Carbon fibre tub??


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Anyone have an opinion as to the durability, streetworthiness, and all aspects of building a tub out of kevlar and carbon fibre with steel tubing utilized for the engine and tranny mounts, suspension pickup points and roll bar. I am not concerned about the cost to fabricate the tub. The car will be used basically as a street car with a big block. Thanks
It is quite doable, and if properly designed will work fine for street driving.

If you are going to go to that kind of trouble and expense, you should probably think about updating the suspension to a double wishbone / pushrod set up all around.

Some downforce would be nice too. So a set of diffuser tunnels could be incorporated without changing the outside look. (You might want the designer to make a slight change to the lower rear to help the tunnels draw better).

As to the big block, are you thinking 460 or FE? The car won’t be authentic with a carbon tub, so there would be no reason to use an FE. You could get far more power from an all aluminum 427 Windsor, save hundreds of pounds, and it would package better.

You will also need to find a company with a set of molds that will make a carbon body for you. No point in spending all that money on the tub and then putting a heavy fiberglass body on it.

The key will be to find a racecar designer with plenty of experience designing carbon tubs to do the actual design. Also, an experienced fabricator with the proper sized autoclave. (You may need to look to England for this).

Good Luck and keep us posted if you go ahead with it.

Although I agree it is doable the longevity of the tub is suspect over the long haul. A good amount of years down the road mind you, but definitely in a car's lifespan.

Structural integrity and such is not to be taken lightly. You need a very talented and experienced engineer with the proper machinery to design this for you. It really is not as easy as molding and "voila!". As for the actual machinery to get the carbon done, I'm guessing you have found your source if you are mentioning price not being an issue. I'm going by that assumption because when working with graphite compounds price is ALWAYS an issue. Even when dealing with the government with their "unlimited" funds.

If you are considering doing this on your own via "wet layup" I strongly suggest you reconsider. Be safe. Making carbon fiber safe in severe structural applications, like a tub, is extremely difficult even for experts. Graphite compound failure is disastrous. It splinters in to millions of shards and is astonishingly sharp. Please use extreme caution with these sorts of projects.

I would not mix carbon and kevlar when doing a tub. Their differing flex capabilities would make the tub comparatively unstable. I would do a carbon x carbon setup with an aluminum honeycomb in the middle for insulation of sorts and stress distribution point. If you go ahead with the body in carbon fiber make sure its stressed carbon fiber. Don't go with the bling bling tight twill for the tub either get heavy gauge carbon. Cross weave when you layer and all that good stuff. Again, do not "wet layup". That sort of sloppiness might be OK for college solar powered car projects and junk like that but a real car with the power a GT40 is capable of putting on the ground is a whole different ball of wax. /ubbthreads/images/graemlins/grin.gif

A little background information as to where I get my information. I own a major carbon fiber research and applications company. Our main customers are governments for their defence and aerospace programs. We also do marine applications in large scale. We have some of the world's largest autoclaves and also have a lot of patents in carbon research. We have developed thrust flaps for the B2 bomber capable of withstanding over 7000 degrees Fahrenheit. Cooool stuff, but definitely not for rookies.

Best of luck!



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Wow, thanks for the replies. Keep them coming. Kevin I will be using old iron. The 427 side oiler is sitting nicely in the garage. I will certainly be printing this and bringing it to the tub builder with questions. Now I need to hear from Lynn and anyone else with their opinions.
Gregg, great idea! I've been wanting to build a GT40 chassis out of composites since 1965. My thinking was that Jim Hall did the Chaparal chassis using fiberglass. I even wrote to Ford looking to by a windshield. I still have the lrtter they sent back to me.
"stichandice" is right with what he said. I do composite fabrication for a living, and now after thirty years of doing composites, wouldn't attempt doing a corbon composite chassis unless I had an engineer design it. There is not many composite engineers out there that have the "know how" to design a carbon composite chassis. Talk to McLaren Racing and see what they say. BUT.... I still would love to do it! Good luck with the idea! keep us posted!
Gregg, I was taken for a ture of the Panos facility in Brazelton, Georgia. They manufacture their carbon fiber race cars there. I was told that to do the body of a GT-40 would cost ( rough guess ) about $50,000 once production was set up. I watched the workers building one. There are many types of aluminum honeycomb used in each car. What was very interesting was that there actually very little carbon fiber used. It is heated in an autoclave in a vacuume, I think, then put under pressure to get out all of the air boubles. This is done one layer at a time. It is very labor intensive. doing a tub would be a
much more difficult than doing a body with all the small part that have to be fitted together. The body might be the better way to go. I picked up one of their noses of a can am car and was ammaized how light it was.
Gregg, I left out the end of the sentence when I said I watched them building one. It was not a GT-40 they were building, it was a can am car.
While the production cost may be $50,000, I would expect the development cost to be ten times that amount. And it would have to be done with prepreg or vacuum bag techniques, because a wet layup wouldn't weigh much less (if any) than a monocoque.

