MG Sports Cars

Anybody care to discuss HP?/Torque?
I want to buy the engine pieces with purpose but I keep wondering what the purpose is. I want a strong motor that'll last. I think lots of power in the low to mid RPM is the way to go. So how much is too much? As MG's go how much do I really need? Maybe there's no such thing as too much. I read about converstions with 250HP up to 400HP. Does the guy with 250HP always end up wanting the 400HP? I think the problem is that I don't have a good handle on what various HP's 'feel' like in the B. I do remember driving Ted Laythrop's TR6 in Terre Haute. I would be very satisfied with that kind of performance. I'm not a race car driver. I'm a weekend cruiser with the occational need to be pinnned to my seat. So how does one put all the puzzle pieces together to make predictable performance? I'm lost here.

Torque is proportional to engine size. HP is where the camshaft makes peak torque. Want more torque? Get a bigger engine.

I tend to lug my engines, so I prefer a low RPM tuning. For me, that means a roller cam engine is a better choice. Although I'm building up an Olds 215 (3.5), if I were starting over, I'd go with a Ford 5.0 roller cam engine, install aluminum heads to save weight, and stroke it to 327/331 ci.

In the first post you mentioned Ted's TR6, which has a Chevy 350. I've driven it too, and agree it's a wonderful car. But I don't aspire to possess that sort of power. A smaller engine can be a lot of fun if it always feels willing when you mash the throttle. Toward that end, I don't think horsepower or torque tell the whole story. A short stroke. A lightweight flywheel. The right throttle return spring and throttle linkage. Setting up the carb's accelerator pump (or EFI) properly. Gearing. There seem to be an awful lot of subtle variables... Of cars I've test driven, Jim Stuart's burgandy roadster especially impressed me with its basically stock Rover 4.0 and EFI. It was a revelation to me because it's so very smooth, quiet, and composed. Great throttle response. No bog ever. Easy to drive well. That's finesse! Another liter or two might be nice, but there are some very satisfying cars on this website that have a lot less than 250hp.

Thanks for the responses. A few others sent me private E-mails with motor specs of their own. Thanks to you guys, too. It's all helping me understand what I'm trying to do here and your perspectives are just what I need.

Paul,
I have the 5.0 roller tappet motor as my starting point. Have you driven a stroker 302? Is that how you know that's what you would do given the chance? What was appealing about it? As far as strokers go, other than more displacement and hopefully more engine performance...would the car feel different? In other words can you tell in 'streetablility' when a crank has been stroked?

Hi Curtis,
I really appreciate your perspective. So there is such a thing as too much...
You mention 'short stroke', just to keep things from getting to big? or are there other disadvantages to a stroker?
Can you tell me more about the 'bog'? Is that inherent with big displacement small blocks or are they just harder to time?
With regard to:
--some very satisfying cars on this website that have a lot less than 250hp--
I'm happy you said that. And to tell the truth, after I posted the initial thread I regretted it. While I am interested in how all the 'subtle' parts come together from a mathematical and practical perspective, I don't think it needs to take away from the fun of doing a project like this. Then I remembered how much fun I had in the B before I took it apart. What was it like 110HP, max? I used to zip around and have a ball. Even with the stock 302 setup and some consciencious weight adjustments I'm ahead of where I was, right? So thanks.
I'm back on the planet again. Still curious, but not concerned.:)

Brian, my 302 has just settled in between the fenders and I can only speculate as how it will perform but I chose to go with a stock 302. I've owned the car for thirty years and for most of that time it has been my daily driver. I have a Ford truck that gets from 7 to 14 mpg depending on how it is loaded and a T-Bucket Roadster that will scare you to death but doesn't do that well when you put your foot in it. I need something that can return a little excitement to my life that doesn’t cost my entire pay check to drive. Of course, when the need arises I can take the Bucket around the block, but for me, the car has got to be street-able, not to say big horsepower isn't, but I went with what met my needs.

"P"

I think some perspective from the big horsepower crowd is in order as well. It's not necessary to have an evil handling or unstreetable car as your power levels go up. In terms of tuning and response, what works well for a small V8 also works equally well for a larger one. It's not necessarily the displacement that determines how tunable or responsive the engine is.

