Slayer

A couple years ago, the head gasket blew in my 1993 Z28. Instead of junking the car, I dumped some money into the engine. Right now, I'm putting down 375 horsepower to the wheels. Today, one of my friends asked me why I'm still using the stock injectors and intake after all the work I've had done. I told him that my engine builder said both of them were fine to run with my setup, but he has me thinking now, so I was wondering what other people think. Here's the current list of mods to my car:

• K&N Filtercharger Injection Performance Kit
• Trick Flow aluminum intake elbow (Summit Racing part number TFS-3150801)
• Trick Flow 58 mm throttle body with throttle body airfoil (Summit Racing part number TFS-24258)
• Trick Flow 54 cc aluminum cylinder heads (intake and exhaust diameter: 2.02" and 1.6"; intake and exhaust runner volume: 185 cc and 67 cc) (Summit Racing part number TFS-30400008-M54) (Yes, I know these have since been discontinued.)
• Hydraulic roller camshaft (lift 234/242 [.539/.558]) (Summit Racing part number NAL-19244485)
• Trick Flow 7.2" chromoly pushrods
• COMP Cams 1.6 roller rockers (Summit Racing part number CCA-1602-16)
• ACCEL 300+ digital ignition and ignition coil
• NGK TR55 IX spark plugs and Taylor Spiro-Pro 8 mm plug wires
• March underdrive crankshaft and alternator pulleys
• Hotchkis shocktower brace
• PaceSetter ceramic-coated long-tube headers, dual catalytic converters (hollow), X-pipe, and Bullet race mufflers (3" true dual exhaust system with 3½" outlets)
• B&M shift kit and transmission cooler
• TCI StreetFighter 3,000 RPM torque converter (Summit Racing part number TCI Auto 243105)
• Yukon 3.73 gears (Summit Racing part number YGA-24146)
• UMI Performance single-adjustable rear control arms and single-adjustable panhard bar (Summit Racing part number UPI-201621-B)
• Tuned computer chip

The chip was tuned after all the engine work was completed, but before the gears and torque converter were installed.

Thanks for the input!

Injuneer

Do you have a dyno sheet for the rwHP? What correction method was used? What was the correction factor? Are you running your 22 #/HR stock injectors at the stock fuel pressure (43.5psi with the vacuum line disconnected)?

375HP at the rear wheels through an A4 requires about 375 / 0.83 = 452HP at the flywheel.

The traditional method for estimating injector size is to assume (normally aspirated) a brake specific fuel consumption (BFSC) of 0.50 #/HR/HP, and to limit the injector duty cycle (DC) to 80%. Using those assumptions, and the correct formula would result in a recommended injector size of 35.3 #/HR

452 x 0.50 / 8 / .8 = 35.3 #/HR

From my experience in sizing injectors, the 0.50 BFSC and 80% DC is extremely conservative. My rule of thumb for recommended minimum injector size is to multiply flywheel HP x 0.07

In your case:

452 x 0.07 = 31.6 #/HR

That corresponds to a BSFC of 0.476, and an injector DC of 85%.

To produce 452 flywheel HP with 22 #/HR injectors, you would have to achieve a BSFC of 0.39 #/HR/HP and run the injectors at 100% DC. Not realistic.

Something is wrong. I have a 381ci LT1 that was run on an engine dyno for numerous pulls to optimize HP and fuel consumption, and the best we could achieve is 0.44 #/HR/HP BSFC. BSFC reflects the quality of the tune, and the geometry of the combustion chambers.

As far as your parts:

-A CAI is essential. Surprised you achieved 452 HP at the flywheel with the stock intake.

-A 52mm throttle body will support 500HP at the flywheel. That is based on dyno testing with my 381, and at 496 HP at the flywheel, my 58mm throttle body was only 77% open, and opening it further did not increase HP.

-The aluminum elbow really offers no advantage over the stock rubber elbow. Might be a tad smoother, but it transfers heat faster. I would use the 1LE elbow though.

-The stock heads can be ported to 500HP. Above that, you should invest in the Trick Flows, which will still need to be ported. Advanced Induction for example offers ported stock LT1 head intake runners of 190, 195 and 200cc. They recommend the Trick Flows, ported to 215cc for 600HP levels. Look at AI or Lloyd Elliot for headwork, and let them match the cam, and the intake porting to their head design.

http://elliottsportworks.com/

Advanced Induction - 200cc LT1 Competition Head Package

-For ignition, I would recommend the Bailey Engineering LTCC, which uses only the cam position signal from the Opti (removing the high voltage function solves most of the Opti problems), and uses 8 LS1 coils in direct fire.

-The TR55 plugs are too hot for your current engine, if its making 450 HP. TR6 would be a better choice, maybe even a step colder than that if you exceed 500 HP.

-You want a stall in excess of 3,500 RPM.

-Underdrive pulleys are worthless. At most, you might gain 1 or 2HP, accompanied by charging problems. Here's a dyno showing a peak 0.7HP gain:

Drivetrain Modifications #2

-At 500+ HP at the flywheel, the stock 7.5/7.625" rear axle assembly may have a very short life, particularly if you run sticky tires on a sticky track. Consider a 12-bolt, Strange 60 or a Moser 9-inch

The other items look OK.

Slayer

Wow, thanks for the reply! It's a lot of information.

All the dyno sheet shows is the horsepower and torque graph, along with the air-fuel ratio at the bottom. No other information is on the sheet. I do know my builder kept removing my chip and rewriting the tune, and he also had his laptop plugged into the car when he was street testing it.

I do have set of Trick Flow heads on the car.

In a nutshell, I should definitely upgrade my injectors and probably my intake.

Until late last year, I was still running the stock 2,000 RPM torque converter. A Summit tech recommended the one in the car now because I wanted the car to still be streetable because it's a sometimes daily driver for me when I'm in the mood to switch from my Cavalier.

I put the underdrive pulleys on years and years ago, but I do notice my voltage sits right under 13 when I'm driving the car, which worries me sometimes, and I did go through a lot of Advance Auto Parts batteries until I finally upgraded to an Optima.

I could change out the plugs to the ones you recommended.

So far, the rear end is holding up, but I don't race it at the track, and I'm on street tires.