engine build 350 or 383?

[pseudomike]

I second TBIchips.com. Brian is a great guy. Something is definitely wrong if you can't pull that boat at 70mph with 4.56 gears. I have a fairly stock 350 TBI in my 2500 plow truck w/the exception of a bored throttle body, punched out Edelbrock TBI intake, 1.6 roller rockers, a mild 4x4 cam (recommended by Brian), 3" exhaust with stock imanifolds, and a hot chip from Brian w/o egr provision. IMO this is fairly stock, stock heads, pistons, compression and so on. The truck has 4.10's, a 4L80E, and 33's. I pulled a 8500lb Kubota 4wd tractor + trailer at 75MPH+ to my hunting cabin in upstate Vermont. I think the truck would have gone faster but thats a lot of weight to try and control with a SRW truck. Untested, but I'm fairly sure that would rival my 454 TBI truck. Oh yeah, and the trucks never thrown a code, my props to Brian's work.

From the factory the TBI motor were far from tuned. There is a lot of potential in that injection system. Have you modified you TBI unit at all? It sounds like you are not getting enough air into that beast to make the power. You need a larger throttle body before you can make power from other things like a cam, high compression pistons, free flowing exhaust, etc. That stock TBI is nothing more than a factory equipped restrictor plate. You also need to pay attention to cam selection. A cam that makes power at 3500RPM is gonna get you in 2nd gear on those hills too.

When I was a kid I built a motor for my '88 K5. I bought all sorts of neat stuff out of summit racing like high compression pistons, a big cam and so on. Put the motor in and it was a complete dog. I had chips burned, toyed with the fuel pressure, but never got it to run well. I sold it to a friend and he installed a Holley 670 TBI on it and bored the manifold. Thing ran like an ape after that.

 

[pseudomike]

If you can afford heads by all means buy them. To each their own. What I was getting at is $ for $ you will make more power where you want it, in the form of torque, with a LO5 topped 383 than with vortec or aftermarket heads on a 350. That vortec swap is not cheap ~$350 for a good set of heads, another $200-400 for the intake, and you still have to address the egr, oh yeah, and to utilize those heads your gonna want a high lift cam so expect to be machining those valve guides down and forking over more $$ for some new springs that won't disintegrate with a big lift. A good set of aluminum head will run $700-1000 comparable to the Dart cast iron heads. You can build a decent 383 for not a whole lot more than a decent 350 build, and if you want more you can get some nice darts or aluminum heads later on. It's a lot harder to add cubes down the road.

Some trivia, a stock 5.7 Vortec made 40 HP and 30lbs of torque more than a 5.7 TBI. It was a roller motor with higher compression and a better injection system. Also, if you notice these things, the TBI HP numbers were rated at 4000RPM vs the Vortecs at 5000RPM.

I've never seen Vortec heads against the LO5 heads. I have read information on them dyno'd against TPI heads, and L98 aluminum heads. They had impressive HP gain ~40HP in the 5000RPM range over the TPI heads ....but they only made about 4lbs more torque which is what I was getting at. They did not make 40HP right across the RPM curve, it was more of an exponential growth function and fairly insignificant under 3500RPM. My 2 cents..5000RPMS..if your running that RPM range in your wheeler you better think about getting tires and some lockers first.

Stock LO5 heads can make loads of power under 4000RPMs, they are more than capable of supporting a 400ft/lb torque 383 with a nice truck cam in it, and with 76cc chambers they are also quite efficient on fuel. Couple that engine with a low stall torque converter and I assure you your truck will plant you pants into the seat. Do your research, this has been talked about many times, keeping in mind you have a truck not an F-body so your modifications will be much different than theirs.

 

[nsxxtreme]

I second TBIchips.com. Brian is a great guy. Something is definitely wrong if you can't pull that boat at 70mph with 4.56 gears.

I thought I would have more power as well. Greatly dissapointed, I'll need to ask the machinist what cam he gave me. I didn't pick it out but I told him it was for a 4x4. The roller rockers I bought were 1.52s. Mine has the EGR valve installed. I have not touched my TBI, I'm a little scared to modify somethings because I still need to pass a smog test. I have the stock exhaust also I don't want headers so they are not an option.

 

[pseudomike]

My 2500 passed MA smog with flying colors, only comment I got was from the old-timer running it on the high speed dyno test who said "well it's definitely making plenty of power". Stock 3" y-pipe, catco 3" cat, and a 3" 2 chamber flowmaster. In MA my '86 2500 is held to the same emissions requirements as a 2008 truck...even though it didn't even come with cats from the factory. MA is strict. Your emissions will be fine providing your fuel mixture is right. As a side note, I did have the EGR provision when I went through smog, it will keep your NOX levels where they need to be. I had Brian remove the provision for $20 after I passed because my truck is now exempt from smog test hooray as MA went to the OBDII and newer test as of Nov. 08, no more sniffer and I'm not due until Dec. I would see if you can get the specs on that cam, your compression ratio, and call Brian at TBI chips. He is an absolute wealth of knowledge and he will get that thing running tip top passing a smog w/o problems.

