1991 RS 305

Hi. I'm currently running a 97 LT1 cam, it runs great and pulls hard. All my mods can be seen it my signature(1991 RS). Below are the three cams I'm debating. Note that I have the 97 LT1 in the list so you can see the specs of the cam I have now as well. The other two are Comp Cams Extreme Energy Cams.


..................Int/Exh @.50....Int/Exh w 1.5's...LSA.....Notes
97 LT1:.............200/207............447/.459.........117..(.477/.490 with 1.6's)
XR258HR-12.......206/212............480/.488.........112..(available in 110 LSA)
XR264HR-12.......212/218............488/.495.........112..(available in 110 LSA)

Now I can keep the LT1 cam and gain some lift with 1.6 rocker arms. I would see a lift of .477/.490 and I would gain about 2.5 degrees of duration with the 1.6's on the LT1 cam. The other option is to swap out the cam for something a little better all around. I like the XR258HR-12 simply because the duration isn't too crazy and the car should run great with it. On the other hand, if I'm going through the work I feel I should just go for the XR264HR-12. I feel like the duration on this cam is a bit much, but I have also read that the extreme energy series cams are designed so that you can run a little more duration and not lose too much bottom end. That is my primary concern, losing bottom end. Now I plan on getting into some mild tuning if I do swap cams and I'm sure this will help. Their are guys running TPI's with this same duration (212/218) on stock tune. I also read a post that stated 212/218 is about the limit on a TBI computer before you need tuning. Anyone have opinions on the matter, or can anyone advise me on how they think the car may react to these cams? FYI, I am aware the heads will need work to accept the higher lifts. Also, I am porting/polishing the heads.

Thanks, Matt

90c350

I would personally go with the last cam that is in your choices and just learn how to tune your ecm. My comp xe256 has about the same duration figures just with less lift and its on a 110lsa. Its not a hard cam to tune once you know how!! I would suggest that you get into ecm/chip burning before you do a cam swap. Anything other than the stock cam with tbi and you will need to tune to get the maximum drivability and power!! Just my thoughts though.

Pre-Tuner

iTrader: (2)

I have the last cam you mentioned. It's actually recommended for the TPI guys, but the guys at Comp Cams recommended it for my TBI application. The same cam with the 110 LSA is recommended for TBI and I have thought about changing it to that cam for a little more bottom end.

90c350

Just out of curiosity what kind of HP are you making with that cam?? How hard was it to tune?? I would think not to bad at idle with the 112lsa?? What type of head work/heads are you using etc?? Not to be nossy but Im going to be upgrading my heads and cam in the new year and would like to hear what type of cam others are running with Tbi Mods etc? Thanks

Pre-Tuner

iTrader: (2)

I haven't had it dyno'd yet, but I'm guessing it's around 320 hp. I'm still tuning, and every time I start to get close, I find something else that needs changing. After I get it closer, I'll take it to the dyno and do some fine tuning.

I don't think it was that hard to tune, but it is the first time I've tuned anything, so there's the learning curve. It is a computer-friendly cam, so it can only be so tough to begin with, right?

I replaced the engine with a new vortec crate engine, so I have vortec heads. In order to run that cam, you have to have the heads machined to fit the recommended valve springs/keepers/retainers. Other than that, the heads are stock. If I was going to go the head work over again, I'd probably have them ported and would have had the studs pinned for piece of mind. The spring pressure is quite a bit higher and I'm always worried they will work themselves out.

It's got a nice idle though.

I'm in the process of installing a vacuum adjustable fuel regulator now. With this cam, I need too much fuel at WOT and it's creating some problems for me at idle. I'm using some 454 injectors, but when the cylinders are cold, it misfires. Not a big deal, but it's an excuse to buy something new.

90c350

HaHA isnt that always the case! YOu can always use more power or better parts etc. Hope everything works out for you!! This combo that im running was also my first attempt at tuning my own. A bit of a steep learning curve but other than that its been fun!