Design Flaws?
Q: In the AETC article in the April issue, Will Handzel points out that the Gen III was originally designed with external oil drainbacks that would have virtually eliminated crankcase windage. Why is it that with all the aftermarket LSx heads and blocks out there, no one has taken the opportunity to add the drainbacks to their castings? Surely, the required new head gasket can't be the problem!
Regarding the new LSXR Intake manifold; in the paragraph about maximizing the plenum size on page 48, it seems like there is a lot of dead space under the valley cover. Why hasn't anyone designed a new structural cover that would allow the manifold plenum floor to drop into the valley, thereby allowing more plenum volume? Even with the LS1-style knock sensors, there is still dead space between them. It seems like this idea would be a definite advantage for the LS3/L92, which use the side-mounted knock sensor. Even more so, I would think the 8+ liter LSx engines would need every additional cc of plenum volume that could be found. Has this been considered?
Don Webb
McCormick, SC
A: Excellent questions, I'll defer to Brian Reese of Comp Cams who played an integral part of designing the RHS block and FAST LSXR manifold. "External drainback for oil requires a cooperating cylinder head and external real estate for plumbing. Our recommendation would be to run a dry sump instead. However, the RHS block features only 'drilled' drainbacks (no cast drainbacks)-we did this specifically so the drainbacks could easily be 'tapped and plugged'. This will serve for easy dry sump setup, or external drainback if desired.
"Dropping the valley plate [on the LSXR intake manifold] for increased plenum was never considered. A very small increase in plenum volume doesn't justify the added expense of a custom valley plate design, relocating knocks sensors, and requiring a custom manifold. Of course, if a user wants more plenum volume and wants to go 'down' with it-he is only a sheetmetal-fabricated valley pan away from a solution."
As indicated by Reese in the article, it seems plenum volume wasn't nearly as critical as tuning the runner lengths and getting even distribution to each cylinder. One of the biggest challenges with any mass-produced intake manifold is getting it to work with radically different combinations, especially changes to the valvetrain that affect optimal engine speed. Thankfully Comp/FAST have a very viable and intelligent solution, which should make a huge difference on naturally aspirated builds in particular. No longer will a carb-style or sheetmetal intake be needed for higher rpm capability in street cars.
Broken Heart
Hi Guys and Girls,
I haven't subscribed to the mag because of a broken heart. You see, my divorce was finalized in December and she was awarded my '99 ProCharged Z28 with 34,000 miles on it, and as silly as it sounds I have a hard time even looking at F-bodies driving down the road. It just reminds me of the fact that I have to start over (and no, I can't afford a new one. I live in Michigan). I do have a 1985 350-cid truck engine, but I think I have to fix it myself before I fix up another car. I do welcome any words of wisdom or motivation, though.
Thank you so much,
John Lamb
Livonia, MI
My condolences, what's that old joke about women being like tornados? Best of luck in replacing your Z, maybe the second time around you'll build something even cooler ... I'm thinking a turbo, maybe two?
Mail
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