Originally Posted by midwest_98

ive heard that switching the intake only really gives you around 5-15 hp is that true?

Originally Posted by Steve Bryant

There have been several threads about the truck intake manifold versus the LS1/LS6/FAST manifolds. I’ve been intrigued by the subject for several years and I’ve done some research so I’m starting yet another thread that I hope will be informative.

As many of you may recall, Chevy High Performance (CHP) Magazine did a comparison of these manifolds (plus one other) in July of 2004 (Ro McGonegal – text and Henry De Los Santos – photography). This issue compared these manifolds plus a Weiland/Lingenfelter manifold on 5.7 L LS1 crate engine with a 10.25:1 compression ratio, long tube headers with no mufflers or cats and no accessories (water pump, power steering, alternator, or air conditioning compressor) to rob any power from the dynamometer. This first round of tests used the stock cam (200°/203° @ .050” duration and .500” gross valve lifts for intake & exhaust), rockers, and pushrods according to the article. The dyno testing was conducted by the fine folks at Westech Performance Group who probably do more testing of this type than any other facility. This round of testing was accompanied by a graph comparing the five intakes with the same engine. OK, nothing new so far, just a review.

To continue the review, in August 2004, Henry De Los Santos did the follow-up article (text and photography) that tested all of the intakes except the Weiland/Lingenfelter with three progressively bigger aftermarket cams. In addition, they changed the valve springs to Comp Beehives (I assume P/N: 26918 probably with titanium retainers) and they went to the Comp roller tip rockers (1.75:1 ratio which adds 3% to the advertised valve lift at 1.7:1). Also, I will assume they used hardened pushrods although the article didn’t mention this aspect. CHP published a side bar with the results of each cam being shown as max torque, max HP and the engine speed in RPM’s for each manifold. This is good information, but not enough to satisfy the engineer in me.

I kept hoping that CHP would do some sort of follow-up article with graphs of the four manifold/three cam comparison, but it never came to be (many stories compete for space in publications). Then in 2005, I decided to write Henry De Los Santos an email and request the graphs. It took a few phone calls and some more emails (Henry’s a busy guy), but we did hook up and he was very kind to send me the data in a file type known as .csv for comma separated values. This type of file data can be easily imported into any spread sheet software so I converted it into Excel files and created the graphs you see below. Hopefully, these graphs will help people interested in any of these manifolds make some informed decisions as to the best course of action for their application.

It appears to me that at wide open throttle (WOT), the truck/LS6/FAST all better the HP and torque of the LS1 through most of the operating range. Further, it appears that the truck and the LS6 hang right in there with the FAST until around 430 HP and a bit over 5,000 RPM’s. Then the FAST and LS6 begin to ease away from the truck manifold. The LS6 pretty well keeps pace with the FAST manifold for a few hundred RPM's and a few more HP before the FAST manifold eases away from the LS6. HP is directly related to mass air flow and I believe that that is mainly what we are seeing borne out here. The graphs just help quantify the differences.

One thing that the graphs do not show and that is the effectiveness of the manifold in part throttle situations. I highly suspect that the truck manifold beats all the others in part throttle torque hands down. According to Chris Endres’ book Chevy LS1/LS6 Performance, the truck manifold’s plenum volume is smaller (4 L versus 5.06 L for the LS1 and 5.19 L for the LS6) and the truck intake runner volume is less (.513 L versus .536 L for the LS1 and .541 L for the LS6) while the runner lengths are 263 or 262 mm for all versions). The reduction in the truck’s plenum and runner volumes increase velocity in the same way a small runner intake does on a cylinder head. All of these things contribute to good torque production at part throttle.

I especially appreciate Henry De Los Santos for sending me the data for without that information, I never could have created the graphs. Hopefully, this information will help quantify the differences in the manifolds by adding some more data to the discussion.

All my best,

Steve