|02-08-2014 01:01 PM|
TBI uses the speed density and as such will not tolerate any changes from stock without changes in the calibration. The Speed Density systems are not as forgiving as the Mass Airflow systems which use a Mass Airflow sensor like teh GMT 400 trucks(88-99) started using in 1996 with teh advent of teh Vortec CSFI(Centralport Sequential Fuel Injection) MAS systems.
A stock Vortec 350 with with a nodular iron crank, hypereutectic pistons and forged PPM rods with 4 bolt mains will cost $2000. With a cam change this would be an excellent way to net 375-400hp at the crank, but a TBI unit will hold these numbers back.
The TBI injection as is, or even a modfied 454 TBI will not allow 500hp.
You can use your ECM to support the firing of 8 fuel injectors in any fuel injection manifold you wish, they will fire in batch fire though, which matters not to power production.
You said you prefer iron heads, there is the Small port 185cc Bowtie Vortec heads and the 225cc Large Port Bowtie Vortec heads.
The Largeports complete are $580 from Summit a head.
|02-08-2014 11:28 AM|
Your aquaintance is probably right about the fuel injection system. The EFI system with TBI could not handle much of a cam change. The engine is probably running lean is why you hear the popping. I have no idea how you family member assembled your engine but with your plans for an engine I hope he used forged FT pistons. As for most tbi heads (76 cc) called swirl port heads are junk because they do not flow much air. Another thing if the camshaft he used has a LSA under 112 your TBI will never run right afterwards. Check your fuel pressure it should be 13-15 lbs. Get a vacuum gauge to check engine vacuum and run some test. Check engine timing. When you begin to upgrade the engine know if you are going to run a supercharger because you will want the engine compression at around 8:1. Yes, you will want a good set of aluminum heads such as Dart, Brodix, or AFR. You will want to measure the distance from the top of the pistons to the deck when at TDC. This will tell you if the block is square and measure the quench. If not square deck will need milling. The quench needs to be at .035-.045. "0" decking allows to simply use a .039-.041 head gasket. Maybe F-BIRD'88 can give some info on supercharging.
|02-08-2014 09:55 AM|
1st thing I'd do is change the fuel Filter, 'n inspect the contents of the old 1 for crap,...
|02-08-2014 09:13 AM|
Check the vacuum at idle and driving - is it steady - it should be. If it isn't, then you have an intake leak causing your issue. Is the timing set right? Make sure it is with a timing light and make sure it is moving accordingly when the engine is warm and the bypass is connected (not bypassing).
New plugs and wires - I would and I'd put on a new cap also.
You can plug the vacuum line to the egr valve to see if the acceleration problem disappears. It might throw a fault code, but if the bogging goes away, then you know where to head. Also, are there any fault codes now, inactive or active?
If all the above check out, then check fuel pressure, compression or leakdown. If those are all good, then try dropping the exhaust off from the headers to eliminate the possibility of an exhaust blockage.
Lastly, if all else is good, do some datalogging to see what is up. But I think you'll find the problem before that is needed.
Good luck - Jim
|02-08-2014 07:06 AM|
Reviving an old thread. Need some help
Due to the economy slowing, my project truck has taken a back seat for awhile. I urgently need some help on this problem...
Recently I came to wreck and total our primary source of transportation due to the great PA winter weather. Lucky for us, I was not hurt and we have two other vehicles (truck and a VW cabrio). Also, we got enough back from insurance to pay off the vehicle and purchase an '03 Tahoe in very very good condition with cash... (no more car payments!). But, I needed to drive the truck daily for work until the Tahoe was purchased and also when the great PA winter weather decided the VW should rest...
Now I drove the truck sporadically since the rebuild. Never been happy with it... seems doggish. Also I know something is wrong as it won't go over a mountain in 4th gear (it is a manual HD 4spd). It will start with a full head of steam but quickly drop rpm's and (if I don't slow and downshift to 3rd) start knocking (pretty intense if I'm not careful). And now it's been pitching another royal fit. Here's what is going on...
When I start the truck and let it warm up, it runs fine. But as I start to drive it, it'll seem to die as I accelerate. The more I push the pedal, the worse it gets until I can hear it "popping" near the headers. So I will back off the pedal and it will run at that current speed, but I'm slowly losing rpm / speed as I work at trying to accelerate and letting off the pedal to keep the truck running. Now if I push the pedal to the floor, it'll bog down for a second or few, maybe pop once or twice, then it will go full steam like a bat from hell (which makes it really interesting and fun in the snow ). I'm thinking it's running too rich because it sounds like it's popping in the headers. The truck being slightly modified (see very first post) still runs the stock injection with the stock fuel lines / fuel pump / intake / heads / ignition system.
An acquaintance of mine said the ECM couldn't compensate / make adjustments for the changes I'd had done and seemed to think that is where the problem lies. I don't think that's entirely it. I am planning on a carb - as stated, this has taken a back seat until I can justify putting it back into the budget plan. Also, I cannot remove the TBI just yet and be minus this vehicle until the weather breaks...
So I've been dealing with it and usually after a few miles the truck seems to even out and is acceptable to drive for what I need to get by. But the other night while coming home from work it continued to get worse and I almost thought I may not make it home. I'm going to change the plugs and play a little bit with the distributor today, but I'm hoping someone can chime in and (with the description I've given so far) be able to diagnose with some degree of certainty what problem I may be experiencing and how to go about addressing it...
