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  #16 (permalink)  
Old 08-21-2008, 04:12 PM
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Quote:
Originally Posted by red65mustang
counterpoint?:

for a 2400lb car to be able to "maintain" 60mph you need (maybe with a strong head wind?) 50FWHP/150FWTQ available....

a bone stock 350 makes approx 90HP/290TQ at 1500rpms......

your motor will be "loafing" with about 18Hg for a lean mix at 60mph with 3.54 gears at 1500...
Yes 90Hp with the pedal flat to the floor at 1,500 rpm.

But we are talking 1,300 rpm, and even the slightest up slope or head wind means you will be into some significant throttle opening and also frequently into the accelerator pump and power valve, and fuel economy will go to hell.

You will get better fuel economy by allowing the engine to rev a little more freely, keeping it at very light throttle than, gearing it excessively tall and loading it up way beyond what it can reasonably pull.

The 4.09 gear came only with the smallest 2.8 liter engine, and even if you find one, it will be extremely old. This diff has 11/45 teeth. Being the smallest and lowest cost engine option, it will almost certainly not have the posi centre.

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  #17 (permalink)  
Old 08-22-2008, 08:07 AM
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stelag,
I screwed up and forgot/ignored you are using a AirGap intake!!!....

that intake has about 1/2" of the dual plane center divider wall milled away under the carb.....

so it does behave "somewhat" like a single plane intake trying to pull Hg over the entire intake cubic inches and both primaries when cruising!

at very slow piston speeds/low rpms that divider wall "leak" really hurts A/F velocity and quality, killing the TQ....

because of the intake, you will likely need more 60mph rpms to have a "practical" 6th gear (or your foot will be constantly into the pedal to make more TQ)

footnote:
yes, imported from the US and assigned a "export only" part number by GM because of some modification to make it correct for Europe and/or legal for that market....
trivia example:
the name "Mustang" was trademarked in Europe....so....all the early Mustangs were shipped to Europe with blue oval "Ford" badges!

Last edited by red65mustang; 08-22-2008 at 08:18 AM.
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Old 08-22-2008, 09:57 AM
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What about 4:54? Will that be too much?
I have found one...
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Old 08-22-2008, 04:46 PM
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Common ratios available for the Dana 44 around the range of interest include:
4.11 (17/70)
4.27 (14/60)
4.56 (16/73)
4.88 16/78)
http://www.ringpinion.com/PartsList....ana+Spicer+D44
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Old 08-23-2008, 02:05 AM
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Quote:
Originally Posted by red65mustang
stelag,
I screwed up and forgot/ignored you are using a AirGap intake!!!....

that intake has about 1/2" of the dual plane center divider wall milled away under the carb.....

footnote:
yes, imported from the US and assigned a "export only" part number by GM because of some modification to make it correct for Europe and/or legal for that market....
The trans is Bought/imported from a wrecking yard in The US, so my guess is that it's not from a "export only" US car.

I've read about the single plane related problems with the Air Gap intake. First I'll going to use the intake as is, of course, but I can not believe it's that hard to weld back on a divider that goes all the way up to the carburetor flange if it became a problem.

Secondly I will be using a 4 hole 1/2" spacer and my QFT 650cfm carburetor have annular boosters.
That spacer and those carb boosters are known to strengthen the signals/ improve the low rpm range, aren't they?
Maybe that will be the "help" the air gap intake needs to make stabile and good power at low rpms too?

Meanwhile I have found a Jaguar differential at a US Jaguar wrecking yard with 4.54:1 ratio. That should be from a 2,8L xj6 68-85 model. Hopefully it's not so very old or woren. I'll ask the seller some more about it over the weekend.

Again: Thank you for your help!

Last edited by staleg; 08-23-2008 at 02:15 AM.
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Old 08-23-2008, 02:16 AM
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I think that Jaguar dealer may have had a momentary brain fart, and really meant to say 3.54 not 4.54
The factory 2.8 engine came with the 4.09 diff.
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  #22 (permalink)  
Old 08-23-2008, 06:51 AM
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I have asked him to to double check, but according to this link
http://www.uk-hotrods.co.uk/v2/tech/...r/tech_jag.php
the xj6 68-85 could have 4.09 or 4,55.
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  #23 (permalink)  
Old 08-23-2008, 08:36 AM
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We run a 351W/360HP crate engine in a Daytona Coupe with a T56 and the same gear ratio. It has 18" wheels but the overall diameter is close( they are lower aspect ratio than 50). We run a little over 2000 rpm at 70 and get app. 24 mpg( A/C blasting). I think a lower ratio as suggested would be a mistake. Unless you are racing I'd run as high a gear as it will pull in the type of driving you do. I wouldn't change ours out . We have almost 12,000 miles on it and it has a well spaced gearing as it is.
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  #24 (permalink)  
Old 08-23-2008, 08:41 AM
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Quote:
Originally Posted by red65mustang
stelag,
trivia example:
the name "Mustang" was trademarked in Europe....so....all the early Mustangs were shipped to Europe with blue oval "Ford" badges!
I believe that it was just Germany that had that trademark, it was for a motorcycle(and maybe bicycle) company. They were shipped with T-5 emblems and referred to as that .
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Old 08-23-2008, 08:41 AM
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Silver Shadow,
I had a brain fart in my "counterpoint" post....
you are correct, it's 1300rpms not 1500 with 3.54 gears...
1300 is very likely too low to be practical...

stelag,
only road testing your specific motor/car combo and tune up with a vacuum guage mounted in the car (or a rear wheel dyno test) will tell you if the spacer is helping the AirGap.....to show you is the Hg is recovering quicker while accelerating (more TQ sooner) and is there more Hg at cruise.....

