After installing the SLP headers and exhaust, along with its intake runners and cold-air k
'We thought we were onto something good back when we decided to turn this '91 Formula into a multipart series. It seemed like the thing to do, since we could hardly believe cars like this could be bought in good shape so cheaply ($1,500). A Tuned Port 350 F-body was a coveted car in its day, being among the first cars out of Detroit since the early '70s that seemed sort of worthy of the term musclecar. Plus, chicks were into F-bodies back then.
But today, Detroit has produced much faster cars, TPI speed parts are still as expensive as they were back in the '80s (only now they're being discontinued), and girls refuse to ride in this thing. Add to this the fact that simply keeping the 'Bird running has at times been a challenge and to this point, the speed returns have been modest at best, and our third-gen project starts to lose its luster. Yet in spite of our troubles, we've managed to maintain some optimism, largely because we know these things can really move if handled properly. We also know that it's easy to spend money and effort on stuff that doesn't help, and it's probably better for us to make the mistakes than you.
With the car up and running again, it was time to address one of its gray areas: fuel pres
RecapFirst up was repairing what seemed to be minor glitches-we thought a new EGR valve and maybe an ignition tune-up for good measure would have the Firebird ready for baseline numbers, but as we outlined in the Aug. '05 issue, a series of failures made preparing for baseline runs a project in itself.
Persistence paid off, and we did get the Firebird sorted out, paving the way to move into the speed parts. That's where SLP stepped up, providing new high-flow intake runners, a cold-air kit, smog-legal shorty headers, a Y-pipe, and Cat-Back exhaust. The dual cats were also replaced with a single, 3-inch unit from Random Tech. With these alterations, the Firebird picked up more than three-tenths from our baseline of observed 15.0s at 91.23 mph to 14.66 at 92.82; that corrects to a 14.19 at 95.9 mph using the factor for LACR's altitude-strong for a stock L98 F-car, particularly one with 150K. If nothing else, our test-mule was healthy. It seemed that if we could get the 60-foot times under 2.00 seconds (from 2.20), we might just break the 13s.
To that end, the next move involved swapping the stock torque converter for one from B&M with 10 inches diameter and a 3,000-rpm stall speed. For our efforts, we received a 1.98 60-foot time and a 14.12 at 92.43 mph (corrected). The short time was better, though it still needed work, and while e.t. picked up appropriately, the trap speed slipped back a lot. This is where things started to get weird.
Even though the preliminary fuel-pressure test checked out, we'd need to monitor it during
The converter was followed up with a set of 3.73:1 gears to replace the stock 3.23s, a standard upgrade that should have helped get it all down the track a bit faster. Instead, we gained more 60-foot (1.88) only to see e.t. stay almost exactly the same. Glad's seat-of-the-pants feedback was that the car leaped hard off the line but was laboring to reach the traps by half track. During this time, we'd also added a ported upper plenum from corvetteplenum.com as well as an Edelbrock manifold base, yet the gains in naturally aspirated form just weren't showing up. We specify naturally aspirated because Glad had also begun experimenting with a Nitrous Works plate system by that time. It pushed the Firebird into the 12s (corrected), but in a sense, only added to the overall confusion of our combination. Where had we gone wrong?
To the Dyno
We needed to answer some questions about the car's setup before moving on, and while further track testing might have gotten us there, a trip to the dyno would involve less trial and error. With a 150,000-mile engine running hypereutectic pistons and nitrous, guessing might not be the best plan. To this point, we didn't know how the engine's air/fuel mix was holding out under full-throttle, and we wondered how much additional ignition
lead was helping under naturally aspirated runs.
The instructions advise removing the upper plenum bolts and loosening the bolts holding on
The first runs on Westech's Superflow chassis dyno revealed some oddities. Most notable, the horsepower curve seemed to go flat once the engine hit 4,300 rpm-it didn't drop off, but hung right around 224 hp, wavering up and down slightly all the way to about 5,200 rpm before declining. The air/fuel was only slightly lean, and we used the new BBK adjustable fuel-pressure regulator to sort that out. Using an Actron fuel-pressure test-gauge, we dialed the regulator to increase fuel pressure with the vacuum line off from 43 psi to 48 psi, taking the wide-open throttle (WOT) air/fuel readings to 12.1:1 from 13.3:1. Despite this, we saw no change in power.
Charting the ignition advance curve during a power pull also revealed that with the stock setting of 6 degrees initial, total timing came in right around 34 degrees, which is what we'd found these engines to favor in past testing. It did, however, point out that we'd need to run about 4 degrees less if we opted to spray nitrous again.
So, with what seemed to be proper fuel delivery and ignition advance, we still couldn't get our power curve to take on a proper bell shape. After some discussion, it was decided that the valvesprings should probably be changed. The hydraulic roller lifters in this 350 are notoriously heavy, and with 157,000 miles, it was easy to believe we were on the verge of valve float as a result. With that mileage, even if the valvesprings didn't cure the problem, changing them would still be a good idea.
