Stock Delorean throttle bodies - why so big?

[Spittybug]

I've totally converted over to speed density rather than alpha-n and have no issues at all. The extra definition afforded by simply reducing the effective area of the throttle body did the trick. It's driving better than ever with no sluggish spots or stumbles. Closed loop idle compensates for A/C kicking on and off nicely. I need to go back in and wire up the buzzer (totally forgot about it) to act as a warning for any overheating should I lose a hose or anything. Easy safety!

While I like the look of Darcom's dual throttle bodies and keeping the long runners of the stock intake (better theoretical power but is it noticeable in actual use?), I have to believe that routing cooler intake air might be better. Looks bad ass!

[nkemp]

I know I'm a bit late to this party but .... I was reading your post http://dmctalk.org/showthread.php?75...l=1#post110541 shortly after reading:

Thegeneral rule is: the bigger the size, the higher the RPM needed for a kick ofpower. If your new throttle body is too big your vehicle will feel tired atlower RPMs, while really taking off powerfully at higher RPMs (when theengine’s demand of air flow matches up with the the internal bore’s biggersize).


From <https://blog.tdotperformance.ca/guid...throttle-body/>

Sounds like the original problem.


But it still begs the original question for this thread. I have three PRV's (last two on engine stands):
- The original in 897: 2 x 46 mm … an area of 3,324 mm2 each, 6,647mm2 total
- '92 Eagle Premier 3.0L: 1x50mm, 150bhp … A≈ 1,964 mm2
- '88 Peugeot 505 2.8L EFI, stock intake manifold same as 3.0L. 145bhp: 1x55mm … A= 2,376 mm2

In the above referenced post you said:

optimal throttle body diameter of 52.6 mm (2176 mm2 area)

Which is pretty close to the 505 2.8L with the newer intake manifold and has a 55 mm TB on it with 2,376mm2

And yet the 3.0L has only 1,964mm2

So why are the originals so big? The big honkin DeLorean intake manifold (area, volume, length, all)? It runs reasonably well theoretically oversized.

What drives OEM sizing? Or TB size in general?

[nkemp]

I think the answer to the original question involves running the equation as a 3 cylinder engine to determine each TB size. In essence, our airflow with the dual TBs is two isolated engines with 3 cylinders each. The air after the TB is isolated from the other. The lower profile intake manifold does not split out the two sides so it gets treated as a 6 cylinder engine. Air is common after the TB in the new intake. And that is likely why the need to run such smaller TBs on the new intake manifold.

If I ran the numbers right, the diameter for each TB in the dual setup is 34.69 mm. That is less overkill than running it as a 6 cylinder.

I was almost asleep when this came to me, and I'm sleepy as I write this. So feel free to give it a dose of reality should it be wrong.

And it still seems that the 3.0L TB should be bigger than the 2.8L TB even though they are not that way on the two extra engines I have.

Now back to

[nkemp]

This post is to correct a math error for any future readers.

Years later I spotted an error in my post. Even with the corrected numbers, the question i presented still stands. Why so big?

Originally I said "3,324 mm2 each" when that should have been the 3,324 mm2 total.

But it still begs the original question for this thread. I have three PRV's (last two on engine stands):
- The original in 897: 2 x 46 mm ? an area of 3,324 mm2 each, 6,647mm2 total
- '92 Eagle Premier 3.0L: 1x50mm, 150bhp ? A≈ 1,964 mm2
- '88 Peugeot 505 2.8L EFI, stock intake manifold same as 3.0L. 145bhp: 1x55mm ? A= 2,376 mm2

It should read as:
- The original in 897: 2 x 46 mm ? an area of 1662 mm2 each, 3,324 mm2 total
- '92 Eagle Premier 3.0L: 1x50mm, 150bhp … A≈ 1,964 mm2
- '88 Peugeot 505 2.8L EFI, stock intake manifold same as 3.0L. 145bhp: 1x55mm … A= 2,376 mm2

[FABombjoy]

My total guess, could be way off. Would be curious if someone knows for sure:

The K-jet metering plate is a 2nd upstream throttle, the opening of which is determined by airflow & fuel pressure.
The primary cable-driven throttle may have to be larger to improve throttle response, so the k-jet plate can react more quickly?

[nkemp]

For the nuts of it, I measured the hole the metering plate sits in, The area of the throat is 5026mm2. The throttle body area is about 1684mm2 less than the metering plate hole.