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Discussion Starter · #1 ·
The stock throttle body for a Zetec is 55mm. Would a larger throttle body improve HP on a bolt on modded zetec? I would imagine it would hurt low end torque since a larger TB would decrease velocity. Would installing a smaller diameter TB improve low end torque but hurt HP? Wondering if a 48mm TB will move the torque curve lower into the RPM's?

Looking to port match the stock intake to the cylinder head. I'll be deburring and smoothing the cylinder head intake path and unshrouding the valves too. Valves will stay stock but may moderately cam it. Is the 55mm sufficient for the increase in CFM? I have an Escort S/R ECM. No issues?

John
 

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The info I have from the Focus builders book shows only a 1-2 HP increase on an otherwise stock Focus zetec with an AEM intake ( which includes a bigger MAF).
I've read that in general, the larger throttle body gives much quicker throttle response ( more air into engine with less pedal movement). Velocity is not so important as this is air only, not air/fuel like a carb in which low velocity can allow fuel to drop out.

I did some estimates of the actual cross sectional area of the stock throttle body and it is much smaller than it first appears because the throttle pivot take out a big piece of the open area. The cross sectional free area works out to being about a 48mm circle. This is 1 7/8", which is the same cross section as the stock exhaust. My thought is that once you begin opening up the airflow in the rest of the engine and with a larger exhaust, that the TB is probably starting to become a more significant restriction.
I hope to do some junk yard engineering if I can next year. 60mm throttle bodies are used on all sorts of Ford standard v-6s and v-8s ( 4.6, 5.4) from that era and back into the 90's. Hopefully I can find something that would bolt only rather easily.
 

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Nova,

Do NOT port-match the intake to the head unless you have looked at both the intake port overall shape/size and the head port size/shape. Introducing areas of velocity drop/pressure increase in the intake tract is serious folly. If there are any restrictions, remove them as long as it doesn't change the overall port shape/velocity profile. Since we have such small engines, we need as much port velocity as possible at lower/mid RPMs as possible. Look at port intel square inch versus overall square inch and find the areas of restriction. Remove the restriction without FUBARing overall flow (PM me, brother, for more info).
 

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Discussion Starter · #5 ·
Nova,

Do NOT port-match the intake to the head unless you have looked at both the intake port overall shape/size and the head port size/shape. Introducing areas of velocity drop/pressure increase in the intake tract is serious folly. If there are any restrictions, remove them as long as it doesn't change the overall port shape/velocity profile. Since we have such small engines, we need as much port velocity as possible at lower/mid RPMs as possible. Look at port intel square inch versus overall square inch and find the areas of restriction. Remove the restriction without FUBARing overall flow (PM me, brother, for more info).
You da man! PM will follow.

John
 

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All the info I've read on the porting the zetec heads is to only clean up the ports (like the split between the two valves) and do not change the shape and size. Open valve pockets to 85%? of valve size and unshroud the valves.

I'd also like to hear what deathride95 has to say, since I hope to do this too someday.
 

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Discussion Starter · #7 ·
I just sent Deathride a PM but you're right. It would be a good idea to share this info on the open forum. This way you and I can ask whatever relevant questions we may have along with brainstorming with Deathride to figure out what would be the best way to achieve our goals.

Death ride if you're cool with sharing on the open forum I'm good with it. If not, no worries.

John
 

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And yeah, open info is good info.

If you are porting, pay attention to the short-side floor area. Be gentle and smoothly reshape it to take the harsh turn out of it (this applies to both intake and exhaust sides). Teardrop the intake port splitter (think leading edge of an airfoil) to improve transition from the throat to the valve. As to opening the bowl area directly above the valve seat, DO NOT go more than 90%, as you want meat there for a good (minimum 3-angle, but for all-out, 5-angle) valve job. Believe it or not, the most positive difference in flow will be made by just that valve job. On the exhaust side, raise the port roof slightly (to match whatever header/manifold you use) and fill the floor the same amount (air flow wants to stick to the roof, and has been known to stall/revert in the lower right corner). This, in effect, is raising the port for a more direct/smoother line out for the airflow to follow. I have done this on 4.6L DOHC heads with success.
As to unshrouding the valves; very good idea but you have to keep the cylinder bore (not the head gasket bore diameter) in mind. That will dictate how much you can potentially remove to unshroud. Pay attention to the shape of your cut, as it shouldn't be harsh. Any removed material in the chamber will drop compression (so keep in mind how many CC's you remove). Some can be regained by shaving the head or using higher compression pistons.

