When It Won't Rev
Byron Bates; Bakersfield, CA: I purchased a 1973 Jeep CJ-5 with a 383 Chevy by the way of another guy's nasty divorce, so I don't have good details. I will drag race it, use it as a local daily driver, and I'd also autocross it if I could figure out a way. I'm about to swap the Jeep three-speed for an M-22 or some form of Tremec overdrive. The Jeep currently has 4:56:1 gears. The engine has great torque but really runs out of air at about 5,200. I want more cam. Currently, the engine has the ZZ Hot Cam. No specific hp or torque goals—I just want it to run stronger. I suppose one begets the other. Couple early rpm exit with the gearing, and acceleration is weak.
Jeff Smith: If you've ever seen the movie The Graduate, Dustin Hoffman is wandering around his backyard college graduation party put on by his well-meaning parents when a relative pulls him aside and tells him to remember one word: plastics. It's a classic movie vignette. The Car Craft version of this scene is we pull you aside from your garage bench-racing session and whisper, "valvesprings." The Chevrolet Performance HOT cam is an excellent street hydraulic roller with specs of 218/228 degrees of duration at 0.050-inch tappet lift with 0.492-inch of valve lift and a lobe-separation angle of 112 degrees. But let's start with the fact that the engine seems to "run out of air" at 5,200 rpm.
You didn't include specifics on the cylinder heads, but let's assume that they are decent. This is a very popular camshaft and somewhat aggressive in terms of valve lift relative to the duration. The advantage of a roller is the lift curve is generally greater than a flat-tappet version. This more aggressive lift curve demands a stronger valvespring to control the quicker valve acceleration rate. Chevrolet Performance sells a complete HOT cam and kit that includes a set of springs that are a 1.320-inch diameter (1.250 inch is stock for a small-block Chevy) with 101 pounds of load on the seat at an installed height of 1.780 inches. The rate for this spring is 332 pounds per inch. This would produce roughly 270 pounds of load at 0.500-inch valve lift. While this is Chevrolet's recommended spring, a slightly stronger spring is probably a good idea. Crane suggests valvespring seat loads of between 120 and 145 pounds for a typical street hydraulic roller camshaft. What you should do first is remove one of the valvesprings from your engine and measure its installed height. This is the distance between the spring seat in the head and the underside of the valvespring retainer with the valve closed. Next, measure the distance between the lowest portion of the retainer and the top of the valve guide. There will be a seal located on the guide, and you are measuring the distance between the seal and the bottom of the retainer. Since your engine is running OK, we will assume that this distance is at least 0.550 or 0.600 inch so the retainer clears the seal at full lift.
Next, take your valvespring to a machine shop and have them measure the load at the installed height you measured. We'll assume this distance is 1.80 inches. Let's also assume a valve lift of 0.500 inch. If the spring measures less than 100 pounds of load on the seat, then you need better springs. Let's also estimate that you measure 250 pounds or less at full valve lift. This tells us you need better springs. You don't have to buy the GM springs (PN 12551483, $127.52, Summit Racing) as there are several other opportunities for better springs. For camshafts similar to the HOT cam, Comp Cams recommends a larger, 1.430-inch-diameter dual spring (PN 986-16, $79.97, Summit Racing) that offers similar load (132 pounds installed at 1.750 with around 290 pounds at 0.500-inch lift). This spring is less expensive but will require new retainers (PN 740-16, $52.97). If your engine has aftermarket heads, it's possible that the seat diameter is large enough to accommodate these larger springs.
Of course, it's also possible that there is nothing wrong with the valvesprings and the engine is wheezing due to other problems. The best way to approach this is to eliminate all of the easy fixes first, so I would suggest looking at the throttle linkage. With the engine off, have a buddy look at the carb while you stab the throttle from inside the car. Are all four barrels opening fully? Don't laugh, because it happens all the time. Next, install a fuel-pressure gauge to ensure that fuel pressure is at least 5 psi at 5,500 rpm at WOT. If not, the problem may be something simple like a restricted fuel filter or a weak fuel pump. If the fuel pressure is not consistently at least 4 to 5 psi throughout the rpm curve, this could easily contribute to your engine's failure to rev. It's also a good idea to check ignition timing and make sure you have at least 32 to 36 degrees of total timing. Assuming the engine is in good shape and everything is working properly, your engine should rev to at least 6,000 rpm and probably as high as 6,500, although the power peak is probably at around 5,800 rpm. You didn't mention the exhaust system, but we'll assume that you are not trying to push all this exhaust out of a single 2-inch exhaust. A dual exhaust of 21⁄2 inches with free-flowing mufflers is what we would consider the bare minimum.
