MT 15 idle vaccum and converter ?

[rockhog]

Anyone here running a MT15 cam with a stock converter?? Also what kind of idle speed and vaccum are you getting??

I plan to upgrade my current cam 216 at .050 with 458 lift. How much should I expect in power increase??

[Nashalac]

Can't answer exactly - but - you will have to machine the guides for clearance or the retainers will hit. Not a good thing. Decent idle and enough vacuum for brakes. Power increase depends on a lot more than just a cam change. This cam RPM range is at top of reliabilty of stock rocker system and stock cast rods. Some make it work and others destroy engines.

[rockhog]

I have manuel brakes so that should not be an issue. More or less kinda seeing if a near stock converter will work OK. I planned to do the shaft mounted rockers at the same time as the cam change.

When I talked to Al about the MT15 he did say anything about any machine work that had to be done. I do have his S/S spring kit on the heads right now. The cam in it is an OLD mt5 cam. Its been along time like 7 years ago when the heads went to the machine shop. I thought they had to do something to get the springs to work. He said my current spring would work with the MT15. Here is the rest of the combo:

76 500 stock short block
800 cfm Q jet
Performer intake
1 7/8" Sanderson Headers
2.5" dual pipes mandrel bent to flowmaster y pipe into 3" single exhaust.
Hei with accel coil

I am also considering the MT10 cam or Comp 270H.....

[Nashalac]

Stock with the 10 series - may need a little more stall with thr 15 - around 2000 - 2200

[curtis73]

Not to pirate a thread, but a quick question along those lines... Let's say a person were to NOT change TCs with something like an MT15 (which is what I plan to do), how much of a drivability pain is it? Wouldn't it just be a touch sluggish for the first two seconds of launch? I understand at the strip that is an eternity, but for just daily driver status, would it be so much of a pain that I'd hate it?

Part of the reason I ask is because I have a great Continental diesel TC that stalls at about 1800 now behind my MT3'ed 500 and I love the low temps and extra 1 mpg I get, but would it be so annoying on the street that I should swap up to a 2200 when I swap cams?

[Nashalac]

What can happen is you need to raise the idle speed up for the cam and you end up having to use both feet on the brake to keep the vehicle at a stop.

[STDog]

Is the MT15 lift too much for stock heads? What's the max lift for the stock heads and springs? Can you change springs/retainers for more lift witghout machine work?

I figure Rhoads lifters would help with the idle issues, and allow one to use a stock TC.

I'm gonna make a change, but I gotta figure out what. The Rhoads lifters (http://www.rhoadslifters.com/why.htm) look like a good option, reducing the duration/lift for better low RPM behavior, but giving you the high RPM duration/lift when you need it.

reduce duration 10* at idle, and lif by 0.025.

So a #15 at idle would act like 220-228 / .515"- .525"
(a lot like a #10 = 220-228 / .525"- .538")
But back to full specs by 3000 rpm

Or #10 would idle like 210-218 / Valve Lift Range: .500"- .513"
(almost an #5 = 208-215/ .495"- .510")

I'll probably go #10 with the rhoads lifters, since a #5 is just a little hotter than the stock '70 cam, and I'd rather not have to machine the heads.

BTW anyone know what the difference in the VT and MT cames are? Other than who grinds them, I mean spec and performance.

Al say the '73 cam was the hottest from GM. So what changed amongst them?

[Ted in Olympia WA]

Just about anything over stock is too much for the stock heads and springs. Stock springs are bad brand new. The factory did not put much clearence between the retainer and top of valve guide. It's easy to cut this down with a hand drill and the right tool but the heads must be off and apart.

It is my understanding that the MT cams are new from Comp and have a very agressive lift at .050. The VT are re-ground and are less agressive (more old school) at .050.

There are two Rhoads, the regular ones work with standard non-adjustable rockers train and the V-max must be used with adjustable rockers. I recently purchased the V-max but I have not installed them yet. I have the MT15 cam. My main problem is that I don't know if I should save the Rhoads for the next cam choice.

I ran it first with the stock converter and it idled at 900 rpm and dropped to 650 in gear. I put in what was suppose to be a 2200 stall converter and it still drops to 650 in gear. It will stall to about 2000 plus under load but it still has just as much drag at idle. When I bring down the no-load idle to 800 and put it in gear it's very lumpy, when I move it to 1,000 it way better but put a lot of drag on the brakes. Vacuum is about 10 to 12 at idle. As a side note my engine is 8 to 1 compression and may not be in perfect tune yet. I think the low end is just as good with the MT15 as the stock cam.

I have the ss springs now with 1.72 lifters and Al says this is a bad idea. At first I had the Buick lifter set-up that was 1.6 and Al says this is fine with the MT15. I plan to change to beehives soon because I don't want to pull the heads now to do the machine work for double springs.

TED

[STDog]

Just about anything over stock is too much for the stock heads and springs. Stock springs are bad brand new. The factory did not put much clearence between the retainer and top of valve guide. It's easy to cut this down with a hand drill and the right tool but the heads must be off and apart.

I don't remember here, but I did see some longer duration cams that don't have high lifts. Maybe that way? Still using the rhoads to keep the duration down at idle.

Al, Care to help here?

I though I saw somewhere that .500" was safe with different springs and retainers. I'll have to go searching now. I really hate to pull the heads again.