How far off is your dash indicated MPH with GPS MPH?


With bigger tires and gears, it is best to change the speedo gear in the transfer case so your speedo is within 1mph of GPS speed. Your trans and ECU will love you for this.

It's only a 6% difference. Close enough for a lazy man.

I was using the wrong percentage. The difference in speed and distance is 6%. I had it at 16.7% earlier. I got 13.45 MPG and on the last tank I had 14.4.

Surprisingly the engine will work better and the trans especially will shift better with the true speed. It is easy to do, just change out the gear in the transfer case, 1 bolt. They are like $20-25 each. 6% is what like dash 52mph and gps 55mph or dash 65mph and gps 70mph?
I guess I mean within 1mph not 1%. I like 0-1mph higher dash than GPS rather than lower. It makes me feel better.


Sounds like you are getting closer with your engine finally.

I went 256 highway miles (55-60 mph) on 14.75 gallons yesterday. Looks to be about 17.3~ MPG. I'm sure it would be a little better without me using the boost 5-6 times and getting lost having to turn around at red lights for about 30 minutes.

That's impressive, only going into boost 5-6 times in 256 miles.

Order was placed with 505 on Dec. 21st and haven't heard a thing from them despite phone calls, voice mail, and email. Just filed a claim with Paypal to get my money back so I can order from F&B instead.

I just talked to Golen and their dyno actually broke while the jeep was on it. I told him about the TB being the bottleneck and 505's sucky-*** service. He's going to order one from F&B and dyno it with both to get the results, hopefully, by the end of next week.

P.S. Don't buy from 505.

Not to defend 505, but it has been the holidays, maybe they closed for 2 weeks as some small companies do, or more likely they don't have one in stock sitting on the shelf and had to order one from F+B and F+B didn't have one on the shelf either and they have to build it and they were on holiday schedule, and so on.
Just saying before you slander someone online.

Finally someone is dyno'ing back to back TBs on a 4.6L stroker. A real TB shoot out.
Maybe they can do a stock TB, a bored 62mm TB and a 68 or 70mm F+B TB.
That is a magazine article in the making.

If someone who owns a business is going to shut down for two weeks, regardless of the time of the year, they should update their voice mail box to indicate that so that people know what to expect or don't place an order that won't be gotten around to until 3 weeks or a month later. That's good business management 101. Failing to do so is a good way to make bad impressions.

There is no way of know what's going on without an appropriate message on the voice mail box or at least an automated out of office reply setup on their email. I don't mind if they're on vacation for two whole weeks, but if that isn't indicated it is vexing.

Been there, I feel your pain.

Golen has dyno'd the before and after results with the 62 and 68 mm TB. ... here are the heart-rending results:

62MM TB: 3PSI max @ 318lbs Tq
68MM TB with bored intake: 5 PSI max @ 325lbs

HP changes were negligible as well.

7lbs of torque were gained with the TB and SC intake modification.

He said he's ordered a SC kit from Magnuson for a buyer in Portugal for building with one of his engines before that claims 100/150 extra HP/TQ at the wheels, and an upgrade that does 200/250 (also at the wheels). The 85mm TB is recommended for one of those SC's.

I'm still going to have my TB installed and the SC ported at the neck and then dyno'd to see where it's at. Since I only had a shoddy dyno to begin with the only way to really tell any difference will be by the seat of the pants. But if I don't feel a difference by the seat of my pants then it wasn't worth doing to begin with, and at least that knowledge will be out there for future buyers. Don't buy a 4.0 SC kit for a 4.6 stroker if you want to gain any real power. The stroker should have had 290-305~ TQ off the bat depending upon your build regardless of boost.

I know I can feel a difference in mine whenever I give it moderate to hard throttle, but part throttle was the same as before.

I'm going to investigate running a 50mm pulley to up the boost level a pound or two when I get the 68mm and see how it fares on my setup.

The larger the engine in relation to the existing airflow capacity of the SC the more of an obstruction the SC becomes. I guess if you think about it like this it makes sense... but going from 3 lbs to another 2lbs and only gaining 7lbs of torque doesn't make any sense; unless it jumped up to almost 5 psi and quickly bled down. I forgot to ask him to specify the exact nature of his boost. If that was the case, and it certainly would be given the nature of building boost in the manifold relative to the ability of the cylinders' displacement being able to displace the pressure quick enough to bleed of pressure until vacuum is restored. So in those instances you will get off the line pull from idle, but not much more power than a stroker at cruising. Possibly even less given the parasitic nature of running a supercharger and the fact that it becomes an obstruction once it's no longer boosting.

He said he was only making about 2 lbs of boost with the Sprintex specified recirc-valve location. When he put it up at the TB like I did mine he gained 1lb of boost.

Ouch! Well thank you for doing all the leg work... I was debating doing the 4.0 sc on my 4.6 sometime down the road It certainly doesn't look to be worth it- Sorry you had to go through all that.

are you using a stock cylinder head?

Golen has your motor and SC and both throttle bodies to dyno?

If that is the case and this is the results of your 4.6L and Sprintex, then +2psi boost no HP and 7 TQ gains tells me that your head flow sucks and the cam is too small. The boost is just 'stacking' up and not getting into the engine. Or the IAT at the manifold is so high without the 7th inj or Meth inj that the increased boost is negated by the increased air IAT.

That is a M90 kit from Magnum Powers. $$$$. $4995 kit, $295 intake air kit, $349 85mmTB. It won't fit under the hood of a XJ and you would lose the A/C.
The 85mm TB is beautiful, I have one.

