Monthly Archives: March 2011

What transmission do i need?

what do i need to get for my transmission and how much will it cost. Well, i truly feel that everyone needs to have a transmission built for their particular needs and desire. this is why i truly believe no “off the shelf” transmission will make everyone happy. usually you end up paying a lot of money for something that gets the job done but really isn’t exactly what you want. i mean you have your engine built to your desire with a cam of your choice and compression/power/budget you want right…..well to me the same applies to your transmission AND rear axle. really they need to compliment what your trying to do otherwise you aren’t taking full advantage of your engine. you’re making due with a one size fits all tranmission. 

when it comes to the th400, it is a very sturdy platform to begin with so to beef it up to handle descent power is relatively affordable. although debatable, i feel in stock form it can handle up to around 400hp in stock form with good stock replacement clutches like a raybestos or borg warner. if you’re going to be using any kind of a shift kit, the next thing is to insure you have an aluminum direct drum piston as not all th400’s had aluminum pistons. when you push near the 500hp mark and are going to hammer on it at the drag strip or upgrade to a full manual valve body of some kind, the next thing is to upgrade to a 34 element performance direct drum sprag. this is the most common weak point of the 400 in 71-later transmissions…..and when it was retired and replaced with the 4L80, they went back to the older stronger sprag.

the next level is over 500hp+ and above 5000rpm, trans brakes, and nitrous oxide. this is a level that most derby engines never get to and if they do-they never apply the power fully. the first thing that needs to happen is to upgrade the input shaft and mainshaft must be upgraded to a hardened aftermarket shaft.  they loosen and snap. the direct drum and intermediate clutch should be upgraded to a 4 disc set up instead of the 3 disc stock….and you must modify or replace the direct drum and sprag to accomodate this. also thrust loading of the rear planetary can become an issue and planetary gears can snap when you get toward the 700hp mark and both straight cut and aftermarket 5 pinion carriers can be used as well. torrington bearings at the rear of the planetary and be machined and installed also.

now spinning a th400 over 6000rpm and up is somewhat of a rarety as a lot of bracket racers usually will opt of a lighter th350 or powerglide as they do not have to rotating mass and do not eat as much power as the 400 does. there are aluminum and lightened components out there to help the 400 in high rpm application hp, and you bend over and take it in the ass on price. so when you get to that point you should definitely consider all options on the table and look across the board at other transmission options for the price. you may want to go powerglide, th350, or even crower or a top loader manual at some point. i mean if the 400 was that great pro stock cars would use them….ya know what i mean? know when to say when.

the th350 pretty much was light duty from the get go and to put any real hp for anything over 250-300hp, you need to upgrade the center support to one out of a later model 4L60 or 700R4, and completely replace the direct drum and sprag assembly to an aftermarket sprag similar to the 34 element th400 sprag. also machining the aluminum piston down to accept 5 clutch discs on the direct is a good idea as well. there were numerous gearsets used on the th350 so you may or may not need to upgrade things like planetary’s and sun gear shell. BUT if you spend the money….the th350 WILL out perform the 400 as far as weight in the car and power put to the ground through the power range. here again- know when to say when.

the powerglide is the choice of transmission for bracket racing in my book. you pretty much have to gut it and use all aftermarket parts, but the consistancy is undeniable when you only have one shift point to worry about.

but as far as derby, the 400 can be built fairly affordable with stock parts and literally has the raw strength needed for the application over most other transmissions period. as i have stated in other parts of my blog, the th350 is not well suited for derby in my opinion, but some people have good luck with them. here again it doesn’t work for everyone.  a lot of guys like running a manual clutch, but for big shows most people go back the 400 and run their clutch set ups at the county fair to have fun. manual trannys for derby are inconsistant and to me it seems like it is a matter of when not if they will fail. the 727 chrysler is a descent tranny, and will work for derby. still not a th400.

1st/reverse only th400 works well for guys running less than a 4.56 gear in old iron and 4.10 in new iron. after that you wind the piss out of your engine. BUT i do know guys running 1st/reverse with 5.13 gears and scream across the track from one end to the other without a care. for the guys that like the 4.88 and up gears i suggest either a regular shift 400 that is modified for holding 1st gear(which is actually quite simple) OR a full manual valve body so you basically have a 3 speed manual transmission without a clutch. a lot of guys prefer the fulll manual over a regular shift as they can hammer 2nd gear to reverse and if they get to a point where they need to move a pile out of their way or their engine is overheating, they kick it down to 1st gear and bull doze around the track with the 5.13 gear. food for thought.

hope this helps guys.

Adjustable Timing Curves and Heat Build Up

Heat build up in an engine is something that is a concern in several different motorsports. although different brand/make of engines/displacement/and fuel type play a major role in how to deal with heat, for arguement sake lets talk SBC with regular 89 octane pump gas for demo derby use, since that is the sport that seems to obsess about heat more than power.

 As a rule of thumb, i was always taught that less timing is less horsepower/more timing usually means more power to a point….which is usually 35 degrees at peak advance under heavy load or full throttle. so more timing-more fuel-more power- and obviously more heat as a result. remember from a previous blog i wrote about basic principles of performance: you don’t make horsepower without feeding the horse.

Now, so i don’t rehash something i already wrote about, here is a link to a previous blog describing advance curves and ignition. .so throwing real performance out the window i rethought a ignition set up.

a normal vacuum can advance will pull as much as 52 degrees of total advance at high vacuum like decelleration or high idle when base timing is set between 4-8 degrees on a stock engine. obviously at mid throttle this is reduced as it is usually plumbed into ported vacuum so it basically only pulls large amounts of advance at light load or cruising speed.

so what if we now use an adjustable vacuum can and plumb it right to the intake giving us full vacuum at everything but full throttle and cranking speed. we then use the can to crank the timing down to something more like 32-34 degrees. then set your base timing damn near stock at idle to just above zero (TDC) lets say 4 degrees, basically a low timing setting for cranking. lets leave the mechanical advance on the shelf for a moment and say it’s locked. Now, we have an optimum cranking timing setting for a hot engine, a quick response once it is started to a descent timing setting, and when you crack the throttle your timing goes into the toilet preventing any real power, which creates heat. so basically if you sandbag and feather the throttle you will build less heat than a stock distributor and have good response….longer overall run time. when you do open it up the 4.56 gear at the back of the car will make up for it. pair this with a loose bottom end and an absolute dog camshaft profile that will pull a high vacuum signal through a large part of the power band…… the thing may never overheat.

Now, if we include the mechanical advance it can be taylored to the rpm you want. a mechanical advance kit will give you the weights and cam to give you a broader range of rpm you can taylor your full throttle advance to. it also comes with different rate springs so the advance will be right where you want it at different rpm’s.

so lets say you use the springs and weights from your advance kit to conform your advance to come into full advance at 24 degree’s at 2000rpm. you obviously set it with the vacuum can unhooked running at above 2000 rpm with an adjustable light to verify the setting. you still have base timing set at 4 degrees remember. you then hook your vacuum can to intake vacuum and there you go.

you have good hot cranking-optimum low throttle timing for performance and heat build up- and and still have an option for full throttle timing adjustment. interesting theory right? well, to be honest i believe there might be something to it but i won’t do it. first off having a vacuum advance is just something else to go wrong and usually gets in the way of the distributor protector or at the very least makes it a pain in the ass. i still prefer putting the curve weights in and setting total timing with the mechanical advance changing around springs to come in at around your power band of your camshaft for full advance, then just chosing one total timing setting and leave it. BUT if you want to mess with multiple advance curves it’s something to think about.