A Jensen Healey on Track - it runs!

Ron Earp

Ron Earp

Administrator
A short update - the Jensen did run this Friday for the Roebling test day. Finally, after Jeff and I have slaved on this thing for 1.5 years (well, we did build two other cars in that time so maybe not that long). A light at the end of the tunnel, or is that firelight?

First drive out, the car caught fire on lap one, so we didn't even make one complete lap. Header wrap with a 907 engine IS NOT a good idea. And someone told me "nah, it'll just soak the wrap and stink, but it won't catch fire". Wrong. Turn 4 - funny smell. Turn 8, some smoke. Seconds later, warm floor board and blistering paint - got to head for the pit!! Fire was extinguished, driver shaken, but not that much since I've been on fire before in the 260z, so this is old hat. Why the header wrap never caught fire during break in, warming up, etc. is beyond me. I suppose a lot of RPM and lots of air flowing over the wrap changes the combustion dynamics appreciably.

Second drive out - all is fine, runs nice, good power, good enough to gain on second gen RX7s on the entrance to the straight. But, after a couple of laps water temp and oil temp got too high, oil pressure dropped so I brought it in again. Not enough cooling.

Ditto third time out. The raditor needs to be larger and we need a larger oil cooler. Lotus 907 engines are incredibly strong on the bottom end, but are well know for oiling issues and heat issues. We've addressed internal oiling issues but heat, we still haven't got.

So, net result is the JH went out and did okay. It is light, turns in very sharply, and stops well. Power is pretty good and I think once sorted it'll be somewhat of a threat in ITS. Weight, with Jeff in the car, is 2290 lbs. I'm about 20lbs lighter than Jeff and we have a couple of things we can drop off the car, so 2240lbs is no problem to get to.

All in all, I'm pleased. We essentially have a car that is as light as a Miata and turns in very well, just like, well, a Miata. Power *seems* to be pretty good, but it is hard to tell. Handling did not seem evil, but I could only drive it like 75% or so, therefore, no good data here. Gearbox SUCKS, like a stick in oatmeal and nothing I can do about that, but the ratios are beautiful with a 1:1 5th that will actually pull at 6000 RPM in 5th on the straight, with another 1500 RPM to go. I can use a stronger and much more positive 4 speed if needed.

I'm optimistic about the future for this little car. We'll have more issues to sort, but I think we can manage and get this thing out on track racing. Here are a couple of pics:

ronjensen.jpg


jensentrack.jpg
 
People just can't get enough of that nonsensical header wrap...

It's completely worthless stuff; get the header coated. I would suspect it was oil on the wrap that combusted.

You may also consider timing--too retarded, perhaps? Would cause the header to get real hot.

Unfortunately, you are probably going to need BIGGER CU$TOM RAD.

Have fun.
 
It is just the good old 907 oil leak from the cam towers that lit up. Timing is fine, motor pulls very strongly too. I think the car needs some more sorting, obviously, but might be able to run pretty decently at some tracks. I'm still worried about aero on the open top cars, and am worried about it on the TR8 too. Can't be good for straight speed and the data we are collecting seems to indicate that.

On the raditor thing, not expensive. There are a lot of off the shelf Jegs/Summit aluminum raditors that will fit. Sure, not exactly and might hang down a couple of inches, but that is just more watter capacity as far as I'm concerned. The big thing is to get the huge oil cooler on it since that is a big part of making a 907 happy.
 
Wanted to get over to your paddock and see the Jensen but it got too hectic. Car looked great! Jeff had two very good runs in the TR8--he did some good driving this weekend.
 
I'm still worried about aero on the open top cars, and am worried about it on the TR8 too. Can't be good for straight speed and the data we are collecting seems to indicate that.[/b]
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Ron,

Buddy Mathews once told me something along the lines of a hard top being worth ver a second a lap at VIR. So, while wind in your face factor is fun, roof over your head is faster.

You guys coming to VIR next month?

hoop
 
In regards to open top and closed top cars and the areo advantages. I have a hard time believing that a closed car is worth over a second. I might by it it the coupe or sedan had its' windows up. I have to believe that with both side windows down that creats a major amount of drag. I would agree that the car with a roof will have a stiffer platform, but the cage can help the stiffness of the convt. In the case of the TR8 convt and coupe, the convt weighs less. Would that offset any advantage the coupe may have. If the coupe could have the windows up, that would be another story. Having both a convt and coupe racecar, there is been no noticable difference.
 
I also think that the TR8/7 coupe is just bad aerodynamically to begin with, negating much of the advantage it might have. The rear window is nearly straight up and down -- imagine a mid 80s Mercury Cougar -- and creates a lot of problems at speed according to the Group 44 guys.
 
Spec miatas are dog slow when the top comes off. The new pro Sm will run topless...it makes for better drafting, which makes for better watching, ala NASCAR.

a sec a lap? probably at longer tracks, like Road Atlanta.
 
In regards to open top and closed top cars and the areo advantages. I have a hard time believing that a closed car is worth over a second.
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Actually, it may be more than that so your hard time believing a second might be half right! :D

SMs have tested it at VIR, 2.6s per lap, or almost 3 seconds. Done on the same car, same driver, within an hour - top on and top off. I read this over on SM last year and the info has been circulating for quite some time . A SM, I think, will approximate TR8/JH drag pretty well, in fact, I imagine it is a slightly better coefficient of drag.

