19 replies to this topic

[LC-GTR-1969]

Gday everyone,

 

Im looking at swapping out my current full-spool and running LSD, mainly for better driveability, however I need to decide whether to stick with my current gearing or change it...

 

My car is an LC coupe, engine specs are;

 

red 202 40 thou oversize

offsett ground 208 stroker crank

starfire rods

12 port head, ported and flowed but no idea on flow specs

1.5 roller rockers

oil injection to 1st and 7th main

Running camtech cam, 266/266 duration at 50 thou, .531" lift

Triple 45 DCOE webers

Lightened flywheel

Crane Cams HI6 Ignition

100hp N2O Direct port injection / pump and regulated (not planning on running this- but set up is all there)

O-ringed block and copper head gasket

 

Has a ford 9 inch diff and saginaw 4 speed... Curerntly running 3.89 gears.

 

Rear tyres are Yokahama 235/60 on 15 inch rims

 

Car has run 13.1 N/A and 11.7 on N20 (as run by previous owner). Have not run it myself, but plan to...

 

Since I am already changing the diff center, I was thinking of putting in 4.11 gears for improved response, pickup and launch.

 

The car sits just over 3000rpm at 110km/h. To be honest I will be rarely driving it on the express way... At present, car is fairly happy sitting at 110... Second gear at 7000rpm car is sitting around 60-65mp/h (haven't noticed where 3rd gear is)

 

However, the car seems to have a fair slump between 2000-3500rpm (it comes on the cam about 4000)... This makes it hard to launch well- if you get too much spin, the revs drop into the "soft" zone and take a little before coming onto the cam...

 

The gearbox ratios are great- once on the cam, shifting between each gear about 7000rpm, the engine stays on the cam and absolutely screams (im presuming the sag is a close ratio? not sure).

 

Should I go with 4:11? What rpm would I be running with 4:11s at 60 mile (100km- wont be going much higher on expressway anyway).

 

Any help/ advice would be greatly appreciated!

Edited by jkirky, 13 May 2014 - 06:08 PM.

[LC-GTR-1969]

i just went from 3.55 to 3.36 . I was advised by a very experienced(and respected) old school mechanic to try this.& in my opinion the drivability is heaps better ,I can really use the engine torque now ,it really changed the whole attitude of the car .

It was fun for short squirts with the 3.55 but wound out way too quickly & didn't give the engine the time to work to its full potential.(if your engine has plenty of torque ,you want to use it .)

I also know a few Lads that used 4.11's & got rid of them as the "street drivability " wasn't what they wanted 

I guess it comes down to how you want your car to feel & perform  ,if u are happy with the thing ringing it's neck at 60 mph then so be it ,& all good if you race it ,but I recommend going longer for drivability .it worked for me.

cliff

Thanks for the reply Cliff...

 

Whilst I am undecided as yet on final drive, I really cant see me going longer gearing mate, I just don't think it would suit the cam (cam tech advise minimum 3.7 for the cam, for what thats worth.. may mean squat ... My car is certainly not a torque machine- its a 4000rpm to 7200rpm powerband, with sweet F-A below that... However perhaps the webers could use another tune, and maybe going smaller on the chokes would help with the torque...

 

As mentioned, its currently sitting at just over 3000rpm in 4th at 110km/h with 3.89 gears, which in my mind, leaves some room for going shorter (my daily drive does 2900rpm at 110...), but would be interested to see hear what rpm 4.11s are running at 100km/h.

[UCgazman]

Calc here - http://www.osella.co...gear-ratios.htm

[LC-GTR-1969]

Thanks again for all the replies fellas...

 

I tried the online calculator (thanks for that), and I must say, that the stats it spits out dont quite match what I observe in my car, which makes me wonder about my speedo/ tacho accuracy... Maybe at 3000rpm im doing 100km/h not 110 like I thought??? Or perhaps my car doesnt actually have 3.89s in it (thats just what I was told, but perhaps the seller got it wrong???)

 

However I am also not really 100% sure what the saginaw gearing is, which may be effecting the 'feel' of the car... Maybe a few more variables to work out!

 

Nonetheless, I still experience what feels like a drop off off idle until the cam comes in, which makes a decent launch hard...

[N/A-PWR]

In my Considered Opinion J,

The 9" is a weight in it's self, and with your Cam, put a 3.08:1 equivalent, and you will be set.

Just Fan the clutch at 4000rpm, and bring the running gear up to speed letting the clutch out there and change gear at 7500rpm. Dave I

The Power of the Clutch is Amazing

[LC-GTR-1969]

In my Considered Opinion J,

The 9" is a weight in it's self, and with your Cam, put a 3.08:1 equivalent, and you will be set.

Just Fan the clutch at 4000rpm, and bring the running gear up to speed letting the clutch out there and change gear at 7500rpm. Dave I

The Power of the Clutch is Amazing

Thanks Torypower...

 

So thats +2 for taller gearing...

