namz7791 Posted March 19, 2004 Share Posted March 19, 2004 Well I bought an 88 Suburban with a 5.7L TBI motor that runs excellent. Has around 145k on it but figured it would be a good motor for this summer to work the rest of the bugs out of the swap. Eventually plan on rebuiilding to around 300 to 325 HP. Should I keep the stock 2 barrel TBI or switch the intake now and get the carb that I will be using next summer after the rebuild? Will TBI support 325 HP? Also, the 87 and newer heads take a different intake. Should I invest in an aftermarket intake or can you not have these particular heads reworked enough to get good flow. Budget will only allow the carb and intake for now; not new heads. Please provide some insight. I am yanking the motor out of the burb tomorrow. Quote Link to comment Share on other sites More sharing options...
A. G. Olphart Posted March 19, 2004 Share Posted March 19, 2004 Since you see this as an interim step... If you've got time, but no money (my situation) wire in the TBI. You can research its' ultimate capabilities as you drive. If you are relatively flush (I know people like that exist) just put the carb and manifold on now and save the wiring hassle. Hey... That was easy Quote Link to comment Share on other sites More sharing options...
strotter Posted March 19, 2004 Share Posted March 19, 2004 I've got some experience with GM TBI's. Like anything else, there are plusses and minuses. On the minus side, you'll be pushing it to get 300-325 hp with the factory unit. It flows about 450 cfm at 3" hg. (3" hg is the standard vacuum with 2 bbl's.) If you compare that to the 1.5" hg on a 4 bbl, you're looking at about 400 cfm (it's not linear). If you think of your motor as an air pump (which really it is), a 350 turning 6000 rpm will need about 650 cfm (@1.5" hg). That means that you can generate plenty of torque, but it'll run out of air at higher RPM's. Holley makes a much larger TBI (supposed to be around 650 cfm) for the price of a carburator: http://www.holley.com/HiOctn/ProdLine/Products/FMS/FMSFI/502-6.html Also, once you make any significant modifications to the motor, you'll need to "chip" it, modify the fuel map in the ECU to compensate for the changes you've made. It's the digital version of tuning a carburator. That is, you can get away with adding an exhaust system or improved intake, but as soon as you change the cam, compression, heads or manifold, you need to adjust it. I'm not saying it won't run, it just won't run well. You can order one of the mod chips from Hypertech or someone else, but they won't be able to nail your tune. For that, you'll need to learn something about chip programming and buy a little bit of hardware to burn the chips. There's an excellent introduction to EFI tuning at ThirdGen.org: http://www.thirdgen.org/newdesign/tech/promintro.shtml On the plus side, an EFI system, even a TBI (which is generally an underrated system) is a great deal more "forgiving" in everyday driving: it starts when it's cold outside, it starts when it's hot, it gets the best performance out of a motor, it gets the best economy out of a motor. Your mileage may vary, but an EFI system will take more work to get running right, but runs more right when it runs (if you get my drift). Quote Link to comment Share on other sites More sharing options...
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