3.4 owners - trans work ?

[johnca]

I am seeing a lot of posts any dyno charts from folks who have done 3.2 -> 3.4 builds. What I haven't seen anyone mention is if transmission work is required for these as well, or if my stock 915 out of my 86 can take the power and torque with the additions. Can anyone point me at number for what HP and torque these transmissions can take or share experiences if it held up ?

[BURN-BROS]

That will totally depend on how the engine is built and how the car is utilized. Cars and coffee, not necessary.

[johnca]

Mostly street driving with some DE days.

[Bill Verburg]

Originally Posted by johnca

Mostly street driving with some DE days.

No problems as long as you learn to be one w/ the trans, don't try to rush shifts

and use Swepco

[spuggy]

Originally Posted by johnca

Can anyone point me at number for what HP and torque these transmissions can take or share experiences if it held up ?

Use the BBS search function (or, better still, Google index the site; use Google and restrict your answers to the forums by adding

site:=forums.pelicanparts.com

to the search string). This has been asked many, many times - most often by guys going forced induction, and thus 100-150 ft/lbs over stock at low RPM.

The short answer is "start with a late 915, rebuild it, consider new gearsets, consider strengthening it while you're there". Should be fine; a 964 doesn't make very much more than a 3.2

915s got stronger over the production run - there is nothing you can do beyond a certain point to make the 915 stronger; the standard "billet cover, bearing retainer, LSD" all helps - but only go so far. Turbos tend to beat up & kill 915s because they make big torque low down - think Hayden of WEVO indicated "300 ft/lbs below 3000 RPM" as the danger point; modified turbos tend to be spooled and making 90% of peak torque by 3K.

915s in a 400 WHP turbo are either babied or not long for this world. You will HATE an RSR pressure plate very quickly if you get caught in stop-go traffic. Anything less will just polish the flywheel over 1/3 throttle... Puck clutches are almost digital, too - hill starts demand your full attention...

I wouldn't be overly concerned; none of this applies to an N/A 3.4 swap.

A pro would surely suggest a transmission rebuild. Because they have a service life (despite an apparently widespread belief that they last forever without). A rebuilt/good 915 is a source of joy; yes, they do shift into 1st at 30 MPH (but once you see the cost of the synchros, you will either refrain or practice double-clutching and rev-matching). You also probably want it in good condition before asking it to exceed original design parameters. Consider too that any original factory gearset still in a transmission would have been timed out literally decades ago in a race car...

While you're in there spending that sort of money on parts/labor, it'd seem kind of silly not to fit at least some of the strengthening parts anyway. Cheap insurance. Late factory cover is probably fine - but the billet one gets you a 930 sized bearing. After I fitted a 35/65 LSD set to 80 ft/lb, I was amazed how much it improved the car.

A Sport clutch would probably be fine with a 3.4 - all of mine were pretty marginal with a stockish 3.3 turbo making ~300 ft/lbs at the flywheel (eg worn out at 12,000 miles), but glancing at a 964 torque curve, it just doesn't get there. There are Sachs pressure plates with less clamping force than the all-out competition one.

Last time I looked at BBII spec's, seem to recall Jack O was using a '77 mag 915 - and apart from an LSD, I think the only special precautions he takes are a temperature gauge for the transmission and an electric fan on the transmission cooler. Because transmission oil breaks down at high temps just like engine oil.

[Dan J]

I have an 84 with a mildly hot rodded 964 3.6. I rebuilt the 915 10 years/12k miles ago when I installed the engine No problems so far. I change the oil every year
Has had no jackass shifting though

[Bill Verburg]

An '86 US 3.2 would have a 915/73 which had all the cumulative updates except the trans cooler used on the /67 & /72. The only place these were shortchanged in any way was the new limited slip which has improved lubrication w/ extra openings on the end of the case but had the # of friction surfaces cuts in half, thus reducing the nominal 40% lock to more like 20%

[Mahler9th]

I ran a 915 with a ~350-370 bhp with a 3.8L in a racing application for a number of years. People I know have run close to 400 bhp with 915s in racing applications.

These cars have all run very big. very sticky slicks.

Most of these have been mag case 915s.

I started with my 3.8 in 2001 and ran for a number of years before servicing the 915. When I did, I converted to an alu cover.

The mag cases have a steel insert set-up for the bearing retainer plate fasteners... despite this I added the excellent WEVO single piece retainer.

In my application... sprint races no longer than about 40 minutes, and in California weather (including temps as high as 105), I have never needed a transmission cooler.

I used Redline synthetic for all of my racing and track driving from 2001 - 2011. After a hiatus I continued to use the same lubricant starting in 2016.

I have been pretty easy on my transmission on track and when racing-- I haven't "babied" it, but I have respected it.

When I bought my car it had the excellent Guard Transmission TB differential. A few years ago, I switched to the excellent Guard Transmission LSD.

I have relied on excellent service and advice from the folks at WEVO (they are friends and nearby), my car's builder (and still my engine builder Mat Lowrance/Reno Rennsport) Jerry Woods, Paul Guard (former owner of Guard Transmission), Matt Monson (current owner of Guard Transmission) and others.

All of the folks know and respect each other.

I have done nearly all of the work on my 915s except for ring and pinion set up.

And again, my application has been racing.

[HaroldMHedge]

An interesting read on the 3.2 ROW 915 with an oil cooler.

Why does the 915 ROW has an oil cooler?

[Jeff Alton]

It is not that interesting, lol. The mother corp expected that cars they equipped with coolers would drive at higher speeds for longer periods..... If they thought the NA market gearboxes were at risk, they would have had coolers....

Cheers