Throttle Body Spacer

[Drahcir495]

I’m having Jeff Leigh bore out my throttle body and I have a question about having my spacer machined to match. There are these inner rings, like a screw for lack of a better word ->

 

 

Are these critical? Will machining some, if not all of these out, negate the benefits of the spacer? Do I even need the spacer because of the bigger bore? 

[Ωhm]

37 minutes ago, Drahcir495 said:

Are these critical? Will machining some, if not all of these out, negate the benefits of the spacer? Do I even need the spacer because of the bigger bore?

 

I think you'll lose the patented Helix Bore Design.

 

The spacer utilizes its unique, patented Helix Bore design to spin the incoming air charge as it passes through the throttle body spacer. The spinning air action boosts the velocity of the incoming air and contributes to better atomization of the air/fuel mixture as the air charge enters the combustion chamber. The end result is more part-throttle torque and improved mid-range power.

[Drahcir495]

2 hours ago, Ωhm said:

 

I think you'll lose the patented Helix Bore Design.

 

The spacer utilizes its unique, patented Helix Bore design to spin the incoming air charge as it passes through the throttle body spacer. The spinning air action boosts the velocity of the incoming air and contributes to better atomization of the air/fuel mixture as the air charge enters the combustion chamber. The end result is more part-throttle torque and improved mid-range power.

I think I would lose that also. I would assume that having just a enlarge tube will not provide any benefit? In your opinion? 

[89 MJ]

I’ve read that having a TB spacer on these doesn’t add any power or mileage benefit anyways. I wouldn’t run it to be honest. That said, on this site, Mod 12 was a spacer on an HO XJ. He said it added a little bit of responsiveness and fuel economy. 
http://www.jeep4.0performance.4mg.com/diary.html

[ghetdjc320]

Removing the taper from the throttle body is also counterproductive to your low end torque. The taper increases velocity.

[cruiser54]

Ditch the spacer. 

[Gojira94]

Saying this may make me sound like the annoying kid in The Polar Express... TB spacers only really have any benefit in systems that either introduce fuel above the plenum (carb, TBI) or early per-bank batch-fire systems like the 92-93 GM 5.7L LT1 ('fogged plenum'). No help whatsoever in systems where fuel is introduced just above the intake runner of the head, especially really short head intake runners like the I-6 heads.

 

An engine is a pump, and at maximum it'll only draw air through itself at the velocity dictated by the head/ cam(s)/ valvetrain, barring restriction at the throttle plate and exhaust. A great flowing intake won't help a restrictive exhaust, and vice-versa. Minimal restriction at both ends allows the heads/ cam(s)/ valvetrain to operate unimpeded at their inherent volumetric efficiency, as good or as bad as that might be. Swirling air in the plenum won't change the nature of what's going on at the intake valve on the 4.0. A spacer on a TBI 2.5L with good flowing exhaust and a cool air charge would see a slight improvement though.

 

Engines make peak torque where volumetric efficiency peaks and, coincidentally, where the least amount of timing advance is needed to meet the point of MBT (maximum brake torque). Nothing changes that, short of changing characteristics of heads/ cam/ displacement or forced induction. And then, adding more fuel via bigger injectors, less restrictive induction and freer flowing exhaust are 'supporting mods.'

 

A taper at the inlet might increase velocity and turbulence in the plenum. However, valve events control the pressure waves produced backward into the intake runner and outward into the exhaust runner, and pressure waves are more pronounced during intake/ exhaust overlap. In short, any swirl/ velocity are of no use if they're halted in the manifold runner/ head intake runner, as air there moves at a rate dictated by the valves. At that point, velocity and swirl are governed by the combustion chamber design, and how efficiently the charge moves out of the exhaust valve after combustion. At which point the exhaust system becomes an important consideration to keep the exhaust pressure wave/ exhaust gasses moving. Needing some amount of "backpressure" is a myth. You can restrict the exhaust a bit to band-aid poor velocity upstream (think cam and heads too big with too little dynamic compression/ "lazy ports") but an efficiently designed engine doesn't need it. Longer intake runners do make more low RPM torque because of consistency of volume and momentum of incoming air, at low RPMs. A spacer only increases the effective plenum/ runners' length by a neglible amount, anyway.

 

None of the Jeep/ AMC/ Chrysler I-6 heads have a very efficient, fast-burning head. This means more timing advance is needed to complete combustion by 12* - 14* ATDC (where MBT lives), as compared to a more efficient chamber design. The Edelbrock head has that more efficient, faster-burning chamber, but it's for a completely different build than stock with some bolt-ons like we're talking here.