Sorry for the long post, but I'm trying to be as thorough as I can...
|08-09-2012 06:00 PM|
|matt167||Oh yea, Almost forgot. With a TKO, I'm pretty sure there is no 4x4 tailshaft available so you'll need to run a divorced transfer case if you want 4x4|
|08-09-2012 04:45 PM|
Lots of companies offer "top end kits".
Here are some examples from Edlebrock and TrickFlow:
Edelbrock.com - Power Package - Top End Kits - Chevy
Chevy small block Gen I, 5.7L/350, CHEVROLET, Engines & Components, Trick Flow Specialties - trickflow.com
You can research the CFM of the heads and cam numbers, and the details of the other components to see what is involved. Keep in mind their HP numbers are going to be on the optimistic side (gotta love advertising), and unless you duplicate their setup exactly (as in buy the kit) you have no right to complain that your power numbers are not the same, because you changed the formula.
Sounds like you already have a solid shortblock. Buy one of these kits and go for it. Of course this route really takes the fun away from researching, learning, part selection, and truly building your engine. But it is just an option to remove some of the internet forum BS (and no I am *not* accusing anyone of that, just saying).
|08-09-2012 04:34 PM|
OK, so I'll ditch the RV cam. I'll look into the heads as well. Would I need to go aluminum? I'm not concerned with the cost, but if iron ones will do nicely I'd prefer them. The pistons should be flat, but I'll find out which ones he installed.
So next would be looking into some cams and internals that would work in harmony to best suit an attainable 400+ hp. Can you name a few that would be wise to look at and would work together?
The more I'm reading, the more I'm coming to the reality that 500 was just a number I focused on. But I'd still like to get as much as I can with a strong power plant under the hood.
|08-09-2012 04:22 PM|
As far as intake system, I'm not following you. Sorry, what exactly are you asking about?
|08-09-2012 10:20 AM|
Did your family member know your audacious goal of 500HP when he started?
Focus your money on the heads. If I was going to try and achieve 500HP I would ditch the Vortecs (and I do LOVE Vortec heads). Get some nice aluminum ones and plan on spending $1,200+.
You are not going to get to 500HP on an RV cam. Nor is an RV cam suited for super/turbo charger. You need to get one suited for forced induction. Also you are going to need a roller cam and full roller rockers. Both these will probably net you 50HP+ and some MPG. A solid lifter is also going to help you get to your power (and you are going to have to adjust valve lash every 3,000 miles).
What pistons do you have? I hope for the $3,000 you have invested thus far you have some flat tops (factory dished pistons are not good for performance).
|08-09-2012 08:54 AM|
the TKO is a super tough tremec.
Getting 500 HP from vortec heads is possible but hardly for a street friendly truck.you could use a 75HP NO2 system? The vortec 350 can be tuned for 400 plus HP and still have decent street manners.The GM hot hydraulic roller,good headers, 1 5/8 long tube seems to work well with vortec heads.3 inch dual exhaust.
what intake system will you use?
|08-09-2012 06:18 AM|
If I'd actually discovered this forum prior to starting this project, a 383 stroker would have been my first step. But alas, I've already sunk $3,000 into the motor and I might as well do what I can and be happy with it.
|08-09-2012 06:13 AM|
I will look into the Tremec or TKO. Which one would be the wiser choice, or are they both about equal?
As for the supercharger... since I will replace the heads with vortec heads, and the motor hasn't changed stroke, would it be safe to assume a supercharger would still be ok? If so, could I manage to squeak close to 400 hp and boost low end torque with it and some minor modifications to what I have now?
|08-08-2012 07:51 PM|
|vinniekq2||go test drive a newer diesel. If you like the way it drives then what you want is torque.Im not saying transplant a diesel,just look for more bottom end stump pulling power rather than high RPM horse power. many ways to get that torque. boost or displacement are the easiest.depends on budget,maybe both?how about a stroker with a small super charger making 500 pounds torque and maybe 400 HP at or below 5,000 rpm|
|08-08-2012 07:01 PM|
The transmission you want won't hold 500 HP, the engine you have is making 250 horsepower, give or take..
You can't boost the compression and add a supercharger, it's actually best to have it a little low for a supercharger. You can probably get an engine to run 350 HP with another set of heads and you will have a ton of fun with it.
As far as the 5spd, what came in 1500's of that era was a NV-3500 which is a very weak/ finiky trans and has a rating of 300 ft/lbs. Any more than that and it starts to come apart ( and there are NO upgraded parts ) What you have is ither a super rare SM-265 that was basicly modified to fit the '88+ trucks ( only found in 3/4 ton and 1 tons for a couple years), a SM-265 for a '73-'87 truck mod'd to fit or an NV-4500, found in M/T 3/4 ton and 1 ton's after like 1992. It's 4 speed plus a granny gear, but is considered a 5 speed, shifts like a truck trans, can't shift it very quick, but it'll take a lot of power ( same trans as 5spd Cummins Dodges ). Your 5spd options are basicly transmissions that will cost far more than a grand to buy ( Tremec 3550 or TKO 500 would do well ).. The easiest thing to do is accept that it's not a race car, build the engine enough that you can have some fun while being practical..
What you want will cost $20k easy.
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