Port my current M1 single plane or install the RPM Air Gap?

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Dezduster

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It's not a drag car although it's been to a few tracks, its not an autocross car however I will do more of them in the future but what it must do more of is highway miles due to my rural location.
The Combo is a 422ci la, 11.2:1, stock RPM eddies, M1 intake, 750 BG, 242/[email protected] 109LS 105IC hyd roller, TTI 1-5/8-1-3/4" step header into 3" tapering to 2.5" on the exit of the X full length mandrel TTI exhaust. Lightweight aluminum flywheel and single disk clutch, manual trans 3.2 gear .068 OD and 3.23 rear gear.
The previous hydraulic flat tappet cam is very similar to the above roller cams specs and the engine idled easily at 800, vacuum was 8" to 10" at idle, at WOT vacuum fluctuated between 1 and 2". The combo had plenty of torque and throttle response was great, mpg a tick over 20 highway cruising with the M1 single plane. The M1 is just damn ugly inside, being a spread bore with the sharp radius into the front intake runners. I cannot stop thinking its killing allot of power, yet I like its exterior look and lower height for hood clearance. How much torque is the M1 down, is the RPM down on HP at 5500 to 6200 and by how much if at all? I don't see M1 dyno results let alone ported results to determine if porting it would be worth the money. I've seen the M1 is mid pack in the Motor Trend LA intake ranking. What are your thoughts and experiences?
 
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Do BOTH, compare them and sell the one you don't like. It's not like you can take the monopoly money with you when you die, and it's becoming worth less and less by the day.
 
I'd say with the cam and gears you have, the AG is going to work better in the rpm range that engine will run in.
 
Based on the engine being a stroker but gears 3.23s I think either will be good. I am biased to the single plane intake. I used a Victor 340 single plane on my stock stroke 360. It ran better then the airgap for my car. However, I do have 3.91's out back.
 
The Engine Masters crew did a Magnum intake shootout a couple years ago, starting with stock EFI manifold then going to M1 on a carb, then RPM Air Gap on a carb. I took the following from someone else's forum post on ramforum.com:

"Now for the spoiler, and these numbers are directly taken from the Motor Trend/Engine Masters show. Stock kegger tq/hp (at flywheel) was 403/326, modded kegger 412/330, modded with big t/b was 414/337. The modded kegger didn't really help or hurt it anywhere in the power range - just SLIGHTLY better through the whole range. The carbed M1 at 410/350 started showing a little promise, and finally (what I consider decent results) with the Air Gap at a best tq of 425 and hp at 365, depending on spacer choice - a best of +20 tq and 40 hp over a stock kegger."

The engine is obviously way more tame than yours, with a mild cam, stock compression and stock heads. The Air Gap made 15 more numbers than the M1 on a mild build, so I would expect you would see more.

They also talked about carb adjustments they had to make after installing the Air Gap. I think they had to lean it out quite a bit to get it dialed in properly, so keep that in mind if you do the swap.
 
I just re-read your post and now realize your M1 is the single plane. I'm pretty sure they used the dual plane M1 in that test, so definitely not as accurate a comparison.
 
Use the M1 and forget about the carb flange.

If it bothers you that bad buy a Magnaflow anti-reversion plate and make the plenum match the gasket that comes with it.
 
Do you have an aftermarket 5 or 6 speed?

That 3.23 rear gear is deceiving with the 3.2 1st gear. Seems like the overall gearing in each each is much more than a 3.23 with an 833 trans.

That’s a healthy street combo. It should be really tough not to haze the rear tires in an autocross course. You want smooth application of power. Violent action equals violent reaction

So I’d rather trade off low rpm torque.

If you want, clean up the M1 by welding the spread bore up and make it a square bore. Then clean up the inside. Fixed my M1 / Strip Dominator

I think the M1 with it’s more curved runners, is a little bit of a compromise from RPM to Victor. But others with more knowledge on this, might have other opinions.

It’s sounds like a great combo as is.
 
I have a similar combo, but smaller cam (236/[email protected] .502 /.511 110 L/C), ported M1, mild ported Edelbrock heads, 9.7:1. 750 DP silver claw carb, TTI step headers.
 
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Rat Bastid said:
Use the M1 and forget about the carb flange.

If it bothers you that bad buy a Magnaflow anti-reversion plate and make the plenum match the gasket that comes with it.
Click to expand...
I was hoping you would reply. Thank you for that nugget of knowledge. I've never heard of anti-reversion plate.
 
autoxcuda said:
Do you have an aftermarket 5 or 6 speed?

