I found a page on here that showed some things to look for to help confirm that a car was a factory 348 car. Dual exhaust, fuel line routing, narrow fan shroud, and no bottom bolt in the voltage regulator. Can anyone describe or show a picture of how the fuel line should be routed so I know what to look for? How to I know which fan shroud I have? Also does anyone know of any other things to look for? Which gears should be in the car? I found information somewhere telling what gears should be in a car for certain engine combinations but can't find it now. This car has a 348 tri power that I originally thought all checked out but now I'm growing suspicious that it was installed later. Please excuse my ignorance as this is the first 50's car I've tried to date match. Muscle cars are easy, nearly everything you need is on the tag. These things leave you guessing on a lot of things.
How to tell if 58 Impala was factory 348 car??
- Thread starter jercars
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ragtp66
Well Known Member
The fuel line is not a good indicator as the 283 with dual exhaust or any hp 348 engine would have come with the 3/8" fuel line and on a 58 it is very easy to spot as it jumps from just behind the passenger side upper control arm over to the backside of the rocker panel then back over to the frame around the area of the rear lower control arm front attaching point to the frame. Single exhaust cars it ran parallel to the brake line right down the drive shaft tunnel. The shroud may or may not be original and could have easily been changed along the way. The voltage regulator bottom being attached by a grommet instead of a screw was either a TSB or a running line I change I forgot which one. The one way to tell is follow the wiring harness back up from the starter, if there is a connector along the firewall (and has not had the wiring changed) then it was most likely born a 348 car the 283 engine did not have the connector and would have just been all wiring to where it passes through the firewall. Standard gear ratio I believe would have been 3:36. If you look at the drivers side of the rear differential housing (pig,pumpkin whatever you want to call it) see if there is a tall skinny capital P next to the numbers if it is you have a posi rear end although it could have been ordered with almost any engine combination. There is a emblem that goes on the dash near the clock that says positraction but they can be added easily. Post up some pictures carbs on a 58 tripower are specific to 58 also the fuel inlets point to the front of the car 59-61 point to the passenger side.
Alright I checked and the fuel line is right and it does have the connector on the starter wires on the firewall way up by the coil. However the voltage regulator has a screw in the bottom that matches the 2 on the top and appears that's it's all original. Forgot to mention before that this is a Turboglide car and I thought I saw somewhere that those came with a 3.08 gear and this one appears to have a non-posi 3.36 (rolling the tires and counting driveshaft revolutions). I took a pic of the fan shroud while I was at it and maybe you can tell me which one I have. Also I took one of the cowl tag to see what you can tell from it. The carb numbers match up to all the other stuff I've read but I'll let you take a look and see if anything jumps out at you.
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'59Imp
Well Known Member
The fan shroud is correct for the big block(348), as the small block one is larger. The radiator looks to be correct for the big block too. As for the transmission, I don't know for sure on this, but I don't think Chevy would put the 348 and Turboglide together in one package. The Turboglide's got a bad rap that they don't hold up well to the 348. On my 59 Impala, I'm running the Turboglide tranny on the 348, original to car motor, but not original to car tranny, as it originally had a 3 on the tree. It has the single 4 barrel, 250 hp, and the tranny has slipped every now and then under load. I'm not staying with this tranny. Another note on this tranny, I'm sure you already know this, but don't think that the "GR" is also a low gear, its only use is like the name suggests, a Grade Retarder.
ragtp66
Well Known Member
Tripower was only available with Turboglide auto or 3speed manual. Powerglide and tripower was not an option. The suffix on the engine pad stamping on the passenger side just forward of the cylinder head should confirm the transmission code FA-3x2 with manual trans 280 hp FB-3x2 with manual trans and 315 hp solid lifters. HA-3x2 with turboglide auto 280hp. Your trim code says interior was grey, black, turquoise and body color onyx black is that correct? As Cecil mentioned something is amiss if your vin is lower then mine but your body number is higher. Was your Vin tag attached with rivets or spotwelds? The firewall tag rivets look correct, sometimes they are filled with some type of sealer/putty but someone might have cleaned it out prior to painting. If the car still has its original springs you might be able to find some of the paint stripes on the coils and that would give more clues.
Lt.FrankDrebin
Well Known Member
From what I can see, your '58 is a factory 348. It's got one of the two shallow fan shrouds and you said it has a starter harness with the connector on the firewall. The only automatic transmission used with the 348 3x2 was the Turboglide, so that also checks. I believe the 348 3x2 came only with dual exhaust, which would mean it should have the 3/8" fuel line. Rear gear ratio was determined mostly by the transmission, and with the Turboglide, I believe the rear would be a 3.36. How well does your car run? I'm curious if you ever "run out of vacuum" while the secondary carbs are open. The carbs' vacuum system should either be tied into the fuel pump, as with earlier '58s, or have a vacuum tank with a 3/8" hose running from it to a check valve on the back of the center carburetor.
What's the suffix code on the engine pad? Turboglide with 348 is very common. Two letter suffix will begin with H on TG engines. 280 hp 3x2 would be HA.
The standard ratio on automatic cars was 3:36, 3:55 on standard trans. PG was only available on 348 with 250 hp engine.
The VR mounting change was a running change in production. Don't recall exactly when it was effected but yours could be early enough to have the 3 bolt mounting.
Many Questions can be answered with just a little research.
1958 Chevrolet
The standard ratio on automatic cars was 3:36, 3:55 on standard trans. PG was only available on 348 with 250 hp engine.
The VR mounting change was a running change in production. Don't recall exactly when it was effected but yours could be early enough to have the 3 bolt mounting.