David Morton

Lifetime Supporter
I was in the BMW Schnitzer garage at Le Mans 97 when JJ Lehto punted the McLaren F1 GTR into the main wall along the start finish straight about 0800 in the morning (fell asleep !) The car did one more lap and came in for major repairs. Gordon Murray was called to look at the damage and retired the car immediately. What, to the casual onlooker, looked to be superficial damage was major. The shunt had caused all sorts damage around the front end. The c/fibre was so strong around the front, it apparently left the front end intact (apart from shagged radiator and coolers, and seemed to transfer the damage further back.(a few small cracks around the front suspension). I've got the video that I took in the garage and since that incident I would shy away from composites on a road car. It is extremely difficult to repair and certainly not something to undertake at home (no matter how big your oven). I think its a great subject for debate ie: weight saving, rigidity, strength, but to do a -40 in c/f would be almost crazy.
Dave M

You need to do what will make you happy, but I fail to see the logic on the FE motor.

An iron FE weighs about 650 lbs. An aluminum 427 Windsor weighs about 375 lbs.

You will spend well over $100,000 to get even a minimally acceptable tub in carbon that will save you maybe 100 to 125 lbs. You then add 275 lbs of dead weight back in with the FE motor.

The FE also will not make anywhere near the power. A good indicator of power output is the flow of the heads. There are not a lot of heads for the FE; Edelbrock makes a set that are much better than the factory medium riser heads.

Edelbrock flow numbers are: 233cfm @ .400 ~ 265 @ .500 ~ 270 @ .600.

AFR 225s for a Windsor are: 264cfm @ .400 ~ 295 @ .500 ~ 315 @ .600

An Iron head FE, in a similar state of tune, will make 100 to 150 hp less than the Windsor based 427 and weigh 275 lbs more. That kind of makes spending $100K + to save 100 lbs on the tub seem a little pointless to me.

As for using Kevlar, I agree that it is not a good structural mix. The only time I have seen it used in a carbon tub, it was the outer layer on certain parts of the inside of the tub and was used for the purpose of containing the carbon shards in the case of a crash. (Stickanddice is not kidding about that stuff splintering).

In any case, I certainly don’t want to talk you out of the car. I would love to see it. If you absolutely have to have an FE you might consider an aluminum Shelby block and Edelbrock heads. It will still be about 75 lbs heavier and down 75 to 100 hp, but it would be a lot better than the iron motor.

Good Luck

Lynn Larsen

Lynn Larsen
The rough estimates from a composite racing car/parts manufacturer is that developing the tooling would run around $120K and then once created it would be ~$25K per copy. These were off the cuff estimates. The issue with developing the tooling is that if you are going to have carbon fiber construction, you have to have carbon fiber molds that can handle the heat of autoclave during curing of the parts. The only way to really do this in a cost controlled, efficient way is to use prepreg layup material that is heat cured in an autoclave. They also employ honecomb layers in their SRP I car, but I have not been to see them since they started construction of their Daytona Prototype car.

Reference: Crawford Composites

Ron Earp

I don't get the FE either, other than for nostaliga purposes, it doesn't seem to be a fantastic motor given the choices these days.

For a given displacement I find the Windsor family far better with respect to power production, weight, packaging, and parts availablilty. And, the 385 big block while heavier (in most cases but not all) than an FE has a far greater power potential with the large availablity of parts. I mean, if you got the FE so you could make a 4XX CI stroker then why not make a 5XX or 6XX CI stroker with the 385 series? Or stick to 429/460 CI and enjoy a nice rod ratio with incredible safety margins for power production.

And the argument on weight is dead on - similar to my analogy with motorcycle weight savings and overweight riders. Go for the low hanging fruit first!
In keeping with the light weight parts Ford does offer a AL 429/460 block Pn M-6010-A96 weighs in at ~179lbs
Listed as avaliable from RaceParts Distribution Inc.
In the virtual catalog, pg 44
This is a bit of a slow load due to a turning page graphic.
Also lists Holman and Moody racing parts including the HM logo 4 webber intake, Pg 178


Ron Earp

I was thinking the Al block was out of production for the 460. Says it weighs around 165 lbs, the 185 is shipping weight I bet. Either way, a big savings over a iron 460. Now, couple that block with Al Blue Thunder heads, 600 inches, and you've got some serious motor. FE guys can't touch that for the money, not many engines will.
With that 460 / 600, the question becomes: Can you get the tires to hook up below 100 mph?

