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Discussion Starter · #1 ·
On my last dyno, I noticed how may car is still pulling well up to 6K RPM, and on past that too. I figure after the cams and intake go in, I should be able to rev the car out to 6400-6700 RPM's. I just have to wait and see the dyno afterwards.

Anyways, assuming you have a SOHC, and it is capable of being revved that high (you also have ModMax valvesprings), what gears do you run???

Do you go with 4.30's, 4.56's, or do you stay with 4.10's??? I'm now wondering if I need something steeper!! :D

So, what do you think???????? :evil:
 

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I would say it depends on what you have planned for the car. For example, I am currently running 3.42s in my SS and I can spin my Nittos through first and catch a good scratch in second. If I went to 4.10s I would probably spin through second. Since my goal is street performance and not track performance (my car will not see slicks), I wouldn't run more than maybe 3.73s. If you plan on going to the track and using slicks, you will benefit from more gear. If your goal is street, you need to find a gear that will give you max acceleration without losing too much traction.

Did that make sense? :D

'Los
 

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Discussion Starter · #3 ·
Yeah, it made sense just fine. The car is a daily driver, that likes to see some strip action every once in a while. Honestly, I'm not real concerned about spin on the street, as I will eventually be using Nitto DR's as my daily driver tires. I'm just after the gear that I can get the best 1/4th mile times with. And I'm almost thinking that it MAY be the 4.56's. If not, then the 4.30's anyway. :D
 

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Discussion Starter · #4 ·
ttt...
 

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OK, now lets hear from someone who actually has a Mustang, and a GT to boot...

Brandon, can a GT be reved to 6700 rpms? Yes
Safely? Yes
Should you spin the stock GT crank that fast or faster? Wouldn't advise it!

The stock cast GT crank is good to about 525 fwhp. And it is fairly reliable till a 6700 rpm range. After that, the design of the crank is just falling short of the task.

If you really expect to run your GT that high into the rpms, first thing to consider is a Cobra crank. Then you start the realize the limits of the stock valvetrain. This will require the use of upgraded springs, and retainers. Then you should start looking into better internals. I am sure the stock GT hypercraptic parts aren't exactly ready for high rpms. (i.e. ARP bolts, etc will be needed.)

This next statement is not a bust on you, but I highly doubt that your pulling much past 5800. And that your numbers start to slide convincingly after 5900. The cams and combo you have is probably making decent numbers up until 5700, after which your breathing capacity is at its limit, with the stock heads, and valvetrain.

But, if you are aiming for making a high rpm GT run, say to 6700, and you want the best performance for the track, then I say 4.56s are the way to go. If you are making the power you should be crossing the traps, in 4th at around 6700. (guestimate of course.)

good luck, and think out the part choices before jumping in to deep.
joe
 

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Discussion Starter · #6 ·
What about 6,400 RPM then, Joe?? Honestly, its hard to tell where the car is gonna fall on its face at, as the parts aren't installed, and I really don't know how its going to respond to them, and where its gonna respond best at. I was just trying to make a rough estimate of where I would need to be revving the car out to. At 6K RPM, the car is still making 230-235 RWHP, and I consider this to be fairly good with the stock heads. Considering that, and added breathing ability with the intake, cams, and springs, the 6400-6700 revving was just #'s that jumped out at me as being possible to rev to safely. I mean, the car makes 250 RWHP all the way from 4750 RPM to 5600 RPM, and then slowly falls off.

It seems like I'm just trying to predict how the car is gonna react, rather than waiting and seeing concrete dyno #'s. If you know how to use files saved to floppy disc, or how to use WinPep, I'd like to post my graph, assuming the file was saved correctly to the disc. But, I'm just jumping the gun right now. I need to wait until the parts are installed before I try to drive the car in my head.

Again, thanks for your help, and I'll see if there's any way possible to post my graphs.
 

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RavenGT said:
OK, now lets hear from someone who actually has a Mustang, and a GT to boot...

Brandon, can a GT be reved to 6700 rpms? Yes
Safely? Yes
Should you spin the stock GT crank that fast or faster? Wouldn't advise it!

