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Stock 360 output

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WesternRed View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote WesternRed Quote  Post ReplyReply Direct Link To This Post Topic: Stock 360 output
    Posted: Dec/06/2017 at 2:54am
Just curious about the figures for 71 vs 72 360 4 barrel engines, both are said to have 8.5 compression.

71 285 HP @ 4800 Gross
72 195 HP @ 4400 Net

I'm well aware that the rating system changed from gross to net HP, which accounts for most of the HP difference. I'm more interested in the accompanying drop in RPM at the peak. Do the accessories suck that much horsepower at high RPM that the peak RPM drops or are there other factors at play.

I'm trying to figure out what I can expect out of the 360 in my Gremlin which as far as I know is a 71 4 barrel engine and I expect fairly stock other than a performer intake. Presumably some horsepower's have also escaped the stable over the years. I really don't have any history on the motor other than it came out of my 71 P Code AMX.

It's hooked up to a 727 via a custom convertor (flat crank engine) and I have an AMC 20 with 4.1 gears in the rear.

Ran at the strip last week with 24.5" tyres and had 88 mph across the line, which works out to be roughly 5000 RPM (didn't have a tacho in the car at the time). Accessories at the moment are the alternator, water pump and factory flex fan.

Based on the 72 peak at 4400 RPM, I'm probably pushing it well beyond optimum RPM.

Heading back tonight with some 26" slicks on the back, which should help with traction and bring the terminal RPMs down a little, so I will have some more data shortly.

Just trying to gauge what would be reasonable to expect from this combo to know if I am on the right track.
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WesternRed View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote WesternRed Quote  Post ReplyReply Direct Link To This Post Posted: Dec/06/2017 at 9:28am
Update with the 26" slicks, I am crossing the line at just short of 5000 RPM on the newly installed tacho as expected. The best ET was 16.07 @ 91.22 MPH, race weight with driver was 3073.

Biggest problem is 60' times in the 2.6-2.8 second range, not exactly what I would have expected from 4.10 gears, it's just got nothing off the line, so I'm assuming I have a problem somewhere.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Sonic Silver Quote  Post ReplyReply Direct Link To This Post Posted: Dec/06/2017 at 9:50am
Originally posted by WesternRed WesternRed wrote:

Just curious about the figures for 71 vs 72 360 4 barrel engines, both are said to have 8.5 compression.

71 285 HP @ 4800 Gross
72 195 HP @ 4400 Net

I'm well aware that the rating system changed from gross to net HP, which accounts for most of the HP difference. I'm more interested in the accompanying drop in RPM at the peak. Do the accessories suck that much horsepower at high RPM that the peak RPM drops or are there other factors at play.

I'm trying to figure out what I can expect out of the 360 in my Gremlin which as far as I know is a 71 4 barrel engine and I expect fairly stock other than a performer intake. Presumably some horsepower's have also escaped the stable over the years. I really don't have any history on the motor other than it came out of my 71 P Code AMX.

It's hooked up to a 727 via a custom convertor (flat crank engine) and I have an AMC 20 with 4.1 gears in the rear.

Ran at the strip last week with 24.5" tyres and had 88 mph across the line, which works out to be roughly 5000 RPM (didn't have a tacho in the car at the time). Accessories at the moment are the alternator, water pump and factory flex fan.

Based on the 72 peak at 4400 RPM, I'm probably pushing it well beyond optimum RPM.

Heading back tonight with some 26" slicks on the back, which should help with traction and bring the terminal RPMs down a little, so I will have some more data shortly.

Just trying to gauge what would be reasonable to expect from this combo to know if I am on the right track.
The difference is that the correct rating for a 72 model 4 barrel 360 was 220 hp with dual exhaust. The 195 figure was for single exhaust. The net versus gross rating is the difference between 285 and 220.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote WesternRed Quote  Post ReplyReply Direct Link To This Post Posted: Dec/06/2017 at 5:37pm
Well that makes sense, presumably that is choking off peak RPM too.

My mph suggests around 180 horses are still in the barn.

Now I just have to figure out why I can’t get it off the line. Convertir problem perhaps, it’s a bit of an unknown, foot on the brake it will rev to around 1500.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Sonic Silver Quote  Post ReplyReply Direct Link To This Post Posted: Dec/06/2017 at 7:44pm
One thing that I noticed in old car magazine tests from the 1970 era was that I remember 2 or possibly 3 tests of AMC's with 3.91 gears. The first was a 70 Javelin SST 360- 4 speed in Car Life magazine that ran a 15.46 at 91.09 mph. The 2nd was a 73 Jav/AMX with a 401/4 speed that ran a 15.4 at 92 mph. I believe the magazine was Road Test.

   The 3rd (also Road Test Magazine I think) was a Rebel Machine with a 4 speed, and I am pretty sure it had 3.91 gears. I don't remember the exact times, but it seems like it ran mid/high 14's at about 92 . I don't remember ever seeing a magazine test with a good 1/4 mile time or mph out of a factory stock AMC car with high numerical gears. I realize it was just 3 tests, and driver, track conditions, weather, altitude, etc. make a significant difference.

   Popular Hot Rodding tested a 70 AMX with a 360 /4 speed and 3.54 posi. They said that their best times (14.90 at 94.63 mph) came by shifting early to where the rpm dropped back to the point where it made peak torque (around 3,300-3400 rpm). They dropped their times down by shifting out of 1st and 2nd at 4,200  rpm, and shifting from 3rd to 4th at 4,500 rpm. The rpm would drop back about 20% from 1st to 2nd and 2nd to 3rd, and about 25% from 3rd to 4th. Remember, these cars were all factory stock with exhaust manifolds, stock cam, tires, carb, exhaust, smog, etc. in all these tests.

   


Edited by Sonic Silver - Dec/06/2017 at 7:58pm
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xtrememotorworks View Drop Down
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Post Options Post Options   Thanks (1) Thanks(1)   Quote xtrememotorworks Quote  Post ReplyReply Direct Link To This Post Posted: Dec/06/2017 at 8:06pm
That 60ft is killing you, my wifes 5.0 with some 2.73 is slow with a 2.19. is it falling on its face? Cutting out?

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Post Options Post Options   Thanks (0) Thanks(0)   Quote xtrememotorworks Quote  Post ReplyReply Direct Link To This Post Posted: Dec/06/2017 at 8:19pm
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Sonic Silver View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Sonic Silver Quote  Post ReplyReply Direct Link To This Post Posted: Dec/06/2017 at 8:47pm
Originally posted by xtrememotorworks xtrememotorworks wrote:

That 60ft is killing you, my wifes 5.0 with some 2.73 is slow with a 2.19. is it falling on its face? Cutting out?

I agree with that, and I know that Gremlins are traction challenged, but that 60 is really slow.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote WesternRed Quote  Post ReplyReply Direct Link To This Post Posted: Dec/06/2017 at 9:46pm
I doesn't seem to stumble off the line, not spinning the tyres either, it's more like taking off with the handbrake on, just seems to take a while to wind up.

Based on your road test numbers Sonic, I should still be well into the 15's if not 14's with the lighter Gremlin body.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Sonic Silver Quote  Post ReplyReply Direct Link To This Post Posted: Dec/06/2017 at 9:59pm
Originally posted by WesternRed WesternRed wrote:

I doesn't seem to stumble off the line, not spinning the tyres either, it's more like taking off with the handbrake on, just seems to take a while to wind up.

Based on your road test numbers Sonic, I should still be well into the 15's if not 14's with the lighter Gremlin body.
You should be. Could be a number of things.
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