converting 350 TBI to 502 Ram Jet?

My truck is an "89" Silverado 2500 with a stock 350 TBI and auto trans. I've never been happy with the trucks towing power. I have a small
aluminum jon boat that I trailer nearly every weekend. My Chevy pulls that boat and trailer just fine because the total weight is only about 1,500 lb. But, we have another boat, a 26 ft. fiberglass pocket cruiser, that we trailer maybe 6 times a year. The total weight is about 9,000 lb and my Chevy can barely manage the task. I am considering swaping out the 350 TBI and installing a 502 Ram Jet. My local crate engine suppliers tell me I'm better off just buying a used truck with the power train that I am looking for. They tell me that the 87 thru 95 Chevy TBI's are just hopeless and I'm better off getting rid of it. Is my truck really that hopeless? I am assuming that the Big Block swap would reguire the crate 502, a compatible auto trans. and a new ECM w/ wiring harness. I know one of you guys out there has successfully done this, right! What am I looking at as far as reguired parts to do this swap? And, is it a managable job for a limited experienced, back yard mechanic? Thanks for any help you can give!
Mike Howard
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Change the rear end. Actually have someone do it for you as you need special stuff to set the pinion and ring gear up.
Anyway check in the glove box for codes. If you have...
GU4: 3.08 gear set... have trouble pulling just about anything. GU6: 3.42 gear set GT4: 3.73 gear set... You want this, -my opinion GT5: 4.10 gear set... Great for pulling stumps out of the ground.
Of course your engine will rev higher so you might spend more on fuel... depending on whether you have an overdrive transmission or not but such is life.
If you have the 3.08 gear set a 600+ hp. 572ci... well I think you still might be scratching your head when pulling the 9K trailer.
It's all in the gears.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
The codes sticker inside the glove box has GT4 on it. So I quess the gears are 3.73's Thanks SLAP, for the help on identifying the gearing!
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

If the truck is in EXCELLENT condition, pull the motor and have it rebuilt by a specialized 4X4 shop or a speed shop. You can get incredible horsepower from a 350. Of course the rest of your running gear won't be capable of handling the added power and torque, so you'll have to have the transmission gone over too. If it's a 4X4, you'll need deeper gears both front and back.
Personally, I'd agree with the suppliers...You'll be better off with a new vehicle. I have a friend with a 2004 2500HD with the 6.0 and the stock 4.10 gears that pulls a 25' fiberglass boat with a cuddy that has been weighed on a scale at 9,300 pounds dry. He says the Silverado pulls it no sweat.
Heck, I pull a 7,500 (the trailer manufacturer claimed 5,000 #'s dry, right) pound travel trailer with my 2001 Silverado 1500 with the 5.3 and hardly notice it behind me...I actually prefer the trucks ride and stability with the trailer hooked up. It doesn't have any problems on hills or accelerating to highway speed. I even get 12.5 mpg towing (sometimes a bit worse but never below 11 in the past three years with this trailer).
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

Very simple solution here Mike, install a set of 4.56 gears in it and it will surprize you how well it will pull that boat. THe 350 is not a bad motor but it needs some better gears than you have for that amount of weight. If you swap engine, I would go for a 454 of that era as it will make a easier swap overall and do not let the HP rating of a TBI 454 fool you as is is a stump puller with the proper gears behind it. With 4.56 behind your current engine though, you will think you had a engine transplant and a little extra RPM will not hurt a 350 and towing MPG will improve some too. ----------------- The SnoMan www.thesnoman.com
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
SnoMan, if SLAP is correct about the gear codes (GT4) then the gears in my truck are 3.73's Do you think that the 4.56's would be too much for everyday, non towing use? My tranny is a 3 speed no overdrive automatic. From what my manual says there is a 3 speed standard and a 3 speed Heavy Duty, I am not sure which one is in my truck.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

