Author Topic: TH400 in an Altered  (Read 4911 times)

Offline H.G. Wells

  • Full Member
  • ***
  • Posts: 116
    • View Profile
  • Your Engine: Mild 383 SBC or 498 blown BBC
  • Your Track: Currently San Antonio, past Amarillo, Ardmore OK, Noble OK
  • Your Vehicle: late 60's FED of unknown origin
TH400 in an Altered
« on: March 24, 2018, 02:45:37 PM »
Looking for some guidance on a trans issue.

Helping a friend with a new altered and he is looking to swap the powertrain from his other car into a new hardtail altered chassis.
Altered was running a PG, but we want to run the current TH400 as a two speed in the altered. This gives a more favorable gear ratio, + saves $$ from buying a new trans. Driveshaft is not an issue as there is only 1/2 difference, but he was concerned about having a rear trans mount.
Never ran mounts on a glide in dragsters that I have played with, but not sure if the added weight of the TH would be a concern?
Anyone experience running a TH400 in an altered?

Ultimately this car will have a clutch.
Racecar spelled backwards is racecaR

Offline Calkins

  • Jr. Member
  • **
  • Posts: 69
  • On Any Sunday
    • View Profile
  • Your Best Time: 1/8th Mile - 5.77 @ 117
  • Your Track: Humboldt, IA - Humboldt County Dragway
  • Your Vehicle: 1997 Canode 225" Ex-Nostalgia Top Fueler
  • General Location: Midwest
Re: TH400 in an Altered
« Reply #1 on: March 24, 2018, 02:59:47 PM »
If you have a motor plate between the engine and transmission and mounting ears at the front of the engine, I believe you do not want to run a rear transmission mount.  If you do, the chassis will flex, and you start braking stuff.  Hopefully Roo or someone with more knowledge than me will add to this.

Personally, I think swapping out a Powerglide for a TH400 is a great idea.  I wouldn't be afraid of running it as a three speed either.  That would keep in engine RPM in the sweat spot (power band).
Justin Calkins - Iowa Falls, Iowa  USA

UNDER CONSTRUCTION:  1997 Hal Canode 225" FED

Offline jeff/21

  • Full Member
  • ***
  • Posts: 186
    • View Profile
  • Your Best Time: 8.24
  • Your Track: any with-in a 6hr radius
  • Your Vehicle: fed
Re: TH400 in an Altered
« Reply #2 on: March 24, 2018, 04:09:26 PM »
That is one heavy trans to hang from the bellhousing I would add a support but wouldn't bolt it solid
what motor are you running?
any pics?
have a nice season

Offline H.G. Wells

  • Full Member
  • ***
  • Posts: 116
    • View Profile
  • Your Engine: Mild 383 SBC or 498 blown BBC
  • Your Track: Currently San Antonio, past Amarillo, Ardmore OK, Noble OK
  • Your Vehicle: late 60's FED of unknown origin
Re: TH400 in an Altered
« Reply #3 on: March 24, 2018, 04:38:49 PM »
Jeff it is a BBC, initially aky injection then blown.
And yes the biggest concern was the weight. But I know in our FEDs you do not run a rear mount with a motor plate. When you tie it all together, if the chassis flexes the trans is going to be your weak point, that is why we leave the PG float.
Racecar spelled backwards is racecaR

Offline BK

  • Sr. Member
  • ****
  • Posts: 311
    • View Profile
  • Your Best Time: 8.45 / 5.30
  • Your Track: Empire Dagway
  • Your Vehicle: Late 70's FED
Re: TH400 in an Altered
« Reply #4 on: March 25, 2018, 01:51:33 PM »
 I tried looking at Promods as a lot of them use 400s. It was hard to say for sure but I think they have rear mounts. I wouldnt worry about adding one if you decide to, my Spitzer Altered has a solid rear trans mount that doubles as the engine limiter. No breakage issues. I dont think you get a lot of flex with an Altered.

Offline H.G. Wells

  • Full Member
  • ***
  • Posts: 116
    • View Profile
  • Your Engine: Mild 383 SBC or 498 blown BBC
  • Your Track: Currently San Antonio, past Amarillo, Ardmore OK, Noble OK
  • Your Vehicle: late 60's FED of unknown origin
Re: TH400 in an Altered
« Reply #5 on: March 25, 2018, 03:17:06 PM »
BK, you say your Spritzer has a sold rear mount? does it use a rubber isolator, or is it actually mounted solid with no give?
Racecar spelled backwards is racecaR

Offline Curly1

  • Sr. Member
  • ****
  • Posts: 261
    • View Profile
    • AireTex Compressors
  • Your Best Time: 7.95 @ 167 1/4 mile
  • Your Track: Texas Motorplex
  • Your Vehicle: 125" Altered
Re: TH400 in an Altered
« Reply #6 on: April 03, 2018, 09:57:41 AM »
Mine has a rear trans mount but I just have rear of transmission sitting on it. I do not bolt it down on it.