engine swap

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  #1  
Old 03-02-03, 09:11 PM
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Question engine swap

I have a 95 chevy 1/2 ton pickup extended cab silverado with tbi 305 engine with around 60.000 miles on it. And it has the four speed automatic overdrive.
The problem is that last summer I bought a bass boat and when I pull it the gas mileage really goes down BIG TIME.
I was told that I should tow in third gear as much as possible and that the 305 is too little to be towing with. Can I swap a 350 engine in place and still use all the computer controls ,distributor,TBI stuff from the 305 on the 350.
Thanks.
 
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  #2  
Old 03-02-03, 10:24 PM
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i believe everything is compatible but i would suggest checking with the dealer to see if it may require a different memcal or reprogramming of the computer.
 
  #3  
Old 03-03-03, 03:43 AM
Joe_F
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Waste of time and money. You have to upgrade the brakes, computer, cooling system, suspension, etc, and you can buy a vehcile with the factory 350 already installed for the same if not less money, and have a more reliable vehicle in the long haul .
 
  #4  
Old 03-03-03, 09:08 PM
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reply to joe

Thanks for your advice Joe but why would I have to change so much to swap the engine.
I have swapped bigger engines before and alot of the times the same radiator and fan keeps the engine plenty cool.
And the suspension? Why, a chevy small block 305 weighs the same as a 350 SB.
The computer I can see maybe .
Why would I have to change the brakes also. The brakes are the same on the trucks of this year with a small block engine.
Thanks but can you explain you advice more.
I can get a 350 long block cheap any time around here without spending big bucks on a new truck from GM to do it.
 
  #5  
Old 03-03-03, 09:56 PM
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Well, of course the gas mileage went down, you're pulling more weight. I doubt your mileage will go up with a bigger engine.

If you want easier towing, swap out the gearing in the transmission to a higher ratio (gas mileage will go down even more, or may stay the same).

I don't think bass boats aren't that heavy, not like it's a 25' boston whaler...
 
  #6  
Old 03-04-03, 03:49 AM
Joe_F
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If you swapped like that in the past without at least INVESTIGATING if there are upgrades needed, it was not a proper swap. It was a cobble together job. If the swap is done correctly, you shouldn't be able to tell a thing and neither should the emission inspector--you also might not be doing a legal swap, depending on the state.

If you buy a 350 originally, you get certain parts that are upgraded over the 305, that is why GM includes them. Many 350's have heavy duty cooling, many have larger GVW brakes, different suspensions (depending on the payload), among many other differences. The rears are different as well.

To do it PROPERLY, these things must be investigated. On a stock application, it is cheaper to buy a factory equipped 350. It will be MUCH more reliable than any conversion cobbled together. It's also cheaper.
 
  #7  
Old 03-04-03, 08:03 AM
short_circutz
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Peace guys.....

All I would do in the situation, is replace the differential gears with a slightly lower gear ratio....now...you may want to ask the dealer what implications that will cause, as you may need to find a custom eprom for the computer.
 
  #8  
Old 03-04-03, 09:04 AM
Joe_F
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We run into this all the time in the F body car groups where someone wants to swap a 305 for a 350 in a 3rd generation.

Time and time again, it comes out to be the same: It is more feasible to buy a 350 equipped vehicle or deal with the undersized 305.

This is the same scenario .
 
  #9  
Old 03-04-03, 10:41 AM
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peace

Thanks Joe for your reply. I am only looking for solutions and my thought was that my little 305 was having a hard time pulling my boat and that a 350 would not be straining so much and so be able to get better gas mileage.
I didn't mean to start some kind of argument,you know how it is with typing a message,it's not always easy to express ideas and thoughts without them being misunderstood as being smart aleck.
I will take no offence to you saying "cobbled" as a type of swap I have done in the past because I'm sure you misunderstood my reply to you.
Many succesfull swaps have been done in racing and off road vehicles and the general builds pretty good cars and trucks that can take a little swapping within reason.
thanks.
 
  #10  
Old 03-04-03, 10:49 AM
Joe_F
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Sure. But, those are for non street use. They don't have to meet emission laws and safety requirements differ. Plus, these guys are old hat at doing it. They also can fabricate what they need .

I have done some 350 G body conversions, from 6 cylinder originals to 8 cylinders, etc, etc, etc, and most times the customer didn't realize "It would cost so much". Well, it does ---that is if you want to do it correctly.

Again, unless you understand WHY GM has put certain equipment packages together with certain powertrains, the swap is not fully understood. If you ordered a 350 originally, chances are that means that you'd get a certain, specifice fan clutch, radiator, fan, and other cooling components---and these are likely different part numbers than their 305 counterparts--and with good reason. A 350 might mean a different master cylinder because you have a different GVW braking system now. It might mean you have a different rear end ratio, because the same ratio with a 305 might prove to be a slug paired with a 350. It probably means different springs too---that is done by payload and a bevy of other conditions too.