[cruiser54]

Yeah. a waste of money

[Drahcir495]

Thank you very much Gojira94 for the awesome explanation. I am going with all your advice and “ditching” the spacer as Cruiser54 said. Thank you all

[ghetdjc320]

Bang for buck, I haven’t seen any 4.0 mods that return decent gains for the cost aside from diy forced induction. 

[89 MJ]

35 minutes ago, ghetdjc320 said:

Bang for buck, I haven’t seen any 4.0 mods that return decent gains for the cost aside from diy forced induction. 

I mostly agree with this. Advancing the timing with a high altitude CPS did have some improvement, but it only helps midrange power. I think the bored TB added a minute amount of power as well. Fuel injectors made no difference on my truck. 

[Drahcir495]

I paid a fair amount of money for it too. I will just end up selling it to offset the cost off of the machining. Thanks again 

[ghetdjc320]

25 minutes ago, Drahcir495 said:

I paid a fair amount of money for it too. I will just end up selling it to offset the cost off of the machining. Thanks again 

You could also offset the machining cost by not having it done 

[TurboedMJ]

If you want to add noticeable power for not a huge amount of money, find a 99+ plenum intake manifold. You will notice the power. 

 

http://mallcrawlin.com/forum/showthread.php?6355-4-0L-99-intake-manifold-swap-with-REAL-DYNO-NUMBERS!

 

[Drahcir495]

Lol - good point.

 

I will have to look into that intake TurboedMJ 

[TurboedMJ]

You may also have to port match the intake side of the head, and if your feeling adventurous you can carve out a straight shot in each intake port on the head to make a better pathway for fuel to the valves. 

[TurboedMJ]

Here's a visualizer. Not sure if it would be wise to do it while the head is on the block, as shavings could get in through open valves...

[75sv1]

I have installed the 99+ intake on a 98 XJ. Also, did the bored TB. Also, with that is a 2.5 CAT back. I gained a few HPs. More I could feel it on inclines or hills. I did not port the intake though. If you read the Mall Crawling thread, not that he also changed injectors and increased fuel pressure. I'd also wonder about having the ECM tuned. I did bore my own TBs. I did put a taper before and after the butterfly. I think it helps, but no real data etc. 

[Gojira94]

Looking for bolt-on gains on the Renix system has diminishing returns with a stock engine, but it's true that a few bolt-on mods can yield an additional 8-12 HP and 12-18 TQ. It can deal with more airflow and corresponding fuel via injector pulsewidth and O2 feedback. I see numerous internet threads that indicate Renix can deal with larger displacement strokers as well, as long as airflow in/out ("VE") and fuel are matched well enough for Renix to make it stoich. My own engine is an HO from a 93 YJ and will be running on Renix with all the required sensor substitutions for it. I'm also going to be running a 99-01 intake because it came with the drivetrain and it matches the PS pulley setup I snagged from the boneyard for $8. Also going to have a CAI, bored TB and full 2.5" exhaust. I snagged some good Bosch 228cc/min injectors to try on the cheap, to see how well it matches the VE requirement of this particular arrangement. Not looking for significant gains, I expect a good-mannered engine with approximate mild gains stated above.

[75sv1]

        One thing to think about is the Compression Ratio. I think stock is around 8.8. I'm at 9.45 on a 2000 XJ on a mini stroker. I'd want a 9.3 CR for 87-88 octane. Mine hasn't settled in yet. Dealing with a misfire issue. I'd look at a Cometic gasket. Reduce the bore from the 4.0 to a 3.8XX. I forget what their min diameter is. I think a stock gasket is 0.042. Might go 0.038-0.040. There is a variation on combustion chambers. My 2000 FSM says 52 to 58 ccs. I measured about 54-55 CCs. I had to open up to 59 CCs and a 4.0 diameter with 0.050 thickness to achieve the 9.45 CR. My pistons are 0.015 above the deck. 

        Also, on the 99+ Intake, I think overall it will add some HP. I think just bolting it on, about 5 hp. One poster from years ago, said he lost 5 hp. I think it has potential for more HP. Still, I think this is more in the lower RMPs. Which for a Daily Driver is good. 

        I am also running the 12 hole injectors. Not sure on them. Nothing negative though. I have run the 4 hole Fords. I saw no real improvements.  I think the engine did run smoother on both '98s I installed them on. 

        I think the main improvements would be in porting the heads, slightly bigger valves. 1.950 intakes and 1.550 exhaust.  A bit higher lift camshaft, up to .450. Also, porting the intake. The 99+ I have, needs the injector bosses reduced and evened up. On the Mall Crawler stuff, Jordan88 did do some porting on his intake, too.