91Z28

Is anyone here running 918s with titanium retainers? In a recent thread there was confusion about which locks and steel retainers to use because comp lists several as being compatible with the 918s in both the 10 and 7 degree variety. I noticed that only 1 titanium retainer part # exists however, and when I had my valvetrain installed in my heads I was told that they could not reach the proper installed height of 1.8" with the titanium retainers. Anyone else run into this problem?

speed_demon24

iTrader: (6)

What height did they end up at? You should set them up at 1.75".

91Z28

Right now they are at 1.8" with chrome moly retainers. 1.75" is the most they could get with the titanium retainers and that would lead to less pressure and decrease the max lift of the springs.

speed_demon24

iTrader: (6)

Um 1.75 = more seat pressure. I was getting valve float at 5800 when mine were at 1.78-1.8".

91Z28

I was told otherwise and didn't know any better. I'm very new to when to the valve/spring assembly stuff, all that I know is what you can read in books for the most part. I could also just be remembering it backwards. When I picked my heads up it was written with black magic marker on the side the max installed height they could get with both retainer styles but I buffed it off unfortunately. Thanks for the help because I really still want to run titanium retainers on my next setup.

speed_demon24

iTrader: (6)

What are your cam specs?

91Z28

232/238 .612/.606 112+4 on XFI lobes.

speed_demon24

iTrader: (6)

Unless you are running 1.7 rockers the lift with the XFI lobes is in the .570's, and a 1.75" installed height would leave you plenty of clearance from coilbind.

91Z28

I am running 1.7s. Right now I'm actually thinking about exchanging my rockers when they get here for 1.8s since I may be ordering some PAC 1518s to replace these 918s. When doing a search on 918s today I found a few too many threads with broken springs and that makes me nervous. Thanks for the help!

96capricemgr

iTrader: (1)

You need to step back and reevaluate what you are doing.

Titanium retainers with beehives is not money well spent, the retainer is already so light and small that titanium stands to gain you little.

The XFI lobes beside pretty much not working well are so aggressive that IMO putting 1.7s on them is asinine and you will not control things, 1.8s will just make a bad problem worse. You want to be silly and run huge ratio rockers to get rediculous lift start with a milder lobe so you at least have a chance of getting it under control.

The XFI stuff is so hard to control that it is best to go beyond Comp's spring recommendations even when sticking with the spec'd 1.6s.

speed_demon24

iTrader: (6)

Listen to the guy above me, there is no way in hell you are going to control the XFI lobes if you have 1.7-1.8 rockers. Even with 1.6's it will be hard to do, but atleast you will be able to setup the springs at 1.75" to get some decent seat pressure on them.

91Z28

My 1.7s are Jesel Competition Series shaft mounts. With titanium retainers on a set of PAC-1518s setup at 1.75" installed height do you think I would still have issues? Even though the 1518s have the same seat and open pressures, installed height, and coil bind height as comp 918s/PAC-1218 they are rated for .650" lift. Thanks for the info on the XFI lobes, I had no idea they weren't easy to get under control. I started looking for extra lift after taking a look at my intake flow #s on my TFS heads:

4" bore 2.02 intake valve ~203cc (1205 port size)

.200 129.9
.300 185.3
.400 230.3
.450 250.2
.500 266.5
.550 280
.600 291.6
.650 302.3

28" in/h20

Looks like the extra lift could really add a few hp, I had no idea the XFI lobes were really difficult to get a handle on. 11cfm is a pretty nice increase from .600" to .650" lift but I'd need 1.8s to see .648/.642 lift with my cam's lobe lift of .360/.357. In this case though it looks like I'll pretty much have to leave that little bit of power left on the table. Hopefully I can get this to work with the 1.7s.

96capricemgr

iTrader: (1)

Here is the thing with being too focused on high lift flow numbers. They are out of reach with a street setup.

My ported LT1 castings flow substantially more at .400 and below and even slightly more still at .500 where it is all still usable. On 918s setup at I think about 1.75 I am running less lift than that XFI with 1.6s and it works, out traps and out ETs cars with "more and better" setups and does so with 10K miles on the topend, about 45K on the stock shortblock. If the shaft rockers and PAC springs are enough to get it under control I still think you will endup changing springs like the rest of us change oil.

It is difficult to keep the valve at peak flow for any length of time, to do so you need to go beyond peak flow. In a perfect world heads would peak down at like .450, use a cam that goes to .550 and have the valve stay near peak flow for a long duration.

91Z28

I hear what you're saying. I would probably need a solid roller with .700" lift to fully take advantage of the peak flow #s. I would love to have gone that route but the 7730 ECM I'm going to use doesn't really handle solid lifter valvetrains very well because of the extra noise causing "false knock". I think my heads flow pretty well through the mid lift range considering the test was done on a 4.00" bore. I know AFR (among others) typically advertise .400" lift numbers in the 24x range but they claim a test bore of 4.030", 4.060", or even 4.125". Dry flow #s never tell the whole story anyway so I'm still having high hopes for my new top end. It certainly won't be the cheapest one out there but I never meant to do a "budget build" in the first place, though I did have a specific amount of cash in mind.

91Z28

Another thing that I want to clarify:

I know that peak flow numbers are not everything. I'm focusing on the high lift numbers because my heads seem to really pickup in the .500"-.650" lift range and are only so-so (by your standards) from .300"-.450". I'm really just trying to make the most out of the heads that I have. If my heads flowed 249cfm @ .400" and peaked out at .550" with 275cfm and then tapered back down to 270 @ .600" then I wouldn't be trying to run the lift that I am. I simply want my intake valve to spend as much time as possible at lift ranges where the heads flow the most air.