Accufab exhaust, tune, & pully warped my vents.


ChipBeck

GT Owner
Staff member
Mark IV Lifetime
Le Mans 2010 Supporter
Feb 13, 2006
5,770
Scottsdale, Arizona
Gentlemen,

Having attended both rallies as well as the Indianapolis GT gathering, I've had a chance to examine several hundred GT's. I noticed both top and side vents were warped on the engine covers of a lot of GT's. Yet my stock yellow GT, with 3000 miles on it that has been regularly driven in our 120° heat here in Arizona was fine. My friend Larry (AZGT) had 4000 miles on his stock Arizona driven GT and his vents were fine as well. The weekend before the California Rally we had the GT guys come out and set up shop in Larry's garage. Larry and I both had the Accufab exhaust installed as well as a 91 octane Heffner tune and pulley. Within 500 miles both of our cars had warped both the top and side clamshell vents. The dynamics of this cause and effect came into clear focus when I was flying my Cirrus SR-22G2 home from Corona California yesterday. The Cirrus has a very sophisticated engine monitoring system that displays, among other things, both the cylinder head temperature and exhaust gas temperature of each individual cylinder. At altitude, with the push of a button, the system will help you find the optimum fuel air mixture for either best power or best economy. Takeoffs are generally made with the mixture control at full rich. Even at sea level this setting is much too rich to produce maximum power, but this setting keeps exhaust gas temperatures almost 300° cooler than they would be with an optimum fuel air mixture. Lower EGT's keep cylinder head and oil temperatures correspondingly lower as well. As the aircraft climbs and the atmosphere thins the mixture gets progressively richer and must be manually leaned. During this process fuel flow is cut with airflow remaining constant until exhaust gas temperatures peak and start to decline again. As I pulled the mixture back gradually and watched my exhaust gas temperatures climb nearly 300° during the process with a corresponding increase in engine power, those warped clamshell vents directly on top of my Accufab exhaust popped into my head. Unless one is flying above 15,000 feet or thereabouts a piston powered aircraft engine is never operated at peak EGT because this would put cylinder head temperatures above safe operating levels and would shorten engine life. So the best power setting for Continental Aircraft engines is 65° rich of peak EGT.

As soon as I got home from this flight I went straight to my garage and sure enough, the section of my vents that were warped most severely were directly above the top curve of my new Accufab exhaust. That portion of the vents closest to the rear windshield directly above the engine but away from the top curve of my exhaust was fine. Three components are coming into play here. 1. The smaller pulley forces a denser fuel air mixture into the cylinders producing more power and more heat. 2. The Heffner tune moves the fuel air mixture away from the very rich (low exhaust gas temperature) stock settings to a more optimum (leaner) mixture that produces more horsepower. This leaner mixture, just as it does in an aircraft engine, will raise exhaust gas temperatures by 200+ degrees. 3. Last, we have the Accufab exhaust itself. The stock muffler, at least with the stock tune, defuses the relatively low exhaust gas temperatures feeding into it over a large space with a lot of surface area. Evidently, the peak temperature radiating up from the stock muffler when a GT is either stopped while idling or shortly after it has been shut off, is not high enough to warp the vents. At least not in my case nor in Larry's case. The Accufab exhaust, when it is being fed by a pulley and tune equipped GT, has much higher exhaust gas temperatures feeding into it and a very small area that all that heat is radiating from. At speed there is no question that the Accufab exhaust will allow far more airflow past it and out the rear vents than the stock muffler. It is at idle and at rest after shutdown and there is no airflow through the engine compartment that this comes into play. Now this much hotter exhaust system radiates its heat from a much smaller concentrated area straight up into those vents. And the plastic doesn't like it.

I am not an automotive expert but I have worked as a test pilot evaluating many different systems on aircraft. And although I'm not in possession of the equipment I would need to prove what I've just laid out here, I'd bet the farm on it. I have noted in a few other posts forum members who mentioned that they had replaced their stock exhaust with either the Ida or Accufab units to reduce under clamshell temperatures "and their vents still warped". I believe their vents warped BECAUSE they changed exhaust systems.