Again, unless you really want to slow incoming air, DO NOT port-match the intake unless you have opened up the upper intake and this will merely align/keep the port velocity moving. Unless your engine has been modded for more low-end torque, losing any velocity down low will make the car very sluggish (even with a larger throttle body) as port velocity isn't aiding in cylinder-filling. The trick is to experiment with throttle body size until you find the one that doesn't kill low-end and hangs on further into the rpm band (just like carburation, there is too big).

What are your overall plans/goals for the engine? Will it see boost? Will you be revving the piss out of it all the time? Auto or stick car? Final drive ratio and tire size? Believe it or not, this all needs to be considered when modifying the engine.

TQ x RPM /5252 = HP
Any change to torque has a greater effect oh HP than RPM does. Higher RPM moves the HP band up.
 

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I haven't had one of these zetec heads off yet, but I have looked at the photos and I certainly can believe that the good valve job will see the most gains. The valve lift is so low on these engines that I imagine its really important to get that flow moving ASAP when the valves begin opening. Eliminating the shrounding and getting the air to flow smoothly around the valve at low left will be a big plus. Also, I read that going too big on the bowl will create too sharp of a turn for the airflow to flow around the valve seat, stalling flow. I sort of wonder why the bowls are so small from the factory.....maybe more velocity and a smoother transition into the valve seat?

My zetec is in a heavier daily driver ford escort wagon (still lighter than the fat Focuses) with a stock auto, so maintaining bottom end torque is important. I am running the Iceman intake with the stock filter housing and a set of pacesetter headers. I have also pulled the knock sensor to keep it from constantly pulling timing. I started using 89 octane when I did that to get rid of the little bit of pinging I was getting, but picked up a better idle, more torque and it looks like about 1.5 mpg ( I've only gone through a few tanks since the change).
I am amazed at the torque of this little motor now that the timing is not getting retarded. The auto trans will shift to overdrive and lock the torque convertor at about 28 MPH. The engine is running under 1500 rpm and still has plenty of torque to accelerate without unlocking. Feels more like my diesel than a typical gas engine. I hope to upgrade my 98 single pintle injectors next to the later 4 hole design to get better atomization at low speed so I can probably further fatten the lower end torque. I still have to get my underdrive pulley back on to free up a little more power too.
 

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As tracer mentioned, less movement of the throttle body is needed to get the same amount of air into the engine, note that opening the throttle is not a linear amount of increased airflow, having a throttle 50% open is actually letting the majority of the air it can flow through. This is one advantage to an electronic throttle body as 50% input can actually be programmed to be 50% output, or be less sensitive at the lower range pedal travel making a high HP car (or even an oversized throttle body or perhaps ITBs) more streetable.

Generally speaking a throttle body never results in more power, however if it is causing a restriction in the airflow then a bigger throttle body can help. What makes people think it gives more power is that a bigger throttle body opening at 10% might be like opening the stock one 20% open. Effectively this would be like having a heavier foot, but at WOT the bigger throttle body might flow the same amount of air as the stock throttle body (or even less if it causes the velocity of the air to be slowed).

I'm fairly certain 55mm 48mm is plenty for this engine without it being heavily modified, probably even with a ported head and intake.
 

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when they say... 1-2hp increase, they are talking at WOT. there is a trade off from higher velocity higher efficient mix and straight up flow. that was the beauty of the split port motor. best of both worlds. what i would do is calculate the cfm each can flow, and find out if your engine can even use it. think back to the carb days. you can drown an engine way easier than you can starve it.
 

