|
Sponsored Links (Register now to hide all advertisements) |
|
|
Thread Tools | Display Modes |
01-20-2016, 08:44 PM | #1 |
Member
Join Date: Feb 2012
Posts: 95
|
Normal compression on a T... high altitude makes a difference?
Hi:
Today we checked compression on my 1923 model T. Pistons 1 and 2 showed 40 lbs both cold or hot, while pistons 3 and 4 showed 35 pounds cold and 40 hot. Is this normal? I live at an altitude of 1.5 miles, if that makes any difference. Thanks! Victor |
01-20-2016, 10:44 PM | #2 |
Senior Member
Join Date: May 2010
Location: Portland OR
Posts: 6,361
|
Re: Normal compression on a T... high altitude makes a difference?
You might try finding a conversion chart that tell you the differences. 35 and 40 at sea level would be on the low side, maybe time for rings and valve job. The 2ed entry on the jeep forum gives a conversion chart.
From a jeep forum; http://www.jeepforum.com/forum/f8/at...esting-722504/ General Google search; https://www.google.com/search?newwin...w=1280&bih=844 |
Sponsored Links (Register now to hide all advertisements) |
|
01-21-2016, 11:56 AM | #3 |
Member
Join Date: Feb 2012
Posts: 95
|
Re: Normal compression on a T... high altitude makes a difference?
Thanks!
So, according to a table I found at your links: Compression Test Altitude Compensation Factors Altitude Factor 500 0.987 1500 0.960 2500 0.933 3500 0.907 4500 0.880 5500 0.853 6500 0.826 7500 0.800 8500 0.773 If I live at around 6000 feet, if I understand correctly I would have a factor of 0.840, which would mean that my engine at sea level when hot would now have 47 lbs of compression. What is the compression it is supossed to have at sea level? I want to find out how far I am from what my engine should have... Thanks, Victor |
01-21-2016, 11:35 PM | #4 |
Senior Member
Join Date: May 2010
Location: Portland OR
Posts: 6,361
|
Re: Normal compression on a T... high altitude makes a difference?
Around 50-55 range for a stock engine in good shape at about sea level.
|
01-22-2016, 08:37 PM | #5 |
Member
Join Date: Feb 2012
Posts: 95
|
Re: Normal compression on a T... high altitude makes a difference?
So, if my equivalent at sea level is 47 pounds and a good engine should be 50-55... should I really be considering doing rings or valves?
I don't want to question an expert's opinion, just wanting to learn if doing it would mean a noticeable increase in power. Thanks! victor |
01-22-2016, 09:26 PM | #6 |
Member
Join Date: Feb 2012
Posts: 95
|
Re: Normal compression on a T... high altitude makes a difference?
Sponsored Links (Register now to hide all advertisements)
Here is the video: https://www.youtube.com/watch?v=gDDgcx0sqRM Thanks, victor |
01-23-2016, 09:47 AM | #7 |
Senior Member
Join Date: May 2010
Location: Tulsa OK
Posts: 476
|
Re: Normal compression on a T... high altitude makes a difference?
Your altitude of 10,000 feet makes a big difference in the car's performance. Your cold cranking pressure measurements (not compression) are normal for that altitude. As you have demonstrated, the cold cranking pressure is down 20% compared to what would be normal at sea level.
You should install a high compression cylinder head, available from any of the T part vendors. Then your car will perform better.
__________________
1910 Touring 1914 Touring 1915 Touring 1917 Torpedo Runabout |
01-24-2016, 12:58 PM | #8 |
Member
Join Date: Feb 2012
Posts: 95
|
Re: Normal compression on a T... high altitude makes a difference?
Thanks! I will look into that. I have talked with my friend that knows T's down here and he suggested starting with changing transmission bands to Kevlar, as the car has a hard time breaking and the high speed is far from outstanding... I will see how much that improves the car's movement, and if not I will consider the high compression head and doing valves and rings.