That 3.23 rear gear is deceiving with the 3.2 1st gear. Seems like the overall gearing in each each is much more than a 3.23 with an 833 trans.

That’s a healthy street combo. It should be really tough not to haze the rear tires in an autocross course. You want smooth application of power. Violent action equals violent reaction

So I’d rather trade off low rpm torque.

If you want, clean up the M1 by welding the spread bore up and make it a square bore. Then clean up the inside. Fixed my M1 / Strip Dominator

I think the M1 with it’s more curved runners, is a little bit of a compromise from RPM to Victor. But others with more knowledge on this, might have other opinions.

It’s sounds like a great combo as is.
Click to expand...
I auto crossed it with 275/60/15 BFG drag T/A, SS springs and Calvert bars. It didn't do anything well, wouldn't launch at the strip and didn't handle corners very well at the auto cross events. I'm in the process of changing it's suspension wheels etc to a more touring suspension. I likely did have inquired here before purchasing the Hotchkiss stuff which I haven't removed from their boxes yet.
 
autoxcuda said:
I have a similar combo, but smaller cam (236/[email protected] .502 /.511 110 L/C), ported M1, mild ported Edelbrock heads, 9.7:1. 750 DP silver claw carb, TTI step headers.
Click to expand...

Ottmundr said:
Do BOTH, compare them and sell the one you don't like. It's not like you can take the monopoly money with you when you die, and it's becoming worth less and less by the day.
Click to expand...
The RPM is on my 72 W300s 408 but it currently has a spun bearing.
 
Dezduster said:
The RPM is on my 72 W300s 408 but it currently has a spun bearing.
Click to expand...

That’s a low cost test.

I have an RPM in the box. The guy that helped build the motor says “don’t touch it! “

… as I need to work on better tires and brakes first (chassis stuff). Sound familiar ?
 
autoxcuda said:
Do you have an aftermarket 5 or 6 speed?

That 3.23 rear gear is deceiving with the 3.2 1st gear. Seems like the overall gearing in each each is much more than a 3.23 with an 833 trans.

That’s a healthy street combo. It should be really tough not to haze the rear tires in an autocross course. You want smooth application of power. Violent action equals violent reaction

So I’d rather trade off low rpm torque.

If you want, clean up the M1 by welding the spread bore up and make it a square bore. Then clean up the inside. Fixed my M1 / Strip Dominator

I think the M1 with it’s more curved runners, is a little bit of a compromise from RPM to Victor. But others with more knowledge on this, might have other opinions.

It’s sounds like a great combo as is.
Click to expand...
It's a TKO modified by Keisler to fit A bodies with less cutting which I feared back then. It's only rated for 375 or 425 torque. The car has been sitting for twenty years lost a cam lobe with less than 3K miles on it and lost interest and then life things happened.
I will definitely check that go check that link out.
 
autoxcuda said:
That’s a low cost test.

I have an RPM in the box. The guy that helped build the motor says “don’t touch it! “

… as I need to work on better tires and brakes first (chassis stuff). Sound familiar ?
Click to expand...
Yes it does and I'm trying to remember exactly why and when.
Suspension suspension suspension, just when you think it's good you add power and find out it needs to be better or coulda shoulda been better already.
 
Ok, this is what I use rather than welding or filling in the SD/M1 carb flange.

You have to lay the gasket on the manifold and grind out and then contour the flange to match that gasket. If you don’t do that, it will NOT work.

That channel that goes all the way around the bores MUST be open to manifold pressure all the way around. Most guys just bolt them on without making the flange match that gasket.

This is actually an anti-reversion/shear plate combo. It works very well. I no longer weld the carb flange up. I use these and make the flange fit that gasket.

D2F84589-D295-48FA-92BE-A8FAC1EFE567.jpeg


D5EB779B-8F14-4DEE-89D8-3A963AB250C5.jpeg


7FE942F0-6B81-428E-B76B-05AD57E884EF.jpeg


This is a MagnaFuel MP-5006 and its for 1.750 throttle bores. If you are running 1.688 throttle bores they make a different part number.
 
Personally I’d run with Ratbastards suggestion.

Your exhaust is TTI W/an X pipe?
This throws away low end torque. A pressure wave cancellation box should have been tested after the header for increased low end torque output.

Questions!!!!

What size tires are you running?
What is your overdrive gear?
What are your cruise RPM’s?
What model carb? (Mechanical or vacuum?)

