Guest Anonymous Posted August 10, 2001 Share Posted August 10, 2001 Does anybody have a guideline on how to tell what throttlebody size to use and what lb/hr injector on a V8? I'm looking way down the line (once I can afford the SDS *gulp*...) of first going injected and then turbo'ing the engine. I'm looking to end up with about 400-450 hp (compared to my 250-260 hp now, before that happens I'll put in the forged pieces of course) which is mild by turbo standards using probably a single turbo. I'm moving in that direction to keep a sweet disposition in the engine but still have a little bit of whoopass if I want it. I'd like to use a Ford throttle body as Blkmgk mentioned because of the availability, variety and price. I may build a custom plenum using an idea I've had for a base manifold (see SDSEFI for what it may look like, except think V8). Ok, background is set, what do you guys think? I was thinking about 70mm on the TB, but don't have a clue on the injectors.. what maybe 30-36 lb/hr or so? My plan is to slowly gather all the support pieces so when I can swing the SDS computer I'm ready to go. Any thoughts would be much appreciated. Thanks, Lone Quote Link to comment Share on other sites More sharing options...
BLKMGK Posted August 10, 2001 Share Posted August 10, 2001 70mm would work fine, I know others running as big as 90mm though. It's not like sizing a carb, you can run BIG throttle bodies but throttle RESPONSE is what suffers a bit. A crack of a 90mm throttle body moves MUCH more air than a 60mm. Throttle feel is WAY different (trust me!). However, as easy as it is to find Ford TBs I'd say go 70 or 75mm and if you ever need to move up bigger ones are readily available. Hrm, and 450hp is going to be hard to hit. I expect that with mild boost you'd be in the 500HP range easy with a well built motor. You could always keep the boost down of course but with only a few lbs used what was the point? Belt driven centrifigul is what's attracting me Injectors... Depends. If the HP rises as you run more boost you can bump fuel pressure but at some point you'll be swapping injectors. What works well for a NA setup will probably end up getting swapped for a blown application. Bigger injectors don't have the "resolution" of smaller ones so you don't want to go too big. My Ford runs 42s and should support over 600HP (there's math for this BTW) but I know guys with blown Cobras running 72s or bigger (gulp). Driveability is slightly compromised but doing the math they can support some serious HP. Actually it's odd, they can support far more with those injectors than they make but for some reason it's felt big ones are required. I dunno. In fact with 42s, which looked good on paper, my car runs a good bit rich. Part of this is an O2 issue but I don't think it's all that. I'll find out sometime in the future but I have a feeling that experience means at least as much in this area as th emath. turning down fuel pressur eonly works to a certain extent BTW - at too low a pressure they dribble rather than squirt. How's all that for really muddy? Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted August 11, 2001 Share Posted August 11, 2001 Thanks for the response Jim. I understand what you mean. It also cleared up what 'throttle tip in' was in regards to having to big of a throttle body, slightly opening a big throttle body causes large changes in flow so its harder to modulate the throttle smoothly the larger it is. I had read that but didn't know exactly what throttle tip in was, now I do. I like the belt driven chargers ok, but my problem is they're to expensive and with all the failures of units and breaking of belts it doesn't sound like something I want to do. (Beside, exhaust energy is free power just waiting to be exploited). I know you've had both types of power, but I really like Turbo cars *shrug*. Anyway thanks for the info, I guess I'll have to put up with 500 hp, jeez I hate it when you have to compromise . Regards, Lone Quote Link to comment Share on other sites More sharing options...
