/weather isn't the same the numbers can easily swing by over 40-50whp.

If you are running the stock LS2 intake a FAST102 will help immensely. I'm still running the LS2 intake but waiting on the Vararam intake to come out for the cathedral heads.

How much did they take off the heads? I've heard of shops taking so much off that the intake won't seal correctly unless they machine that surface as well. Was it a reputable machine shop that did the porting? How much lifter preload did you end up with?