Okay if no OD try 4.10 if you have stock sized tires and you will feel a difference towing. If you have oversized rubber on it, install 4.56's. Another thing that will help a lot with that engine is to set timing at 8 BTDC and use premiun gas and you will see a improvement in power. With premium gas just costing 5 to 7& more than 87 these days it is a good deal because MPG will increase too especailly when not towing and likely outset the increase in fuel cost. I have a 89 4x4 burb with same engine and a 700R4 OD tranny and the best I ever got was 15 MPG on highway with 87 when it was new. When I switched over to 93 and change timing I now get as high as 19 MPG and with more power now and just completeed a trip from Ohio to North Carolina and back and it never left OD either on whole trip at speed and I averaged between 17 and 18 MPG for 1000 miles and I have a 40 gallon tank that a run down a good bit before filling so the MPG figures are accurate. Burb has 177K on it now too. (it has stock tires with 3.73 gears too). If you want to get extreme, you could install a 4.56 or 4.88 and a 700R4 (they are not computer controled) and it will hold up fine for your needs and give you a much deeper first gear and a .7 OD with a locking converter when not towing to give you better MPG. (better MPG towing too because it can lock in drive too) Your THM 400 never had a locking converter and when it became a 4L80E, they simply added a OD to a THM 400 and a locking converter. ----------------- The SnoMan www.thesnoman.com
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
SnoMan, I am leaning towards your recommendation of 4.56's with a 700R4 tranny. My 350 has just over 100K on it and I believe the valve seals are bad because it is blowing smoke when I come to a stop and then accelerate again. I was considering just replacing the seals, but a few days ago the motor developed an intermitent noice that to me sounds like a collapsed lifter. So I have decided to replace the motor with another 350 TBI crate motor and let the rear gears take care of my towing needs. One other problem I have had regarding towing our Big boat is losing traction on some steep launch ramps. My truck is 2WD. So what do you think about while the differential is apart, installing a Detroit Locker. Nobody I have spoken with regarding Lockers has had any experience with them. To me it seems like a logical solution. My only concern is how dependable the DL's are. From what I understand they clunck in and out of engagement when cornering. Seems to me that they may be prone to failure considering the harsh operating conditions. Thanks for your assistance!
Mike Howard
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
If you have stock sized tires, 4.56 gears will probably bother you on the highway as your engine RPM's will be too high - especially if you don't tow very often. I've got 35" tires (with a 4L60E - OD and locking converter) and I run 4.56 gears to bring the gear ratio back to stock. I ran with a set of 4.88 gears for a while, and even with these bigger tires and the 4spd trans, the RPMS were just too high. The highest I'd go with stock tires would be 4.10, and even then that's pushing the limit of reasonable.
As far as lockers go - I doubt you're going to break the DL, but you may not be very happy with the locker on the street either. They are a little clunky/noisy and may surprise you from time to time until you pass the learning curve of how to survive with a DL. In your case, a limited slip/posi-traction unit would probably work better. Leave the DL to the guys that spend lots of time off-road, they need the traction and can live with the negative aspects of the locker.
With a 2wd truck of that year, I'd think hard before spending several thousand $$ on it. You just might end up spending as much as would have cost you to get a newer truck. That being said.. I love my 1996 and have spent much more than it's street value in additional parts for it.
If you love the truck, drop a 383 crate engine in it, and either get the trans done at the same time or plan on doing it shortly after when it blows up on you. If that doesn't buy you enough push - then consider getting the gears done as well. If you aren't that attached to the truck, then price out a slightly newer 3/4 ton 4wd truck.
SuperDave
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

Mike
For starters, do not use a detriot locker for towing because it does not have the ability to power the wheel at a different speed when towing in a turn. It is 2wd same speed or 1wd with other wheel coasting. I would install a Eation LSD or a E-Locker. A ARB is a option to as well as a stock GovLoc. You need to determine which axle you have to know your options and below you will find a link for a GM axle ID. Also bear in mind that deeper axle gear give you better traction and there is a link below on this too. Valve guide seal problems are very common on 350's as they age and can be easily changed. As for lifter, there are additives that can free them and when they stick like that it is because either the oil being used is not keeping them clean or it is not being changed enough. Given age of engine and duty it preforms, you want to change it no more than every 3K and a little more often would not hurt. Alos do not let RPM scare you as some think they need to turn 2000 RPM at 70 MPH to get good MPG with a 350 in a truck but this is not the case in a heavy truck and you really want about 2400 RPM or so at that speed with right gear combos. A 4.56 with a 700R4 and stock tire will put you dead on 2400 RPM at 70 MPH. (gear ratio calculator include below too)
Axle ID Gudie http://forum.snoman.com/viewtopic.php?t 8
Some towing and gear ratio info http://forum.snoman.com/viewtopic.php?t 9
Some more info http://forum.snoman.com/viewforum.php?fQ
----------------- The SnoMan www.thesnoman.com
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.