3.0" SC Pulley?

Originally posted by turtleman:

"A friend of a friend has a 98 GTP with a 3.0" pulley and a tuner and claims no increased KR. he has the blower ported, FWI, and 3" no cat exhaust (that i know of) does this seem impossible? I would think if you have a pulley that size with no I/C or anything, you would have stupid amounts of knock and would loose lots of power..."

The ported blower and 3" exhaust helps. Does he have a cam or rockers? If so, I can believe it. When you open the exhaust like he has, some boost is lost, so you can run a little smaller.

Then again, some will scan during normal driving, or a 0-60 launch, and see no KR, so think they're safe. Need to run WOT from 0-100 mph to be sure. My KR doesn't start to act up until the 2-3 shift (95 mph).

definitely stock valve train. i have no idea what kind of plugs or tstat or anything like that. I only looked at it for a few minutes while i was at work.

does anyone in the forum have a cam?

Need more than plugs/T-stat to run a SC pulley that small. In addition to a cam or full-size IC, you need to upgrade the fuel injectors to keep up. He's knocking, whether he wants to admit it or not. Lots of folks don't know and they don't want to know... I meet people like this at the track sometimes. They won't believe in the power of KR until one of their pistons goes pop!

You could run a 3.2" safely using ZZP's short stack IC, but need a full size IC to run 3.0". You can also go lower with a cam or high-lift rockers + opened exhaust. Below a 3.1", you must upgrade injectors to supply enough fuel.

Jason has a cam.

this might be a really stupid question but can you use high ratio rockers 1.9 or more and a hot cam?

and do you know what kind of head work needs to be done to put a cam in (other than obvious valve springs and such - machining wise)[/i]

No, can't run 1.9s with a performance cam. The resulting lift would be too extreme. I think you run 1.6s or 1.7s depending on the cam.

I don't think any head work is needed. Jason or Urbs would know.

AA wrote:

No, can't run 1.9s with a performance cam. The resulting lift would be too extreme. I think you run 1.6s or 1.7s depending on the cam.

I don't think any head work is needed. Jason or Urbs would know.

based off of that, would it be reasonable to suggest, getting high ratio rockers is much more cost effective and yields similar results as a performance cam? I know that there are many ways you can manipulate the engine with a cam and rockers just pretty much gives you lift but for our purposes, rockers will do the trick?

btw, what is the stock rocker ratio?

HEY IF I GOTTA SS intercooler from ZZP would i be able to run a 3.3 inch pulley with my mods?????

quote: "HEY IF I GOTTA SS intercooler from ZZP would i be able to run a 3.3 inch pulley with my mods?????"

Most likely, yes.

quote: "based off of that, would it be reasonable to suggest, getting high ratio rockers is much more cost effective and yields similar results as a performance cam? I know that there are many ways you can manipulate the engine with a cam and rockers just pretty much gives you lift but for our purposes, rockers will do the trick?

btw, what is the stock rocker ratio?"

It's a hard choice. To begin with, a cam is cheaper to buy than a set of rockers, plus the 1.9s require changing out springs/rods, which adds to cost. I think you can keep stock valve train intact using a mild cam.

On the other hand, a cam install is more work than rockers, requires more tech know-how & mechanical skill. Easier to do if you drop the engine. No everyone knows how or feels comfortable doing that kind of thing.

Power increase is different. Rockers gain up high (4k rpm+), while a cam gives a solid power increase throughout the entire band. Some feel having more power mid-band is desirable, some think a boost up top helps offset our low-rpm torque curve.

Because rockers only work higher up, they don't affect low rpm operation, idle, or general fuel economy. Cams do alter how your engine runs at all rpms. Tuning is necessary with some cams to get everything right.

Stock rocker ratio is close to 1.6:1.

go to regalgs.org or clubgp and do a search on cam vs rockers. There are a LOT of threads on the subject. Aaron's assesment is right on. A cam adds lift and duration while the rockers add only lift. I don't remember reading about many L67s using a cam AND rockers. I know Zoomer ran 1.7s with a VS cam, but ZZP states that "The 1.7 rockers don't make HP on stock heads with the VS, GT or S1x cams. We've dyno tested." Unless you just want to reduce friction by having full roller rockers, I would just go with a more aggressive cam. Remember that aggressive cams (more than the XP) require head work. Interesting info on stock rocker ratio

You need a lot of little parts to do the cam. I kept the stock valvetrain and went with a VS (I haven't changed my shiftpoints yet). Vendors claim the VS and stock drivetrain can support shifts @ 6200 rpm before experiencing valve float. With all parts (timing chain tensionner, various gaskets) required to do the cam, I thought it was quite expensive. It's very labour intensive. You can get the cam out through the wheelwell like I did, but if you have the equipment to get the engine out, I would recommend that. I'm sure Dave's install involved less swearing and throwing of tools. If you think you can do rockers, I think you can do a cam, but be patient and take your time. Definately go with the "cam install kit" offered by the vendors. I didn't (due to shipping prices to Canada but in retrospect it probably would have been cheaper.

If I had to do it all over, I'd go with rockers since my car isn't an all out race car. Not that the gain with the cam isn't noticeable, but it's a lot of $ and effort for what it yields. On my roadmaster, I got a set of 1.6 roller rockers to install and I am not going to install a camshaft, even though they yield great gains on the LT1.

I regret not porting my blower while it was off

I have heard of people running 1.7s with mild cams. This is the only case that has shown any benifit. None of the vendors reccomend this combo because the gains are just not there. Part of the reason is that the cam was tuned for a stock valve train.

If you put in a really HOT cam, you have to have the valve guides machined. For my xp cam I just needed lower profile valve seals and spring retainers.

A bit more lift and the valve seal will get chewed up.


As for the 3.0 pulley: Fact of the matter is you have to scan for anything smaller then a 3.4. (really anything smaller then stock) Wont the PCM pull wot timing if it is seeing too much boost? I think stock advance is 15* at wot, which will drop down to poop the pcm is seeing too much kr.

i'd stay with rockers if reliablity is a factor.

if you are going to do a cam, might as well do alot more while you're in there. And that will all cost more. as stated earlier, need new springs or new heads (if going with a real hot cam), timing chain, might wanna port the blow too since its off. plus all new gaskets. it really adds up.

I agree, rockers will get you pretty far. A cam install is more likely to expose other problems in the engine. The worst part is, you wont know of a problem till it is too late. Rockers are great. Any problems and it only takes an hour to inspect them.