The stock cast GT crank is good to about 525 fwhp. And it is fairly reliable till a 6700 rpm range. After that, the design of the crank is just falling short of the task.

If you really expect to run your GT that high into the rpms, first thing to consider is a Cobra crank. Then you start the realize the limits of the stock valvetrain. This will require the use of upgraded springs, and retainers. Then you should start looking into better internals. I am sure the stock GT hypercraptic parts aren't exactly ready for high rpms. (i.e. ARP bolts, etc will be needed.)

This next statement is not a bust on you, but I highly doubt that your pulling much past 5800. And that your numbers start to slide convincingly after 5900. The cams and combo you have is probably making decent numbers up until 5700, after which your breathing capacity is at its limit, with the stock heads, and valvetrain.

But, if you are aiming for making a high rpm GT run, say to 6700, and you want the best performance for the track, then I say 4.56s are the way to go. If you are making the power you should be crossing the traps, in 4th at around 6700. (guestimate of course.)

good luck, and think out the part choices before jumping in to deep.
joe
Joe,
I know that you know your stuff... but when I last dyno'd my car was still pulling at 6k and I decided to stop the dyno at 6k. There is no doubt in my mind that it would spin to 6200-6400, however, you're correct with the GT crank CAST vs Forged prolly won't like that too much .... although I've never heard of anyone screwing one of them up ------ yet :) Just thought I'd add a few cents in here. No pun intended of course.

-Tim
 

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Tim you cannot compare a NA car to your blown car, of course your car is gonna pull to 6000 it continues to build boost as rpms go up.


Now to answer the Original question, If your car does indeed keep pulling to that RPM then you choose the gear that is gonna have you at the traps at that rpm. That is the answer, that is the correct answer and nobody can paint it any different assuming we are talking about drag racing. IF you run a 26inch slick the 4.3 is your gear if you run a 28inch then look to 4.56s. If you run street tires better stick to 4.1s.
 

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Discussion Starter · #9 ·
NOVIFED said:
If your car does indeed keep pulling to that RPM then you choose the gear that is gonna have you at the traps at that rpm. That is the answer, that is the correct answer and nobody can paint it any different assuming we are talking about drag racing. IF you run a 26inch slick the 4.3 is your gear if you run a 28inch then look to 4.56s. If you run street tires better stick to 4.1s.
Ok, well, for a while, I'll just be using drag radials. I'm not gonna upgrade to ET Streets or slicks until I have the rear end parts to support them. Anyways, I believe I'm crossing the traps right now at around 5400 - 5600 RPM. To me, I think that even right now, I would benefit from more gear, because I'm making peak power right at 5100 RPM, and stays fairly flat, only with an ever so slight downslope, until around 5700 RPM, where it starts to drop off faster. Having a new intake and cams SHOULD bump up the RPM where I make peak power, and this tells me that I could benefit from more gear. The only thing, is that I plan to supercharge the car on down the road, and I really don't wanna pay for another gear swap. I suppose the 4.10's will still work well, but I think that to maximize my RPM band while N/A, 4.30's or 4.56's would be the best choice.

Also, if I'm revving the car out higher, this tells me that I may very well cross the traps with 4.10's at a higher RPM than I had been crossing them before. So, maybe this IS the right gear for being N/A. Who knows?? :confused: I think Bill (Mustang92) only picked up ever so slightly, and probably wasn't worth the $$$, unless you are out for every thousandth that you can get, as I assume Bill is. Maybe he'll chime in here and let us know how those 4.30's do. :D
 

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Craig what RPMs are you crossing the line at ? What MPH in the 1/4 ?



Lemme rephrase the correct answer : Use the gear thats gonna get you thru the [email protected] RPM where HP peaks. If you got DRs your better spending the cash on Rear end Vs Gears at this point.
 

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Well I guess you are useing a T-45? I am planning on running a 4:30-4:56 once I get my car off the dyno and figure what I need to be crossing the traps at. I am hoping that my car will be able to rev to 6400-6800. I have added all forged internals, mod max valvesprings, still useing stock gt crank. I have not heard of anyone breaking a GT crank so I guess I will see.