a 1/2" 4 hole carb spacer is for sure not likely a "magic bullet" cure.....

all the oems did use (typically 1")2V and 4V 2 and 4 hole spacers,,,,,
,typically in a heavy car/too small cube,lack of TQ motor/tall gears/LOW profile "true" "heated" dual plane intake car combo to shift the TQ curve a bit lower for less pedal/better accelerating normal....
(that's not your car combo)

more spacers info:
http://www.gnetworks.com/v4files/bar...h%20images.pdf
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Old 08-23-2008, 11:33 AM
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Quote:
Originally Posted by red65mustang
Silver Shadow,
only road testing your specific motor/car combo and tune up with a vacuum guage mounted in the car (or a rear wheel dyno test) will tell you if the spacer is helping the AirGap.....to show you is the Hg is recovering quicker while accelerating (more TQ sooner) and is there more Hg at cruise.....

a 1/2" 4 hole carb spacer is for sure not likely a "magic bullet" cure.....
I know. What I ment was that it MIGHT help a little in the correct direction. Or i might not help at all. The actual reason for using the spacer is that the otherwise the vacuum port right behind the carb flange is covered by the carbs rear float house.

Since I work in a mechanical factory, I can have velded up that divider for free IF it makes a problem.

But your inputs and some calculations have nevertheless shown me that a 4,55 ratio probably will work better than the 3,54 that I have today.

woodz428: I assume you mean I shold use the 4,55 ratio? Because when I do the math on this, the 4,55 ratio will result in 1938 rpms in 70 miles pr hour, while the 3,54 ratio will result in 1508 rpms at the same speed.

Last edited by staleg; 08-23-2008 at 03:00 PM.
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Old 08-23-2008, 05:54 PM
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Quote:
Originally Posted by red65mustang
Silver Shadow,
I had a brain fart in my "counterpoint" post....
you are correct, it's 1300rpms not 1500 with 3.54 gears...
1300 is very likely too low to be practical...
Yeah, it is a tough judgment. You not only lose engine torque at the very low engine rpm, but overall torque multiplication as well.
So a very tall gear is doubly cursed trying to pull the car.

Try it with the 3.54's first and see how it goes. Fifth gear will likely be a bit too revvy on the freeway, but I would expect sixth gear to be not only gutless, but give worse fuel economy than fifth on a journey. But try it and see.

First gear overall reduction needs some thought too. It is all a compromise.

I played with all this many years ago when I had two Ford top loader gearboxes, one was close ratio with 2.32 first gear, the other the more common wide ratio with 2.72 first gear. It also had a nine inch diff, and I had six different ratio diff centers between 2.75 and 4.57 to play with.

I went nuts trying different combinations, but one thing is for sure, gearing the car too tall definitely hurt fuel economy.

It seems that with too tall a gear you spend a longer time on the throttle to get up to speed, as well as requiring wider throttle openings. Even though you drive like a granny, and everyone passes you, it still drinks fuel. With a shorter gear, the engine revs a bit, but it is under much less load, and vacuum is always high.

Of course you can easily goo too short a gear, and it drinks fuel too, but there is an optimum gear for each engine size and vehicle weight/frontal area. Factory cars are usually geared pretty close to that optimum, especially late model stuff.
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Old 08-24-2008, 07:44 AM
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stelag,
with a 2.66 first gear and 4.56 rear gear 27.6" tire 3000rpms is only 20mph!!!!

from a stop sign, that is maybe(?) one second's worth of acceleration time before the normal 1-2 shift....

having a "granny gear" 1st gear does get reeeeally irritating real fast in stop and go traffic.....

I would leave the 3.54's in it....
and drive in .76, 5th on the Hwy....
most Hot Rods are driven maybe(?) 5,000 miles a year..
so mpg isn't a top priority....
"Fun" is not free!

LOL, if mpg was a priority it would have a 150HP 2L four banger with the 6 speed T56 which is all 2400lbs needs to drive decent

handy tires/gears/mph calculator:

http://www.tciauto.com/Products/Tech...culators.asp#6

Last edited by red65mustang; 08-24-2008 at 07:58 AM.
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Old 08-24-2008, 05:52 PM
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By my calculation, 2.33 first gear x 4.56 diff = 12.13 overall
Specified tires give 753.3 revs per mile
In first gear 12.13 x 753.3 or 9,137 engine revolutions per mile

If the engine could actually reach 9,137 rpm it would be doing 60 mph in first gear.

If we rev it out to 6,000 rpm it will be going 6,000/9,137 x 60 mph = 43.8 mph

To me that is not at all unreasonable.
12.13 overall in first is not bad at all, a pretty strong gear, and it would allow a very light flywheel, and be easy on the clutch.

And yes, anyone that installs a six speed close ratio box is going to be doing a lot of shifting. That does mean shifting to second gear at maybe around 20-25 mph, in traffic, so what?
I don't really see any problem with that either. I enjoy driving, and shifting gear is all part of the fun. About two seconds in each gear accelerating sounds about right, if driving either fast or slow.

Last edited by Silver Shaddow; 08-24-2008 at 06:33 PM.
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  #30 (permalink)  
Old 08-24-2008, 06:51 PM
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Drive it and find out how it cruises..... your cam might not like 1400 rpm cruising.... you might need only 5th gear, 6th might be autobahn only...LOL.

My T-5 car, I do a lot of 1-3-5 shifts
sometimes 2-4-5 because of the high rpms in 1st gear in traffic.
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