Originally Posted by RandyJ75
I am a refuge from some of the Corvette forums on the web, and I'm looking for some honest advice on my new engine build. If you have never been on one of these forums, everyone will tell you to buy the most expensive parts for your engine; but to me, it's still just a sbc, and I don't feel it's necessary to spend a lot of money to build a strong engine.
OK, with that said, here's what I have and what I want to get too. I am buying a 406 from a friend who has in in his F body running a carb. I am just buying the short block, he is keeping the heads.I want to make it fuel injected, and I am thinking of using a converted LTx intake, or maybe a Miniram. The heads will be either TFS or AFR, but I am leaning towards the TFS 195 heads. Not sure about the cam, but I want it to be mild and very streetable. I may have to take the car though emissions at least one more time before I can get classic plates.
So here are my questions-
What size cam would work best? I want it to be a hydraulic roller. What size injectors to run? I have had people tell me to run 30lb to 42 lb, any ideas? Also, where to buy injectors at a good price?
Sorry for the long post, and thanks.
You answered my first question in another post which was the year "1990".
That means this is an L98 which is a Gen 1 with TPI. That tosses LTx intake out as its for reverse flow heads and does not have coolant return passages compatible with Gen 1 heads. You need to think around your existing TPI if you want to keep costs down. The system you have is OBD1, to get into an OBDII system of the LTx engines takes a new computer and matching wire harnesses, which is a lot of work and expense. Doable, but you've got to understand it ain't a cheap nor simple swap if you've never done it before.
The 406 is going to take a custom chip in the existing computer. The question of 30 or 42 pound/hr injectors comes to how much duty cycle you want to run. A 30 pound/hr injector will be on for more time than a 42 so it will run hotter and last less long, that probably is the answer without doing the math to see if 30 will support that engine even if on all the time. The chip, the injectors, the cam all need to be selected together. The LT4 HOT cam will work with a chip but it will take a batch flow TPI like you have to the edge of emissions compatible. The LTx engines used sequential injection so the injectors were off during overlap, so heavy loads of raw gas were not going straight out the exhaust as it will with your's. This can be compensated for with TPI by using AIR injection into the exhaust and fresh cats. Or, heaven forbid, a milder cam such as the either the standard LT1 or 4 or an equivalent. The other trick with TPI is to use a cam with a long LSA, this minimizes or eliminates overlap which just does away with raw fuel going out the exhaust.
Your big problem will be compression, while small chamber heads do better at power generation and emissions reduction, to keep the compression at something pump gas will handle would require a dished piston. Of these the best design selection is the "D" dish as these present a highly effective squish/quench surface while managing the overall CR with the dish below the valve/sparkplug pocket. The other solution would be a large chamber head with a flat top. But these are unfriendly to emissions and aren't as efficient at lower RPMs due to a lack of turbulence and slow (by milli-seconds) burn times. These need more advance which leads into higher NOx. Sometimes this seem like a dog chasing its tail, but there are "better" solutions hiding in there.