Please note that I enjoy my Accufab exhaust, the additional 100 hp provided by my Heffner pulley and tune, and I have no intention of removing them. I am making an assumption that the experts at Heffner, when they developed this tune, did measure exhaust gas temperatures and that they are in a safe range for long engine life. I do wonder what the effect of this high peak temperature will be over the long term on the composite clamshell itself. :ack At the minimum, I must have both the top and side vents made up of a different material as replacing these with the stock plastic units is whistling in the wind. Cost be damned, I would like machined aluminum or stainless steel powder coated black. Cheers. :cheers

Chip
 

BlackICE

GT Owner
Nov 2, 2005
1,416
SF Bay Area in California
Chip thanks for the post. It seem like a very reasonably conculsion. I will keep an eye out on my car too. I have a Heffner exhaust, and Whipple with HP tune ready to install soon.
 

nota4re

GT Owner
Mark IV Lifetime
Le Mans 2010 Supporter
Feb 15, 2006
4,177
Chip,

Some very interesting observations. I believe that the primary factory at play here is the physical location of the exhaust and tube bends (heat concentration points) of the Accufab. I believe that this is much more a factor than the pulley/tune. Unless you are driving aggressively, the car will operate at 14.7:1 a/f ratio - regardless of tune or OEM set-up. The Heffner (like most tunes) will run leaner and higher HP in open-loop (aggresive driving) mode but will quickly settle down to closed-loop 14.7:1 as soon as you are "off of it". Your around town, stop and go city driving will closed loop and 14.7:1 (unchanged from OEM set-up). I guess what I'm saying is that the Heffner tune/pulley will in fact produce higher temps and more HP but this is typically and higher road speeds with more airflow in and around the exhaust. I think that your highest under hood air temps occur in "normal" driving - especially in stop & go with high ambient temperatures. As such, you pulley/tune are not in play - but the physical properties of your exhaust is still a contributing factor.
 

TEXAS GT

2006 Twin Turbo
Mark IV Lifetime
Le Mans 2010 Supporter
I sounds logical, but I've had a Whipple, Heffner tune and Accufab on my car for 6 months and about 1500 miles with no problems. I don't go to the trouble of opening my hatch after every run either. Maybe the Whipple tune is different but I would think it would run hotter if anything.

The longest non stop run (except for gas) was 400 miles. I then did 4 one mile runs at top speed and drove it another 400 miles back home. If it were going to cook the vents I would think that would have done it.
 

dbk

The Favor Factory™
Staff member
Le Mans 2010 Supporter
Jul 30, 2005
15,187
Metro Detroit
I've had the Heffner Pulley and Tune for 7000 miles, and the exhaust for probably 2500, and no vent warping. That includes some serious high heat desert driving as well as enormous heat and humidity up here. What can I tell you?
 

dbk

The Favor Factory™
Staff member
Le Mans 2010 Supporter
Jul 30, 2005
15,187
Metro Detroit
Some very interesting observations. I believe that the primary factory at play here is the physical location of the exhaust and tube bends (heat concentration points) of the Accufab. I believe that this is much more a factor than the pulley/tune.

P.S, this man is dead on, as usual. I remember long back when the first of these style Ford GT exhausts came out, and they were billing that it would drastically reduce the temps to prevent the vent warping stock cars get, one of our favorite FGT team people told me specifically that it would not only make no difference, but possibly exacerbate it.

Mine hasn't warped though, so who knows...
 

427Aggie

GT Owner
Mark IV Lifetime
Aug 18, 2005
885
Frisco, Tx
Mine were warped with the stock exhaust and replaced under warranty last year at the rally by Salleen.

I changed over to the accufab and did both the pulley and then went to the whipple..no warping with over 5000 miles on the accufab exhaust now.

Davids is stock except for his exhaust and I believe his are still fine now with over 2000 miles on his.

Matt
 

Spirit

Heritage GT Owner
Mark IV Lifetime
Le Mans 2010 Supporter
Have had the Heffner Pulley, Heffner Tune [run both their 93 & 91 octane tunes – 93 in Texas & 91 in other states], along with the Accufab Exhaust for a little over 10 months.

Driven more than 10,000 miles with this set up. Miles include all types of weather, temperatures, altitudes, and terrain; not to mention the Texas summer heat. Outside temps going through NV, AZ, NM, & West TX were 100f+ at speeds of 100mph+ much of the way back from Rally II.

No warping of either type of the vents to date [by the way, I DO NOT open the Clam Shell at shut downs].

Another GT in the area [Silverbullitt] had vent warping issues with stock muffler, he put on the Accufab [No Pulley or Tune] and no warping to date.

I have no explanation.

Seems to be an individual case by case situation.

Possibly the type driving and driver technique is a factor, my technique is to run it long and hard [not much city stop & go driving].