Can it be done? Sure. Can it be done correctly? Sure, but it involves more than just an engine drop in---doing it correctly.

The F body group is filled with 305 to 350 conversions that are problematic and where the owners have gone WAY over their head over just buying a 350 outright .

My .02.
 
  #11  
Old 03-04-03, 06:02 PM
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Thanks Joe

Thanks alot Joe.
You said you have dealt with Gbodys. Do you hang out at any web sites on G bodys.
 
  #12  
Old 03-04-03, 11:35 PM
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If you really want to do it go to www.advanceadapters.com. You can get a 5.7 with 380Lbs and 390HP. I have used them in the past and have been very pleased with there products. Donít think you would have very many problems putting one. You brakes should be fine for you towing duties. The work fine now, right? They should work after the engine swap. But you will go ware them quicker. The motors form advance adaptors come with a standalone engine control module so you computer problems will not be an issue. Your wiring harness will be different but most of that is an easy fix. With any gas motor you will see a hit in gas mileage when towing, but the larger the motor the less the hit will be. If the motor has to be in the higher RPM range to move the load you will use more gas. In higher RPM ranges most stock motors loose efficient operation. A larger motor will be lower in its RPM range and closer to is optimum RPM. So even though the motor is larger it will be more efficient. The other question is how often do you two the boat? If you tow the boat a lot the swap makes more sense. But if you drive you truck a lot unloaded you will still have lower gas mileage with the larger motor. Dose that make sense? You only gain mileage IF you are towing something.
 
  #13  
Old 03-05-03, 03:57 AM
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Umm, mostly F bodies, but the 305 to 350 conversion is a quandary most people come up against no matter what the body line .

F car, G car, A car, truck, van, etc .

Again, there is more to a swap that dropping in an engine----doing it correctly, safely and efficiently.

We warned the G body guy that he'd have to upgrade things with the very mild 350 he was putting into the Grand Prix. But he was short on cash and trying to cobble things together. That cark always came back on the hook for more work and snapped parts and he paid for the upgrades probably twice over than if he had waited and done it once .
 
  #14  
Old 03-05-03, 10:46 PM
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I swap motors on a daily basis in to all sorts of things they were never intended to go in. I agree there are many issuers to deal with bust most of them are think less things. What type of safety issues are you talking about Joe? I cant think of much. The only thing I can think of for him is that he might need a new torque converter to work with his engine. A transmission cooler might be a good addition if you do not already have one. But, than again a transmission cooler is a good idea on any tow rig.. The truck has a 10bolt axel if it all stock, while not the ultimate in strength I have seen the hold up well under medium loads and off road use. For normal use I donít think it will be a problem
 
  #15  
Old 03-06-03, 03:53 AM
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Simple:

Check a GM Parts Imager/Catalog/Bell and Howell machine.

Look up suspension, cooling, rear end, and electrical parts for the same vehicle with a 305 and a 350. You will find different parts with the 350 applications. When you order a 350 originally, it comes typically with items intended to go with the 350.

Look at the brake booster charts as well as the master cylinder charts, as well as most other listings. They often differ by the engine option. The rear end ratio likely differs on a 350 versus a 305. Your brake parts are chosen on GVW, engine option and RPO "J" brake option. They can differ depending on what is ordered. Would you use brakes intended for a Chevette in a Corvette?

I could go on, but there are differences. Can it be done? Again, yes. Can it be done correctly? Again, yes, but it's more costly than buying a 350 originally already to go. You will not see much difference between a 350 and a 305 if the load of towing is that great.

Again, if you are doing a swap right, you should not be able to tell a 305 from a 350 down to each and every part that is in a 350 against a 305. That is the only way to do a conversion correctly. It's more than an engine swap.
 
