Can you manipulate the pully combos to start making boost lower???

Eventually once I get it tuned with zero knock I want to use a different pull combo. The goal is to start making boost earlier... I don't have my boost gauge yet but based on what I feel and the little light on the BTM knob, boost starts coming at high 2's low 3's... I'm trying to see boost at 2k real low... how can I do that???

Of course you can pulley up to make more boost at lower rpm. What you want to avoid is spinning up the blower such that you hit the max impeller rpm before your cam gets into its' sweet spot, or alternatively that you are making more boost than the rest of your combo is setup for.

If you plan to do this, much of your tuning will be wasted and you will need to tune again. So, you should decide now, if possible. What are the details of your combo? Especially CR, cam, type of blower, and fuel you will be using?

Rich Krause

But we also have to keep in mind that the SC has to spin fast enough to generate boost. This will not happen at very low rpm.

When you reduce the size of the SC pulley or increase the size of the crank pulley you will get more boost sooner. Most changes will be to go to a 7" crank pulley which will result in the SC spinning much faster earlier. If you do this, it will also increase you final boost so you need to make sure that your car is tune and is safe for that. If you do get the 7”, you can get it at www.performancess.com and tell Steve that Hugh and Quang told you.

I probably won’t be thinking of this until later. Have you done LT, gears, cam, or heads(to increase your exhaust flow and also decrease your compression ratio to make it a little safer for the increase boost).

Good job on your car!

Thanks for the info guys...

Rich - That post you responded to about choosing the right cam for the blower was really helpful. I'm going to order the cmotorsports cam kit very soon. After that I'm going to overhaul the heads and bottom end and upgrade the fuel system and rear end. So you are saying that my tuning will be wasted if I make boost earlier??? I know the general details of what I want my combo to be but maybe you can help me with the specifics... I was plannning for a stock cranked 383, I want aftermarket heads but most likely stock castings hogged out to the max with some nice inconel exhaust valves or something... somewhere in the 8.5-9.0 compression ratio range and 12# of boost with the s-trim. What do I need to realiably run 550 to the wheels give or take 25... that's what my goal is when the car is done (if it ever is really 'done'). For right now, I want it to be tuned perfect, I want that cam kit in, and I want a power pipe/bigger filter combo...

Hugh - Hows it goin buddy. We gotta meet up sometime so I can see your car so it will want to make me finish mine even faster haha. As for my car... the entire engine is stock all bolt-ons. Now I'm ready to get into the engine though... the cam is next along with an intank fuel pump. I'm leaving the stock gears in the car until I have enough for a new rear end. LT's are something I will do in the future not anytime soon. I know these damn SLP's are hurting but I did it just to stay legal AND because I used to have a turbotech kit... its hard to not get stared at by cops now with that whine under the hood. How much boost would I gain by going to the 7" pulley? The way the car is right now, I am not worried about boost killing the engine. I rarely get on it hard right now (especially since the gauges are not hooked up yet and I can't watch the laptop 24/7) when I drive it. The bottom end is going to be here before the engine decides to pop. Well anyway... let me know if you have any advice for me.

The thing is that when you pulley up you will be making more boost everywhere. You will need more fuel and less timing. So it's necessary to tune with the pullies you are going to be using. You can't just slap on a bigger pulley and expect it to be right.

Rich Krause