For what it’s worth.

Fred
 

ChipBeck

GT Owner
Staff member
Mark IV Lifetime
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Feb 13, 2006
5,770
Scottsdale, Arizona
No airflow= radiated heat.

It appears that the one part of my post most respondents seem to have missed is.....

It is at idle and at rest after shutdown and there is no airflow through the engine compartment that this comes into play. Now this much hotter exhaust system radiates its heat from a much smaller concentrated area straight up into those vents. Chip

High-speed driving, even in the hottest or most humid conditions, would keep a large volume of air flowing through the engine compartment and preclude any damage from radiated heat. Thus, top speed runs or 400 mile drives are not the type of conditions that would allow radiated heat damage. For example, turn your kitchen stove on high and hold your hand 12 inches above the burner. You can only keep your hand there for a few seconds. Now place a fan next to the stove and have it blow air between the burner and your hand. You might just be able to keep your hand there indefinitely as even this relatively low-speed air will carry a tremendous amount of heat away. The heat warping of my vents was almost certainly done while my GT was sitting still idling for about 10 minutes while in line between runs at El Toro. During those runs my car was run flat out for about 31 seconds, a good part of the time at full throttle where the leaner air fuel mixture and correspondingly hotter exhaust gas temperatures would come into play. Then, with my sweet sounding Accufab exhaust glowing red hot, I panic breaked to a complete stop (in one case taking out half a dozen cones at course end), and then sat there completely stopped for 10 minutes waiting in line for my next run. Here, I believe I unknowingly created the perfect storm for maximum heat generation directly underneath those plastic vents. Aggressive driving triggers the Heffner tunes leaner fuel air mixture and hotter EGT's, bringing the Accufab to a much higher temp which will only have an effect if you then stop completely so there is no airflow to carry radiated heat away. The top bend of the Accufab, like the stove in my example without the fan, radiates the heat straight up. Were I to do that event again, I would've kept driving up and down the access road after each run for a few minutes to let things cool down before I got back in line. With my stock exhaust I have made similar runs, stopping my GT without opening the clamshell, and without warping my vents. I am certainly not an end-all authority on the GT, I am simply posting my observations. Many of them are theory and open to debate. A few of them however are absolute.

1. Under wide-open throttle the leaner mixture of the Heffner tune will produce higher EGT's than will the stock tune.
2. Radiated heat damage will be most pronounced when there is no airflow, with a stopped car at idle or parked after shutdown.
3. Peak surface temperature of an Accufab type exhaust system for any given EGT will be higher than the peak surface temperature of a muffler that has 30 times the surface area and over four times the weight of the Accufab.

Obviously, based on feedback here, those vents can and have warped with the stock exhaust system. Perhaps I would have warped mine at El Toro even with the stock exhaust system, though I hadn't in the past in similar circumstances. So here's what I'm going to do.

1. After running my car hard, I'll drive it mildly for a few minutes to let it cool down before I let it idle with the clamshell closed. If I can't do that I'll stop and open the clamshell.

2. I still want my vents made out of machined aluminum or stainless steel and powder coated black to match my stripes perfectly. Who can make them for me? :cheers

Chip
 

dbk

The Favor Factory™
Staff member
Le Mans 2010 Supporter
Jul 30, 2005
15,187
Metro Detroit
2. I still want my vents made out of machined aluminum or stainless steel and powder coated black to match my stripes perfectly. Who can make them for me? :cheers

Chip

Consider it done. I'll have a friend of mine who can look right into my garage from his patio that owns a Heritage GT see what it takes. He owns a great big machine shop that does tons of auto aftermarket stuff.

Anybody else?
 

TEXAS GT

2006 Twin Turbo
Mark IV Lifetime
Le Mans 2010 Supporter
Consider it done. I'll have a friend of mine who can look right into my garage from his patio that owns a Heritage GT see what it takes. He owns a great big machine shop that does tons of auto aftermarket stuff.

Anybody else?

Hell yes, count me in for two. I don't have a problem yet but I'll save them for future use if needed. Plastic can't last forever.
 

Chris A.

GT #32
Mark II Lifetime
Feb 6, 2007
1,233
Ortega Mountain, CA
Consider it done. I'll have a friend of mine who can look right into my garage from his patio that owns a Heritage GT see what it takes. He owns a great big machine shop that does tons of auto aftermarket stuff.

Anybody else?