Chevrolet Performance; 800/450-4150; ChevroletPerformance.com
Comp Cams; 800/999-0853; CompCams.com
Crane Cams; 866/388-5120; CraneCams.com
Summit Racing; 800/230-3030; SummitRacing.com
Pierce Peck; Beaumont, Alberta, Canada: As you're the Chevelle guy, you should be able to answer my questions in your sleep. I have a 1967 Chevelle with a 540ci big-block. I'm currently running a TH400 but would like to make the switch to a 4L80E. I'm already running EFI, using a Big Stuff 3 ECM, which has the controller for the 4L80E built in, so from an electronic standpoint, I'm good. My first question is: Will I need to modify my floorpan and/or firewall to fit the bulkier transmission? Second question: What will I need to do for the trans crossmember? Can my current unit be moved back, or will it need to be modified or replaced, and if so, with what?
Other info on the car: Dart Big "M" block, 10.2:1 compression, SRP pistons, Eagle crank, Scat rods, AFR 305cc heads, Edelbrock Pro Flow XT EFI, Lemons custom 21⁄8-inch headers, 3-inch Flowmaster mufflers, X-pipe, Edelbrock 2263 hydraulic roller cam, TCI Super Street Fighter converter, 9-inch Ford rearend with 3.89:1 gears and a Detroit Locker, with 275/60R15 M/T drag radials.
The car is intended for street/strip use, with the emphasis on being a very quick street car. It will never be used as a daily driver, but I would like to be able to take it on short highway trips.
Jeff Smith: We spent a long time looking around but did find a company called Performance Automotive and Transmission Center (PATC) that offers a 4L80E crossmember called the G-Force that's designed specifically for the early 1964–67 Chevelles. The crossmember can be found under PN RCAE-4L80E, and it sells for $259. As you are probably well aware, the 4L80E is a much larger, heavier trans than even the TH400. We have personal experience with our 1964 Old F-85 with a TH400 that the trans will sit very close to the floor. The 4L80E will probably fit, but you might have to tweak the floor in a couple of spots to make it fit with the proper driveshaft angle. If you want to take a shot at making your own crossmember, it appears that removing the welded-on mount for a typical TH350 or TH400 can be relocated on the front side of the crossmember to clear the transmission and still bolt up to the 4L80E. Since the new trans is 57 pounds heavier than a TH400, it might be a good idea to consider strengthening the old crossmember to support the greater weight of the 4L80E. This is especially important because the 4L80E mount location is 31⁄4 inches farther to the rear than a typical TH400. This places more load on the crossmember.
The obvious advantage to the 4L80E is the Overdrive, which is 0.75:1. In Overdrive, this effectively converts those 3.89:1 gears to a 2.91:1 rear gear, which will reduce your cruise rpm by 25 percent. We've spoken to a couple of performance transmission builders, and they tell us that the 4L80E integrates many of the aftermarket TH400 upgrades in the stock configuration, so right out of the gate, the 4L80E is stronger (although heavier). As you've also noted, the trans does require electronic control. For those who may not know, the Big Stuff 3 ECU that Pierce refers to also integrates transmission control with a very sophisticated EFI system that can run as many as 24 low-impedance injectors and do so for a very reasonable price. The base EFI system that also integrates the transmission control goes for less than $2,500. If the Big Stuff 3 name is not familiar, we can tell you that the men behind this are the same Meaney brothers, John and Leo, who were the co-founders of the original Digital Fuel Injection (DFI) system created in 1988. John Meaney was also the creator of several other name EFI systems over the years before creating Big Stuff 3 in 2003. It's beyond the focus of this story to go into the Big Stuff 3 system, but just know that many big-time drag racers use Meaney's system because the system works and is affordably priced. So, Pierce, you've make a good choice with the Big Stuff 3 system since it integrates the transmission control with the fuel and spark control.
