TPITuned Port Injection discussion and questions. LB9 and L98 tech, porting, tuning, and bolt-on aftermarket products.
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I would get the EFI friendly grind, aka the 112 LSA. EFI doesn't seem to be able to tolerate intake reversion like carbs can so the intake valve event was bumped up a bit. The overlap helps on the amount of fuel that goes right through (hydrocarbons).
I would get a set of the Comp Magnum 1.52 ratio rockers. With the set that you show, they would bring the exhaust side to about .486" which is a tad much on the factory heads. Now, if you get the .050" retainers, then that's a slightly different story. But I wouldn't run the stampled steel anyways. They're basically the factory boat-like rubber pieces but in an increased ratio. Get the Magnum roller tips.
I run the 256h cam (110 LSA version) in my LG4 with 1.52 Magnum roller tips. I use Isky 235-D valve springs (much like the Manley's) and their recommended retainers. Those are on on 416 heads.
In this post http://www.thirdgen.org/techbb2/show...hlight=110+lsa TRAXION seems to think it's easy to get a 110 lsa cam to work with TPI. I don't know myself, I'm just trying to wiegh all my options, and if I can get away with 110 lsa I will.
Originally posted by SMURFN' Z28 In this post http://www.thirdgen.org/techbb2/show...hlight=110+lsa TRAXION seems to think it's easy to get a 110 lsa cam to work with TPI. I don't know myself, I'm just trying to wiegh all my options, and if I can get away with 110 lsa I will.
i will be using stock 85' (perimeter bolt) LB9 heads with the manley spring and retainer combo mentioned above. Also keep in mind the particular cam I want to use is considerably smaller cam than the ones mentioned in the thread mentioned above.
Last edited by SMURFN' Z28; 10-14-2004 at 07:01 PM.
Originally posted by SMURFN' Z28 Also keep in mind the particular cam I want to use is considerably smaller cam than the ones mentioned in the thread mentioned above.
That's the key. Lobe seperation angle by itself means little. Combine LSA with the seat duration and you establish the overlap period which is critical to idle vacuum, idle stability, computer compatibility (all the same thing).
Take a look at the cam GM put in it's Ramjet crate EFI engine. It's ground on a 109 deg LSA but is short duration so not a lot of overlap.
Valve overlap at .006" for the XE256H is 38 degs on a 112 deg LSA and 42 degs on a 110 deg LSA. For comparison, 2 cams commonly used in EFI engines have the following overlap at .006": ZZ3/4 cam - 44 degs, ZZ9 - 48 degs. Both values were determined by measuring each cam on a Cam Pro Plus machine. Conclusion: you can run 110 deg LSA on that Comp cam and still be EFI friendly.
I think Im pretty much set on the 112lsa version now unless sombody convices me otherwise. Im also probably going to get so better quality rockers. either full rollers or roller tip, as long as they can fit under the stock 85' perimeter valve covers. Is there any reason NOT to get the largest ratio rocker possible from a performance stand point? Can more lift ever be bad? (excluding physical limitations of the valvetrain) I guess what I am trying to say is.... as long as the heads can handle it, does it or does it not make sense to always opt for the larger ratio? any input is welcome.
Last edited by SMURFN' Z28; 10-17-2004 at 06:31 PM.
I just noticed this little detail, but isn't the crane cam a Hydraulic roller, while that comp XE256H is a hydraulic flat tappet? completely different style.
neither cam i mentioned was a roller. my lb9 is not a roller block. Crane makes the 2040 in both rolloer and non-roller versions. It really is unimportant now as I found this particular comp cam, It completely smokes the crane 2040
i will be running an xe292 grind in my lt1 intaked 355.... with tfs heads.... dont know how its gonna go yet but will keep yall up on the info as i get it motor will not be ready will after christmas though.....