And, it has long been known in automotive tests top down/up terminal speeds differ greatly. Some magazines occasionally still publish the numbers when done that way. I can remember the 5L LX Mustang from the 80s with top down/up speeds, seems I recall 131 and 142 but I bet the bigger difference not reported would be the time to 131 and 142, the 131 top end would be slow coming.

Open tops make a difference, that is for sure. I have sourced a hard top for the JH and we're considering the coupe on the TR8. It is amazing that Jeff can drive and hang with a unrestricted BMW at Roebling, and sometimes gain, but can only stay with that car, the RX7s, etc. on the first 1/4 to 1/3 of the straight, after which the car lengths get larger and larger between the 8 and the other cars, some of which we know for a fact have the same power (+/- 1 to 2) and much less torque (down 20-30 ft/lbs or more). But he still gets pulled at the end.

R
 
In those automotive test with convt and hard top, were those test done with the windows down or up. That would make a big difference. It would make a difference if there was a test with the hard top with the windows up vs with the windows down. Also can you put a hard top on the JH. I am not sure about the GCR, but I thought that it had to be approved or listed that a removeable hardtop is allowed. I thought in IT that removeable tops were not allowed, with the exception that miatas can run the hardtop ( were it is listed on the spec page.) It is not listed for the JH or the TR8/7. I am considering building a 8 coupe, but I do not think that the convert. has a major disadvantage. I would say that my 8 convt does not loose any ground to the 8 coupe at the end of long straights, and even may pull alittle. I am not saying that coupes or sedan are not better, I just think in our applications and the fact that we have to run with the windows down and that the convt weigh less there can't be much of a major differeince
 
In those automotive test with convt and hard top, were those test done with the windows down or up. That would make a big difference. It would make a difference if there was a test with the hard top with the windows up vs with the windows down. Also can you put a hard top on the JH. I am not sure about the GCR, but I thought that it had to be approved or listed that a removeable hardtop is allowed. I thought in IT that removeable tops were not allowed, with the exception that miatas can run the hardtop ( were it is listed on the spec page.) It is not listed for the JH or the TR8/7. I am considering building a 8 coupe, but I do not think that the convert. has a major disadvantage. I would say that my 8 convt does not loose any ground to the 8 coupe at the end of long straights, and even may pull alittle. I am not saying that coupes or sedan are not better, I just think in our applications and the fact that we have to run with the windows down and that the convt weigh less there can't be much of a major differeince
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Regardless of how the automotive tests were done, the Miata tests were back to back under actual SCCA running conditions on a race track we run on all the time - windows down in both cases as required. SM with hard top windows down, and same SM without hard top, windows down - cost almost 3 seconds. Difference in weight is just the weight of the top, about 60lbs and that isn't going to cost that sort of time. So there is a real aero penality with an open top car, at least THAT open top car and I don't think the TR8 and JH are exceptions.

As far as using them it'd be a matter of writing the board. Since there is a preceident for it, Miatas with hard tops that are removable, I don't think it'd be a problem for the JH or the TR8. My main concern would be re-working my cage to fit the thing as it is rather small. And fitting in the car afterwards!!
 
I think you may have hard time getting a removable top approved. Is the miata hardtop a factory item? I know the Tr8/7 only had aftermarket tops. You might have a very slight chance if the JH's top is a factory rather than a aftermarket top. I think the real reason you might have a hard time is that I thought I heard that Mazda work with the SCCA to get the top approved and the same with BMW with the Z4. I do not think we can expect the same with Triumph and JH.
 
The top already came with the SM class when SCCA adopted the regional rules. The class was created by racers not by SCCA. It is a factory top.

Regarding Cd for top up and down...I don't have hardtop figures but for NA miatas without the lip or decklid spoilers it's .38 softtop up, .44 softop down.

Using 17.7 sq. ft frontal area...loss of HP from top up to top down at different speeds:

80mph ~3.6HP
90mph ~5HP
100mph ~8HP
110mph ~10HP
120mph ~12HP (this is close to the highest speed I've seen at Texas Motor Speedway in my SM doing WOT for over a mile)
130mph ~16HP

And that's why the track makes such a huge difference because if you're not getting to the higher speeds the difference is reduced.

Some interesting stuff I found...according to some sites the R package lip and decklid spoilers reduce the Cd to .36 That is a gain of ~4HP at 120mph. That's cheap huh? :-)

Now getting back to the JH...do you think it was wind tunnel tested and you could find that info? :lol:
 
Thanks Antonio,

That was some of the data I was looking for on sm.com as well as the VIR laptimes. I saw a similar calculation on the Cds with similar results. It is significant and those that think not are losing a lot on the long tracks. Roebling Road with that straight is one, as well as VIR and Road Atlanta. 10 hp is huge is the SMs at 110mph, you can tell that real fast.

Yes on wind tunnel testing, at least as far as you can believe a 1973 magazine. The JH Cd according to this back issue of Motorcar I bought from England is 0.41, top up, no figure given for top down.

The JH did have a factory hard top, just like the Mazda, so I don't think it will be a big deal to get them into IT SCCA racing. Don't know about the TR8 though.

Ron
 
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