 

Very interesting, however the opposite to what I was thinking...

 

In reality my car wont be traveling above 60mp/h on the street, hence my initial thinking to shorten up the gearing (as well as the long duration cam), as I was thinking this would improve the apparent lack of low end torque. whilst providing better 1/4 mile times.

 

I might drive and play with the car for a while more to help with my decision...

[N/A-PWR]

Mate J,

when you have more power, you can use Taller Gears,

In my case, the wearing part was the Clutch,

It is up to you, but you need to be prepared to change Diff Ratio's,

I was Lucky, as the Power at the Motor still Revved as Quick as I stepped up the Taller Diff Gearing, which Made the Torana Faster and Faster. Dave I

 

 

 

on the other Hand, when you increase the Tyre Diametre, then you go the other way with the Diff,

Let's say you leave the Diff as it is, and Put 26" O.D.  wheels on, and Test that First, and Lightest one at that Too

[greens nice]

There will only be about 200rpm difference with the 4.11's, I would not hesitate to swap them in even for the street.
Your gears are rather tall now with those tyres.
It may even run a 12 aspirated.
Is it worth the cost?? Maybe

[LC-GTR-1969]

There will only be about 200rpm difference with the 4.11's, I would not hesitate to swap them in even for the street.
Your gears are rather tall now with those tyres.
It may even run a 12 aspirated.
Is it worth the cost?? Maybe

 

Thanks for the reply Kevin,

 

In honesty, I would like to run high 12's- my thinking is that is may be possible with all things lining up correctly.

 

As mentioned earlier, I will be replacing the diff center anyway as I am a little frustrated with the locked diff (full spool) and would rather an LSD. Locked diff makes roundabouts, tight corners, parking, well most things, lets say, difficult). Hence, the change is gearing isn't really costing anything (unless I hate it and need to do it twice

 

The current gearing certainly doesn't feel short by any stretch.. First gear feels quite tall but then shifting to second, and then third is very close ratio (by feel)- when I shift from 1st at 7000rpm revs drop to about 5000rpm, which keeps the car right on the cam.

 

Might throw some smaller stockies on the back and try to see what the smaller wheels feel like (as to simulate shorter gearing).

[warrenm]

I have a similar setup to yours, with 4.1 diff gears, at a 100km I'm doing 3300, 110km 3600, tested following another vehicle & verified using a Navman. As Kev stated, it's only about 200 revs, but maybe enough to get a 12 n/a. I generally run the 1/4 with 4.88 gears & my "highway" gears are 4.1 which on a long trip of 200km it does rev a bit but still returns a fuel consumption of 9.5 L/100ks never going over 100 km/h

[LC-GTR-1969]

I have a similar setup to yours, with 4.1 diff gears, at a 100km I'm doing 3300, 110km 3600, tested following another vehicle & verified using a Navman. As Kev stated, it's only about 200 revs, but maybe enough to get a 12 n/a. I generally run the 1/4 with 4.88 gears & my "highway" gears are 4.1 which on a long trip of 200km it does rev a bit but still returns a fuel consumption of 9.5 L/100ks never going over 100 km/h

 

Thanks Warren,

 

For curiosity, what is your launching technique?

 

Do you slip clutch? What rpm would you launch at?

 

Cheers

[warrenm]

I've got a metal clutch, so no slip. 7000 & side step the clutch.

You'll probably find using a light flywheel that you'll have to use some revs of the line or it will bog, that's why I use a std weight flywheel.

[LC-GTR-1969]

Just took car out to test a few things...

 

Car definitely feel better when abusing the clutch- really helps to keep the engine on the cam...

 

Car was sitting on 2900rpm at 60mp/h, however I have yet to verify my speed. The bigger wheels may be impacting on the accuracy of the speedo.

 

I have decided to hold off on the diff for a little while.

 

I want to check a few things first- I will have webers dyno tuned, I suspect they are a little fat... Engine runs crisper when removing foam socks, so I am thinking that the restriction from the socks are slightly richening (not sure if previous owner jetted to run ram tubes only, or the socks/filters). Will then take it to track and run it over the quarter to establish a baseline. Its too hard (and silly) trying to test the car on the street.

 

Thanks for all the input and advice

[N/A-PWR]

Excellent,

and as Oldjohhno has said in the past, keep notes on what you change, and what did change from those single changes. Dave I

Times, Wheels size, Carby types, Clutch use, Fuels etc

[LC-GTR-1969]

Awesome

Haha... I tried this, and lets just say WOW!!!

 

In all seriousness- Im getting a fair degree of wheel spin at 4k with 235's. I would love to try 12 inch slicks!

[warrenm]

I'm using 8" slicks & this is the result.

 SD20120211_T&T_SuperStreet_0774 (600 x 401).jpg   57.25K   2 downloads

You can't compare it on the road, mine bags them in 3 gears, probably in 4th as well I never kept the boot in that long on the road.