Aluminum 302

Anybody run an aluminun 302 based in their Gt40. This would be significantly lighter than even the iron blck 302, which the cars seem to be setup for. Will reducing the mass fromt he rear make the car more twitchy at the limit, or less.
 
On the face of it this (lighter block ) would appear to lower the polar moment of inertia - less twitchy. However, it depends where the car's centre of gravity lies; the GT40 has a rearward weight bias so the C of G will be to the rear of the vehicle physical centre.
 
Sean, I'm no expert on this one....but what I've heard discussed around here is that while the aluminum is lighter, to achieve reasonable rigidity there has to be a fair bit of extra webbing. The extra webbing v. the iron block adds weight, so the delta in weight savings is modest for an aluminum block of good/decent rigidity. Maybe 60-80 lbs? That's certainly something but it's not a couple hundred pounds difference. Just my $.02.
 
My Ford Motorsport 8.2 alloy block - 46 kilos.
Iron block is around 20k heavier from memory.

It's all mass, matters more to some than others.
Light block, heads, crank, flywheel, etc - it all adds up (or down).

Tim.
 
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Sean, I'm no expert on this one....but what I've heard discussed around here is that while the aluminum is lighter, to achieve reasonable rigidity there has to be a fair bit of extra webbing. The extra webbing v. the iron block adds weight, so the delta in weight savings is modest for an aluminum block of good/decent rigidity. Maybe 60-80 lbs? That's certainly something but it's not a couple hundred pounds difference. Just my $.02.
Between block and lightweight internals maybe 100 lbs. Compared to an Iron 351 based motor 200 lbs and also a bunch of that lost from up on high.

But yes is it worth 60-80lbs over an iron 302?
 

Mike Pass

Supporter
Any weight removed from the motor will help. A car with a rear/mid engine is like throwing a hammer handle first. I have tried both 302 and 351 engined cars with ally heads and you can definitely feel the difference in the handling. The heavier engined car has more of the pendulum effect when you turn into a corner. If I could afford it I would get the ally block.
Cheers
Mike
 

Howard Jones

Supporter
The difference is the same as running a half of load of fuel instead of filling them both up. On track running the drivers side tank dry and removing the passengers seat does make a little bit, and I emphasise LITTLE, bit of diference in that the car just feels a little bit lighter on the brakes and corners just a bit more responsive. Lap times really don't change much but it seams like the car is easier to drive at near the limmit.

60 pounds is enough to effect performance AT THE LIMMIT, but unless the car is driven that way then you will never feel it. What's a second worth per lap? If you aren't racing, nothing. The car will still be a blast to drive at the track and faster than you will ever be able to drive it on the street. Any serious oversteer can be tuned out and should be anyway. If I can make my GTD push then anything can be done with suspension tuning.

Save the money and buy a second set of wheels and tires would be my recomendation. R6 Hooizes will get you at least 4-5 seconds a lap over street tires and THAT"S a difference you can feel!

Of cource we all are on difference budgets. If the money isn't the issue (god bless you) then an all aluminum engine IS cool. Kinda like webbers, they look really cool but they really don't make the car much faster.
 
The difference is the same as running a half of load of fuel instead of filling them both up. On track running the drivers side tank dry and removing the passengers seat does make a little bit, and I emphasise LITTLE, bit of diference in that the car just feels a little bit lighter on the brakes and corners just a bit more responsive. Lap times really don't change much but it seams like the car is easier to drive at near the limmit.

60 pounds is enough to effect performance AT THE LIMMIT, but unless the car is driven that way then you will never feel it. What's a second worth per lap? If you aren't racing, nothing. The car will still be a blast to drive at the track and faster than you will ever be able to drive it on the street. Any serious oversteer can be tuned out and should be anyway. If I can make my GTD push then anything can be done with suspension tuning.

Save the money and buy a second set of wheels and tires would be my recomendation. R6 Hooizes will get you at least 4-5 seconds a lap over street tires and THAT"S a difference you can feel!

Of cource we all are on difference budgets. If the money isn't the issue (god bless you) then an all aluminum engine IS cool. Kinda like webbers, they look really cool but they really don't make the car much faster.

Thanks for the feedback. Car wont have webers or stacks would rather spend that money (5-7k) on internals.

Def getting anotehr set of wheels, the car will be mostly if not entirely for track. In my Lotus I sure can feel the effects of 1/2 tank of gas, this si marked on corners and in braking. I always read GT40s of all stripes could use more brakes, so I figure thye can use less weight.

The price difference is about $1500 to go aluminum. Not huge in the scheme of the whole car.
 
