Why does everyone say I can't do this cam?

[curtis73]

First of all you have to know that I have many years experience "bench building" engines, but only built about five myself, none of them caddys. So as far as the theory behind how engines and parts work to create VE, I'm great.

So, in building my Caddy 500 I'm getting conflicting reports. I'm probably going to be using bulldog heads and the shortblock is already built and capable of taking 5400 rpms.

Now I'm trying to pick the cam. So, when I was trying to pick a mid-range cam that will support 500 cubes to 5400 rpms, I decided on a dyno-proven selection of the MT15. I'm not sure about LSA since it wasn't listed but given their description of "noticable lope, 950 rpm idle" its gotta be like 112 or 110. Not too wild on a 500-cube engine, right? I'm now being told that I'll never be able to run modern digital EFI since the idle vacuum signal will be so terrible. I agree that a poor idle vacuum will confuse EFI, but 230 degrees? HRM just did the LS1 this month with a 232/234 cam with 112 LSA in only 345 cubes.

Are people just stuck with the "caddys don't like to rev" mentality, or is there some volumetric reason why I really shouldn't go that big with a cam? It seems so easy to make 1hp/ci on the street with any other engine, but why am I getting so much negative response when I mention this cam?

[CadilaChris]

If you read Hotrods Caddy articles, they maid 1 hp/ci on the stock cam at just over 3000 rpm. A stock botom end can handel 5400. As you probably already know, the springs and rockers are the weak link. In the junckyard gem series, the heads flowed well up to 4500 when the cam fell way off.
If you want to turn a Caddy into anyother streat engine and rev for power, then go the way your going. But, if you buy iron heads and a #10 cam, you can put the money tward building the stronger frame you will need.
Caddys dont falow the same VE standards the other engines do. You dont need biger is better when you already have the biggest engies ever maid.
Chris

[curtis73]

I'll search for that article. It might have been one that I didn't get to yet on the website.

I did the shaft rocker conversion (not the rollers, just the stamped rockers) and I forget which springs I have but they were an upgrade.

When you say they don't follow the same VE standards, what exactly do you mean? They fall under the same set of physics, but here's where my inexperience with Caddys doesn't really help me.

[STDog]

What does vacuum have to do with modern EFI systems?
I though they worked based on crank/cam sensors, throtle postition, exhaust gasses, and temperature sensors, and used with digital processing of the inputs to controll the amount of fuel added to the intake air charge. It's up to the programmer to caculate the desired amount of fuel based on RPM and air charge.

Any cam that will work with a cab should work better with EFI. I could see trouble with some cams and a carb at low RPMs if there;'s not enough vacuum for the carb to meter properly,

And who's been saying the MT15 and EFI is a no-go? I haven't seen that thread.

[curtis73]

What does vacuum have to do with modern EFI systems?

And who's been saying the MT15 and EFI is a no-go? I haven't seen that thread.

Vacuum has a lot to do with EFI. MAP sensors are responsible for telling the computer how much fuel to inject. You could design an EFI system that worked solely on throttle position and crank sensors, but it would be wildly inaccurate based on temperature, altitude, barometric pressure, etc. You set the base fuel map, but that is just a ballpark. The MAP and or MAF sensors along with all the others set the actual cuve. A MAP sensor needs a relatively steady idle vacuum to make it idle well.

I asked the question about the MT15 and EFI as part of another question at another automotive forum in a discussion about VE. I just get so cranky when I think I have it all figured out and then someone says I can't.

By the way, CadillaChris, I found the junkyard jewel article but it showed them making 450 hp with earlier heads, 12.5:1 and 100 octane and an MT15 cam. Is there another article that you might have been thinking about?