Of course it's easily possible to build an engine that is not well suited to street use, people do it all the time. But the opposite is equally true and the secret is in the right combination of parts as Curtis said.

So I will say this. There's almost a magical line you cross with an MGB when you get into the 300 HP territory. The car will handle that level of power well and it will do things not formerly possible. It will demand a different driving style as well, and will insist that you mind the throttle. One of our group posted a track video not long ago of his car which is in this range and watching closely you can tell that the car just itches to get loose coming out of the corners. For someone who has driven such a car, just watching that video gets the adrenaline going, and I will say this about horsepower, it is highly addictive. You can increase it, but it's very difficult to willingly go back.

JB

Not being a wordsmith Jim, I didn't explaine myself well, sorry. I drive a rather big horsepower 1800 lbs car also and wouldn't take for it; I find I need an occasional adrenaline fix too. My intent was to suggest he build the car to fit what he wants it to do, I just didn't say it very well.

"P"

Brian, I haven't (yet) stroked a 5.0, but I do drive an 86 5.0 HO. Yesterday I got 26 mpg on a 300 mile trip. When I got home and saw the soft tires I kicked myself because I could have gotten an easy 27 or more.

I would go with a stroked 5.0 because it's the easy way to get more cubes in a small engine block. Also, the extra stroke gives the engine a more low-end torquey feel, and that fits with the way I drive.

No problem Paul, my comments weren't directed at anyone in particular. From what Brian has said it sort of sounded like he'd be pleased with a motor that has a good bottom end. So far as I know there's no better way to get that than more displacement. (A blower would be a close second though.) And so far there's no better example of the "Too much is just right" approach than the MGB-Roadmaster with it's 455 Buick engine running mild compression and a very streetable tune. Only a few of us have driven it up to now and only for short distances but it definitely has the bottom end covered. Is it too much? So far nobody thinks so.

So I think the question of how much horsepower is too much is best answered by looking at the state of tune of the engine. 250-300 hp in a 215/3.5L is likely to be too much for the street in the minds of at least a few drivers, whereas 500 hp in the MGB-Roadmaster or in my blown 340 is not. It's a pretty relative question.

Jim

Yes indeed, it is all realtive.
There are Camaros and GTO's running around town with welll over 1000 hp and driven on the street. You can only drive at or a bit over the speed limit. So the 1000 hp is good for ???? show and tell, unless is those ponies are at the track.
It is nice to say" I have 1000 hp" great or I have a 572 ci now when are you really going to use it.

I have well over 550 hp in on of my cars. Very rare can I really open up the Throtle body to feel the ponies doing its thing.
and that is in the desert and praying that I do not get the car impounded.

Nothing wrong with lots of power, it is never enough I am all for it. But I am a bit practical, even in this hobby there is some logic to what we do. As an exercise to see what if...etc great, why not

If somone has 1000 hp and keep those pomies in a harness and that is what they want THUMBS UP TO YOU !!!

There is always a good conversation on how it was done and many of us can learn from it.

Most of all it is fun building something that has been done,but different. I suppose that is the real reason.

Brian, a lot of the feel of a car is determined by the gearing and engine torque and it doesn't have to be extremely high to feel that rush and be pushed back in the seat. You get good torque coming in low in the rpm range and a medium rear gear aroung the 3.4 range and you'll feel that rush when you mash the throttle in first or second gear. My little 2.8 Midget with all of 120 screaming hp will definitely push you back a good bit, just have to keep the weight down and the gears right and I still get around 25 to 27 mpg on the road. That said, I can't wait for a chance to drive the Roadmaster and feel all that torque. It's been years since I drove a big block car, nothing like them for sheer lower end power.

Yes, there is always a rush when big hp comes in to paly, correction, when the torque starts to work.
Regardless of size. I agree with Bill Y.

As Jim put it, it all depends on the choice of parts and combination. With the new electronics 900 lb of torque in the street is like a @#$%& cat. Both, the big V8 and V6 will drive at the same hwy speeds.

