I'm looking at installing a set of LQ9 heads on my car which will put the CR at about 9.5:1 and a Speed Inc SC1 cam. I have a vortech V-9 pushing 6lbs(3.70 pulley), I want to step up to at least 10lbs. My question is which size of pulley should I go to? I know the 8-9lbs kit comes with a 3.12. Should go with that one or a different one?

 

Well if they are ported I would start with a 2.65" pulley if not then the 2.75" will probably get you there.

 

3.12 is the 9 psi pulley. Next lower is 2.95.

 

Funny The 3.12 Pulley On My Car Only Pulled 7 Lbs Right At Redline. I Stepped Down To A 2.95 To Get 9.

 

Well, since boost numbers are a function of resistance to air flow (higher boost number = more resistance to air flow), it could be a lot of things. The car with the lower boost number could actually be faster because it will flow more air. The only way to expect the exact same results would be for the cars to be set up identically. If one guy has headers or even a freer flowing catback and the other doesn't, cam spec difference, head flow numbers, etc., you will get different boost levels even thought the s/c is putting out the exact same amount of air. If the cars in question are very similar, you were probably getting a little belt slippage. Was your belt new, was his? If your car was only running 7 psi and his was running 9 and his car was obviously faster, then most likely your belt was slipping.

Firewood, as PSJ said, the 2.95 is next step lower from the 3.12 and will likely get you to the 10psi you are looking for, more than 10psi you will need the 2.75. 3.7 to 2.95 or 2.75 is a pretty good jump, just make sure your fuel system is up to it and you will definitely need a fresh tune. Sorry for stating the obvious if you were already aware of that.

Good luck,
Tom

 

Well you have some wide choices from what we have all said LOL! I will say this it really depends how your car is setup right now and how many lbs of boost you are seeing right now. Elevation will also play a part. PSJ and everyone were right the 2.95" pulley in the next step up from the stock 3.12" that comes with the kit. If you have a 3.70" I would start to question what has been done to your car and did you install the kit purchase the car with it etc... I personally never installed the kit on my car without the heads and cam. So I have had a few people tell me that the kit with the 3.12" pulley doesn't pull 8-9 lbs as advertised more like 6-8 depending on the person that I have recalled talking to. I also would advise starting bigger and working your way down, so my suggestion maybe to aggressive for you, but the pullies are a little pricey when you factor in your new belt etc... So more info on your setup would help us give better recomendations on what you are trying to get out of it. I run the 2.65" pulley with ported heads and cam and I see around 7lbs in the cold weather I was seeing 9lbs.

 

They are not a million bux, but I have a new 3.12 lying around if u are interested.

I'd go no lower than 2.85 personally for pump gas with that kit.

 

Thanks for all the info guys it's going to be really helpful, but to help you guys a little. The heads are ported stage 2 patriots. My elevation is about 5000ft and the kit I have know I bought new a week after buying the car and installed myself, it pushes a max of 6lbs at approx. 6000rpm. The air up here sucks for making power so you do what you have to. I was also thinking of either the 3.12 or the 2.95, but thought I would ask to see if anyone else has done this. Your help is greatly appreciated.

 

Well with the ported heads they will be less restrictive and so you will need to go smaller to make up the difference. Also your elevation is makeing a difference too. I'll bet you will need a 2.75" pulley or larger to generate your 10lbs I am just guessing though I know several people running the 2.75" pulley down here with no ported heads and they are not haveing any issues ( Make sure you have it tuned). If it were me I would start there,but ofcourse you can start where every you want the pulley is the smallest one Vortech offers for the G-trim after that you will have to contact ASP or Reichard racing for other sizes. Oh the ASP's are cheaper and they are made of steel vs Aluminum. The T-rex pump will be fine for this level on the fuel system and more than likely the fuel injectors will make it maybe you will find out on the dyno tune etc... Unless you have the nonaftercooled version you should have a 3.12" pulley on your S/C. Good luck and just be safe with your tune for that stock bottom end.

 

I don't know anything about sea level but a 2.75 is probably only worth spinning to like 6200 or something cuz you would be overspinning the blower quite a bit right?

My concern going too small is that it won't be pump gas friendly, and that's a pretty small pulley to use, belt slippage could creep up.

You may want to get 2 blower pulleys and go from there. I'm running a 2.85/8.00 combo with my YSi and we have seen 21psi. (eek)

 

PSJ the 2.75" pulley will not overspin the blower according to my calculations. The 2.65" will at 6500 overspin it by a couple hundred rpms. I am running the 2.65" on 93 no race gas and no additives. We have a 6" crank pulley if that helps. I haven't had any belt slipage at all and I am happy with their design it works pretty good. The higher the alltitude the more air you need to acheive the same boost levels as a car at sealevel.

 

no belt slippage, Vortech's don't have that problem. Boost is dependent on rpm and since I was only goin to 6,000 rpm i was only getting 7 lbs. If I would i have taken it higher I very well could have reached 9 but neither I nor my tuner trust my stock valvesprings.

I switched to the smaller pulley to the boost in a little sooner and to up it just a bit.

Unfortunatley a ringland let go so I couldn't enjoy my car too long, it was running great.

So now forged bottom end and maybe 2.75 pulley and 10-12 lbs and that should be enough for me.

 

I think I'll try the 2.95 and see where that gets me. Hopefully it's what I'm looking for, but if not then I'll try again. Thanks again for all the help.

 

Get Me SOM, Holding back, that's a good one, I would have never thought of that.

Sorry about the ring land, glad about the forged bottom end. Interested in seeing how it runs when you get it all tuned.

Good luck,
Tom

 

yep it'll be a while before she's all done i'm saving up as much cash as I can right now, then finance the rest. Should be done in March , possibly might have my pending lawsuit money by then. maybe just might throw a nice cam in there as well.