 

[4X4HIGH]

I thought I would have more power as well. Greatly dissapointed, I'll need to ask the machinist what cam he gave me. I didn't pick it out but I told him it was for a 4x4. The roller rockers I bought were 1.52s. Mine has the EGR valve installed. I have not touched my TBI, I'm a little scared to modify somethings because I still need to pass a smog test. I have the stock exhaust also I don't want headers so they are not an option.

The cam needs to be a TBI friendly grind. Also headers are the first thing to add to achieve more power. The stock exhaust is too restrictive. A nice 3" single exhaust is also a big help.

 

[dyeager535]

Some trivia, a stock 5.7 Vortec made 40 HP and 30lbs of torque more than a 5.7 TBI. It was a roller motor with higher compression and a better injection system. Also, if you notice these things, the TBI HP numbers were rated at 4000RPM vs the Vortecs at 5000RPM.

Close, according to GM:

1995 5.7 Liter 200 @ 4000 rpm 310 @ 2400 rpm
1996 5700 .....255 @ 4600 rpm 330 @ 2800 rpm
Change +55+20

Regardless, you are right...better induction system and roller cam must add something, but the actual dyno'd 40HP over older heads means something, especially considering that's not including cam or induction differences. Don't forget, TBI was already running 9.2:1 compression, while the Vortecs were only slightly higher at 9.4:1.

600/400 RPM difference is very little, but undoubtedly is near worthless info if the curve isn't shown, and few dyno tests start at idle, which is important for a truck.

I suppose we are getting a bit into the weeds here. However, one thing that won't change, and that the OP mentioned, is fuel mileage. A larger displacement engine, all else equal (as it would be 383 vs 350) will use more fuel under most conditions. The argument can be made with the 305 vs 350 in these trucks getting near identical mileage,...but the 350 is nowhere near underpowered for these trucks, which is why the 305 economy was not any better than the 350...350 will get better economy than a similar build 383, but by how much, I have no idea. It would depend on tune and driver too much to know for any application.

 

[pseudomike]

I agree 100%. I wasn't trying to get us off into the weeds, I was just trying to help the guy out, and it's just that heads are a huge investment and I have never seen anything indicating a huge gain on the low end with even the best heads. For $200 you could chuck that clutch fan and swap in some electrics out of an F-body LS1 and pickup 20hp right across the enitre power band. I don't think any head can match that.

Going with the fuel mileage thing you could build an argument that with 400ft/lbs of torque you could gear the beast down and increase mileage via less RPM's. As stated, too many variables and hard to tell. More cubes will drink more gas w/equal RPM's, an engine is just an air pump and thats just physics. Would none the less be an interesting test. My 454 TBI with 3.73's and a TH400 gets ~14mpg on the highway. It makes 380ft/lbs of torque outa the box. My 2500 doesn't fair much better than that when not in overdrive. I doubt that motor makes 300ft/lbs but I guarantee it makes more HP than that 454.

As for the cam, TBI setups really like tight duration cams regardless of lift. It is true that you can make power more easily with greater separation of the lobes but that won't fly with the TBI. You can still make good power with a tight cam but your band will be lower in the RPMs. In my experiences you can make a lot of torque with a TBI motor but i have yet to see any real high RPM screamers. With the correct gearing things will be fairly equal...look at that Duramax wow those things move out.

I've never had good luck with headers, the salt belt really does a number on them. They definitely flow better but my experiences are much more maintenance. Could be I never had a set of really nice headers. Either way i was sick of tightening the bolts into the block and replacing both collector an manifold gaskets so I put the manifolds back on.

 

[cuervo]

Would you like to buy some beach front property in Arizona? I've got some i'll sell you.

Nice dig at how gullible you believe me to be.

While I will not argue with about the possibilities of building a 383 that will make 310 hp on 500 cfms I will suggest there are engine builders/designers that can and do.

Thanks.

 

[4X4HIGH]

Nice dig at how gullible you believe me to be.

While I will not argue with about the possibilities of building a 383 that will make 310 hp on 500 cfms I will suggest there are engine builders/designers that can and do.

Thanks.