I would say get all your stuff done then get it tuned. Then you will know right were you are making your power and be able to figure out what you should be crossing the traps at. Then only buy one gear.
 

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Tim, yes John is correct, an NA car is completely different than the blower car. You are still building boost, when an NA engine is starting to wheeze!

Brandon, if you have no intentions of using slicks, don't go higher than 4.30s. You will spin right past the rev limiter with the 4.56s. John is also correct here, choose the gear that will respond the best with the rubber you use. When you hit the last 60 feet of the track you want to be at peak HP levels, whatever that may be.

One word of caution Brandon, get that rear-end built up, or invest in a tow-truck company's services, cause you are gonna break stuff up out there.

joe
 

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You guys are obviously talking about doing computer mods to get the rpm limiter up for these levels but what about fuel mapping. Does the stock computer have fuel maps for rpm's over 6250? I noticed that the hypertech programmer can extend rev limiters but was wondering how it tells the computer how much fuel to give past 6250. Any info would be great.

I am considering the hypertech now as I don't want to buy pullies to adjust timing since I plan on going S/C later on and would be wasting money on pullies and a timing adjuster. I also want to do 3.73 gears and would be able to fix this with the power programmer. Essentially, it appears to be the most cost effective way to do what I want while still N/A, and then when I get a chip with the S/C, I won't have wasted so much money, only $300 instead of $450 or more for pullies, TA and speed cal. I could also put the car back to stock for emmissions testing without having to open the kick panel to remove a chip.

Anyone use one of these things yet? (Hypertech?)
 

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Discussion Starter · #15 ·
98N2OGT... Well, the Bullitt intake, cams, and new valve springs should be in the car in about a month. I plan to have it tuned as soon as I can after that, along with getting some subframes welded in. Can you believe I haven't done that yet??? :eek: :D And I plan to use the dyno sheets from the tune, to see where I need to shift. And BTW, yes, it is a T-45.

Joe... I WOULD like to use slicks eventually. I don't plan on that for at least another year or so, if I even do it then. As you had advised about the tow truck, I'm gonna see what kind of $$$ I can save, and get back from next year's tax return to see about new axles, and a new differential. Maybe by then, I can save up, and go over to the Hooker longtubes, so that I can save myself $$$ for clutch and tranny work, and my mechanic a pain in the a$$. But a tubular K would also help too!!! Damn, I've got WAY more plans than I have $$$. :lol: Actually, thats not funny. :D

aggie97... You know, I never did really think about the fuel map issue after so many RPM after the rev limiter. I know that with my JMS chip, the limiter is raised to like 6500 RPM, so I'm sure they've done something with the mapping, just in case you plan to spin it that high. If nothing had been done by them, or from Ford, as far as mapping goes, I'm sure that it would be pig rich. But, I've never really heard of anyone having issues with this. Maybe someone will chime in and let us know???
 

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Brandon-well i got from a good source that a Gt crank should handle 7000rpm and around 700 horsepower. So if you make power to 6400 or so I say go for it.
 

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NOVIFED said:
Craig what RPMs are you crossing the line at ? What MPH in the 1/4 ?
That is the real question. Everything else doesn't matter. Heres the numbers for a T45, 4.10s, stock diameter tires up to 6700 rpm.