BLKMGK Posted August 12, 2001 Share Posted August 12, 2001 Breaking belts? Never done that before on a blower I AM starting to hear rumblings about ATI's blowers though. The shop is starting to see more failures than they have in the past. Were they not as closely tied to ATI as they are they say they'd have more trouble warranteeing the blowers. This is torubling since they've had such good results with ATI in the past. They've actually said the Paxton word which is scary as I've had such a low opinion of their stuff in the past (having owned some of it). We'll see - if they switch I'll be surprised but bad product is really bad for business! Who pays for the R&R of a bad blower? Ouch... Paxton outlet temps are supposed to be noticably lower too but the ATI intercooler makes up for that. ATI could be in trouble if Paxton starts using intercoolers... Dunno what I will do in th efuture with my car, I'll watch to see what the shop does. A turbo is nice but the plumbing and heat issue turn me off. Been there, done that. If this were a Ford 302 I'd be more interested since the manifolds would be "free" Maybe a 2nd Z later on? The woman would kill me (lol). I'll keep my eyes open for SBC turbo stuff guys... Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted August 12, 2001 Share Posted August 12, 2001 Was it John Scott that mentioned eating belts, or maybe Fast Frog?, one of the members mentioned it. I donno, they're both the same devices in reality, just ones mechanically driven and the other exhaust, from the gearbox back on a centrifugal unit, there isn't much difference than your average compressor wheel just like on a turbo. *shrug* One has high heats, the other has mechanical gears and extra bearings that wear, its sort of a toss up the way I see it, with the turbo only slightly edging out the centrifugal due to it not requiring any HP to drive the turbine and it costs a bit less. Regards, Lone Quote Link to comment Share on other sites More sharing options...
Drax240z Posted August 12, 2001 Share Posted August 12, 2001 Yeah it was John who was going through that. He also had some pretty brutal main bearing wear after a relatively short distance due to the tension put on the crank nose from the belt. Seems like everyone has their favorite between turbo/supercharger. Quote Link to comment Share on other sites More sharing options...
BLKMGK Posted August 13, 2001 Share Posted August 13, 2001 Don't get me wrong, I love turbos! However they're comlex and generate heat. Blowers make power differently too. Done properly you'll have a belt that's wide enough and has enough "wrap" that high tension isn't required on th ebelt. I used to run my Paxton tight as a bowstring and I have no doubt that it contributed some wear. Heck, I even used belt dressing to get more traction! The ATI unit I have now on the other hand has a very wide belt, tons of wrap, and a spring loaded tensioner - it's about as tight as a standard fan belt if that. Shouldn't be any big wear issues with that sort of setup... P.S. just read a dyno test where a 75 and 90mm TB were checked out on a 427cube motor. No significant HP differences found. 75mm should be good for most apps. [ August 12, 2001: Message edited by: BLKMGK ] Quote Link to comment Share on other sites More sharing options...
John Scott Posted August 24, 2001 Share Posted August 24, 2001 If I were satisfied with a 10-12 lb boost my belts would last. I like the 16+ which requires the 2.95 or 2.75 pullies. This makes grip on the 8 rib difficult. Hint: get the 12 rib. BTW, bracing has done wonders to extend belt life. If I had a big ol' nasty v8 with the procharger, I wouldn't need that much boost to be happy.....for a week or two JS Quote Link to comment Share on other sites More sharing options...
Owen Posted August 24, 2001 Share Posted August 24, 2001 Back to the injectors issue, this site has some pretty good reading dealing with injector sizes, fuel pressure, etc. http://www.grapeaperacing.com/GrapeApeRacing/tech/fuelinjectors.htm I assume the SDS uses low-impedance injectors? Owen Quote Link to comment Share on other sites More sharing options...
Mike C Posted August 24, 2001 Share Posted August 24, 2001 As far as throttle body size, the RamJet 502 from GM, fuel injected 502ci 510 hp has an L98 throttle body on it. Same as the 245hp Corvette TPI which should show you how much power the (I think) dual 48mm throttle body can support. Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted August 25, 2001 Share Posted August 25, 2001 Thanks, I've seen a few LT1 TB's on Ebay fairly cheap, maybe I'll jump on the next one I see cheap. Thanks for the info guys, appreciated. Regards, Lone Quote Link to comment Share on other sites More sharing options...
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