Pennock's Fiero Forum
  Technical Discussion & Questions
  Speedo reading after 3800 swap

Post New Topic  Post A Reply
Email This Page to Someone! | Printable Version


next newest topic | next oldest topic
Speedo reading after 3800 swap by Lou6t4gto
Started on: 01-16-2015 04:02 PM
Replies: 12 (227 views)
Last post by: Lou6t4gto on 01-25-2015 04:23 PM
Lou6t4gto
Member
Posts: 8436
From: sarasota
Registered: May 2008


Feedback score:    (7)
Leave feedback

Rate this member

Report this Post01-16-2015 04:02 PM Click Here to See the Profile for Lou6t4gtoClick Here to Email Lou6t4gtoSend a Private Message to Lou6t4gtoEdit/Delete MessageReply w/QuoteDirect Link to This Post
After installing the 3800SC, the speedometer is hooked up and working. Question is the Fiero was calibrated for 215/60-15 tires, the 4t65e-HD from a 1997 Riviera was calibrated for WHAT Tires ? Is there a dimensional difference that affects the Speedometer reading ?? didn't Riviera's have 16 or 17 inch rims? Diameter difference ? Thanks
IP: Logged
PFF
System Bot
Lou6t4gto
Member
Posts: 8436
From: sarasota
Registered: May 2008


Feedback score:    (7)
Leave feedback

Rate this member

Report this Post01-17-2015 12:39 AM Click Here to See the Profile for Lou6t4gtoClick Here to Email Lou6t4gtoSend a Private Message to Lou6t4gtoEdit/Delete MessageReply w/QuoteDirect Link to This Post
All these swaps, and no one's asked this before ? Diameter of a stock 97 Riviera tire ?
IP: Logged
PaulJK
Member
Posts: 6633
From: Los Angeles
Registered: Oct 2001


Feedback score:    (25)
Leave feedback





Total ratings: 237
Rate this member

Report this Post01-17-2015 03:15 AM Click Here to See the Profile for PaulJKSend a Private Message to PaulJKEdit/Delete MessageReply w/QuoteDirect Link to This Post
After my swap was done (1999 3800SC w/ 4 speed auto), I was using my TomTom GPS and found the fiero speedo was reading 6 mph higher than my real speed at 65-70 mph, e.g., 70 mph on the speedo meant i was really going 64 mph. This meant the odo was also off and gas mileage calculations would be higher than actual. I later installed digital guages with a GPS speedo that correcte the problem.

sorry i couldn't answer the exact question you asked, but this is all the info i have that applies

[This message has been edited by PaulJK (edited 01-17-2015).]

IP: Logged
nosrac
Member
Posts: 3500
From: Euless, TX, US
Registered: Jan 2005


Feedback score:    (6)
Leave feedback





Total ratings: 50
Rate this member

Report this Post01-17-2015 02:34 PM Click Here to See the Profile for nosracSend a Private Message to nosracEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Lou6t4gto:

After installing the 3800SC, the speedometer is hooked up and working. Question is the Fiero was calibrated for 215/60-15 tires, the 4t65e-HD from a 1997 Riviera was calibrated for WHAT Tires ? Is there a dimensional difference that affects the Speedometer reading ?? didn't Riviera's have 16 or 17 inch rims? Diameter difference ? Thanks


yes, I upped my rear tire height an extra size. I think you need to calibrated to the GP tire diameter. I think it is 26". So you would want to get a tire that is once size larger than recommended for the Fiero. If you have 15x7x60 in the rear get 15x7x65.
IP: Logged
Phil
Member
Posts: 7029
From: Coventry, RI
Registered: Apr 99


Feedback score: (2)
Leave feedback





Total ratings: 154
Rate this member

Report this Post01-17-2015 04:58 PM Click Here to See the Profile for PhilClick Here to Email PhilSend a Private Message to PhilEdit/Delete MessageReply w/QuoteDirect Link to This Post
Dakota digital sells an adjustable speedo interface that you can install.
IP: Logged
Lou6t4gto
Member
Posts: 8436
From: sarasota
Registered: May 2008


Feedback score:    (7)
Leave feedback

Rate this member

Report this Post01-17-2015 05:27 PM Click Here to See the Profile for Lou6t4gtoClick Here to Email Lou6t4gtoSend a Private Message to Lou6t4gtoEdit/Delete MessageReply w/QuoteDirect Link to This Post
OK, I' was planning on 235 /60 -16s (they ARE 26" tall, so that should work) Thanks
IP: Logged
jmbishop
Member
Posts: 4419
From: Probably Texas
Registered: Jul 2006


Feedback score: N/A
Leave feedback





Total ratings: 168
Rate this member

Report this Post01-17-2015 05:36 PM Click Here to See the Profile for jmbishopClick Here to Email jmbishopSend a Private Message to jmbishopEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Phil:

Dakota digital sells an adjustable speedo interface that you can install.