Weight is the enemy in car racing, dead weight has to be carried, accelerated & stopped.... dont believe me, chuck a 20kg sack of whatever over your shoulder and run up an 100 meter hill, walk back down and do the same thing without the 20kg, provided you dont die or injure yourself from the first attempt you will find the second run is faster... the simple answer is most folk are too lazy or lack the drive/knowledge etc to optimise the car to the lighter weight, there never has been the perfect car, probably never will be, too many variables..weight & brakes do not necessarily go hand in hand, other factors like aero downforce & anti-dive geometryplay a huge part, problem is then that in the case of aero you might have good brakes at higher speeds,& crap at slow speeds, antidive might help at slow speeds, but impose issues in roll center height & tire contact etc, its about finding balance...
 
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Howard Jones

Supporter
Jac, I can't dispute you other than to say that open track day running isn't racing. Real race cars always have a weight minimum in the rules and running a 2060 pound car in a class that has a minimum weight limit of 2000 pounds will be a huge disadvantage. Hell just look at FF lap times and you can see that weight is the factor that makes them so damn fast. It sure isn't power, brakes or downforce. It would be a hell of a self built GT40 that gets around most tracks that fast. 1.26 at laguna for a FF

Mazda Laguna Seca - Trackpedia

check out everything else

Laguna Seca lap records - FastestLaps.com

But an open track car can be run at 95% (usually should be) and be more fun than a barrel of monkeys. All things being equal 60 pounds low in the engine room won't make enough of a difference for most people driving a 2500 pound car in a open track session. The fun factor to cost ratio just doesn't justify some expensive things like alum blocks, at least for me.

I think I would be looking for really light wheels for the slicks to spend the extra money on instead.
 
Weight is the enemy in car racing, dead weight has to be carried, accelerated & stopped.... dont believe me, chuck a 20kg sack of whatever over your shoulder and run up an 100 meter hill, walk back down and do the same thing without the 20kg, provided you dont die or injure yourself from the first attempt you will find the second run is faster... the simple answer is most folk are too lazy or lack the drive/knowledge etc to optimise the car to the lighter weight, there never has been the perfect car, probably never will be, too many variables..weight & brakes do not necessarily go hand in hand, other factors like aero downforce & anti-dive geometryplay a huge part, problem is then that in the case of aero you might have good brakes at higher speeds,& crap at slow speeds, antidive might help at slow speeds, but impose issues in roll center height & tire contact etc, its about finding balance...
My interpetation from what you are saying is the aluminum block weight loss wont matter and could be counterporductive without the proper setup. As the setup with a iron 302 is well established its the easier route.
 
Jac, I can't dispute you other than to say that open track day running isn't racing. Real race cars always have a weight minimum in the rules and running a 2060 pound car in a class that has a minimum weight limit of 2000 pounds will be a huge disadvantage. Hell just look at FF lap times and you can see that weight is the factor that makes them so damn fast. It sure isn't power, brakes or downforce. It would be a hell of a self built GT40 that gets around most tracks that fast. 1.26 at laguna for a FF

Mazda Laguna Seca - Trackpedia

check out everything else

Laguna Seca lap records - FastestLaps.com

But an open track car can be run at 95% (usually should be) and be more fun than a barrel of monkeys. All things being equal 60 pounds low in the engine room won't make enough of a difference for most people driving a 2500 pound car in a open track session. The fun factor to cost ratio just doesn't justify some expensive things like alum blocks, at least for me.

I think I would be looking for really light wheels for the slicks to spend the extra money on instead.
Are you saying loose the weight elsewhere, where it can do more good, ie unsprung weight.

I have heard the Gt40 auminum wheels are heavy, is there a source for really light wheels.
 

Howard Jones

Supporter
I guess I am saying that if you are going to race it then build it to the rules and get the weight down to the limit. If you are going to open track it then 60 pounds won't make enough difference to matter in a 2500 pound 400 hp car.

Tires, limited slip, gear ratios, balanced suspension setup, brakes, weight, then power would be my order of importance given the baseline 2500lb/400hp car.
 
My interpetation from what you are saying is the aluminum block weight loss wont matter and could be counterporductive without the proper setup. As the setup with a iron 302 is well established its the easier route.
Wrong, your ideal setup should always be for what you have got, ie: if your car is 20kg lighter due to an alloy block then the perfect setup should require lighter spring /bar rates & softer shock settings, if you run lighter wheels, more of the same.. in other words thinking light but strong right from the start will be best...but if your from Howards 95% category it probably does not matter:)
Look at it this way since you only have a paper car at this point in time.... if you build it with an iron block now and decide to change to alloy later it will cost you the block plus all the parts & labor to make the conversion & that adds up to a hefty $$$ number, not simply of buying a block and fitting the bits from the iron version...more like hone job, stud kits, ring set, machine work( deck clearance etc), gaskets, fluids plus labor and thats only the bare minimum
 

Rick Muck- Mark IV

GT40s Sponsor
Supporter
Are you saying loose the weight elsewhere, where it can do more good, ie unsprung weight.

I have heard the Gt40 auminum wheels are heavy, is there a source for really light wheels.
There are magnesium versions of the BRM wheels available, when you lift one the difference is VERY noticeable. The cost difference is also very noticeable.