Many Questions can be answered with just a little research.
1958 Chevrolet
This is an HA block so that checks out with this being a 3x2 TG car. However that may be a coincidence since I'm questioning if it's the original block. There are some inconsistencies with the motor as far as dates go. I will put a picture of a paper with all the numbers. The rear end isn't on the sheet but it is dated A318. As far as the 3x2 only being on a turbo glide I've read that a lot of places but there is a suffix in the list on this page (I copied it below) that shows a 280HP 348 with powerglide but 4bbl was only 250HP. Perhaps it was issued a code but was never actually made a available? The vin plate didn't appear to have anything wrong with it but I will take a look again. Also with the VIN I know the first unit was 100001 but what date would that have started? January 1st or would it have been in late 57 when the 58's first started production? The interior and paint match the cowl tag. It's funny Frank mentioned the carbs because currently the end carbs are not opening and that's another thing I haven't been able to solve. I've been through all 3 carbs and it runs great but the secondaries don't even budge. I even put a camera and a light under the hood to watch. Vacuum gauge is reading 18 and in the shop I can hold it half throttle and hit the button and they pop right open. However out on the road they don't do anything.
GB 1958-60 Pass. Car 280HP 348 V8 Powerglide
GB 1958-60 Pass. Car 280HP 348 V8 Powerglide
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Lt.FrankDrebin
Well Known Member
Yeah, you need to have a better vacuum supply to operate the secondary carburetors. Earlier '58s used a vacuum pump that was part of the fuel pump. A line went from the back of the center carb to the vacuum pump and a second line went from the vacuum pump to the slider switch. Later '58s and on up to '61 used a check valve at the back of the center carb and a vacuum reservoir (same tank as for power brakes). With your current setup, you don't have enough vacuum supply to properly operate the secondaries, especially since vacuum drops significantly as soon as the engine come off of idle. IMO, the later vacuum system is the way to go because you're not wasting energy on a vacuum pump when vacuum is already available naturally by engine operation.
You most likely just solved my problem. I've questioned for a while if there was something missing. Currently it's hooked up directly to the port on the back of the center carb the way I got it. I've wondered for quite a while how vacuum can pull the secondaries open during acceleration when the vacuum drops during acceleration.
This is my first dance with a multi carb setup so I'm learning. I've tried to research this several times but as typical with internet I can find everything except what I actually want. I've already found a correct NOS pump for it but by chance do you know where I can see a diagram or a good picture so I can see exactly how the lines are suppose to be routed?
"It's so much easier to get when you're going when you start moving in the right direction"
This is my first dance with a multi carb setup so I'm learning. I've tried to research this several times but as typical with internet I can find everything except what I actually want. I've already found a correct NOS pump for it but by chance do you know where I can see a diagram or a good picture so I can see exactly how the lines are suppose to be routed?"It's so much easier to get when you're going when you start moving in the right direction"
Lt.FrankDrebin
Well Known Member
You can catch a glimpse of the vacuum lines in the 1958 Shop manual. I think these metal lines are available as repros. Both ends of both lines attach to their respective nipples by short pieces of rubber hose. Make sure you have the correct line attached to the correct nipple on the vacuum pump. The nipple where there is vacuum pull goes to the slider switch.
Alright things are finally starting to make a lot more sense. Since mine is an early car and does not have the vacuum tank it appears that it should have the fuel pump vacuum source. Should there be a special valve of some sort on the back of the center carb or just a plane nipple?
Lt.FrankDrebin
Well Known Member
I'm not certain on that, but I don't think it's a check valve; more of a plain nipple. To see a good picture of the lower end of the vacuum lines near the vacuum pump, do a Google search for '1958 Impala Convertible 348 tri-power'. There's an underhood pic of a nice black '58.
Alright lots of problems getting solved. What about the date codes on the motor? It looks like the block and intake can't be right but what about the heads? Is it possible that two heads casted 2 weeks apart could have been put on the same motor or should those be a same day pair? Can anyone shed any light light? Also still curious when the first VIN number 100001 is produced....Jan 1st or in late 57 when the 58's began production?
The vin is for the production year,not the calander year.Typically the new cars would be ready for opening shows by September.Usually during the month of June,the plant would "re-tool" for the next model year.Production would start in late July.As to your heads,two weeks apart from the block is good,no worries there.All the "Dual diaphragm" style fuel pumps are of the booster varity,meaning that one sise of the pump gets engine vacuum,and the pump then boosts it up to a more stable condition to work the wipers and other things under acceleration,or a long hill.Fine for a show car,sucks on the street.The person who said to look up a diagram or pictures is spot on.
Maybe I misread his dates but the heads are almost 4 months away from the block which a matching number motor normally would not be that far apart.
Right, and the heads are January. Too far apart. Chances are components have been replaced.
The car is what it is. you'll never prove any thing with dates and such. Only orig docs would prove it. BUT it is what it is-a very very nice car. Drive and enjoy
ragtp66
Well Known Member
My heads are jan 20 and jan 29 and are also 791's I was wondering if maybe why your block is from may could it have been a warranty replacement? But if that were the case I would think the intake should be around the head dates not the block. Not sure if they would have replaced a short block. Although I would have thought by May the block would have the cooling holes which would have needed different heads. Would a warranty block have the turbo glide stamp or the CE suffix like later blocks? Last since both our cars are model 1847's hard tops and not convt which would be 1867's that still leaves the vin and fisher body discrepancy. One other date code I forgot was on the glass if you still have original glass.