I was going to order a spare set from Ford but I'd rather have those..I'm in
 

Kingman

GT Owner
Mark II Lifetime
Aug 11, 2006
4,072
Surf City, USA
Please put me down for a set. Thank you.

Consider it done. I'll have a friend of mine who can look right into my garage from his patio that owns a Heritage GT see what it takes. He owns a great big machine shop that does tons of auto aftermarket stuff.

Anybody else?
 

richardhead

GT Owner
Sep 19, 2006
169
It appears that the one part of my post most respondents seem to have missed is.....

............

2. I still want my vents made out of machined aluminum or stainless steel and powder coated black to match my stripes perfectly. Who can make them for me? :cheers

Chip

Ceramic "thermal barrier" coat ("Jet Hot", "High Performance Coatings", or comparable) your Accufab , except for the outlet tips (for appearance sake, if you so desire...), and you will see a marked drop in temps of the exhaust pipes.
 

OCPETE

GT Owner
Nov 20, 2006
490
Killer Dana, CA
I'm in for metal vs plastic...maybe even carbon fiber?
Surprised no one hasn't capitalized on this yet :cheers
 

Edson

GT Owner
Mark II Lifetime
Mar 28, 2007
103
Santa Monica
I would definitely purchase a set.
 

S592R

GT Owner
Mark IV Lifetime
Dec 3, 2006
2,800
put 4000 miles on the car with the accufab on the 65 car. No warping ... but that was all high speed driving and I open the clam for a few minutes after I stop.

I have a roll of exhaust wrap and am thinking about wrapping mine ... more to lower the under clam temp than anything else.

Regarding the vents .... if DBK's guy doesn't work out ... I'll call a AC fabricator that I know and see what we can do for us.

Thanks for the post Chip .... it got me to look at mine .... I noticed that I needed to re torque a few things back there.

S
 

B O N Y

MODERATOR & FGT OWNER
Mark IV Lifetime
Sep 5, 2005
12,110
Fresno, Ca.
no warp issues on #1153
but I am in for a set of CF vents... helloooooo Kip!
 

dbk

The Favor Factory™
Staff member
Le Mans 2010 Supporter
Jul 30, 2005
15,187
Metro Detroit
The guy that I'm going to have make them has a 280,000 sq ft facility that does stuff for OEM's, architectural firms, etc. They built and did all the tooling for Chip Foose's custom chopper, supply all the metallic components for American Expedition Vehicles custom Jeeps, do alot of SEMA stuff...this is right up their alley and I know he's been itching to do some GT stuff. If you watch Rides on Discovery HD he's been on it making stuff for Chip more than once.
 

PL510*Jeff

Well-known member
Mark IV Lifetime
Le Mans 2010 Supporter
Nov 3, 2005
4,876
Renton, Washington
Warpage

Hello All-

Thank you Chipster. Nice thought process.
Sometimes I feel that I'm flying my GT @15,000'.

DBK - put me down on yea list.

Richardhead - ceramic coatings do reduce temps. Even more if you the interior of the pipes are coated rather than just the outside.

I noticed this last Friday that my right vent was very slightly warped. As my GT has higher mileage than most, 42K and counting, I found it interesting that it took so long to warp, and then only the right one. And I almost never open the clam shell, except to show it off at the gas station for the interested bystanders.

I figured it started to warp just after the Mountain Run at Rally II, when we got off the 210 and crawled the 52 blocks to the Peterson Museum. Hour plus on Friday evening. Temp stayed a bit north of 200 with a/c on for the whole way.

There is not much of a correlation seen so far in these recent posts. Stock, upgraded, driving styles etc. Seems as though the vents just warp. Heat soak I would guess. What about installing a pair of small button fans that could be turned on and programed to run for 10-20-30 minutes and then shut off? Or have them thermostatically shut down when a pre-determined underhood temp. is reached? As Chip said earlier - air flow will reduce surface temperature drastically.

Has anyone had a conversation with the GT development Team about this? The question I would ask of them - if you guys had more development time what direction had you planned to go? What about removing the "under" tray? Is there a down side to that other than when washing the car. (But that's why we have towels handy.)

I watched the Saleen Girls change out a few at Rally I on their lunch break. And those were low mileage cars. Most still are.

I stopped off at Gennadi a while back. I saw some prototype GTX1 vent "grills" that used a pretty cool looking black wire mesh. But were not intended to be installed where the stock vents go.

Just some random thoughts on a Sunday evening.