Comp 918s and titanium retainers
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Comp 918s and titanium retainers 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?
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Originally Posted by speed_demon24
What height did they end up at? You should set them up at 1.75".
Originally Posted by 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.
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Originally Posted by speed_demon24
Um 1.75 = more seat pressure. I was getting valve float at 5800 when mine were at 1.78-1.8".
Originally Posted by 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.
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Originally Posted by 91Z28
232/238 .612/.606 112+4 on XFI lobes.
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Originally Posted by speed_demon24
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.
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.
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.
Originally Posted by 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!
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Originally Posted by speed_demon24
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.
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.
Last edited by 91Z28; Jul 1, 2007 at 01:01 PM.
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.
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.
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Originally Posted by 96capricemgr
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.
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.
Last edited by 91Z28; Jul 1, 2007 at 03:59 PM.
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Originally Posted by 96capricemgr
Here is the thing with being too focused on high lift flow numbers. They are out of reach with a street setup.
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.
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.
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.
Last edited by 91Z28; Jul 1, 2007 at 10:14 PM.