Big Stuff 3; 248/887-5636; BigStuff3.com
Performance Automotive and Transmission Center; 888/877-1008; TransmissionCenter.net
Stop the Hop
Bernard Quinlan; Oahu, HI: I have a 1979 Chevy Malibu classic 350 four-speed with a 3.73:1 locker rear with 225/60R15 tires. My problem is I cannot keep the rear wheels on the ground. The wheelhop is so bad I have to shut down or I will break something. I have a stock rear suspension with heavy-duty rear springs and air shocks. Can you please tell me what I have to do or get to make the car stay on the ground? The 350 has the power to lift the front.
Jeff Smith: I have some personal experience with my Chevelle and air shocks that dates back to my high-school days. While that was a long time ago, the physics haven't changed. I learned very quickly that jacking the back of my big-block, four-speed 1966 Chevelle with a set of air shocks resulted in violent wheelhop. Conversely, lowering the car back to nearly the stock ride height eliminated the wheelhop. I will assume that you are using the air shocks and stiff rear springs to raise the car, perhaps to clear the rear tires. But since a 225/60R15 tire isn't that big, it's possible that the backspacing on the wheels is the reason for tire-clearance issues. If this is the case, the solution is to perform some careful measurements to determine the amount of room between the inside edge of the current tire and wheel package and the closest inner fender obstruction. Let's assume you have 11⁄2 inches of clearance to the inside and an 8-inch-wide wheel with 4 inches of backspacing. We define backspacing as the distance between the wheel mounting pad surface and the inboard edge of the wheel. You can measure this easily by laying a straightedge across the back side of the wheel (not the sidewall of the tire) and measuring straight down from the straightedge to the wheel-mounting surface.
By changing to a set of wheels that increase the backspace from the original 4 inches to 5 inches, you will move the wheel inboard, allowing the outboard edge of the tire to clear the inside of the fender lip. This will then allow you to lower the ride height in the rear. With the car at rest, shoot for a ride height that will place the lower rear control arm roughly parallel with the pavement. This will change the location of the rear suspension's instant center (IC), thus eliminating the violent wheelhop.
It might also be a good idea to replace the air shocks with a quality shock absorber. For the street, you don't need expensive adjustable shocks. A quality shock like the Bilstein (PN F4BE5E250M0, rear, $62.97 each, Summit Racing) is an excellent choice that will offer great ride quality as well as improved handling. The best idea is to change the front shocks, as well (PN 24-009492, $69.97 each, Summit Racing). I would also suggest checking the upper and lower control arm bushings in both the front and rear suspensions just to make sure they are in decent shape. It's possible that after 35 years of use, these bushings have never been replaced and may be cracked, broken, or even non-existent.
If the lower rear control arm bushings are in need of replacing, consider upgrading to a pair of aftermarket control arms. Global West builds an excellent tubular lower control arm with Del-A-Lum bushings (TBC-2, $279.60, Global West) at one end and a high-quality spherical bearing in the front that allows the arm to articulate but not bind. Even with the spherical bearing, minimal road noise is transmitted through the car. The advantage is the arm will accurately locate the rear axle under the car, which will eliminate lateral movement of the body over the rear axle. This is a common problem with stock, stamped lower control arms that flex horribly and allow the tires to rub on the body. My 1965 road-race/autocross Chevelle uses an 18x9.5-inch rear wheel with a 275/35ZR18 tire with barely 1⁄2-inch of clearance to the wheelwell on the outside. Yet even under hard, 1-g cornering, my tires never rub using the Global West arms. Other companies like Hotchkis and Currie sell a similar lower control arm, although they do not use a spherical bearing. Above all, however, beware of cheap Internet rip-offs of these quality arms. There are many unscrupulous vendors out there selling fake arms as the real thing. If the price for a brand-new part looks too good to be true, it probably is. Buy Global West, Hotchkis, or Currie parts from the vendors themselves or a known source such as Jegs or Summit Racing to be sure that you're getting the right parts. I recently spoke to Doug Norrdin, owner of Global West, and he told me that these off-shore knock-off parts are a huge problem because customers often unknowingly buy these cheap parts only to have them fail. So be smart and avoid the rip-off parts.