  #16  
Old 03-06-03, 04:36 AM
mikejmerritt
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This is only an opinion on this subject so please take it for what its worth. The 305 in a full sized truck is meant to be used mostly for transportation despite what GM would say. I have had many GM trucks, some with 305 and some with the 350. I have always based my decision on the trucks intended use. If I found myself pulling very much and had the "95 with the 305 first I would do as Joe suggests and begin by INVESTIGATING my options. I can't help but think that if you value your time and add the costs into the deal you would be better off to sell the "95 and put all into a truck with a bit more engine but I think the fuel consumption with a 350 would be about the same pulling a light boat as an overworked 305. You could buy a lot of gas, no doubt less every day, with the money spent on the engine swap.....Mike
 

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  #17  
Old 03-07-03, 12:36 AM
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Itís also wise to look at your rescores. It would be lot cheaper for me to swap in a motor then to buy a whole new truck. But I also have the experience and tools for a quick swap. If you have all of the tools and know how to do the job you could save lots of money and trouble this way. But at the same time if you donít have the tools or the experience it could be the worst idea of your life. You could end up with a truck out of service for along time and end up spending a lot of money. I agree that it would not be worth the extra motor if the primary use of the truck would be back and forth to work, especially with gas prices like they are. Sure parts are different between two trucks but I have never seen a 305 to 350 swap that did not work with the stock brake setup and rear-end. At a off road shop I worked for we swapped in Chevrolet Small Blocks in to lots of trucks with minimal problems. Sure it might be a different part but will it do the job just as good? Sure I find lots of things everyday that works better than what the maker put in them. I have seen GM run though 5-10 thermostats in a year all with different part numbers for the same motor. When it bugged us enough to call the GM engineering division to ask about it they told us that any of them would work, itís a supply and cost thing, they were just a little different, but all still function as well. I have seen this same thing over and over with many parts and most of the auto makers I have worked for. I have seen five or six ratios offered in rear ends with the same motor. Some ratios are better for different things than others, but I grantee that a 4:10 pinion will have more power behind a 350 than a 305. We are not talking about dropping a diesel in a Suzuki, it a very similar swap. I guess I look at things a little different than most because I have been building stuff that know one made for along time. I donít worry about part numbers I worry about the part. What makes the two parts different? Will this part do the job? Will a part with a different number do it better? When I was working at dealerships we mostly went with part number for the fact that it took the thinking out of finding the right part and speeded up the process. But if we could not find the right part you could always get out the operating specks and compare them. Part numbers are mostly for people who do not have the time or the education to make an educated decision if a part will fit or work. Can most people do this? Of, course not. But I think itís a huge handicap to only consider ďwell itís not the same we better switch itĒ There is always more than one way to do something right. This brings us right back to the question of the 3Tís (Time, Tools, and Training). If you have all of those it would be easy to do it safely with out major part changes. But if you donít have the 3Tís you are asking for trouble.
 
  #18  
Old 03-07-03, 05:49 AM
Joe_F
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Good advice. However, most of us are not engineers and simply looking at the parts may tell you nothing. Internally they could be different.

It IS cheaper in the long run to buy the truck with the 350 already done up. For instance, in 1979, to buy a 400 in a 10th Anniversary Trans Am like mine, you were talking 90 extra bucks. That's it. You can't find a used 400 intake for 90 bucks anymore. LOL.

To put a good 350 in this truck, you're looking at a grand or more for a decent motor. Then there's the swap of the rear, easily another 500 bucks. You're already up to 2000 by the time you shake a stick. Before long for 3000 bucks or less you can buy a 350 equipped truck ready to go!
 
  #19  
Old 03-07-03, 07:47 AM
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I happen to know that manufacturers share parts across model lines. GM in particular. And yes, that includes major parts, such as brakes, engine pieces, even trim work.

And yep, the part #'s are different, and so are the prices, but the parts are the same.

Like a motorcycle I had. A 250cc, used the SAME clutch plates as a 600cc.. different part #, different price, same plate. The 900cc I have know also shares parts with it's smaller and larger siblings.

Look at the Pontiac Fiero (owned one for 14 years), it was virtually nothing but parts pulled from other GM vehicles at the time. Once you found out what other car it came from, you could order that part, which was often still available, and usually cheaper than the fiero part #..

So, just because it's a different part # doesn't mean it's really a different part.
 
  #20  
Old 03-07-03, 09:47 AM
Joe_F
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Yes it does and no it doesn't . It depends.

305 parts are lighter duty than 350 where the part numbers vary. Period. GM does not want multiple part #s that do the same exact thing in their line. If they did, it would consolidate them to one part.

A 350 equipped vehicle comes with different options, parts and attributes than its 305 counterpart. Otherwise, GM would simply use 305 parts and options with a 350 . This is not the case.

The 1984 to 1987 Fieros shared their suspension with a Chevy Chevette. 1988 was unique. After 1988, the Fiero was no more, GM dropped it.

Most conversions are NOT done properly because most people don't know to consider, or ignore the consideration of what comes along with a 350 engine when you order it. For example, you could not in certain years order a 350 and T-tops in an F body because GM determined that the body could not hold up to the power/torque of a 350 with virtually no roof .

Bottom line: The original poster has varied opinions on the subject and knows what to do/not to do. It's up to him/her to heed the advice presented or not.

Post closed .
 
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