Butler

I've run into a snag on the 20B project. I'm running an MSD alternator 160amp and am not charging enough. I have a Unorthodox main drive pulley at about 97mm in diameter. The MSD stock pulley is 52mm and MSD recommends a 3:1 ratio. I'm running a TEC3R for my computer and ignition. The easy answer is to find a smaller alternator pulley at about 32mm in diameter which is unlikely to fit the alternator. Option 2 is to get a bigger main drive pulley. The stock 20B pulley is only about 115mm, so even with that, I'd be under the ratio needed.

After all that verbage, my question is maybe should I just go with a different alternator all together? My friend with his 20B is having some charging issues with his TEC and a 200-240amp alternator, so I'm wondering what you guys with functional 20Bs are running and how many amps? Should I try a high output 300-350amp kind of deal? All input appreciated greatly to get my money pit running consistently and well.

Thanks,
Aaron

MrRx

iTrader: (1)

If you wanted to go with the smaller pulley answer, all you would have to do is get a machine shop to make you one so you wouldent have to worry about the fit. It might be more expensive than getting a different alternator. I know you can get a 200A at idle alt for the FD, but I cant find any of the links.

there is even A online machining service were to design the part and they make it and send it to you.

Butler

You're right about having it custom made. The problem is it will likely cost more than the new alternator, and to get the alternator down to the 33mm range will make it unlikely to be able to get a nut in it to anchor to the drive shaft of the alternator.

t-von

iTrader: (8)

Most guys here run the stock 90 amp 20b alternator or the 100 amp fd alternator. Not sure why your having this kind of problem. Have you checked to make sure your alternator is putting out the correct amps?

Butler

We need to check the amps output, but it really looks like an underdrive issue. Once I'm up to 1500K plus on the rpms, then everything is fine. Under that and it's a direct drain on the battery. If the battery is externally charged, then we run fine at low rpms for awhile until the battery runs down. I talked with my builder again and we're going to try to downsize the alternator pulley by 12-15 mm and upsize the main drive back to closer to stock size or a little bigger to see if that does the trick. To be continued.............

Turbo 3

iTrader: (3)

The amps check out fine, that's why we both know what outputs they are doing so that is not the issue. Mine is only having a voltage dip when at idle, after it has been warmed up and all the fans, are running. Then it dips from 14V down to about 12.9 and the idle fluctuates correspondingly down to about 500rpms and then dies. I have other issues as well so that may not be the root cause but a secondary effect. I found that when I apply a battery charger at 2A the idle gets better but still fluctuates a bit and when I apply 40A the idle is rock smooth at 850 and the voltage stable at 14.

Butler's issue is that he is not maintaining a charge on his battery, i.e., the alternator is not charging the system, only supplying enough at idle to run everything.

Turbo 3

iTrader: (3)

Oh, and Butler's car is not on the road yet, just going through starting and building a base map so there is no data on after it's been running and accessories are on, etc.

We may indeed need to change alternator pulley sizes through a machine shop although shopping around may be the answer for cost effectiveness...

MrRx

iTrader: (1)

http://www.emachineshop.com/

design the pulleys in their cad software and they will make them for you. Its pretty reasonable.

onefastrx7turbo

iTrader: (5)

it was posted above, but im wondering too. why not run the FD 100amp alternator? it should be enough to run the iginition, fuel pump(s) and fan(s)?


neil

Turbo 3

iTrader: (3)

Because he has a 1 wire system (as do I) and none of the stock wiring is left on either of ours in the engine bay. Plus, why would you reverse engineer back to stock when the hardware works, it justs needs a little tweaking? Not to mention brackets, idler pulleys are different now, etc.

And to answer your question, no, it's not enough to run the fans. You guys are assuming a small amp load and you have no idea what either of us have for load on our systems. 100A is not nearly enough for peak load.

Thanks for the emachineshop link, appreciate it.

onefastrx7turbo

iTrader: (5)

ok, sorry turbo 3. I didnt mean to insult you. me and sillbeer are both using the stock fd alternators and it runs fine. granted, our fans dont run 100% and the fuel pumps draw minimal amperage. stock is workin for us, thats why
I asked.


neil

IronMdnX

iTrader: (1)

Stock FD alt here. MY fans runs most of the time on high, and twin fuel pumps. No issues at idle, even with the headlights and blower fan on high. I run the FD main pulley, underdrive water pump and alt pullies.

sillbeer

Actually my car ran fine with the stock 90 amp cosmo alternator when I was in Japan. I had a single 16" perma cool fan that ran constant, 3 bosch fuel pumps, 11 gauges, ignition box, etc.... Even with the lights on at night it was fine.

-Destin

Turbo 3

iTrader: (3)

Let me clarify a little, you guys are all running stock pulleys it sounds like as well as near OEM electrical loads and this is not the case with either of us so that's why we went with bigger alternator's in the first place as well as most of our pulley's are modified, removed, etc. My point is that you can't compare the two setups as they are not identical but we do appreciate the information. It confirms what we were thinking from the start anyhow. At this point the discussion is moot, pulleys are going to be modified and get some data on the results as to the outcome.

That's interesting from Ironmdnx...so you are running all underdrive pulleys on both water and alternator? That is most likely the problem with But's is that he has a normal alt. pulley and an underdrive water. Mine is the opposite; running a normal sized main pulley and alt. but probably need a smaller alt. to spin it faster at idle, other than that mine is fine at anything but idle.

Sillbeer; interesting to see what your amp load was both at peak and continuous. My bet is that while working, it was undersized.

Our goal is to run everything not at the "acceptable" or ragged edge level but within enough extra available so that in the event of future loads, etc, there is capacity available in addition to not running it hard, but steady at light to medium load.

sillbeer

Thats what I got the first time I read this was that there was an issue with the sizing of the pulleys that are being ran. If it matters mine are all stock. Water pump, alternator, and crank.

-Destin

RotorMotor

iTrader: (5)

sorry to get off topic a bit.... but, are you positive the FD alt. is 10 amps more than the 20b alternator? the 20b alt is HUGE in comparison to the FD unit.... is the FD unit just that much more efficient? if this really is the case then it saves me a big headache as the alternator was the one thing that ive been worried about (as im switching all of the other accesories over to FD ones). sorry to digress... please resume. -heath

t-von

iTrader: (8)

I'm positive it's 100 amps. It says so on the alternator itself. I was shocked also. Go out and look at it.

onefastrx7turbo

iTrader: (5)

yup. T-von is correct. the 20B alt is only 90amps, where the FD is a mere 10 amps more.


neil