old truck guy

I'm building a low rpm motor for my 95 k2500. I want lots of low end grunt and good economy. My plan so far was a 383 and I've accumulated most of the parts but have developed some concerns about fueling.

My build so far consist of the following. I have a set of vortec 062 heads that I have blended the valve seats to the bowls, rounded off the valve guide bosses, mild porting and polishing on the exhaust side and spring upgrade for roller and more lift. I have a scat stroker crank, scat 5.7" stroker clearances rods and speedpro hyper dish pistons which should give me low 9's scr after decking the block. Edelbrock 2716 performer eps intake, 46mm bored throttle body w/adaptor and small tube headers w/dual exhaust. My cam is comp 08-464-8 xfi252 hr13. It is 202/212 @ .050 and a113 LSA. I know its small but again, looking for excellent low/mid range, good vacuum/idle and best economy I can get while keeping some good grunt.

My concern is TBI injection. Trying to stay at no more than 18 psi fp and 350 truck injectors. Based on comp's camquest and everything I've been reading, I'm estimating my current build plan at about 330-340 HP. Getting into big block injector territory.

So my questions are these:

1) I wanted the 383 for the additional torque, between a 355 and a 383 cam and everything else being the same, will the HP of the 383 be up or down from the 355? Camquest shows tq going up but peak HP going down. Is this right?

2) fuel needs based on HP produced not cid, correct? Which one is going to use more fuel?

Bottom line, if its going to be easier to fuel I'm going to revert back to building a 355.

Night rider327

iTrader: (13)

The 383 will gain 20 HP or so over the same built 355.

At those specs and power, the 383 will need a touch more air flow coming in (throttle body size) and that means to have correct air/fuel ratio it will need a touch more fuel flow (injectors) than the same built 355..

Now this does NOT mean it will burn more fuel than the same built 355 though, as the 383's VE (volumetric efficiency) will be higher, thus will use/burn same if not alittle less than the same built 355.

Go through as planned with the 383.. The only thing I would do diff is the cam. I know your after low RPM torque, but remember the bigger the engine is the smaller the cam acts. That 202/212@.050" cam is gonna act like a stock 190's duration cam in a 383 which will not keep the valves open long enough to take effect of the better flowing heads and large C.I.D engine.

I would bump it up 10 degrees to a 212/222 give or take for your monster torque 383. This will work better all around in your engine.

2005Impalla

If all you do to a motor is stroke it with out changing any thing else it will just shift your power band to a lower RPM with out having much of a change on peak HP. You will increase torque with very little gain in HP. Your heads, intake carb and cam selection will only flow so much air and adding more CID will not improve the flow of these parts. A 350 that makes 350HP will use close to as much air and fuel as a 454 that makes 350 HP at peak HP. I would not use a TB for a 350 HP motor. I would swap to a carb. Your not going to loose much MPG going to carb over TB as long as you tune your carb for your motor. I would look at trying the new Street demon carb. I plan on using this on my new motor. It has very small primaries to keep velocity high for good fuel atomization like a Q jet.

old truck guy

My build is largely inspired by the gmpp ht383 which is rated @ 340hp but from what I've read, more like 320 HP as it comes. This is with untouched stock vortec heads and a smaller cam (196/206 I think) with less lift and not as aggressive of a ramp profile as what I have. I'm guesstimating I'll be closer to the actual 340 HP which is plenty for my expectations. I know with the cam I have chosen I'm leaving power on the table but my main focus is staying with 350 truck injectors and getting as much as I can. Everything I have read says big block injectors in a small block application tends to run rich/poor spray pattern/poor economy at idle and low rpm/low DC. Brian with Harris performance (tbichips.com) says its hard to find a set in good condition and that he can get up to 340 HP out of the 350 injectors and higher FP. I also like the fact that if I ever lose an injector, you can find the 350 ones all day long.

So in a nut shell, I want to stay below 340 HP even if it means ditching the 383 and going back to a 355.

Fast355

iTrader: (2)

I wouldn't take any advice from Brian personally. The factory marine engines have 2" bores with 61# 350 injectors running at 30 psi fuel pressure for engines up to 400 HP.

With a 4bbl carb and headers the HT383 is more like 350 HP. The marine 6.2 also makes 340-350 HP. Same cam just a crossram L31 marine intake.

old truck guy

You don't like Brian? Seen his name come up in a lot of posts, mostly good. Do you have another tuner to revomend?

What do you think of the cam i've chosen?

Where do you think my build HP will be at?

Fast355

iTrader: (2)

Dave W or Eaglemark would be my recomendation although Mark has had some health concerns that might be keeping him away from tuning.

I cannot stand Brian. He is a fraud as far as I am concerned.

Research Brian and TBI Chips on here and you will find all the information you need.

http://www.gearhead-efi.com/Fuel-Injection/forum.php

The cam is smallish but I think will work toward you goals.