310 hp is easy to come by and yes 500cfm can do it (with a 350). Hell the TBI engines are 210 stock and that's conservative. Why are we talking about HP though? Torque is what's needed in a truck. Now i guess if you don't care about lots of torque then by all means use the stock 350 TBI. The engine i built makes 506 ft. tq. from 2000-3500 and that requires alot more air and fuel. The HP is 4000 @ 4500 rpm but like i said, it's torque i'm after.

 

[pseudomike]

I think you could run a 383 on 500 CFM...but it would depend on the volumetric efficiency of the motor, single plane/dual plane intake, and my gut feeling is you would start loosing a lot of power encroaching 4000RPM. There are calculators on the web that can do this calculation. I would ALSO be concerned about being emissions legal w/454 injectors and a 500cfm body. Not to say it's not possible, but there is a lot of information out there about this usually titled "ultimate TBI mods" and it's recommended for anything above ~270HP.

 

[cuervo]

If you build a 383 your 350 TBI unit will not support the HP/TQ numbers even using the 454 injectors, you're going to need a 454 TBI unit with the 454 injectors. My hot 350 build would not even accept a 350 TBI unit to support my numbers.

Well, first you say a 350 TBI will not support a 383 build and tell me to buy ocean front property. Then you tell me it can but will not make high Torque numbers.


I guess I can't find a reason to post on this subject without seeming like I'm just here to question you further about your information.

Thanks again.

 

[4X4HIGH]

I never said a 383 can use a 350 TBI, i did say it's not enough cfm.

EDIT: i see the confusion, my last reply was talking about making 310hp with a 350 using 500cfm not a 383, sorry for that confusion.

 

[cuervo]

I am not confused at all. I believe I have the facts correct.

A 383 using a 350 TBI with 454 injectors and a custom chip is very doable. I'm sure it's not the right choice for everyone's application.

And for reference I was talking about making 310 hp from a 383 running a 350TBI with 454 injectors. That's the part where you tell me to buy land.

 

[pseudomike]

For close to $5000 I do not see the advantage. I could build a motor for much less that uses an oversize TBI and makes all of that power and I would have a fully rebuilt TBI. To each there own but i would take the beaten path.

 

[dyeager535]

You may be able to do it, but as mentioned, in other words, you'd essentially be running a restrictor plate on the motor.

If running restricted gains you nothing, except loss of power higher up, there would seem to be little reason to do so. If you limit air but not fuel, you are still limited. Doable? Of course...there are people running 383's with bone stock 350 TBI setups, for now at least.

 

[cuervo]

Well, losing some HP because I'm down a 100 cfm is a far cry from it will not work at all. I have more money then time so if I have someone else build it for me I'm all the better.

 

[4X4HIGH]

Well, losing some HP because I'm down a 100 cfm is a far cry from it will not work at all. I have more money then time so if I have someone else build it for me I'm all the better.

Wow, i guess you have to fully explain to people what you mean by "won't work".

Yes a 350 TBI will make a 383 engine run, but it sure as hell isn't enough CFM to make any kind of power that you would get from using the proper CFM TBI unit. I'll bet that you're thinking to yourself "this guy keeps contradicting himself" when in actuality i'm talking about "waking up" an engine and trying to build an engine with more power but using the same CFM throttle body sure isn't how it's done.

I guess my 22 years of building engines professionally doesn't mean anything to you.

 

[nsxxtreme]

The cam needs to be a TBI friendly grind. Also headers are the first thing to add to achieve more power. The stock exhaust is too restrictive. A nice 3" single exhaust is also a big help.

I'm going to find out which cam I have tomorrow. I did not pick it. Honestly the truck is a gutless turd. I'm ready to dump it if I can't get more power.

Header are out don't want to deal with them or the under hood heat they produce. So all options are available except headers.

 

[4X4HIGH]

I'm going to find out which cam I have tomorrow. I did not pick it. Honestly the truck is a gutless turd. I'm ready to dump it if I can't get more power.

Header are out don't want to deal with them or the under hood heat they produce. So all options are available except headers.

You are really limiting the potential by insisting on not running headers. An engine is a pump, if you want more power you need to pump more but in order to pump more you need to also remove more. You can't pump more and leave the exhaust alone. If you buy a good set of headers (cost about 400-600 depending on what you get) they won't leak and if you buy quality bolts they won't come loose.

 

[dyeager535]

x2.

Scott's probably got dyno experience, perhaps his results don't bear out what magazine dyno testing has shown again and again, but you are talking the same gains from headers that you see from a head swap when talking pretty mild, or stock small block. +40HP, +20-30TQ are commonly seen, and not all on the upper end either.

If you feel the motor is gutless, why on earth would you eliminate headers from consideration? It is absolutely certain that there is NOTHING that works as well as long tube headers in overall numbers when talking exhaust. Ok, now that I've made that overarching statement, someone can come in and sharpshoot me.