Speed costs, how fast do you want to go?

At this point you have not driven much less tracked a GT40. You are looking at items that are a tenth here or there for a track day car, not a vintage sanctioned legal car (for which most organizers the alloy block will be a "no go").

Not to be a bigger dick than normal but this is still a lot of bench racing. Build the car the way you want and it will go as fast as it (and the driver) can go.
 

Steve

Supporter
Agree with Rick's comments. Build it safe and reliable first. You're not going to make a living tracking/racing this car. If you do race vintage sanctioned events an aluminum block won't let you in. My advice would be to have a reliable engine builder build you a 400-450hp engine that will go all day long (most if not all will choose a Dart or Ford Boss iron block to start with). Then have Dennis O fit the roll cage that suits your needs, all the safety items that are pertinent (fuel cell, fire suppression etc) and the suspension setup that is tried and true. If it works for Dennis it'll work for you so why reinvent the wheel. Next step, get out and enjoy!

I can appreciate your desire to address the minutiae before the car arrives, I'm a very detail oriented person as well. Still, if you're thinking a lot about unsprung weight, mag wheels, alum block etc I wonder if you should consider the SLC or some other build as it would be a better all out track car.
 
Thanks for all the feedback. And no one is being a dick, so all comentary welcome. Yes its a bit of bench racing, alas once the car is built spec is hard to change, and as most cars have varied spec its hard to get experieced data, except here and there.

I come from a lotus, where everything is about weight. We can say that in my world lightness is next to godlyness. So losing wieght is a bit of an obsession. Maybe on a Gt40 with 500ish hp its irrelevant, certainly in terms of acceleration.

To me weight is about braking and cornering. Yes its maybe fractionaly quicker, but if it helps the brakes work better and last be it shoudl be worth it? But then again maybe on this car 60 lbs down low is somewhat irrelevant. On my Lotus I went to a Lipo mtorcycle batery lost 30 lbs right over the left rear wheel, the difference was very noticable on lhd car on clockwise tracks.

On thing I agre is I dont want to reinvent the wheel. So if the suepnsion setup is already well known, and the aluminum block changes that then its not worth it.

I guess my biggest concern is brakes. I see the rotors are 12.75 inches which is pretty good. But then even in my 1900lbs 200hp lotus the brakes get pretty soft at the heel of the boot at the glenn, and that is with proper rotors pads and fluid.

So maybe its a very different drivig style in the gT 40 like braking early and powering out of bends more than carrying speed through. But it seems like this car will have a lot of speed at the end of the straight. Maybe I am overthinking, or trying to max soemthing that is not so critical.

Yes its going to have fuel cells fire supression, proper seats and harnesses and a cage/bar.
Motor will be 8.2 dart block, 4.125 bore 3.25 stroke, 10.5-11.1 comp ratio for pump gas,
really light internals. Shaft roller rocker, prob hollow stainless valves.

Suspesionn 600lbs springs Da Bilsteinsupgraded roll bars.

So maybe excess power for the track, and a track suspension setup all of which makes it easy to convert to street use(put stock shocks/springs back for road rallies), or useable for the occasional drive on smooth roads.

Since there really is not standard spec in terms of a trackable car, its all theoretical best guess in terms of spec that works for me, other people experiences with their specs and general knowledge helps greatly.
 
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Howard Jones

Supporter
Jac hit on something about building it strong from the start. Open track cars usually will be used for many years. Racecars usually (broad term) are competitive for much shorter timeframes and then are retired. Parts that wear or fatigue on them are replaced on a time in useage schedule. Some of this is to prevent DNF's and increase safety margins for a car that is driven at the limit for much longer periods but both of these considerations seldom apply to a fun day track car.

The open track car on the other hand can remain fun enough for many years, even decades. So what am I getting to. Adding weight may be in your long term interest, at least as far as increased reliability/life cycle is concerned. For instance when making upper a arms for my GT40 I decided to use a heavier wall thickness instead of just thick enough because I didn't want to make more later or be concerned about failure (pot holes again). Think about at least building it a bit stronger than you think it requires. A few more pounds if used correctly can make your car a lot longer lived. Sort of endurance racing instead of sprints.

If you look at bodywork for example. Super thin fiberglass body panels are a lot lighter but will crack with the first pothole. How many engine covers do you want to buy over the life of your car? Same thinking with a lot of this stuff like a pump gas 6K RPM motor instead of a race gas motor run up to 8K+. Same fun more or less at the track but a lot less maintance and $$$$$'s.

In the end, it's your car and your money, you should do what makes your panties wet. IMHO while you are in the planning phase, spend a little time thinking through what you really want when it comes to really high dollar race parts. Like the man said. How fast do you want to go?

Just something to think about. Smart move by the way, asking these questons before you start spending money. Ask away, thats what this website is for.
 
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