I'm doing a 914-6 GT conversion project and just trying to decide if it is worthwhile fitting one or both of these kits ?
Do they both make a real difference to the handling or does one of them make 90% of the improvement ?
(Money being no limit, then I would probably just fit both, but if only life was that simple ! - If both deliver a notieable improvement then I'll fit both)

Any advice welcome from all you racers out there !

The best bang for your buck is the Engman chassis stiffening kit offered in the resources section. The GT kit would make a nice complement.

There was a long, detailed engineering debate on boxing the trailing arms last year. Racerchris was expirimenting with several different methods. Do a search for the thread, I don't recall the conclusion (or if there even was one), but it was shown the GT boxing did little more than add extra unsprung weight. The discussion also centered around the need to stiffen the trailing arm mounting to take advantage of the stiffer trailing arms.

I think it was Eric Shea that said something like this, What would you rather have

bent, your trailing arm or your tub/attachment points. A trailing are is alot

cheaper to replace and more available.

I seam welded everything from the fire wall back.
I have a cage that mounts in 10 places but is not(yet) tied into the suspension towers.
I have no stiffening kits and no breakage after 6 years of autocrossing on *very* rough venues with big sticky buns in each corner & stout springs. You may well ask why I would want 40ishlbs of road hugging weight.

If I had my druthers I 'd pick neither one of them bending. I boxed my trailing arms because one of them nearly split in half. I didn't like that. I admit that since I boxed the trailing arms I've had multiple chassis flex/crack issues. I keep reinforcing from the roll cage to the shock towers with triangulation, circles and arrows and three part harmony, and I feel I've now got this tub stiff and safe. I really don't think Porsche engineers designed these cars for heavy racing on sticky Hoosiers. So, if it's not a track car I wouldn't box the arms. If it is a track car you better plan on fully inspecting it between each event because eventually somethings going to give.

The conclusion of that thread was that boxed trailing arms had one and ONLY one effect.... they added weight. The FEA analysis proved that boxing the trailing arms did not prevent arm twisting under load. Chris Foley can do more to strengthen a trailing arm with 8 oz of metal than the pounds added by the boxing kit.

I checked the factory welds on the trailing arms for my six project. They were not anywhere near as good as the welds on my 75. So I spent some time

Boxing the arms is a waste of time....

Spend more time and capital re-inforcing the tub than the trailing arms.

They're already pretty damn tough.

I put a kit in my last car. my next car will get one as well. I noticed a huge loss of flex. I thought the car handled better afterwards.

Engman kit is the one to install. The other don't really do much at all. Do a search for detailed threads about "why".

When you say the 'Engman kit' do you mean the chassis stiffening kit mentioned on some posts above, and therefore not bothering with the boxed swing arm kit ?

Jason, Mark, Zois...

I disagree with your interpretation of the Racer Chris testing.
the Thread proved that the boxed trailing arms were significanly better than nothing.. If my memory serves they were about 80% as good as what chris came up with.

So my interpretation of the testing was that chris' new and improved bracing was better than the boxed arms.. but that the boxed arms were much stronger than stock.

this doesn't answer the original threads question, but I think its worth noting that there may be different intrepretation of the results of actual testing.
My own personal opinion is based upon AJRS results that the boxed arms are very necessary and put onto every single car that he builds.

brant

Your opinion seems to stand alone in a sea if derision regarding the benefits of fitting the boxed swing arm kit.
I'm intrigued - what made you think it gave you an improvement over and above just fitting a chassis stiffening kit ?
(Nothing like a bit of healthy debate !)

Engman kit thread

From the classics...

Great kit.

KT

Ok, you can interpret Chris Foley's data however you choose.

Al Swanson, an aerospace engineer for Ratheon did computer modeling on the rear trailing arms and found that installing the rear trailing arm kit can actually weaken the rear trailing arms! Why? When you weld these on such a small part they aneal the steel, which weakens it.