Victor |
01-25-2016, 04:40 PM | #9 |
Senior Member
Join Date: May 2010
Location: Tulsa OK
Posts: 476
|
Re: Normal compression on a T... high altitude makes a difference?
The bands do not have anything to do with high speed (direct drive). Braking, reverse, and low speed yes. If they are adjusted too tight they can make the car overheat and accelerate slowly.
__________________
1910 Touring 1914 Touring 1915 Touring 1917 Torpedo Runabout |
01-25-2016, 05:21 PM | #10 |
Member
Join Date: Feb 2012
Posts: 95
|
Re: Normal compression on a T... high altitude makes a difference?
Mmmm... that's a tough blow. I was hoping it could have to do something with the lack of power in high. Anyhow I am going to order the Kevlar bands as the car right now brakes almost nothing.
And I will have to look carefully into determining wether I need to do the engine or not. What puzzles me is that the engine is not smoking... One question which has nothing to do with it, but perhaps I will save everybody reading a new post if I can find the answer here: Were T's in 1922 supposed to have the rubber pedal covers? Thanks! Victor |
01-26-2016, 09:01 AM | #11 |
Senior Member
Join Date: Apr 2012
Location: Parkerfield KS
Posts: 526
|
Re: Normal compression on a T... high altitude makes a difference?
It depends on what the meaning of "supposed to" is. Rubber pedal pads didn't come with the car, but are a period aftermarket accessory.
|
01-26-2016, 09:21 AM | #12 |
Senior Member
Join Date: Sep 2010
Location: Toms River N.J.
Posts: 515
|
Re: Normal compression on a T... high altitude makes a difference?
5 Lbs. is a jump for a low comp. engine but it's there so it's probably the result of expansion/heat. Rings do this but if a short warm-up evens it out just drive. As to the performance issue: long dragged out inclines are not what the T wants on a good day. There might not be much you can do without spending $. Re-build, high comp head, on & on. 40 isn't the best but not worst either. I'm saying a re-build might not be worth the $ performance wise.
|
01-26-2016, 11:17 AM | #13 |
Senior Member
Join Date: May 2010
Location: now Kuna, Idaho
Posts: 3,791
|
Re: Normal compression on a T... high altitude makes a difference?
OK: Compression test is normal for your altitude, so even a complete engine rebuild will not help the low power situation. In fact, it will make it worse for awhile as a rebuilt engine will have significantly more internal friction, and any power gained will be lost. You can advance the timing more at high altitudes to somewhat compensate for the slower burning fuel mixture, and you need to lean out the fuel mixture to somewhat compensate for the reduced oxygen level reaching the cylinders.
BUT, you cannot get around the need for more compression! Best advice is a high compression head. |
01-26-2016, 12:24 PM | #14 |
Senior Member
Join Date: May 2010
Location: Lehighton Pa
Posts: 1,085
|
Re: Normal compression on a T... high altitude makes a difference?
A high compression head is the best bang for the buck performance wise.It really wakes up a model T.
|
01-26-2016, 02:48 PM | #15 | |
Senior Member
Join Date: May 2010
Location: Tulsa OK
Posts: 476
|
Re: Normal compression on a T... high altitude makes a difference?
I don't like the rubber pedal covers. They tend to turn hard after a year or so, then they won't stay on the pedals. I just toss them in the trash because they just get in the way of driving the car.
Quote:
__________________
1910 Touring 1914 Touring 1915 Touring 1917 Torpedo Runabout |
|
01-26-2016, 03:32 PM | #16 |
Member
Join Date: Feb 2012
Posts: 95
|
Re: Normal compression on a T... high altitude makes a difference?
Well.. $400 for a high compression head sounds like quite a bit... and it will give you 7 additional HP, so it is interesting, but I don't think it would make a HUGE difference. Anyhow it sounds like a good possibility. I will go over the suggestions with my mechanic and see what he thinks...