[CadilaChris]

You cant think in turms of horse power with these engines. The opened up Caddy made 500 lb/ft with just an intake and headers.
The physics of it is the same, your just coming at it the rong way. The same duration from a #15 in a Chevy small block will make a nice little moter. Were as, in a Caddy, it be a bit too much.
Most guys like me are going to run their Caddys in the 8.5-10 to 1 range that they came with. Also, we use the same rear gearing, around 3.00 to 3.25 with a tight converter.
It isnt that these moters dont like to rev, its that they dont need to rev. If you put a #15 in anything other then a towtruck or an RV, it should only see Friday and Saturday night use. The size gear and carb needed for the street wouldnt be friendly to the walet.
The old foram started with, You need to look at the hole package. Another foram has guy that races a modified Model T, 500 with uper #10, 2.73 gears going upper 10sin the 1/4 mile. That would be all I need to hear right their.
I think the way Caddy designed their cams, it made an S load of vacume. Wonce a lope idel comes in, their intake wont flow right. I'v herd of guys bolting a Holly 750 on to a 500 with a #10 and an Edelbrock and the moter ran like a dog because the guy jetted it to high. He had jetted the carb for a GM 500, not a Caddy 500. You put down that the cam has a 950 rpm idel. Almost 1000 at hot idel when a stock Caddy will idel at 650 with a toothy groule. The ultimate sleeper. Mul over that alittle.
Chris

[DOC]

Hey curtis73,
I have some experiance with that cam in a couple of instances. I used the MT15 in a 5000 lb desert truck. The engine had stock crank, cast pistons, Olds rods, and Krusik rockers and springs. It had Edelbrock intake and modified QJ carb. It made mountains of power from about 1800 to 6100 rpm. The truck had 4.56 gears and 38 in tall tires. Idle vacuum at 4500 ft was steady at 16 in. The truck performed fantastic until one real long stretch of road (about 125mph) for a few minutes each lap and 270 degree cooling system fried to pistons (calapsed skirts). This driving is from 5 mph in the rough stuff to flat out on the big end.

We also used this cam in Dodge PU for street/strip use. It had a noticible idle, but was very well mannered. Both vehicles were carbed, and the Dodge had power brakes. I believe that fuel injection would have worked on both, but we never tryed it (no need).

500 cubic inches does alot for mellowing a camshaft that is to "much" cam for a smaller engine.

I say go for it.

Just my 2 cents.

DOC

[rockhog]

Why not get the same cam and have it ground on a 114 lobe for the EFI???

[curtis73]

the 114 is smart. I'm kinda torn though. The car could benefit from a mild and calm-sounding engine since this is a big luxo cruiser, but I sure do like the tick tock idle :)

What I should do is try to predict EFI performance using desktop dyno's IMEP values, but I don't know how to read them. Not sure what they mean and how they would translate to the real world, but someone out there knows :)

[Andy V]

Curtis,
What compression are you going to run?

I think a 230ish cam with a 112 to 114 will be great with EFI, if you are running a 10:1 motor, or something with some compression.
If you're running a 8.5:1 motor you may want a little different. Is Al at MTS telling you the MT15 is not a good choice for the EFI, or someone else?


I wouldn't compare this to that LS1 either, you're comparing a roller cam to a flat tappet here.

[curtis73]

Yeah, the LS1 is also MAF which makes a big difference. Not sure why I even made that comparison other than frustration

Al didn't tell me anything about the MT15 and EFI, in fact I've yet to consult him. The question was posed as part of a thread at another forum about VE and MAP sensors. That particular forum is a great resource for advanced tech stuff, but the same guys who are running 255 cams in a 383 with EFI are telling me that I can't do a 230 cam in a 500 because "those engines don't like to rev." It just bugs the crap out of me. Volumetric theory applies to all engines regardless of size.

Anyway, I plan on either 9.2:1 under iron heads or 10:1 under Bulldog heads. The plan is set for Bulldogs, but I'm entertaining offers to port my iron heads too. :) The engine is currently at 8.8:1 with mildly ported 552 heads and MT3 cam.

[Andy V]

with over 9:1 and a 230 @.050 intake cam on a 500, I think you should get 13" vacuum at a minimum. Idle maybe around 800rpm. Don't know if that is enough vacuum or not?

You may want to ask MTS what they think, as they may have a customer that has tried a MT15 with EFI....

Al's probably buried in snow right now so maybe he'll see this post and give some advice ????

[curtis73]

I'm getting 15" from a 224 cam in a 454 at 600 rpms, so I sure hope I get at least 13. I've had pretty good luck with power accessories at 12", but I might use a vacuum canister just to be safe.

