ok i just rebuilt my lt1 and i got the comp cam 292 xfi 242int/248exh, 0.584/ 0.579 lift, i still have the stock heads can anyone recommend me what kind of valvetrain should i go with? my car its a 97z28,m6 3:42s

 

Why not use what Comp recommends?

Rich

 

I first went with the Comp 918 beehives as they recommended, however, I had some high RPM issues with the XFI-292. And, most valve-train experts here on the forum don't think the 918s with 130# seat pressure is adequate for the 292 cam (even though Comp lists them for the 292).

I just installed some new PAC-1518s (with 1.785” installed heights) but haven’t been to the track yet to see how well they perform and it they fixed the high RPM problem. Additionally, some people think I could have made an even better spring choice other than the PAC-1518s. We’ll see.

WD

 

I haven't jumped on the beehive bandwagon myself. What seems to work best for me is a small diameter dual spring with a Ti retainer. Unfortunately Ti is very expensive lately. Setting them up with 0.060" clearance, not more, also seems like the way to go. With the XE/XFI lobes, they do seem to need more spring than Comp specifies. That seems odd to me, one would assume they test these things? I would not use the XE/XFI lobes in a high rpm setup, no one seems to be able to get them to rev. They are good for blower cars operating at less than 6,500 or so. Or, with any setup where the r's are kept down for whatever reason. That's with a good dual spring and Ti retainer. Comp used to be a great company, I am getting unimpressed with some of their newer stuff and their manufacturing practices (the Hecho in Mexico beehive springs, for example).

I'm curious how it works out, how high do you plan to spin it? I have never seen the XE/XFI's do the job once the r's approach 7K.

Rich

 

I'm turning my stroker just slightly over 6500 (shifts complete just before 6500) with the XFI-292 and that is all I'm expecting from it. However, I'm at about 6540 as I cross the stripe, and if I don't get out of it immediately at the stripe the valvetrain floats. Also, it feels like the torque curve is going flat just before and at the 6500+ range. So, I don't need a lot more RPM, just a small amount.

Additionally, I have the Crane high-performance HRs and they are telling me to run more preload with their lifters to improved the RPM issue. Specifically, 1 to 1 1/2 turns of preload as a standard setting on their HRs. So, I have them set to 1 full-turn and we'll see what happens.

We'll see how the new PAC springs with titanium retainers and the additional lifter preload works when the track opens Feb 3 (weather permitting)

WD

 

I think that may give you a couple hundred more. Please post up the results, one way or another after you test it. I bet Ti valves would help, and they would also double the cost of the valvetrain!!!

Rich

 

If this combination doesn't work better, I'm going to back-off the lifter preload to 1/2 turn. And if that doesn't make any improvement, back to 1/4 turn preload, which is what I have run in the past.

WD

 

IMO the XFI was a huge mistake and you comounded it by going WAY WAY too big on the duration for a 350.
You are going to need to rev it too all the pcm allows to have a prayer of making it work and at that I bet the shortblock is not long for this world because I bet it was not put together for that rpm.

As covered the recommended springs are not even enough for a 396 which will tend to lower the needed rpms.

If it is not too late send it back and get something decent, maybe a Comp 503 and a set of the 918 beehives you will be better off.

If you go ahead with this it is not going to work out. You may think it is fast but it could have gone faster with better parts selection and no more money. A LOT of people out there tout their setups as fast when for the investment they are NOT, unfortunately you are too far into this project to go back and get the research right.

 

I still don't understand why you didn't setup the springs at a lower installed height. I was going to run my 1518's @ 1.75" and my cam had .605" lift. I would set yours up .060" from coilbind since valvefloat can destroy an engine if left untreated.

 

i thought about going with the cc503 but i couldnt find it anywhere for sale

 

You couldn't find a 224/230 camshaft on sale. So, you settled for a 242/248 cam.............and this is on a stock head 350ci.

 

Are you kidding? It's available everywhere

 

My question is why are you trying to spin that cam above what comp says its rpm range is witch is 2200 to 6200 rpms?

 

yeah i know lol. so its the 292 that much aggresive than the 503? cause it spins 6200rpm similar to the 503 or maybe im just wrong

 

Comp's published RPM range on all their LT1 stuff is WAY off. Engineer has to spin a 396 ro 6500 a 350 will spin a lot higher.

My best guess is they are applying gen 1 duration=rpm rules to the LT1 ignoring the fact our intake shifts the powerband up several hundred rpms.

What the hell do I know though I am just capable of processing information rather than blindly believing marketing BS?