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Marclar....the dual runner intake has always intertested me. I have never been able to come across the runner lengths for the SVT dual runner intake that can be used on the ZETEC. It would be nice if they were at good street usable lengths, however, everything I've read shows that the optimum switch over point from short to long runner is way up at 5200 to 5500 RPM. Does anybody know what length the short runners are? I think the stock zetec is around 15 inch which, IIRC. would pulse the intake at about 3500 Rpm and then again around 7000RPM. Nothing on the road is built like the old 1960's Chrysler RAM AIR set up with 30 inch long runners using,IIRC, the 3rd order pulse.
 

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ya nothing like the 36in ramcharger intakes. i actually learned alot about tuning the cvh back in the day by researching the old chrysler and hemi stuff.. hemis actually are terrible at scavenging on their own, but really take well to forced induction
 

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I've looked at my wife's 2007 Jeep GC with a 3.7 v-6 and there is loads of room for a ramcharger manifold. It seems that the really good basic engineering just doesn't happen so much anymore. I still would like to know the runner lengths on the SVT manifold. I need to start digging around. I do have a friend with an SVT.... I could at least maybe measure it.
 

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On stock FOX Mustang throttle bodies, we would profile the throttle body blade shaft, and knife-edge the blade itself. That was good for quicker tip-in, along with checking/tightening the throttle cable.

What we found best was to keep at least a 5mm difference between the MAF opening and the throttle body throat. That gave us the best of both worlds; good tip-in/low rpm with enough top end enhancement to make it all worth it.

If you experiment with the IMRC opening rpm, you can also find that sweet spot between long-runner (low-rpm) and short-runner (high-rpm) transition.
 

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I did some digging around the net last night and did not come across any kind of generic TB sizing formula.... i guess just too many variables ( throttle body design, number of cyclinders, etc) but I did find some numbers over at the neon forum ( they have little 47 mm TB''s stock). If you figure an 120 cu in engine running 6500 rpm and 100%VE efficiency you need about 225 CFM.

I pulled this off the Neon Forum......

Gary Howell wrote:

"49mm TB flows 252 cfm
52mm TB flows 283 cfm
55mm TB flows 317 cfm
60mm TB flows 377 cfm


It sure does look like the stock 55MM throttle body is big enough for our engines. Estimating VE was all over the place. Old school street engines were estimated at 75 to 85%. But with 4 valves heads and the HP to Displacement numbers from engines, VE has to be pretty high. 145HP from 120 Cu in is 1.2hp/ cu in and is way beyond the old holy grail of 1 hp per cu in.
 

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122*6000/3456 = 194cfm

the 3.7/4.7 s are actually prety good engines. all mercades by design. ive replaced a bunch over the years from overheating, check your water pump. the sad truth, is that i dont even own an escort anymore.. but i have 11 jeeps lol
 

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Our 3.7 has 212,000 miles, mostly suburban and city and doesn't burn a drop of oil. I just got my best mileage ever yesterday at about 24 MPG highway with the A/C on. I am pretty sure the O2 sensors need to be replaced.... it takes a lot of miles after accelerating before the mileage comes back up. From the dyno data I've seen, a good Cat back exhaust and a tune can really wake up the 3.7. Also, it looks like it wouldn't take much to dramatically improve the front aero on the GC. I already closed up the gaps around the radiator and that may be why my mileage was so good.
I just did my water pump, a cooling system clean ( the cleaner really broke loose alot of muck) and put in the larger rad used with the 4.7 (it was even cheaper than the 3.7 rad), flushed brake system, power steering system, and put in a separate trans cooler because the stock one was leaking and the hoses were seeping too (common problem). I hope to keep it another 4 to 5 years and then go to southern CA and get another one to rebuild the drivetrain and upgrade the aero. I bet I can get 28 highway or more with the proper aero out of the low revving 3.7.
 
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