LS7 DCR, and data needed
Thread Starter
Launching!
Joined: Dec 2003
Posts: 251
Likes: 2
From: Portland OR
LS7 DCR, and data needed Does anyone know the piston/deck clearance, and head gasket thickness, on a stock LS7? Are they the same as an LS1 (.007 out of hole, .051 gasket)?
Has anyone used a thinner gasket, e.g. Cometic, on the LS7 to boost compression? I haven't noticed this being done by any of the LS7 tuners that I've seen so far, but I'm thinking about modding my LS7 this way. Conventional wisdom is that added compression via tighter quench is "free" - the tighter quench reduces detonation sensitivity faster than the additional compression adds it.
All of this is because I've noticed that the LS7 seems to tolerate very high dynamic compression ratios compared to what we're used to. Rule of thumb on an LS1 seems to be 8.6, 8.7 with careful tuning. Looking at the Katech Torquer cam, I come up with about 9.15 on a stock short block LS7 - no wonder that cam makes lots of low end torque. And there are a number of builders out there pushing static CR to 11.5 and even 12.0 with bigger cams, on pump gas.
Has anyone used a thinner gasket, e.g. Cometic, on the LS7 to boost compression? I haven't noticed this being done by any of the LS7 tuners that I've seen so far, but I'm thinking about modding my LS7 this way. Conventional wisdom is that added compression via tighter quench is "free" - the tighter quench reduces detonation sensitivity faster than the additional compression adds it.
All of this is because I've noticed that the LS7 seems to tolerate very high dynamic compression ratios compared to what we're used to. Rule of thumb on an LS1 seems to be 8.6, 8.7 with careful tuning. Looking at the Katech Torquer cam, I come up with about 9.15 on a stock short block LS7 - no wonder that cam makes lots of low end torque. And there are a number of builders out there pushing static CR to 11.5 and even 12.0 with bigger cams, on pump gas.
On The Tree
Joined: May 2005
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Mine is milled to 67cc from 70cc w/ a .040 Cometic. The torquer cam with stock LS7 c/r yields 8.8 DCR.
On the LS7, I would concern myself more with IVO (later), exhaust side duration split and overlap (lots) to achieve great torque numbers. 11.5 SCR will definitely help, but the valve events are much more important.
On the LS7, I would concern myself more with IVO (later), exhaust side duration split and overlap (lots) to achieve great torque numbers. 11.5 SCR will definitely help, but the valve events are much more important.
Thread Starter
Launching!
Joined: Dec 2003
Posts: 251
Likes: 2
From: Portland OR
Thanks for the response. I've gotten responses on CorvetteForum which also suggest that an .040 Cometic works fine. The way I crunch the numbers, you're pushing 11.8 - 11.9 SCR, which is consistent with what I'm seeing from a lot of aggressive LS7 builds.
The Torquer has a 269 duration intake lobe on a 106 ICL, which yields an IVC of 60.5 ABDC, and a DCR of 9.10, using the following calculator:
http://www.wallaceracing.com/dynamic-cr.php
The first version of the Torquer had no advance ground in (110 ICL). Using that gives 8.85 DCR.
In general, I'm noticing similar trends in camming the LS7. Early EVO is pretty much universal, leading to more "split". Overlap in the range of 10-20 degrees at .050, and fairly late IVO compared with more conventional performance V8s. Where different builders seem to make different choices is mostly with the IVC, and the corresponding compression ratio. The Torquer uses a very early IVC, with stock compression, yielding strong low end and midrange, with a power peak a bit early. Most other builders choose a later IVC to push the RPM range up a few hundred, giving higher max HP, but requiring more compression to help maintain cylinder pressure at lower RPM.
So I'd say the principal tradeoff with these motors, at least with the stock intake, is IVC/compression, which is why I'm interested in what DCR I can "get away with".
The Torquer has a 269 duration intake lobe on a 106 ICL, which yields an IVC of 60.5 ABDC, and a DCR of 9.10, using the following calculator:
http://www.wallaceracing.com/dynamic-cr.php
The first version of the Torquer had no advance ground in (110 ICL). Using that gives 8.85 DCR.
In general, I'm noticing similar trends in camming the LS7. Early EVO is pretty much universal, leading to more "split". Overlap in the range of 10-20 degrees at .050, and fairly late IVO compared with more conventional performance V8s. Where different builders seem to make different choices is mostly with the IVC, and the corresponding compression ratio. The Torquer uses a very early IVC, with stock compression, yielding strong low end and midrange, with a power peak a bit early. Most other builders choose a later IVC to push the RPM range up a few hundred, giving higher max HP, but requiring more compression to help maintain cylinder pressure at lower RPM.
So I'd say the principal tradeoff with these motors, at least with the stock intake, is IVC/compression, which is why I'm interested in what DCR I can "get away with".