RPMs 1st 2nd 3rd 4th 5th Ratio Tire Dia Tire Size
4000 22.1 37.2 56.4 74.4 111.1 4.10 25.68110236 245 45 17
4100 22.6 38.1 57.8 76.3 113.8 4.10 25.68110236 245 45 17
4200 23.2 39.1 59.2 78.1 116.6 4.10 25.68110236 245 45 17
4300 23.7 40.0 60.6 80.0 119.4 4.10 25.68110236 245 45 17
4400 24.3 40.9 62.0 81.9 122.2 4.10 25.68110236 245 45 17
4500 24.8 41.9 63.4 83.7 124.9 4.10 25.68110236 245 45 17
4600 25.4 42.8 64.8 85.6 127.7 4.10 25.68110236 245 45 17
4700 25.9 43.7 66.2 87.4 130.5 4.10 25.68110236 245 45 17
4800 26.5 44.6 67.6 89.3 133.3 4.10 25.68110236 245 45 17
4900 27.0 45.6 69.1 91.2 136.1 4.10 25.68110236 245 45 17
5000 27.6 46.5 70.5 93.0 138.8 4.10 25.68110236 245 45 17
5100 28.2 47.4 71.9 94.9 141.6 4.10 25.68110236 245 45 17
5200 28.7 48.4 73.3 96.7 144.4 4.10 25.68110236 245 45 17
5300 29.3 49.3 74.7 98.6 147.2 4.10 25.68110236 245 45 17
5400 29.8 50.2 76.1 100.5 149.9 4.10 25.68110236 245 45 17
5500 30.4 51.2 77.5 102.3 152.7 4.10 25.68110236 245 45 17
5600 30.9 52.1 78.9 104.2 155.5 4.10 25.68110236 245 45 17
5700 31.5 53.0 80.3 106.0 158.3 4.10 25.68110236 245 45 17
5800 32.0 53.9 81.7 107.9 161.0 4.10 25.68110236 245 45 17
5900 32.6 54.9 83.2 109.8 163.8 4.10 25.68110236 245 45 17
6000 33.1 55.8 84.6 111.6 166.6 4.10 25.68110236 245 45 17
6100 33.7 56.7 86.0 113.5 169.4 4.10 25.68110236 245 45 17
6200 34.2 57.7 87.4 115.3 172.1 4.10 25.68110236 245 45 17
6300 34.8 58.6 88.8 117.2 174.9 4.10 25.68110236 245 45 17
6400 35.3 59.5 90.2 119.1 177.7 4.10 25.68110236 245 45 17
6500 35.9 60.5 91.6 120.9 180.5 4.10 25.68110236 245 45 17
6600 36.4 61.4 93.0 122.8 183.3 4.10 25.68110236 245 45 17
6700 37.0 62.3 94.4 124.6 186.0 4.10 25.68110236 245 45 17

Heres the same setup with 4.30s.

4000 21.1 35.5 53.8 71.0 105.9 4.30 25.68110236 245 45 17
4100 21.6 36.4 55.1 72.7 108.5 4.30 25.68110236 245 45 17
4200 22.1 37.2 56.4 74.5 111.2 4.30 25.68110236 245 45 17
4300 22.6 38.1 57.8 76.3 113.8 4.30 25.68110236 245 45 17
4400 23.2 39.0 59.1 78.0 116.5 4.30 25.68110236 245 45 17
4500 23.7 39.9 60.5 79.8 119.1 4.30 25.68110236 245 45 17
4600 24.2 40.8 61.8 81.6 121.8 4.30 25.68110236 245 45 17
4700 24.7 41.7 63.2 83.4 124.4 4.30 25.68110236 245 45 17
4800 25.3 42.6 64.5 85.1 127.1 4.30 25.68110236 245 45 17
4900 25.8 43.5 65.8 86.9 129.7 4.30 25.68110236 245 45 17
5000 26.3 44.3 67.2 88.7 132.4 4.30 25.68110236 245 45 17
5100 26.8 45.2 68.5 90.5 135.0 4.30 25.68110236 245 45 17
5200 27.4 46.1 69.9 92.2 137.7 4.30 25.68110236 245 45 17
5300 27.9 47.0 71.2 94.0 140.3 4.30 25.68110236 245 45 17
5400 28.4 47.9 72.6 95.8 143.0 4.30 25.68110236 245 45 17
5500 28.9 48.8 73.9 97.6 145.6 4.30 25.68110236 245 45 17
5600 29.5 49.7 75.3 99.3 148.3 4.30 25.68110236 245 45 17
5700 30.0 50.6 76.6 101.1 150.9 4.30 25.68110236 245 45 17
5800 30.5 51.4 77.9 102.9 153.6 4.30 25.68110236 245 45 17
5900 31.1 52.3 79.3 104.7 156.2 4.30 25.68110236 245 45 17
6000 31.6 53.2 80.6 106.4 158.8 4.30 25.68110236 245 45 17
6100 32.1 54.1 82.0 108.2 161.5 4.30 25.68110236 245 45 17
6200 32.6 55.0 83.3 110.0 164.1 4.30 25.68110236 245 45 17
6300 33.2 55.9 84.7 111.7 166.8 4.30 25.68110236 245 45 17
6400 33.7 56.8 86.0 113.5 169.4 4.30 25.68110236 245 45 17
6500 34.2 57.6 87.3 115.3 172.1 4.30 25.68110236 245 45 17
6600 34.7 58.5 88.7 117.1 174.7 4.30 25.68110236 245 45 17
6700 35.3 59.4 90.0 118.8 177.4 4.30 25.68110236 245 45 17

Now 4.56's.