I haven't seen any numbers like that except estimates and computer sims.

We have a 49mm SC pulley on the Sprintex and that really pumped up the boost. With 4.0L, Sprintex, stock crank pulley, 49mm SC pulley, ported big valve head, stock cam with 1.7:1 Yella Terra roller rockers, 70mm TB and ported SC inlet manifold, revolver headers and 2.5" down pipe and exhaust, We are getting 10-11 pounds boost and IATs at the engine intake manifold, after the SC, 140's*F and dropping when under boost with the 7th inj and Meth, No Intercooler.

There is no SC obstruction when not in boost. The bypass valve opens and intake air bypasses running thru the SC and the SC is free spinning and only requires like 2-3 HP to spin when not making boost.

I don't understand this. Where did he have the recirc/bypass valve before and where did he put it?

I found that when the valve was plumbed to the inlet side of the SC after the TB and only saw vacuum and 0 vacuum, the valve would creep open and leak boost backwards thru the valve and lose/drop boost.
When I plumbed it to the engine intake manifold, after the SC where it saw vacuum and boost, the boost would help the valve stay closed and not leak any boost.

Forgot to mention, this is a 4.2 liter AMC engine turned 4.6 stroker. I believe it was an old CJ of some sort utilizing the long tube headers, so it's not a precise replacement, but the displacement and choice of SC in regards to that displacement shouldn't be far off from my setup. The actual tune itself will make the most difference and I forgot to ask what he was using.

1.7 YT's? I thought you said you had Harland Sharp make you a a custom set for 1.7's? YT only sells 1.6 unless you call them directly and ask to have 1.7's made it seems.

The head on this engine is a custom golen head that is the same as the stock design as far as flow goes, but improves upon the chambers to prevent it from cracking (as was the case with a 2000-2001 style engine which I have).

WHen I say obstruction, I mean the juice isn't worth the squeeze. You're using HP to turn $3800 rotors that are not eliminating the vacuum condition inside the manifold. It could go either way since they might reduce the vacuum which is still a positive pressure reading over total vacuum of a stock engine. Is the bang worth the buck? Good question. It would take someone with a stock 4.0 to measure the air intake readings at the TB in relation to the vacuum readings and someone with a supercharged stroker to do the same to tell just how much of a difference there is between the two all throughout the RPM ranges to see what's what where and when. In the end I had to purchase the SplitSecond FIC and the 68mm TB, along with some extra tools. Total price of a truly supercharged Sprintex Stroker... $4600. Plus the Wideband 02 sensors I had installed? $5000. That's not including the labor of course. I should have just installed the thing myself. If I would have been privy to the Split-Second plug and play box before hand I probably would have. I'm horrible at soldering, and soldering onto a wiring harness in the engine bay with 30+ extra wires around it? Out of the question.

He had it where Sprintex told him to put it, which is the bypass tunnel location. It is now at the TB as mine is. He had 2lbs and gaines 1lb for 3. I had 0 and gained up to 3. It definitely works for strokers.

You must have some serious cold in PA to get those numbers. I only have 15%~ more displacement but you have 400% more boost. My cam is only stock, but it's staying that way. This is the 4th and LAST stroker. No more cam failures. I don't care if the Comp/Crane-Cams-manufactured-in-China-ground-in-the-US company claims it's made of Wolverine's claws. A fully functional OEM cam with low end torque that lasts tens of thousands verses tens of tens is unconditionally superior in my book.

"I found that when the valve was plumbed to the inlet side of the SC after the TB and only saw vacuum and 0 vacuum, the valve would creep open and leak boost backwards thru the valve and lose/drop boost.
When I plumbed it to the engine intake manifold, after the SC where it saw vacuum and boost, the boost would help the valve stay closed and not leak any boost."

Speak for yourself. Stroke it and your results will change. The amount of residual vacuum from the stroked engine is too much for the SC to build enough pressure fast enough to reach the initial 15 inches required to close the port. Putting it at the TB solved that problem for me since the second you hit the throttle it sees atmospheric pressure. The vacuum that is existing inside of that small manifold in regards to a 4.6 vs a 4.0 is too much for the SC to kill off and therefore leaves me with 0 boost. I'm a living testament to that fact.

Alright, back to the reason I came here. I bored out the SC neck-intake and plugged in the 68 MM (after a little angle-grindery to shorten it).

When I floor it now it will pop up to 3.2-3.4 (vs. 2.9-3.0 previously). The throttle cable had to be bored out a hair to fit on the **** of this F&B TB. I had it half forced on before that and after taking a short joy ride it got stuck canted at an angle and I was idling at 1300 RPM's at a long red light and idling through the neighborhood at 30mph on my return. If it's not loosey-goosey and fits snug, fix that before you go on a long journey. Otherwise bring your battery powered drill and bits along.

Now for the important part since none of this has been exactly scientific, seat of the pants. Let me say.... wow. I get pulled into my seat with I floor it from a stand still and the front end raises up. More noticeably when it's dark and you have the lights on. My dad gave it a go after I got it all done and the 34" knobby tires actually spun a little. That's saying a lot since they're about 100lbs a piece and I have an extra 1000lbs of metal on this thing.

If you decide to supercharge a stroker, a 68mm TB with a little dremel work is the only way to go. I'm not sure about the part throttle response as I haven't driven it enough to know, but the fact that I can tell when I floor it means there is definitely more air flow which means at part throttle there is less restriction I'm sure.

.... hmmm, it's about time for a dyno.