The first dyno runs were made on the motor alone, and the findings were a bit confusing. T
We went back to the shop and ordered a set of Comp Cams' new beehive springs as an upgrade. The conical shape of the springs combined with the ovate wire they are made from allow the springs to compress further before experiencing coil-bind; the smaller diameter of the top coils and the retainer also make them lighter. All of this adds up to a drop-in spring that will add lift capacity and improve valve control without placing undue stress on our stock hydraulic lifters. While we were at it, we installed a set of Comp's Pro Magnum roller rockers with 1.6:1 ratio for a little extra valve lift. These rockers are self-guided, like the stockers for '88 and later Chevy small-blocks, and after a little trimming, they fit under the stock valve covers.
Converter in Question
Back at Westech with our new springs and rockers, we were bummed to see that the output had only increased by 3 hp. We were now making 228 hp at 4,800, but at least the power curve was indeed a curve, not a flat line. Were we on the verge of valve float before? Not known, but obviously the real problem remained. Tom Habrzyk was doing the driving on the dyno, and after a couple of pulls, he wanted to try a different test. To him, the converter felt unusually loose, particularly for a 3,000-rpm stall rating behind a fairly tame engine. He started to accelerate very slowly, holding the trans in Second gear while he programmed the Superflow to maintain 30-mph wheel speed. Next, he proceeded to roll into the throttle gradually while watching the rpm on the dyno's readout. Confirming his suspicions, the engine reached just shy of 4,000 rpm before it started to bog due to the limited wheel speed-our converter was amiss.
Although we didn't expect the curve to change much, we used our new fuel-pressure regulato
If our torque converter isn't stalling until 4,000 rpm, which is well past our torque peak and very close to the horsepower peak, it's no wonder the car wasn't improving its quarter-mile performance. The off-the-line hit of the high stall was working to improve 60-foot times, but excessive slippage was shaving off the gains before the big end.
That leaves us to move to the next level of diagnosis: The B&M torque converter dyno. We'll pull it back out and have it tested to see what went wrong, then correct the situation and retest. Maybe we're already in the 13s. Stay tuned.
On The Rollers
Test One is the best of our naturally aspirated runs with the original valvesprings, all of which were similar. This one had the best air/fuel mix after tuning fuel pressure and 34 degrees total timing (6 initial). Test Two is the best with new valvesprings and 1.6:1 roller rockers. These pulls begin at higher rpm.
|RPM ||TQ ||HP ||TQ ||HP |
|3600 ||217 ||148 || || |
|3700 ||246 ||169 || || |
|3800 ||270 ||195 || || |
|3900 ||283 ||210 || || |
|4000 ||287 ||219 || || |
|4100 ||282 ||220 || || |
|4200 ||277 ||222 ||260 ||207 |
|4300 ||266 ||218 ||262 ||216 |
|4400 ||260 ||219 ||262 ||219 |
|4500 ||257 ||220 ||260 ||223 |
|4600 ||253 ||222 ||257 ||226 |
|4700 ||250 ||224 ||253 ||227 |
|4800 ||245 ||225 ||250 ||228 |
|4900 ||240 ||224 ||241 ||226 |
|5000 ||233 ||222 ||233 ||222 |
|5100 || || ||223 ||217 |
|TRACK ACTION |
|TUNE || |
|Bone-stock ||14.51 ||2.20 || |
|SLP runners, headers, Cat-Back, cold-air ||14.19 ||2.15 || |
|10-inch 3,000-stall converter ||14.12 ||1.98 || |
|3.73:1 gears in place of 3.23:1 ||14.13 ||1.88 || |
|Nitrous plate, 150hp shot ||12.95 ||1.79 || |
|STICKER SHOCK |
|DESCRIPTION ||PN ||SOURCE ||PRICE |
|Adjustable fuel-pressure regulator ||1714 ||BBK || |
|Beehive valvespring kit ||982 ||Comp Cams || |
|Valvespring compressor ||GP4930 ||Powerhouse || |
|Roller rockers, 1.6:1 ratio ||1318-16 ||Comp Cams || |
|Valve seals ||N/A ||B&C Auto || |
|Sub total || || || |
|Previous total || || || |
|Just-as-slow total || || || |
Stock initial ignition timing on a TPI 350 is 6 degrees BTDC, and that's where the Firebir
Changing the valvesprings with the heads still attached to the engine and the engine in th
While we had the valve covers off, we opted to install a set of Comp Cams roller rockers w
The flat line of the power curve persisted, and there weren't many variables left untested
Despite our efforts with the springs and rockers, the power peak was only 228 hp, but at l
Another rocker-arm requirement when dealing with center-bolt valve covers, as used on most
Westech Performance Group
11098 Venture Dr., Unit C