Question about Ford Tbird 3.8L Supercharger
07-30-2017, 04:58 AM
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Year: 1998
Engine: 4.0L 162,000
Question about Ford Tbird 3.8L Supercharger
Here is part of a conversation I recently had-
1) How much boost does a Tbird 3.8L SC make? Im guessing 5-6avg?
2) What are your thoughts on the Split Second FC's
Response-
The Ford Tbird SC is a M90. Same 'size' M90 as I use, I just use the GM M90. Same rotor pack just different housings/case.
Boost mostly depends on the pulley used. Stock intake, heads and cams are such low flowing that Boost is really just a measurement of the 'back pressure' built up in the manifold.
Things that will increase boost is free flowing air inlet, cold air, bigger TB.
Things that will 'decrease' boost but make more power are porting, higher ratio rocker arms, bigger valves, bigger cam, headers and high flow cat and exhaust.
So boost is sort of irrelevant. For a stock piston, head bolt, head gasket engine, the safest and most reliable boost to shoot for is 5-6 pounds. 7-8 pounds of you have an AFR meter and watch it and tune accordingly and run 93 octane. 8-9 pounds if you use water/meth injection and/or intercooler and keep the Charge Intake Air Temp under 140-150*F. Over 9 pounds requires a MLS head gasket and ARP head bolts.
The Split Second FTC1 has worked great for us. It is plug and play with connectors that plug right into the stock ECU. It controls the timing retard and fuel during boost. It has it's own 2 bar MAP sensor built into it and monitors vacuum/boost. It intercepts the CKP and CMP signals and delays they to retard the timing during boost. It also uses the CKP to determine RPM and also controls the 7th injector to add the additional boost needed during boost. The FTC1 comes preprogrammed for a 60lb/hr 7th injector and is user programmable iff desired with vac/boost vs rpm tables for the timing retard and fuel during boost. There are different variants of the FTC1 which Split Second knows all the applications. We have used like 5 different ones.
The nice part of using the 7th injector method is that you leave the stock injectors and ECU tune along. So cold starting, idling, cruising, OBD/emissions are all stock as designed by Jeep. The 60lb/hr 7th injector only turns on during boost. This 1 injector can supply all the fuel needed for boost and is the same as adding 6 10lb/hr bigger than stock injectors (30-36 lb/hr). But instead of adding 6 injectors and having to tune the stock ECU, you just add 1 injector and leave the stock ecu alone and tune the 7th injector with the FTC1.
By spraying the fuel 'thru' the supercharger it cools the compressed air by about 70*F and helps seal the rotors to the case and makes it more efficient.
I will say one thing about the '05-'06 TJ 4.0L and the JK 3.8L and it's stock ECU tune. If you watch/monitor the closed/open loop status on the OBD2 reader, you will see that when it should go into open loop, like WOT of in boost, it will hold/delay and stay in closed loop for about 5-8 seconds before going into open loop. For a SC motor this will cause a lean condition when just going into boost and is a big problem. For the '05-'06 TJ 4.0L and JK 3.8L we use HP tuners and change this time delay into open loop from 5-8 seconds to 0 seconds. Such that as soon as you are in WOT or boost you immediately go into open loop and are able to add the additional fuel needed and avoid the lean condition.
A cobbled together SC system that doesn't have this done will fail.
So a well designed and tuned M90 supercharger will add a real +60 rear wheel HP and +70 rear wheel TQ. All this TQ from just off idle. And will extend your rpm power range by 4-500 rpm. The 4.0L I6 really runs out of steam at about 4000 rpm but with the SC it easily pulls up to 4500-4800 rpm.
Heat is really the supercharger Enemy. It is the charge intake air temp, that is after the SC that matters the most.
A fun thing to watch is on your stock engine, get an OBD2 reader and watch/monitor the IAT while idling, driving and cruising around. Stock it is very high!
For SC you want charge IAT 140-170* under max boost. Over 200*F and you need a spot on tune and good quality gas, over 250*F and you start detonation, over 300*F and you will see engine failure.
Imagine your 3.8L 187hp/200tq becoming 245HP/270TQ. That is what 5-6 pounds of boost can do when properly fueled and cooled.
Building your own kit is fun, satisfying, frustrating, time consuming and risky all at the same time.