RPMs 1st 2nd 3rd 4th 5th Ratio Tire Dia Tire Size

4000 19.9 33.5 50.7 66.9 99.9 4.56 25.68110236 245 45 17
4100 20.3 34.3 52.0 68.6 102.4 4.56 25.68110236 245 45 17
4200 20.8 35.1 53.2 70.3 104.9 4.56 25.68110236 245 45 17
4300 21.3 36.0 54.5 71.9 107.3 4.56 25.68110236 245 45 17
4400 21.8 36.8 55.8 73.6 109.8 4.56 25.68110236 245 45 17
4500 22.3 37.6 57.0 75.3 112.3 4.56 25.68110236 245 45 17
4600 22.8 38.5 58.3 76.9 114.8 4.56 25.68110236 245 45 17
4700 23.3 39.3 59.6 78.6 117.3 4.56 25.68110236 245 45 17
4800 23.8 40.1 60.8 80.3 119.8 4.56 25.68110236 245 45 17
4900 24.3 41.0 62.1 82.0 122.3 4.56 25.68110236 245 45 17
5000 24.8 41.8 63.4 83.6 124.8 4.56 25.68110236 245 45 17
5100 25.3 42.7 64.6 85.3 127.3 4.56 25.68110236 245 45 17
5200 25.8 43.5 65.9 87.0 129.8 4.56 25.68110236 245 45 17
5300 26.3 44.3 67.2 88.7 132.3 4.56 25.68110236 245 45 17
5400 26.8 45.2 68.4 90.3 134.8 4.56 25.68110236 245 45 17
5500 27.3 46.0 69.7 92.0 137.3 4.56 25.68110236 245 45 17
5600 27.8 46.8 71.0 93.7 139.8 4.56 25.68110236 245 45 17
5700 28.3 47.7 72.2 95.3 142.3 4.56 25.68110236 245 45 17
5800 28.8 48.5 73.5 97.0 144.8 4.56 25.68110236 245 45 17
5900 29.3 49.3 74.8 98.7 147.3 4.56 25.68110236 245 45 17
6000 29.8 50.2 76.0 100.4 149.8 4.56 25.68110236 245 45 17
6100 30.3 51.0 77.3 102.0 152.3 4.56 25.68110236 245 45 17
6200 30.8 51.9 78.6 103.7 154.8 4.56 25.68110236 245 45 17
6300 31.3 52.7 79.8 105.4 157.3 4.56 25.68110236 245 45 17
6400 31.8 53.5 81.1 107.0 159.8 4.56 25.68110236 245 45 17
6500 32.3 54.4 82.4 108.7 162.3 4.56 25.68110236 245 45 17
6600 32.8 55.2 83.6 110.4 164.8 4.56 25.68110236 245 45 17
6700 33.3 56.0 84.9 112.1 167.3 4.56 25.68110236 245 45 17

Looks to me that if you really want to spin it that high you could do 4.56s. But like the others have asked, "How wise is that really?".

Ed
 

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Brandon, I also have it from a good source, where I have seen a stock GT crank disintegrate at 575 under 7000 rpms. And it ain't pretty what happens to the rest of the front of the car.

joe
 

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I think Raven is right. For two years now I have been reading that the GT crank is reliable to 525 crank hp only. Also, maximum rpm has always been 6500rpm. You are moving into territory that has always been reserved for forged cranks or superior balancing with lightweight rods and pistons.

Just think about it......Cobras spin to 7200rpm and that is why they have forged cranks. It is not because of the HP that the engine generates.

Just some food for thought.
 
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