This should not be confused with seam welding the trailing arms. There have been a couple instances that I know of where the bearing race (the part the bearing slides into) were not welded on the trailing arm adequately and came apart under stress.

agreed...

everyone is going to have to form their own opinions.
did Al measure deflection or actual failure?

my learning curve has always been to see what the absolute fastest guys are doing and use their baseline as a starting point.
from that I've choosen to believe that the boxed stiffening kits are worthwhile.

I highly value the instruction and advice I get from AJRS. He absolutely insists upon them. I have ran a set with the kit for 14-16 years now and not had any failures or problems. I choose to trust his advice based upon results. For example I think AJ was running about 10 seconds per a lap quicker than Rich Bonatempi. at one of the PCA club races a couple of years back...

so everyone will have to form their own opinion.
but I'll try later to dig up Chris' testing thread.
I really remember that it showed an unboxed, or non-reinforced stock trailing arm had significant deflection (and less when boxed)

now interpreting how "significant" is really significant will be up to the individual user.

brant

Ok... I found the link.


Chris test showed that his reinforcement was lighter (2lbs lighter than boxed)
and also superior/stronger (by about 20% than boxed)

however the boxed kit according to Chris is; "Yup. Actually more like 38%" stronger than a stock unmodified arm. (page 7 of the thread)

Chris' testing

I'm with Brant and it wasn't I who said the "what would you rather have bending?" I think Chris' testing is the best we have to date. What I take from it is; for 6lbs. of weight you get a control arm that is 40% stiffer. I like that.



I also like:

* The factory chassis stiffening kit. All of it.
* Seam welding is a must.



I believe the chassis kit is something like 16-19lbs (JP is old and he keeps forgetting these things and he fudges numbers to support his delusion)

Read in the link Brant posted above. Also find Jeroen's post about his semi-tube project... there's some good debate on the factory kit in there.

Old myths die hard... weed through and make your decisions. If I were in your position (which is what I'm doing now) I would (am) use the control arm kit along with the factory chassis kit (along with rear mounting ear braces and camber braces). I would also seam weld the entire lot. I spent a great deal of time snooping around the 914's at the HRS race at MM. All the top cars were seam welded. Ask Mike's buddy Jim Patrick what he thinks about seam welding. I don't believe there's a (race prepped) car that leaves his shop without it.

Flame away.

Seam welding is a must as if you have ever cut apart a car you would see how many of the factory welds don't hold crap! The spot welds are hit and miss so the seam welding has to be done.

I thought Jeroen thread showed how the kit didn't address the shock tower/ long weakness which the kit doesn't address at all. Its a bandaid on the surface of the problem.
The Engman kit addresses the biggest weak spot on the car, the bulkhead to long connection.

I agree, the kits address two different areas. Factory kit is for the suspension tie-in area and the Engman kit is the bulkhead to long joint area. Two differnt problems and two different fixes.

Just my 2 cents.

Johnman and I have a chassis that has been on the track for 18 or 19 years with pretty heavy de hours on it on 245/45x16 Kumho victoracers or ??.
We have similar reinforcement on the inner longs and have a cage in the car. The outer longs are also boxed in, and the car is still very solid and stiff. If we jack it up at the front donut that whole side of the car lifts and the door gaps do not move, and this is 18 years after installing the inner boxes and the cage....

On another chassis we opened up the outer long at the jackpoints, and you can see right through the car!!!, right through the gap between the inner and outer lower firewall member!!!. There is a HUGE hole through the inner long where the heater hose makes its transition from the engine compartment into the long, and it is immediately behind the jack point. So the great german ingenirring designed a hinge point into our beloved 914's and they did it on purpose!!!!!!!!!!!!!

The real fix is to give up on a heater/defroster, open up the outer long at the jack point, make sure the car is straight, and weld a plate into the inner long (we cut open the lower bulkhead inner and outer so we could plate about 6 inches fore and aft of the bulkhead on the inner long. Then we closed up the outer long.

