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VolvoHeretic
VolvoHeretic GRM+ Memberand Reader
5/21/22 12:10 p.m.

I always wanted to put 3 Chevy TPI 48mm throttle bodies on my 3 liter Volvo 6 cylinder fuel injected B30 engine. smiley But now just dream of stuffing 2 Mitsubishi td03 turbos in the trunk, each run off of 3 cylinders through dual exhaust. Maybe td04's?

Pete. (l33t FS)
Pete. (l33t FS) GRM+ Memberand MegaDork
5/21/22 1:02 p.m.
DarkMonohue said:
Pete. (l33t FS) said:

How big are the cams?

The ITB-ified bridge ported 13B in my "fun" car has low load/part throttle drivability like a stock engine.  Way way better than similar engines I have had using OE type manifolds or godawful plenum manifolds that I thought were a good idea at the time.

Not enormous. They're 226° @ .050" (Web 577).  Peak power comes in around 7000 RPM, though I am starting to wonder if it's not valvespring limited.   Drivability with a stock plenum style manifold is acceptable, but not inspiring.  Would be better with more time tuning the MS.

 

The real key will come up with a tight lobe separation.  You would be able to advance the intake and/or retard the exhaust to bring midrange torque up with little loss in low speed drivability.

 

The top end would drop, but you have to go through the midrange to get to the top end...

DarkMonohue
DarkMonohue HalfDork
5/21/22 5:50 p.m.
Pete. (l33t FS) said:

The real key will come up with a tight lobe separation.  You would be able to advance the intake and/or retard the exhaust to bring midrange torque up with little loss in low speed drivability.

 

The top end would drop, but you have to go through the midrange to get to the top end...

LSA is probably pretty tight.  Many, many years ago, before I went to MegaSquirt and was still messing around with cam timing, I set the cam timing up to give as much area under the curve as it would give.  I used Streetdyno back then to measure acceleration (by way of ignition waveform) and approximate a dyno run.  Not glamorous, but entirely repeatable.  Based on comparison with a bone stock example, this should be roughly comparable to Dynojet numbers.

The point is that this engine makes a pretty good spread of torque and is incredibly flexible, minus the slightly crappy low-throttle behavior below about 2100 RPM.

There's also a bigger set of cams (234° in / 240° ex @ .050") on the shelf, but I have always assumed they'd be too much for street use (and the stained glass connecting rods), even with ITBs.

Maybe the answer to David's question is, "Yes, and some cams while you're at it."

DarkMonohue
DarkMonohue HalfDork
5/21/22 6:08 p.m.

To clarify the above a little bit, I don't actually know where the cam timing is by the numbers. This is an oddball engine with a tall block, and consequently, cam timing is skewed relative to the crank, so rather than doing the math every time and keeping records like someone who knows what he is doing, I just moved them until I stopped seeing improvement.

 

Pete. (l33t FS)
Pete. (l33t FS) GRM+ Memberand MegaDork
5/21/22 6:14 p.m.

In reply to DarkMonohue :

In your case, they would probably help with the drivability, although it seems like your engine is pretty well sorted, and who drives below 2k anymore anyway? smiley

DarkMonohue
DarkMonohue HalfDork
5/22/22 1:09 p.m.
Pete. (l33t FS) said:

In your case, they would probably help with the drivability, although it seems like your engine is pretty well sorted, and who drives below 2k anymore anyway? smiley

As ludicrous as it sounds, I upshift at 2100 around town if I'm not in a hurry.  And the car will probably get a transmission swap to bring the engine speed down at cruising speeds. With the driving I do and the grunt on tap, there's just no need for stump pulling gears. So maybe the ITBs, with a nice progressive linkage, would bring some tractability back to the combination.  Or maybe I should just start taking the bus...

Anyway, this has derailed the thread long enough. Hopefully there is enough relevance to the original question to be of some value. 

 

David S. Wallens
David S. Wallens Editorial Director
5/22/22 6:34 p.m.

In reply to DarkMonohue :

It's all good info. 

The biggest concern about going to throttle bodies: losing the car's current drivability. Even with the tuned ECU, the aluminum flywheel, the typical bolt-ons, etc., etc., the car still starts, idles and behaves like a stock Miata. 

But IRTBs would look and sound so sweet....

Noddaz
Noddaz GRM+ Memberand UberDork
5/23/22 6:39 p.m.

Here is the answer for your problem.

3D print some fake throttle bodies and glue them to the plenum.

Still drivable?  Yes!  Throttle-body-ness? Yes! 

David S. Wallens
David S. Wallens Editorial Director
5/23/22 8:29 p.m.

In reply to Noddaz :

Ooooo, I like that. :)

 

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