Q&A

Mailbag: Building a Camshaft & Valvetrain Combo to Boost Bottom-End Performance

 

You’ve got questions. We’ve got answers — Mondays, when we work with the Summit Racing tech department to help you tackle your auto-related conundrums. In this week’s Monday Mailbag, we’re looking at cam and valvetrain options that will help bolster bottom-end power.

Q: I have a 1976 Toyota FJ-40 with a 350 small block from a 1973 Camaro. The engine has been rebuilt and is stock internally. The heads have a fresh valve job, and the engine features a Holley 650 cfm carburetor on an Edelbrock Torker II intake. I am using the stock four-speed transmission and stock axles with 4.11 gears and 33 x 12.15 tires.

I want to install a mild performance cam. COMP Cams recommended a hydraulic grind with 203/212-degree duration and .421/.451-inch lift, and I really don’t know how much this cam will affect my vehicle. I want to have plenty of bottom end, but I also want enough cam so people will be able to hear it.

Will this camshaft give me the sound and performance I’m looking for? Will I need to change valve springs? I am also considering the use of 1.6-ratio rocker arms. I have heard that overhead valve engines respond well to short-duration, high-lift cams with wide lobe centers (the COMP cam has a 110-degree lobe center). I have also heard that 1.6 rockers by themselves will give my engine the rough idle like a mild cam would. Should I use both the cam and the rockers, just the cam, or the just the rockers?

A: The COMP Cams grind is a good choice for your Toyota. It has an operating range of 1,200-5,500 rpm and offers excellent bottom-end torque. Matching valve springs to the cam is very important. If the spring pressure is not right, you can severely damage the cam and lifters. COMP Cams recommends its 1.230-inch single-with-damper springs (980-16). These springs have an open load rating of 230 pounds @ 1.250-inch and a seat load rating of 85 pounds @ 1.700 inches.

As for the 1.6 rockers, they don’t always produce the instant power they are known for. The added lift creates a bigger “hole” in the powerband that the engine has to compensate for. That hurts bottom-end torque. Any power gains you get from 1.6 rockers will be in the higher rpm range.

You may want to reconsider your Torker II intake manifold. It’s designed for engines operating from 2,500 to 6,500 rpm; since the Torker is a single plane design, it also offers limited off-idle response. Something like an Edelbrock Performer dual plane manifold, which makes power from just off-idle to 5,000 rpm, would be a much better choice.

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6 Comments

  1. I have a engine im building and its from a 76 gran fury police car and its all high compression what is the biggest cam i could put in it with out changing much

  2. No intake manifold gives better real low end torque than a slightly modified stock dual plane manifold.
    Most 350 CID V8 engines with a good free flowing, zero bakcpressure exhaust system wil work best with 106 – 108 LSA cams. 🙂
    Quick lift rocker arms are also beneficial.

  3. Fred Leastman Jr says:

    I have a 350 turbo long shaft and I’m tryn to figure out what it came out of, right now it’s in an 81 ElCamino…any ideas?

    • OnAllCylinders Staff says:

      Hey Fred, sorry for the delayed response here, but from what we’ve seen, the long shaft TH350 transmission was found in GM’s full size trucks and large passenger cars (e.g. Impala, station wagons, etc.) throughout the 1970s and early 1980s. Outside of the shaft length, they’re mechanically identical, which means the two are mostly interchangeable–though you may have to modify your driveshaft length to accommodate.

  4. Looking at building a blowen 383 street strip car what camshaft would you recommend to use thanks

  5. Hmmm. Never heard of additional lift creating a “hole” in the power band. Seems like Vizard recommends cams with the most lift per degree of duration. That’s not to say all stock small block heads will benefit from more lift than than the Comp Cams .421″/.451″.

    To David: There are at least 3-4 factors besides cubic inches that need to be known before choosing a cam for your 383. Primary is the RPM range where you want to make good power–typically 3000 RPM wide for a flat tappet cam and 3500 RPM wide for a roller.

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