Based upon our experience buying the Engman kit or making one similar is a big help, but it should extent CLEAR through the bulkhead and into the engine compartment, and then probably all the way back to the inner suspension ear.

Good luck to all of us.. because these little light tubs were designed for up to 100HP and 5 inch rims with 155 or 165 tires that were not sticky at all, and we overstress them a big bunch, and then they are 30+ years old!!!!!!!!!!

A+. The factory welds on these cars have been known to be poor at best. Follow Chris' thread on the suspension console fix... insane.



I feel this is a myth. Jeroen's thread is about a semi-tube car. There are all sorts of things he did that I would do if I were making a semi-tube car. All sorts of things that I would "not" do to a stock-style unit chassis. The main concern addressed in that thread was the rear shock tower bracing and a section that looked as though it needed addressing. It involved cutting a bulkhead to access. Again, apples/oranges. For a tube car with the reinforcing he was doing... not a problem. For a stock car (many people were faithfully following along) it was my opinion that was unneccessary. The bulkhead that has to be cut to access this spot is literally 1" away from the so-called bad seam. It's a double walled bulkhead and it's basically a ladder frame component. It stregthens that specific area in question. I wouldn't cut one of those unless I had to (read: rust). On Gint's stock tub we were able to access that same seam through the shock tower. On Jeroen's semi-tube tub... not a problem. The reason I suggest reading that thread is, we found out a lot about the factory kit and discussed it in that thread.

The bandaid part comes from comments made about the kit being welded across the inner fender well and not the longitudinal. Well... the inner fender well is the longitudinal at that point. There was a comment that the actual longitudinal is just (a layer) below that area but, there was a car cut up that proved that the area covered by the so called bandaid is the actual extension of the longitudinal. The kit spans that area from the transmission mounting dogbone bulkhead (there can be a bit if torque there) back to the shock towers. It literally ties those two critical areas together. Instead of throwing it away, it can be one of the most valuable pieces in the kit.



Sorry... the bulkhead to longitudinal is again double walled. My money is on that unless it's rusted. I'm not, in any way, panning on Mark's kit but I wouldn't call that the biggest weak spot on the car.

so far I've only chimed in regarding my opinion on the trailing arms.
I agree with much of what Eric has outlined here.
There are some very valuable pieces to the chassis stiffening kit.

when we build the orange car we used about 4 pieces
we also made our own items for some of the other areas that we especially wanted.

we also seem welded.

so my opinion is that some of the kit is invaluable.
its worth using what you want from it.
but again each person will have to form their own opinion about what they think is important.

this has been gone over and over in threads.
there are some amazing threads on this board with amazing info.

brant

For what its worth my car has...

I have boxed trailing arms (wish I didn't)
I do not have any stiffing kits on the chassis.
I do have a semi-tube frame that I would guess is stiffer than a car with sheetmetal kits.

amallagh,

Here is my advice, but I will start with a question.

How will you be using the car? Street cruiser? DE car? Full out balls to the wall race car?

If it is a car that you want to keep for a good long while and are not concerned with carrying a few extra pounds, have both kits installed.

They won't hurt if installed by a capable welder.

They do add extra weight.

If I didn't fabricate my own stiffening kits, I would probably buy:

Engman kit
Factory Chassis Stiffening kit
Boxed trailing arm kit.

On my street car, I have the chassis kit + some extras that I do to the little cars to keep them untwisted. I did not do the trailing arms at this time as I am not pushing the car on the street and right now I only have 185 tires on it and not very sticky at that.

When I flare my car (hopefully this winter), I plan on bracing the rear suspension inner ears (to the firewall) and also installing toe-in adjusters/turnbuckles/braces.

To re-iterate, to answer your question, you will need to define how you plan on using your car/toy.

Good luck with your GT project.

John

Oh... I finished reading Chris's wonderful thread
I love the summary from Jlueten on page 14:

"What we've learned along the way since they consisentanly came out in our tests and model -- no matter what we did to them.

