Quote:
Originally Posted by chrisheltra
Maybe Randy will chime in here because my memory is a little fuzzy here but I think Lightning heads stock are 90# and usually if increasing the boost past 18 psi it is recommended that you upgrade the springs. IIRC mine are 120#.
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35# in stock PI heads
One of the first PI springs out there were 90# and later it was found that 110-120# were optimal.
Rob, I'm not even gonna begin to try and point you in any direction because I literally have 0 experience with your type engine combo. What works for us, may not work for you...... However we do have some similarities with regards to weight and aerodynamics.
I'll start out by saying, what works for cars in a similar engine transmission application, usually turns out to be shit for us and typically that's due to weight and aerodynamics above all.
I know your a turbo guy, and i'm sure you know all about bigger turbos and HP vs TQ. The a smaller turbo usually runs out of HP steam fast and starts making gobbs of TQ and hardly anymore HP, you want more HP get a bigger turbo slap it on and there it goes, but the byproduct is usually a drop in TQ at the same boost levels. Torque is important to us because like a tow diesel or anything else that moves weight real good they have gobbs of it, the same goes for us (well lightnings at least).
With that bigger turbo you have and less efficient transmission you may need to find something that gets you some torque back like a good cam with some mid range grunt while not sacrificing top end, but not soo large that you loose more in the middle and turn it into a top end roll car/dyno queen like a supra.
Now springs, I know your heads are different and I know that they flow better than ours, but this is what I personally learned. I put some 90# springs in my heads the first time, and when I started to make around 20 psi I noticed the power start to wobble and then abruptly tank and that was on a stock crap PI cam, I put some 135# PAC springs in and I noticed it hang on to the power a lot longer with the same cam, apparently I was getting some float at 90# closed and 20 PSI of boost.
I also noticed that the more CFM that I made at the same boost number from a better flowing blower would Blow out spark up top and kill my power up top. (not sure how much gap you have, but its another guess)
Cams, my truck woke up on cam's I was amazed how much I picked up on the top end with a really mild cam, I picked up a bunch of mid range TQ and top end HP on what would be considered a stage 1 cam (for our motor's).
In short and for us TQ= MPH vs HP for our transmission/ converter/ weight in a Lightning at least and the same may work for you.