Hey guys.
does anbydody know about regearing a 914 transmission with a steeper final drive ratio differential. do they make aftermarket differentials? if so any links?
thanks
steven

The final drive/5th gear setup was setup to keep the fan moving at the right speed for cooling.

Changing that for a street car means looking at how you will cool the engine.

I've looked into it, BUT most of the options of flipping gears are going to have a "too tall" final drive.

An easy way to do it is taller tires.

What tires do you have now?

my dad has done such extensive polishing to my heads and pistons that my engine runs about 65 degrees cooler than stock. so there for if i can gear it steeper i can get back some of that heat for efficiency and then have more topend if i have the power and have more efficiency becuase of lower rpms. i have video of my heads that are polished. they look like mirrors. you can see the reflection of my dad with the camera in the valves. it took him about 4 months to do the two. but it was well worth it. next best thing from ceramic coating.
steven

How do you know it runs cooler than stock?

Polishing does not help you loose heat. If you polish the inside of your ports and combustion chambers you increase surface tension and hurt mixing, and if you polish the outside you loose surface area over the rough castings (heat exchange is dependent on surface area).

I've looked into it, BUT most of the options of flipping gears are going to have a "too tall" final drive.

An easy way to do it is taller tires.

What tires do you have now?
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hey kieth. im running on 205/65/r15 s in the back. my dad runs 205/75s they are a lot taller than my tires but they are just nasty for handling. sidewalls are too big. i think i might get where i want when i convert to 5 lug 17 in rims. we will see tho. heres a pic of my dads car with his monstrous tires. it has no engine. so its high. and then the one under neath is mine

Click to view attachment

Click to view attachment

his tires are much larger and nastier. for handling.

get some pics.

65* cooler is great.

Taller rims/tires may be an easier, less expensive way to go. A setr of 16 in wheels and 60 series tires will get you to a stock wheel/tire height. this will yeilsd about a 3k rpm range at about 70ish mph

If you are really interested in going into the tranny, there are gear charts avail if you do a search. It will give you some ideas of what flipping gear pairs will give you for a final drive.

The final drive that looked good to me was a flipped second gear combo but most second gear combo's have one gear that's fixed to the main shaft.

All others are too tall.

its just physics. when you polish the chambers. you remove surface area. the casting has peaks and valleys if you stretched those peaks and valleys out its more surface area, which collects more heat. if you remove those peaks and valleys the chambers dont soak up that heat. that heat is therefore used more in pushing the piston instead of being soaked up in the chambers. your right in saying that polishing doesnt help you lose heat, when you polish that extra heat
was never able to be soaked up by the chambers in the first place. and i have seen the results first hand on my car. and im not sure wut you mean by surface tention and hurt mixing?(typo?). polishing the chambers helps keep the engine run cooler but polishing the rough castings on the outside of the head is counterproductive.
steven

205/65's are close to stock height

17"/60series will get you a bit of overdrive.

There is a tire calculator on the main page that will give you your tire compared to stock with a spedo differential calculator.

I've been looking into boxster 16'/60 sries boxter wheels.

It requires a 5 lug but no spacers.it will give the stock tire height and still handle well

i would get pics but its from video on vhs tape. he polished my heads back in 2000.. they have sinced been used on 4 different engines. and still going no cracks. i agree bigger rim and tire would most likely get me where i want to be. looking about 2600ish rpm around 70ish

hey jd74914
tell me something. have you ever run into over heating troubles?

I know that polishing will reduce heat into the heads, but it also will create more surface tension which slows down airspeed. The increased air speed and eddy currents cause by a slightly rough texture are important for mixing. While you are keeping more heat in the exhaust you are at the same time impeding mixing. At best its a trade off.

I wouldn't' think my engine has overheated lately (from looking as the valve seats and lack of cracks). I haven't personally run it enough to know. You didn't answer how you definitively know it runs 65* cooler.

Click on the gearing links in my sig line for more info.

havent quite tested it yet. sorry i shoulda tested b4 i said something.speculation. i feel stupid now . oh well. but i know that it runs cool enough to slow the rpms on the freeway. it runs cool enough to drive it at 2400 in fifth for mile after mile. but there is added life when you polish out the roughness or just get it to run cooler.

An easier trick is to use a different cam than stock as the stock cam intends to keep the engine hot for emissions and fast warmups.
Changing to a cam with the exhaust overlap and duration altered drops 50F off your CHT's and that I have tested on a couple of cars.

thanks for the tip. my have an aftermarket cam that was meant for carbs and i think it was a mid to high range cam but i dont know the grind on it. do the #s on the cam gear give any indication as to what grind it is. or should i buy a new one so im sure on the grind?