Thanks for the replies. If Al doesn't see this thread I'll call him. Unfortunately he doesn't have time to shoot the bull about stuff like this. Totally understandable, but I thought I'd hit you guys up here since we tend to have a bit more time to BS :)

[shiftless]

You cant think in turms of horse power with these engines.

Huh?

Horsepower and area under the curve are the only thing that matters when you're building a race car. Most people here are building street cars so torque is very important and HP not very important. But saying "you can't think in terms of horsepower with these engines" is rather naive. If you have two cars, both geared for the same speed (MPH) range, and assuming all else is equal, then the higher horsepower car will be faster.

Horsepower is not a myth somebody made up, it's a way of showing how much power an engine is capable of producing, thus how much work it can do in X amount of time.

[Nashalac]

think I have to dissagree Shifty. All things equal the car with the highest horsepower AVERAGE through the rpm range be be quickest.

[Terrible One]

It isnt that these moters dont like to rev, its that they dont need to rev. If you put a #15 in anything other then a towtruck or an RV, it should only see Friday and Saturday night use. The size gear and carb needed for the street wouldnt be friendly to the walet.

Why should it only see Friday and Saturday night use? I've got a cam with more lift than the MT15 and a JET Stage 2 Quadrajet that can handle it for a plenty fair price.


I think the way Caddy designed their cams, it made an S load of vacume.

Then why did the hydroboost get invented? Not enough vacuum was made for the engine for a vacuum booster.

[CadilaChris]

first off, S load maens ALOT! second, even I plan on using a hydroboost on a cady, no vac hose to leak.
If all you guys out there want to have 2200 + stall speeds in your cars, fine by me.
You can just look for the guy getting 18 mpg with the bigest croud at the car show since everyone will think I have a small block till I open my hood. Nice to know people still like the sleeper sound sneak attac.

[Terrible One]

I know that S load means a shitload. I was telling you that you were wrong by saying that, because in fact, the later Eldorados made so little vacuum that they couldn't power a vacuum break booster, which is why Hydroboost came about. Yes, earlier models made more vacuum, but not necessarily a shitload.

[campagna]

Please splaine to me what too low vac is. My 76 eldo idles at 21.5 ", high and rock steady, box stock.

[CadilaChris]

Thank you for clarifying. I know Eldos had hoter cams. I didnt thint they went that high. I supose Id be ronge in saying that the hampered breathing of these engines has anything to do with low or high vacume, just thinking out loud

[Terrible One]

It has a lot to do with it. I'm not saying that the Eldo had no vacuum. It had enough, it just wasn't very high, especially when comparing later to earlier. They also had to run a lot of other vacuum powered accesories.

[CadilaChris]

I alwais forget about the accesories. Vac cruse control, exhaust crosover.
tomuch even for a 500 to handel.

[shiftless]

think I have to dissagree Shifty. All things equal the car with the highest horsepower AVERAGE through the rpm range be be quickest.

Not necessarily. There is a reason they make 5, 6, even 7 and 8 speed transmissions. It doesn't matter if an engine only makes power in a 100 RPM wide band; if the transmission can keep the engine in its sweet spot then it'll perform well.

The point I was trying to make is horsepower is not something somebody made up just to have something to do. It's the only way to measure how much work an engine is capable of doing. An engine that makes more horsepower can do more work. A broad powerband is an added bonus but not an absolute necessity. And low end torque is good for nothing except making a car fun to drive on the street and for pulling people out of ditches.

[Nashalac]

Shifty - you are correct in the description you gave. If an engine has a very narrow torque curve it will require more gear changes to keep it in the proper range - However an engine with a broader torque curve will need fewer gear changes. If both are set up properly the highest average hp through the range should be faster.
For those that don't know - HP is a calculation derived from the measurment of torque times RPM time a constant I don't remember. So you don't actually measure HP, you measure torque on a dyno

[shiftless]

Then why did the hydroboost get invented? Not enough vacuum was made for the engine for a vacuum booster.

Could you please quote your source on that?

[Terrible One]

Then why did the hydroboost get invented? Not enough vacuum was made for the engine for a vacuum booster.

Could you please quote your source on that?

My friend named Jordan :(

Basically that comment was dead wrong. My apologies, espeically to CadillaChris :D