1) The stock arm does flex.
2) Adding an internal bulkhead stiffens it some.
3) Adding an external gusset stiffens it more.
4) Combining the two approaches stiffens it even more
5) There are some concentrated stresses in the hub area (where Porsche's designers kindly designed in a fairly massive piece) and where the arm attaches to the outer end of the front pivot tube. "


brant

Wow !! what a lot of information. Interesting just to sit on the sidelines and watch. All your inputs are much appreciated and I'm glad to have provoked some healthy debate. (Hopefully nobody has fallen out !)

I don't have the engineering or fabrication experience to do much more then buy someone elses kit and get a welder here in the UK to install it.

After initial threads the weight of opinion was against the significant benefits of the boxed trailing arm kit. Then the Engman kit was introduced to complicate the party. After many more threads I think the balance of opinion is that all chassis stiffening options are worthwhile to some greater or lesser extent but none are a waste of time.
1) seam welding
2) chassis stiffening kit
3) boxed trailing arms
4) Engman kit
In terms of the order of additional benefit then 1) appears to No 1 (If someone would like to list what seams need welding then that would also be helpful ?)
After that then everyone seems to have different opinions about which option gives the greatest stiffening, strengthening and handing benefits. (Of course stiffening, strengthening and handling are all related but not exactly the same thing).

My car will be set up for track use with a cage etc., but will also be a road car that will need to cover some significant distances. I sue my classic sometimes doing drive and track tours round Europe.

If I can afford to get it all fitted then I think I will try to do all 4 items above. If not then I think I will carry them out in the order listed above.
If anyone feels I have got this order definitely wrong then I would be glad to hear about it (some reasoning or justification always adds credibility!)

After over an hour of reading the attached links I'm still not quite sure how exactly to get hold of an Engman kit , who makes them?, who sells them? and how much it costs?
I someone just wants to put this simply for me rather than giving a link to other multiple page threads then that would be appreciated.(lifes too short !!)
Regards
Andrew

A roll cage probably eliminates the need for some of the chassis kit and also perhaps the engman kit.

the engman kit is listed in the resource section here.

depending upon your rules, you could design a roll cage to be sufficient and avoid the weight penalty of doing "everything"

but each person has to make that decision on their own.
I used about 4 weld in reinforcements, a cage and a number of aluminum bolt in reinforcements due to my concern about weight.

as long as your examining reinforcments in general, you might want to consider some rear suspension console bracing too:

and:

Although I had little to do with the testing phase, and certainly not the FEA modeling. The exercise that Chris performed was for us to find out what was shite and what wasn't.

I have found so many things while building my EP 914-6, "oh those won't work", or "that part is bulletproof"????, Sure buddy.

I ran a completely stock trailing arm with CFR bushings, and zero stiffening. The car was also prone to oversteer, and Chris and I discussed the possibility of the trailing arm flexing and really wondered what, where, when and how.

Chris built a fixture and started some measuring, and some additions. Jay Leutien started some FEA work, and the info was out. Nice work all. Dropping my trailing arms off in a couple weeks.

My chassis is reinforced (semi monocoque) by tubing with the raised trailing arm pick up points (by CFR) and one tube each pick up point at an angle attaching the forward engine bulkhead to the pickup point. The chassis was the best I have driven to this point, but there is room for improvement.

Erik Madsen

The boxed trailing arm kits are heavy, mostly unsprung weight. Welding them on usually warps the trailing arms so that the wheels are toed out. Stronger trailing arms are more resistant to damage and at the same time transmit damage further into the chassis.

The process I developed stiffens the trailing arm in bending and twisting and spreads the load in some high stress areas, but it doesn't add a lot of weight and it doesn't over strengthen the trailing arm. The process also allows me to alter the static camber of the trailing arms for extremely lowered cars on slicks. Now if I can just find the time to complete my fixturing...