Given that the 1968 Mclaren M8A Can-Am car made about 650 hp from its all aluminum big block Chevy (and used 15" wide rear wheels), you are getting into some very serious teritory here.

Ron Earp

I doubt it. Not unless you can run some serious rubber aka like what you can fit onto Cobra replicas. And then the transaxle, well, whew. I think it is more of a mote argument but fun nonetheless. Heck, I imagine even with a well built FE or Windsor power can be beyond what can be handled, with a 600 inch motor, well, I really don't know what you do with it.
There was an extensive discussion of this topic when I first got on this forum, which I thought was very interesting. So...
The good news is: you can get a GT40 body in carbon/Kevlar from Safir GT40 in Cinncinatti. They have done it from their molds and would do it for you. It is impressively light; two thirds if that the weight of my FRP GT40 body, I compared it myself. If you want to save weight, that is a lot easier and cheaper than a carbon tub. And a hell of a lot safer.
I agree with the above as far as the engine goes; if you are going to spend huge kilobucks to make a light rigid GT40 chassis, you should put in the lightest hottest motor you can. Every pound you save will have cost you a fortune; why throw the weight saving away in the engine room?
As for a carbon tub, I think it's a mistake. I thought, and still do think, that an composite tub for a GT40 is a great idea, but I think you could do the same thing, or very near it, with S-glass, some Kevlar, VE or epoxy resin and good prepreg or vacuum bag technology. OR, you could build the entire tub out of preformed FRP structurals which are easily available; the disadvantage there, though, would be that you couldn't as easily specify fire-retardant resins. Which you would want, but then it wouldn't be any more fire-resistant than a steel tub.
All of this is about getting weight out of the tub, in order to go faster, I guess. One thing that we haven't discussed is that there are now intermediary sandwich type materials that allow you to weld steel to aluminum. Possibly some weight could be saved in a metal tub by making some parts of aluminum. If properly painted, it wouldn't corrode, and would be just as strong if it were done carefully.


Lifetime Supporter
I am amazed at the responses and the knowledge of the forum members on this subject. It certainly has given me numerous questions to discuss with my friend who owns a composite shop. We will put the FE question to rest first. The engine is built, Kennedy adapter paid for and G50/52 sitting by its side. The engine was chosen because of originality to the car. I guess I could've sold the engine but it was one less thing to acquire and deal with later on. On to the tub. I have a friend who owns a composite shop. He is currently building a one off car to his own design with a little artistic license borrowed from Ferrari. He intends to build a composite tub with steel tube fabrication for the engine, trans and suspension points. The tub would basically be a box the size of the fuel cells and the width of the car, steel rollbar with composite roof. Engine & suspension pickups would be tube frame design like the ones used on the old Jaguar XKE's, but for this application and bolted to the front and rear bulkheads. As he plans to build a tub for himself we have been discussing building another one for a forty. The side effect of weight saving has never been a concern of mine. I know there has been a lot of talk on this thread and others about saving weight, however, as the car will be used primarily for a street car I'm not concerned about the weight. It will be plenty fast for my purposes, for the street and my abilities.

Stick and dice, I sent you a private email but don't know if it ever went through as there was no confirmation. I would like to talk to you via the telephone if possible.

Kevin McGowen, I would also like to speak with you via the phone if amenable.

Jin R. I will be in Baltimore for the holidays. Have your received your tub yet?

Thanks to all who responded.

Have a Merry Christmas and a Happy, Healthy and Safe New Year.
After thinking about all of this, I’m not sure it really is about saving weight. I think maybe Gregg just has a dream of a particular car that he thinks would be really neat. It is not the car I would pick (Fair enough, no reason we should have the same dream). But when you really look at it, none of what we are doing here makes sense.

Some of us want an exact replica and will pay a lot of money to make sure the rivets are in exactly the right pattern. Others think that is a complete waste of money to duplicate known faults at great expense.

If we say we want a fast track car, there are much more modern cars with better aerodynamics like the Ultima that could certainly be made faster… but we don’t want those, for whatever reason we like the GT40.

If we say we want a fast car for the street, a Corvette or a Porsche would be far more useful, comfortable, and about as fast as we can really go on the street. But that is not what we want. This is why we can have endless discussions about the best size engine to use, etc. Because there is no best size, there is really little use for these cars at all in a practical sense.

We want these cars because they hold some emotional appeal to us that goes very deep and that we probably don’t understand completely ourselves.

So, I retract my comments about the weight of the FE motor. They are completely true for me, but they may not be true at all for Gregg.

Gregg, build your car just the way you want it to be. Ignore all of us and how we want
our cars to be. I can’t say that this will make you happy in the end, but I think I can say with reasonable certainty that if you let yourself get talked into something else that is not what is really in your heart, you will never be happy with that.