Of course, we all enjoy a mild "exhibition of speed" every now and then, if it's nothing more than rolling away from a stop and then just barely breaking the tires loose. If you drive in the hills, even more so, since there you have ample opportunity to use all of that torque passing on 2 lanes uphill and running the twisties. But don't get me wrong, Bill G has a valid point. Somewhere along the line enough is enough. For some (You Bill? ;-) ) it may be a V6 or even a 4. For others it may be when full throttle at 70 mph breaks the rear tires loose, and even that may not be enough for some. The beauty of living in this country is that we don't all have to have the same thing.

JB

Yeap, enough would mean a 572 ci V6

Bill, I think you mean the 478 ci GMC truck V6 from the mid sixties! LOL Now that would get you some torque. Seems that talk about a similar V12 version of that engine was the start of some brainstorming that led to Project Roadmaster if I remember correctly. [en.wikipedia.org]




Edited 1 time(s). Last edit at 03/25/2010 02:50PM by Bill Young.

Brian wrote:

Quote:

So there is such a thing as too much...
You mention 'short stroke', just to keep things from getting to big? or are there other disadvantages to a stroker?
Can you tell me more about the 'bog'? Is that inherent with big displacement small blocks or are they just harder to time?

For the record, I didn't actually say there's such a thing as too much. In specific reference to the Chevy 350, I said "I don't aspire to possess that sort of power." I understand why other people want a lot more. There are pro's and con's to each of the popular engine choices.

Why did I mention stroke length? There are in fact a couple advantages to a shorter stroke, but first and foremost is inertia. Unless you go to significant expense and/or effort, it's very difficult to increase stroke length without also increasing rotating mass, so in essence you get similar result as if you used a heavier flywheel. (The engine doesn't want to rev up as quickly when you mash the pedal, or slow down as quickly either. It makes the car feel less sporty.)

Historically, most British engine design had long strokes and small diameter pistons. In the early sixties, British Ford introduced a short stroke / big piston four cylinder engine. In any racing class where people had a choice, BMC (MG's parent company) popularity immediately dropped. Companies like Elva, Turner, Ginetta and others switched from BMC engines to Ford engines. Ford gradually became the main supplier to open-wheel classes too. However, I believe Ford's success was because they exploited a second advantage of a short stroke / big piston design: it gave them room to package bigger valves and better flowing ports, and the result was better combustion.

With regard to 'bog', I think I was mainly thinking of the difference between a large throttle butterfly and a small one. A carburetor (or EFI system) should be sized appropriately for the engine and the engine's use. Very often, a modestly sized carb actually makes a car feel snappier in traffic. That's not really anything to do with big displacement engine vs. small - I was only reinforcing the point that there's more to the story than torque and horsepower.

Curtis wrote:

"Historically, most British engine design had long strokes and small diameter pistons."

Funny thing is this had little to do with engineering and more to do with the British road tax structure which was determined by multiplying piston diameter by the number of cylinders. So a small piston/ long stroke motor would be taxed less than a large piston/short stroke motor of the same capacity.

Regarding the HP/torque discussion, I've always thought too much torque in a lightweight British roadster can be a liability. Torque is that twist that helps launch a car off the line, in other words, "tire fryin' power". In order to effectively use that torque it has to get to the ground, which usually means big tires and tubbed-out wheel wells. I've been wondering how the Roadmaster is going to control the torque that big Olds is going to put out. Should be interesting!

Quote:

Torque is that twist that helps launch a car off the line, in other words, "tire fryin' power"

That's just one aspect of it. Torque is also the twist that helps you get from 45 to 70 in the passing lane. You don't have to be a drag racer to appreciate/enjoy gobs of torque.

It's Buick engine Rick.

JB

Doh!!!! Sorry, Jim, don't know what I was thinking. I'm still interested in the torque factor in the Roadmaster. I have a Chrysler SRT-8 with 425/400 hp/tq. Even in a heavy car like that and traction control I have to be careful, particularly in the wet. I imagine you'd have to be a bit more careful in the MG.