And gps senders are available, they run
Around $100
IP: Logged
PaulJK
Member
Posts: 6633
From: Los Angeles
Registered: Oct 2001


Feedback score:    (25)
Leave feedback





Total ratings: 237
Rate this member

Report this Post01-17-2015 09:09 PM Click Here to See the Profile for PaulJKSend a Private Message to PaulJKEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Lou6t4gto:

OK, I' was planning on 235 /60 -16s (they ARE 26" tall, so that should work) Thanks



just a thought. Changing the tire size might also screw up your gas mileage. Don't know what you pay for tires, but you might consider changing to a gps speedo. Might be cheaper in the long run.

Or put a little GPS unit like TomTom or Garmin in the corner of the windshield.

[This message has been edited by PaulJK (edited 01-17-2015).]

IP: Logged
Lou6t4gto
Member
Posts: 8436
From: sarasota
Registered: May 2008


Feedback score:    (7)
Leave feedback

Rate this member

Report this Post01-18-2015 12:10 AM Click Here to See the Profile for Lou6t4gtoClick Here to Email Lou6t4gtoSend a Private Message to Lou6t4gtoEdit/Delete MessageReply w/QuoteDirect Link to This Post
I would think "Taller tires" would be Better on gas, not worse. (Less RPMs)
IP: Logged
PaulJK
Member
Posts: 6633
From: Los Angeles
Registered: Oct 2001


Feedback score:    (25)
Leave feedback





Total ratings: 237
Rate this member

Report this Post01-18-2015 05:25 AM Click Here to See the Profile for PaulJKSend a Private Message to PaulJKEdit/Delete MessageReply w/QuoteDirect Link to This Post
That's what i first thought too, but putting on taller tires is like putting in taller gears in the rear end. Anytime i've gone with larger wheels and tires, 15" to 16", 14 to 15, my mpg has gone down; put on smaller ones 16" to 15", 15 to 14, and the mpg went up. (?)
IP: Logged
Phil
Member
Posts: 7029
From: Coventry, RI
Registered: Apr 99


Feedback score: (2)
Leave feedback





Total ratings: 154
Rate this member

Report this Post01-18-2015 08:14 AM Click Here to See the Profile for PhilClick Here to Email PhilSend a Private Message to PhilEdit/Delete MessageReply w/QuoteDirect Link to This Post
Your odometer works on the RPM of the output shaft of your tranny. If you put on smaller dia tires your car your actual miles traveled will be less that your odometer indicates. Visa versa for larger dia tires. You would have to calculate mileage on actual miles traveled not on your odometer reading.
IP: Logged
PFF
System Bot
fieroguru
Member
Posts: 11307
From: Champaign, IL
Registered: Aug 2003


Feedback score:    (45)
Leave feedback





Total ratings: 255
Rate this member

Report this Post01-18-2015 09:03 AM Click Here to See the Profile for fieroguruSend a Private Message to fieroguruEdit/Delete MessageReply w/QuoteDirect Link to This Post
You can also adjust for the tire size (whatever size you want to run) in the tune to make the speedo work right too.
IP: Logged
Lou6t4gto
Member
Posts: 8436
From: sarasota
Registered: May 2008


Feedback score:    (7)
Leave feedback

Rate this member

Report this Post01-25-2015 04:23 PM Click Here to See the Profile for Lou6t4gtoClick Here to Email Lou6t4gtoSend a Private Message to Lou6t4gtoEdit/Delete MessageReply w/QuoteDirect Link to This Post
What I'm thinking, the 4t65e-HD out of the riviera was calculated for the Riviera's 16" wheel / 25.5" tire, so as long as I keep the outer diameter the same as the Riviera Was, it Should read correct, right ? And, whatever MPG the Riviera got, the Fiero should do "Better" because of 1000 pounds Less weight, correct ?
wouldn't the theory of a smaller tire getting better MPG Only work "around town", Not highway ?
IP: Logged

next newest topic | next oldest topic

All times are ET (US)

Post New Topic  Post A Reply
Hop to:

Contact Us | Back To Main Page

Advertizing on PFF | Fiero Parts Vendors
PFF Merchandise | Fiero Gallery | Ogre's Cave
Real-Time Chat | Fiero Related Auctions on eBay



Copyright (c) 1999, C. Pennock