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Why upgrade to a late model Denso alternator?
Just becuz we can, mang!
|The Great Nippondenso Alternator Swap (on a small block MoPar)|
Hi folks. I'm not going to go into too much detail about why this should be done. If you've found your way to this page, you probably already understand the benefits of having a newer late-model higher amperage Nippondenso alternator under the hood and all you wanna know is how it's done. It's a relatively bolt-on project. The particulars of this article will specifically cover the installation of a 90amp Nippondenso, originally from a 1992 Dodge Dakota, on my non-AC, 1968 318 LA small block with factory water pump and factory iron heads.
This Denso is externally regulated and has 2 FLD terminals, just like the squareback style MoPar alternator it's replacing. Because of this, you can keep your voltage regulator and just make the same three connections at the back of the alternator without a special alternator plug, making it as "bolt-on" as possible without any real major modification to existing wiring OR mounting bracketry. Should I want to re-install the original style round/squareback alternator for any reason, I would be able to do so with very little effort.
List of minor modifications:
- The late model Denso will likely have a serpentine belt pulley; a new V-belt pulley will need to be installed to run the old belt; alternator rebuild shops typically have these lying around and they should be able to furnish you with a cheap GM pulley that fits.
- The new V-belt pulley will need to be held in place with a nut: 14mm 1.5in thread.
- A new V-belt may be needed; on my particular 1968 LA smallblock, I was able to re-use the factory alternator belt for a non-AC car. You may need a replacement belt measuring somewhere between 44" to 48" inches. See chart below for Dayco belt lengths and corresponding part numbers.
- New alternator bushings/spacers will be needed which sleeve the bolt that holds the Denso to the cylinder head. Cutting these spacers to the right length might prove to be the most time consuming part of this swap. A lathe is quite useful here, but a hacksaw, vise and handfiles will work equally as well. Because bushings are typically installed through the second mounting ear on the alternator, spacer length between the second ear and the cylinder head may differ. Assuming you press or knock the spacer out, find the optimal dimension from the front of the cylinder head to the back of the second mounting ear. Have enough clearance to maintain some belt alignment while having enough to clear the BATT output stud from the cylinder head (to avoid creating a short circuit). Note that in the photo, I chose to retain the bushing and compensate for correct clearance by having the correct length spacer made and cut (yes those are spare nuts I had lying around). This is the trickiest part of this whole project.
- Lower mounting bracket extension: the factory lower mounting bracket turns out to be too short to be used with the Denso. A cheap chrome Spectre brand Chevy alternator bracket (part 42263) was procured and the curved, slotted section was cut off. This new slotted piece is fastened to the end of the factory bracket with (2) nuts and bolts. Alternatively you can change out the lower bracket altogether, but I wanted to do as little removal as possible of factory parts so that the old alternator will still drop back in with the least amount of work. (I also wanted to avoid removing the lower bracket mounting stud due to the fact that this stud penetrates into the water jacket of the water pump. The last time I removed this bolt, coolant came rushing out.)
- Added a new nut and bolt to secure alternator to lower bracket to adjust belt tension. Self explanatory: the factory alt has a threaded hole in the front case which accepts a bolt for adjusting belt tension; the new Denso does not.
- Trimmed the alternator output stud (and it's protective plastic housing) to clear the cylinder head. Reduced height of the stud and plastic housing to about half. An additional plastic insulator was added to cover the BATT output stud in the rear to prevent an accidental short circuit between stud and cylinder head.
- New 8g charge wire (w/12g fusible link) was run directly from the alternator output stud to the POS (+) battery terminal. This extra wire serves to offload the extra amperage, now afforded by the new Denso, from burning up existing wiring going through the bulkhead connector. Do not perform this or any other alternator upgrade without adding this new charge wire or you will run the risk of starting an electrical fire trying to pass higher amperage current through factory wiring designed originally to handle 40amps. This new charge wire will of course render your factory dash ammeter useless as the majority of current will new use this fatter wire to reach the battery and power your car, but it is a small price to pay for the added electrical convenience. For extra credit, reach back behind the dash cluster, find the two wires running the ammeter, disconnect one wire from its' post, slide it over the other post and secure both wires to the same post. This effectively takes the ammeter (one of the weakest links in the Chrysler electrical system) out of the equation. READ AGAIN:
VERY IMPORTANT: In it's stock form, your existing MoPar WIRING WILL NOT BE ABLE TO HANDLE THE HIGH AMPERAGE generated by a 90A or higher Denso alternator. If this is your first attempt at upgrading from a stock MoPar alternator (ie stock = 35amp or 40amp), YOU WILL NEED TO UPGRADE YOUR CHARGE WIRE as well.
To upgrade your charge wire, you essentially run a fat gauge wire right from the output terminal on the Denso to the positive battery terminal (or to the starter relay). What gauge wire you pick however, will be determined by the alternator you choose to install. For example, a fat 4gauge charge wire will handle just about any amperage up to 150amps. If you are running the 90amp Denso, an 8gauge wire will suffice.
As a sidebar, there is the question of how to properly fuse and protect this charge wire. The advice I got from a knowledgable fellow at a local alternator rebuild shop was essentially that I didn't need a fuse. So long as you ran charge wires rated higher than the amperage your alternator could possibly put out AND you insured that wire would not short, you were safe.
For my 90amp Denso, I've been running an 8gauge wire protected by a 12gauge fusible link. This is a street driven car and I haven't had any issues so far driving it regularly on the weekends for the past year now. Eventually I will install a 4gauge wire run from the Denso to the battery without a fuse or fusible link (since the 4gauge is rated up to 150amps). Here's a good chart i done borrowed right off the internets detailing various common wire guages and their amperage ratings:
Items to note:
- A smallblock (SB) MoPar 318cid LA engine mounted in a 1968 Dodge B-Body was used for this project. Conceivably, the following information may apply to a wide range of MoPars which are powered by an LA series smallblock 318/340/360. Note however, that the water pumps installed on 1969 and earlier smallblocks differ from 1970 and later units. As such, the alternator mounting bracketry will vary slightly causing dimensions and distances between the back of the alternator and the front of the passenger side cylinder head to be different. All information presented here is based on the mounting dimensions available for a 1968 SB utilizing a 1968 water pump. 1970 and later style dimensions will differ; not by all that much, but they will differ. I have seen this install performed on a smallblock with a 1970 style water pump and if anything, it would appear the '70 style pump and bracketry offers more clearance from the cylinder head as well as better pulley alignment; but this is just my observation.
- The original external voltage regulator was retained during this swap. Note that while the engine is 1968 vintage, the charging system is based on the 1970-and-later design. All this means is that a transistorized voltage regulator (VR) is used and the wiring has been slightly modified to utilize the '70 style VR. You might note this discrepancy in the photos, so this is being mentioned to avoid confusion as to what has been done. You can read more about the subtle differences between a 1968 charging system versus one that is 1970 and later by clicking here.
Part numbers for other externally regulated high amp Denso alternators:
LESTER Partnum: 13256,13312 : 90amp, w/dual V-belt pulley
*15470 belt is OEM for 1968 LA engine without AC
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