A well made complete SC kit is ready to install in 1 day and works as designed reliably and is removable and returns to stock easily should you sell the vehicle. Used kits still have a value of about $1500.
1) How much boost does a Tbird 3.8L SC make? Im guessing 5-6avg?
2) What are your thoughts on the Split Second FC's
Response-
The Ford Tbird SC is a M90. Same 'size' M90 as I use, I just use the GM M90. Same rotor pack just different housings/case.
Boost mostly depends on the pulley used. Stock intake, heads and cams are such low flowing that Boost is really just a measurement of the 'back pressure' built up in the manifold.
Things that will increase boost is free flowing air inlet, cold air, bigger TB.
Things that will 'decrease' boost but make more power are porting, higher ratio rocker arms, bigger valves, bigger cam, headers and high flow cat and exhaust.
So boost is sort of irrelevant. For a stock piston, head bolt, head gasket engine, the safest and most reliable boost to shoot for is 5-6 pounds. 7-8 pounds of you have an AFR meter and watch it and tune accordingly and run 93 octane. 8-9 pounds if you use water/meth injection and/or intercooler and keep the Charge Intake Air Temp under 140-150*F. Over 9 pounds requires a MLS head gasket and ARP head bolts.
The Split Second FTC1 has worked great for us. It is plug and play with connectors that plug right into the stock ECU. It controls the timing retard and fuel during boost. It has it's own 2 bar MAP sensor built into it and monitors vacuum/boost. It intercepts the CKP and CMP signals and delays they to retard the timing during boost. It also uses the CKP to determine RPM and also controls the 7th injector to add the additional boost needed during boost. The FTC1 comes preprogrammed for a 60lb/hr 7th injector and is user programmable iff desired with vac/boost vs rpm tables for the timing retard and fuel during boost. There are different variants of the FTC1 which Split Second knows all the applications. We have used like 5 different ones.
The nice part of using the 7th injector method is that you leave the stock injectors and ECU tune along. So cold starting, idling, cruising, OBD/emissions are all stock as designed by Jeep. The 60lb/hr 7th injector only turns on during boost. This 1 injector can supply all the fuel needed for boost and is the same as adding 6 10lb/hr bigger than stock injectors (30-36 lb/hr). But instead of adding 6 injectors and having to tune the stock ECU, you just add 1 injector and leave the stock ecu alone and tune the 7th injector with the FTC1.
By spraying the fuel 'thru' the supercharger it cools the compressed air by about 70*F and helps seal the rotors to the case and makes it more efficient.
I will say one thing about the '05-'06 TJ 4.0L and the JK 3.8L and it's stock ECU tune. If you watch/monitor the closed/open loop status on the OBD2 reader, you will see that when it should go into open loop, like WOT of in boost, it will hold/delay and stay in closed loop for about 5-8 seconds before going into open loop. For a SC motor this will cause a lean condition when just going into boost and is a big problem. For the '05-'06 TJ 4.0L and JK 3.8L we use HP tuners and change this time delay into open loop from 5-8 seconds to 0 seconds. Such that as soon as you are in WOT or boost you immediately go into open loop and are able to add the additional fuel needed and avoid the lean condition.
A cobbled together SC system that doesn't have this done will fail.
So a well designed and tuned M90 supercharger will add a real +60 rear wheel HP and +70 rear wheel TQ. All this TQ from just off idle. And will extend your rpm power range by 4-500 rpm. The 4.0L I6 really runs out of steam at about 4000 rpm but with the SC it easily pulls up to 4500-4800 rpm.
Heat is really the supercharger Enemy. It is the charge intake air temp, that is after the SC that matters the most.
A fun thing to watch is on your stock engine, get an OBD2 reader and watch/monitor the IAT while idling, driving and cruising around. Stock it is very high!
For SC you want charge IAT 140-170* under max boost. Over 200*F and you need a spot on tune and good quality gas, over 250*F and you start detonation, over 300*F and you will see engine failure.
Imagine your 3.8L 187hp/200tq becoming 245HP/270TQ. That is what 5-6 pounds of boost can do when properly fueled and cooled.
Building your own kit is fun, satisfying, frustrating, time consuming and risky all at the same time.
A well made complete SC kit is ready to install in 1 day and works as designed reliably and is removable and returns to stock easily should you sell the vehicle. Used kits still have a value of about $1500.
