Large plenum conversion for EFI
 

I'm curious what the board thinks of these large plenum conversions for EFI applications. Once again I'm running into hood clearance issues when attempting to convert from my pin-on fiberglass TA hood to a bolt-on steel TA hood. Not to get off topic, but my current hood has the shaker moved 2" forward. I didn't realize this until starting the steel hood conversion. ps. having highport heads on a 70 TA is a major pain in the ass :mad:

I'd like to hear opinions on the effect of opening up the plenum of a Northwind/Victor like the pictures below. I'm concerned with the runner length being too short, although short runners with a large long plenum seems to be the direction most EFI intakes are going these days. I'm liking the idea of more plenum area and the ability to get a custom intake elbow lower than my hoodline.

What do the airflow folks in here think about the whole idea? :popcorn:

417 Motorsports does the conversions.
https://417motorsports.net/collectio...num-conversion

https://lstwo.com/images/51801530633944272751.jpg
https://lstwo.com/images/81386634095219683962.jpg
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https://lstwo.com/images/15752983783748230018.jpg
https://lstwo.com/images/80793663636936419708.jpg

What level of power are you looking for out of this 480 plus CID motor , and maybe even more importantly what do you see the average and peak rpm range of this motor being ?

Conversions / modifications that lean back the roof of the runners to gain more volume are not a bad thing in and of itself, because it does help to equalize the runner length difference between the overall length of the roof path and the floor path within the whole intake tract , and this at least in theory helps peak air flow.

In terms of tuning for the rpm of peak HP Your dealing with two major factors with mods like your looking into.

.1) how it effects pulse tuning rpm of the intake .

2) the rpm of ram tuning.
Ram tuning is highly dependent on the overlap of the Cam and if the exh header is tuned real well so a vacuum is presented to the cylinder while the intake valve is open during the number of degrees the Cam has for overlap.

Unfortunately whatever you do to a NA motor to maximize the power in what is always a narrow power band will detract from the power level that there could be either above or below that narrow rpm band .

Here’s an example for the pulse tuning effect provided by the Superflow corp in there general information section of there supplied flow bench guides.

There are 3 Harmonic pulses in a V8 engine you can choose to tune for.

Make note of how tuning off of the 2nd Harmonic produces not only the strongest pulse, but the widest rpm range of usefulness .

If your running your motor to 6800 rpm then your 2nd Harmonic tuned length would be 19.4”.

If you where shooting for a peak Hp rpm of 7500 then that length drops down to 17.6”.

The runner length in your heads is around 5”, so now look at the stock average runner length of the intakes your thinking of using on this motor.

Here’s the chart and the formula.

The shown example formula is using 8000 rpm as an example.

Just be sure to note that this is total intake runner length from the back side of the intake then up thru the centerline of the head runner and then on up thru the centerline of the manifold runner until it terminates at the start of the Plenum.

Current configuration is in the 650hp-660hp range based on timeslip (10.50@129mph old set-up carbureted on race gas). Shifts at 6800-6900 rpm.

IA2 4.285" bore x 4.21" stroke (3.25" main block)
Northwind EFI intake with Wilson 105mm TB and Steve Morris 100* Elbow
13.8:1 compression on E85
Solid roller [email protected] .726" INT .696" EXH on a 109
2" Header with Flowmaster 4-2-1 merges and full 3" exhaust with X pipe
T400 and 3.90 gear
30x12.5 ET Street or 275/60/15 drag radials

My seat of the pants-o-meter feels like it gained a bit of low-end torque when I switched from the Dominator carb to the EFI with the TB and elbow. I don't have any data to back it up but it feels like it liked the added plenum area with the elbow. I'm trying to find the time to get it on a hub dyno to finish off the tune.

I do have a billet 4500 throttle body on the shelf to try out, but future plans are to add turbos so the front entry throttle body configuration is necessary. It would be an interesting comparison on the dyno though... elbow and 105mm TB vs 4500 TB.

Picture of current set-up for reference

https://lstwo.com/images/24628592108733642281.jpg
https://lstwo.com/images/17653240732016874691.jpg

That thing is begging for a turbo.

Looks like Wilson's is having their annual black Friday sale. I'm considering this low profile elbow. This would add even more plenum area. Overall height is 4 1/8". I need to go out to the garage and measure a few things.

Also, if anyone is considering a switch to EFI, I'm pretty sure the Black Friday 20% off applies to EFI conversions as well.

https://www.wilsonmanifolds.com/coll...acing-95-105mm

If you can't get PKMM heads that's not a bad second choice :D

I couldn’t pass up on the Black Friday pricing so I ordered one. Still expensive but $747 is a lot better than $934. Hope it fits

Good for you! Ya can't take it with you