Currie Enterprises; 714/528-6957
Global West Suspension Components; 909/890-0759; GlobalWest.net
Hotchkis Performance; 562/907-7757; HotchkisPerformance.com
John Raczka; Golden, CO: I'm looking for some direction on my 1969 Nova drag car. It has a 468ci big-block Chevy, a Comp 11-250-3 flat-tappet cam, AFR 265cc oval-port Magnum heads with roller rockers, Hooker Super Comp headers, full MSD ignition, a TH400 tranny with a 3,500-stall converter, CalTracs, a Dana 60 with 4.11:1 gears, and a spool. I have been running an Edelbrock Air Gap intake with a Holley 850 carb and 1-inch phenolic spacer. I live in the Denver area, and I run my car at Bandimere Speedway at a 5,800-foot altitude. My car is street-legal, and I had never driven a high-stall-equipped car before. I always thought the car was sluggish from a start, which I related to the stall converter. The Nova ran 12.20s at 108 mph.
I decided to try a 1050 Dominator carb and used an adapter plate approximately 21⁄2 inches tall and no other spacer. OMG! The car woke up! It is snappy and a ball to drive. I guess it wasn't the stall. I had to tweak on the CalTracs because of traction issues. I only had one chance at the track, but it ran an 11.92 at 112 mph. Now for the question: I developed an oil leak at the rear of the intake, so should I just fix the leak or is there a Dominator manifold that will work better than my Air Gap and adapter?
Jeff Smith: The question is finding an oval port, single-plane intake manifold that will also fit a Dominator flange carburetor. I think that going to a single-plane intake would certainly benefit your combination. A good single-plane intake will make more peak horsepower and probably raise the peak horsepower rpm point by roughly 200 to maybe 300 rpm. This would also complement your camshaft with its specs of 240/246 at 0.050 and 0.574/0.578 inch lift. I looked in the Edelbrock catalog, and the best manifold for your application would be the Victor Jr. 454-O, (PN 2909, $289.97, Summit Racing). This will allow you to bolt that Dominator carburetor directly to the manifold, and the oval-port configuration should be very close. Don't sweat the interface between the manifold and the heads if there is a slight mismatch. You can port-match it if you choose, but honestly there is very little to be gained by spending any time port-matching. The majority of flow occurs in the middle of the port, and if you mapped velocity, you would discover minimal flow activity near the walls. That's why nobody polishes intake ports anymore—there's no benefit. Finally, in almost all cases, a dedicated Dominator manifold will be better than a 4150 flange manifold with a Dominator adapter. One thing that might have also helped you with this is the fact that you had a 21⁄2-inch-tall spacer between the carb and the manifold. If you have underhood room with the Victor, Jr. intake, a spacer would probably also be beneficial.
Of perhaps more interest is why the larger carburetor really helps. I spoke with Westech Performance's Steve Brulé, who has a ton of experience with big-block Chevys. He said that big-blocks are very responsive to bigger carburetors, and this isn't necessarily related to the engine needing more airflow. As an example, way back in the late '80s, Kenny Duttweiler was testing a normally aspirated Buick V6 engine on Edelbrock's dyno and discovered significant power increases when he adapted a 1,050-cfm Dominator carburetor to the little V6. The engine didn't need the additional airflow, but it did respond positively to the larger carburetor, which reduced the air velocity exiting the carburetor. This allowed the heavier fuel traveling at a slower speed to make the transition from vertical flow out of the carburetor to horizontal flow into the intake ports.
Following that theory, your engine probably responded both because of reduced air speed out of the carburetor and perhaps also to a change in air/fuel ratio. I noticed you mentioned that you race at Bandimere Speedway, which is in the mountains just outside Denver at 5,800 feet of altitude. This means the air is a lot thinner where you race. This also means that it would be very easy to make an engine run a very rich air/fuel ratio because of the greater elevation. I'll assume that the Dominator was already tuned for use at your higher altitude, but it is something you may want to look into a little closer. Further tuning with the carburetor or possibly using a tapered carb spacer might just deliver even better performance.
Edelbrock; 310/781-2222; Edelbrock.com
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