I've run a very similar engine at Flowmaster and produced numbers of 400 hp at 6,000 rpm and 434 lb-ft of torque at 4,100 rpm. This is with the XE268 camshaft, Performer RPM manifold, and ported L98 aluminum heads. The engine produces 352 lb-ft of torque at 2,000 rpm! The XE274 produced 407 hp at 6,000 rpm, the same torque at 4,100; however, it lost 20 lb-ft of torque at 2,000 and 2,500 rpm over the smaller camshaft. This will scoot your Chevelle around nicely. Have fun with your project.
Can I Breathe?Q What is the cfm rating of a stock TPI air-cleaner assembly on a third-gen Camaro? Nobody seems to have an answer. I'm asking because I came up with a custom cold-air induction system using a TPI air cleaner for my carbureted '86 IROC-Z. I replaced the original LG4 with a kick-butt 350 completely rebuilt to 355, fed by a 4-inch high-rise aluminum intake and an old Holley 750-cfm 4150. Because of extremely low hood clearance, with about an inch left at the front of the car, I couldn't find any air breathers that would fit under the hood. I tried several different models; the ones that would fit were way too restrictive. I bought the Edelbrock ProFlo 1000 and even had to shave off 1 inch at the base so it would fit. After installing headers and a 3-inch cat-back exhaust, the heat coming off those headers melted the foam filter into the carb. So I came up with an airbox and bought a TPI air cleaner assembly at a junkyard and created my own cold-air intake system. It looked OK and it solved my problem. Having too many problems with the old Holley, I replaced it with a new 600-cfm Edelbrock Performer 1405 last year and decided to build a newer, nicer-looking airbox using the cover and base from a regular 14-inch air cleaner.
Some say the 3-inch intake is too restrictive. That's the 3-inch air outlet on the stock TPI breather? OK! Then why am I seeing all kinds of aftermarket TPI plenums and throttle bodies rated at 1,000 cfm using the same 3-inch air-breather assembly? Why do I not see a bigger 4-inch or even a 5-inch throttle body out there? Sorry for the long letter, but this is the only way to explain my problem.Rob MitchellOttawa, ON, Canada
A The stock Camaro hood heights have caused many a problem for high-performance intakes on small-blocks and big-block engine conversions. You've really come up with a workable solution for this problem. Engines need large doses of fresh, cool air to produce good power. You have some good questions, so let's take a look.
Yes, the 3-inch tube that connects your air cleaner assembly to the 14-inch air cleaner housing would seem to be a problem. However, using a SuperFlow SF600 flow bench flowing a straight section of 3-inch-od, 0.063-inch-wall tubing at 28 inches of water gives you 828 cfm of steady-state flow! Now, your 355ci engine has a max flow of 668 cfm at 6,500 rpm at 100-percent volumetric efficiency! At that engine speed, you've driven well past the peak V.E. of your engine. If you're still at 90 percent we would be surprised. At 90-percent V.E. your engine is ingesting 601 cfm. With all of this said, the 3-inch tubing will flow enough air with 30 percent extra to spare
Do we know what the third-gen Camaro air-cleaner assembly flows? No, we've never had the opportunity to check the airflow on that assembly. If you are using performance-type air filters, like K&Ns, they will support the airflow requirements of your 355 with no problem. There are water baffles installed below the filters in your assembly. Removing those will help free up the air getting to the filters. You will need to be careful not to drive the car into too deep water.
Can we answer the reason you see 1,000-cfm throttle bodies for a 305-cid engine? There is only one answer: overkill. We've made over 440 hp through a stock L98/T1 throttle body. If you really drive the cubic inches of your engine up there, yes, the engine would respond to a larger throttle body. A 1,000 cfm? I think not.