And also, since mine is the only T I have driven, I will visit a friend that has a couple and ask him to let me drive them and compare. If there is not much of a difference, the most likely thing to happen is that the car would remain as it is. After all, one does not buy a model T because it is a fast or very enjoyable car! I don't like the rubber pedals either, so I am glad they were not origianal equipment. Glad I asked before I bought a set just because I though they could be correct. Thanks for all the help victor |
01-26-2016, 05:52 PM | #17 |
Senior Member
Join Date: May 2010
Location: now Kuna, Idaho
Posts: 3,791
|
Re: Normal compression on a T... high altitude makes a difference?
Rule of thumb is a 3% horsepower loss for every 1000 ft. gain in altitude so if you are at approx. 8,000 ft. you are down to about 15 HP, maybe less. A high compression head probably won't add 7 HP at your altitude; maybe more like 5. So the head will give you back what was lost to altitude, putting you around the original 20-22 HP. That's about a 25% increase. That's a lot!
|
01-26-2016, 06:02 PM | #18 |
Member
Join Date: Feb 2012
Posts: 95
|
Re: Normal compression on a T... high altitude makes a difference?
Well... looking at it that way, YES, 25% is a lot of increase! I will seriously consider it. I guess the $400 investment is really worth it.
Thanks! victor |
01-26-2016, 06:05 PM | #19 |
Senior Member
Join Date: May 2010
Location: Lehighton Pa
Posts: 1,085
|
Re: Normal compression on a T... high altitude makes a difference?
"Not a enjoyable car" Not so!! The model T is one of the best driving old cars,not fast,but can be!They are one of the easiest to drive, most reliable,and most enjoyable cars I have owned! Phil
|
01-26-2016, 06:55 PM | #20 |
Member
Join Date: Feb 2012
Posts: 95
|
Re: Normal compression on a T... high altitude makes a difference?
Well Phil, I said "After all, one does not buy a model T because it is a fast or very enjoyable car!", but I have to say, I agree with you, it is a nice little car and it moves fairly well... in fact I am amazed of it's turn radious, the little space it takes in the garage and it's fairly brisky moves, almost like a go-kart, but I still get scared of the brakes every time I need to stop!
Once I change transmission bands I am sure I will gain more confidence with it and enjoy it more. Thanks! victor |
01-26-2016, 11:01 PM | #21 |
Senior Member
Join Date: May 2010
Location: Lehighton Pa
Posts: 1,085
|
Re: Normal compression on a T... high altitude makes a difference?
I have a modified 12 torpedo roadster that will do 70 mph,but not safely!It has rocky mtn brakes which help stopping somewhat.But, it is like driving a ill handling top heavy go cart. But I have a blast driving it.On a tour it has humbled many a 40 hp big brass.I not bragging,just commenting on the virtues of the humble T. Phil
|
01-26-2016, 11:53 PM | #22 |
Senior Member
Join Date: Apr 2012
Location: Parkerfield KS
Posts: 526
|
Re: Normal compression on a T... high altitude makes a difference?
"...one does not buy a model T because it is a fast or very enjoyable car..."
It's not fast, and it IS enjoyable. Wherever you go, you are your own parade. And wherever you stop, you are your own car show. If you want to go fast you turn it into a speedster or you buy a Packard. |
Sponsored Links (Register now to hide all advertisements) |
|
01-27-2016, 10:11 AM | #23 |
Senior Member
Join Date: May 2010
Location: Lehighton Pa
Posts: 1,085
|
Re: Normal compression on a T... high altitude makes a difference?
Victor,Sorry I misunderstood your intention.As far as bands may I recommend Kevlar they seem to work better than the old cotton and don,t require the constant adjustment. Phil
|
01-30-2016, 08:04 PM | #24 |
Member
Join Date: Feb 2012
Posts: 95
|
Re: Normal compression on a T... high altitude makes a difference?
No need to apologize for anything, Phil, thanks!
Yes, I am ordering Kevlar bands. I've read they are a much better option that the cotton bands that may easily burn... and I live in a neighborhood with a VERY long and steep uphill... and donwhill, of course. |
|
|
Sponsored Links (Register now to hide all advertisements) |
|