At 422 cubes, getting a tic over 20 MPG‘S is very very good.
The 2.196 final drive ratio with the cubes and cam size, WOW!
 

Rat Bastid said:
Ok, this is what I use rather than welding or filling in the SD/M1 carb flange.

You have to lay the gasket on the manifold and grind out and then contour the flange to match that gasket. If you don’t do that, it will NOT work.

That channel that goes all the way around the bores MUST be open to manifold pressure all the way around. Most guys just bolt them on without making the flange match that gasket.

This is actually an anti-reversion/shear plate combo. It works very well. I no longer weld the carb flange up. I use these and make the flange fit that gasket.

View attachment 1716032469

View attachment 1716032467

View attachment 1716032468

This is a MagnaFuel MP-5006 and its for 1.750 throttle bores. If you are running 1.688 throttle bores they make a different part number.
Click to expand...
I searched that product minutes ago and was reading posts by D Morgan from R Morrison, Wilson, Kasse! Thats exactly what I will use and as luck would have it, I'm going to Reno and will pick it up from Summit if they have the correct one in stock. Thank you thank you Sir.
 
That’s a list of the who’s who.

Leave some links?
 
rumblefish360 said:
Personally I’d run with Ratbastards suggestion.

Your exhaust is TTI W/an X pipe?
This throws away low end torque. A pressure wave cancellation box should have been tested after the header for increased low end torque output.

Questions!!!!

What size tires are you running?
What is your overdrive gear?
What are your cruise RPM’s?
What model carb? (Mechanical or vacuum?)

At 422 cubes, getting a tic over 20 MPG‘S is very very good.
The 2.196 final drive ratio with the cubes and cam size, WOW!
Click to expand...
Tires are 275/60/15 BFG drag T/A 28
OD gear is .68
1700 1800 RPM@ 70 72 MPH.
Model carb? It was a BG Street Demon mechanical 750 the secondary linkage is set progressive. The body is a Proform center and the BG center is in a box in the shop I'm not sure of part # or if it's legible still. I swapped everything over so I could get screw in air bleeds as the carb was on my 340 first and needed bleeds to get the idle circuit functioning correctly, the stroker needed the bigger bleeds back in. I talked with BG three times to get it dialed he made suggestions, and I just did everything he suggested and tested it. I was going to purchase an 850 from when #6 exhaust lobe and lifter lost elevation. I would probably remember better if he hadn't made it so easy. I drove with a vacuum gauge connected for weeks as well as my mighty vac connected to my vacuum advance tools and jet kit in the trunk. My timing curve is 18 initial 18 mechanical for 36 at I think 2000 2400rpm the vacuum is pulling up to 44 and is adjustable. If I was in 5th cruising 15 1600 it would have a slight surge that I believe was likely a vacuum advance / timing surge. Where I live and travel to has allot to do with MPG. I'm 72 miles to Fallon no stops and 15 miles of 55 to 60 mph zone, Reno is another 60 miles with maybe two stops back then. Vegas is a 300 miles south and one stop sign in Beatty. I did fuel average to and from Reno twice being responsible 5 over max each fill got me just over the 20 mpg, but it's difficult to drive so reserved. Most of my miles would be in the mid-teens not that I checked often when driving spirited.
 
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rumblefish360 said:
That’s a list of the who’s who.

Leave some links?
Click to expand...

rumblefish360 said:
Personally I’d run with Ratbastards suggestion.

Your exhaust is TTI W/an X pipe?
This throws away low end torque. A pressure wave cancellation box should have been tested after the header for increased low end torque output.

Questions!!!!

What size tires are you running?
What is your overdrive gear?
What are your cruise RPM’s?
What model carb? (Mechanical or vacuum?)

At 422 cubes, getting a tic over 20 MPG‘S is very very good.
The 2.196 final drive ratio with the cubes and cam size, WOW!
Click to expand...
The X pipe is from Dr Gas the rest is TTI. I ordered a cam and RHS cast iron X heads for the 408 in my truck from Brian at IMM and I asked if he had tested X pipes as I like the sound and wanted them on everything no matter how difficult they are to plumb correctly. I had mentioned my Dusters exhaust telling him I was considering stepping it up to 3" at the exit of the X and 3" all the way out and installing that X on my truck. Brian said there was power to be kept by not going 3" and leaving it as is on my car and getting new for the truck. Was he saving me work or keeping me from making the car worse IDK?
 
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