DB 7 vs Jaguar XKR

[Boxer]

How different under the skin is the DB 7 vs the Jaguar XKR ? I have heard that the engine block and chassis are shared.

[BrentC]

Boxer,

I have been reading up on both cars lately and actually pulled out stacks of my old car mags with articles on DB7's and XK8's to compare.

If the articles are correct, both were based on the existing Jaguar XJS platform, which is hardly something to crow about. As to engines, I can't see how the blocks could have been shared or even related - the Jag had a 4.0l V8 from its introduction and the DB7 had an I6 with a supercharger. Maybe the DB7 shared engine architecture with the Jag XJ6 that was its contemporary in the early 90's.

In any case, most enthusiasts would argue that regardless of their common heritage, anything other than an Aston is just not cricket.

[Boxer]

BrentC, I stand corrected on the engine :oops: . I believe that there are a lot of shared parts under the skin between the two but clearly not the engines.

I really need to learn a lot more about the modern Astons. :roll:

Cheers

[BrentC]

Boxer,

I hope that is what this forum will provide - an opportunity for all of us to get our questions answered. I'm by no means an expert, but have recently been researching Virages and early DB7's.

I hope I can be of help in the future as well. This is a great to have a place to share info.

Brent

[Jags]

Hi,

The DB7 6 cyl (1994-1999) is build on a XJS platform, sharing front and rear suspension witch is modified.under the dasboard you see an XJS and the engine is a AJ6 3.2 from jaguar with different pistons (Cossworth, oil cooled) and a compressor on it giving it 340 Bhp instead of 202 in the Jaguar.
The DB7 V12 is still the XJS platform but with a complete new build V12 Cossworth engine with no Jaguar parts on it.
The 6 cyl makes it the most easy (???:)) AM to have at the lowest (????) cost ever.
A very good website is www.astonmartins.com

[Squid]

Then you have the GT model - DB7 GT

Revised everything, steering layout, suspension, gearing, gearbox, rear diff, engine power and torque, brakes, wheels, seats and aerodynamics + a few extra little details.

Basically the GT is what the DB7 SHOULD have been from day one and then improved upon.

I read many reviews on the DB7 and most of them are based on the older 6-cylinder model.

The GT although technically not as good as the latest XKR's can certainly give them a run for the money and depending on driver skill can often beat them.

Top speed in the JAG due to gearing etc is 175mph max.. the GT can squeeze 196mph again due to it's revised gearing, also it has a load more stability at higher speeds thanks to the 50% increase in downforce, the faster you go the more it hunkers down.

I've had my GT beyond the top speed of all previous DB7's and it's as solid as a rock with plenty of pull all the way.

[altawashm]

The DB7 GT wooooooow what a car, I loved it there was one in Dubai for sale but when I call "i send it back to US" said the owner.

[Serega91]

Yes, the engines for all versions of the DB7 that I am aware of so far were different from the engines in the XK8-XKR (X100 Jag), however the platform was the same.

The DB7 i6 came several years before the XK8, around 1994 (and I say XK8), so the early models were not very well built. I believe the DB7 itself was based on Jag concept cars, XJ 41 coupe and the XJ 42 convertible, off the top of my head.

The XJ 41 and XJ 42 were supposed to be Jag GT cars that would go in the bracket under the XJ220 supercar, and replace the aging XJS/XJS V12 while using the same steel chassis (My guess is tight budget). The XJ41-42 developed ~late 80s/early90s, used an AJ6 unit and went though several iterations before the project was abandoned. I believe the XJ41/42 were never produced/ or produced one off, however these two cars ARE the missing link between the XJS and the DB7/first generation XKs produced in the early-mid 90s.

Now the DB7 was to be slotted under the Virage V8 (which was expensive), so they used the less powerful and the existing AJ6 to power the DB7 (the engine comes out of the XJS-6), along with the upgrades mentioned above, most notably a roots supercharger... The car had performance slightly below the Virage, while it seemed like a significant advancement from the XJS (at least on the exterior).

The XK 8 came later, 1997. It was based off the same 41-42 concepts mentioned previously, and was to be slotted under the DB7... The AJ26 V8 engine used in the car was brand new, it was slightly less powerful than the unit on the DB7 (for a reason explained below), and naturally aspirated for 1-2 years (for which the DB7 i6 remained on sale).

Now I would like you to take a look at the two companies simultaneously...
The supercharged version (or the XKR ) featuring the 370 BHP did not come out until Aston prototypes using the cosworth SG V12 engine were being tested.In 1999, the year (or the year after) when the first XKR just was released, the DB7 Vantage with a significantly more powerful V12 was also released to replace the DB7i6.

Interestingly enough, the V8 of the Jag was not stroked up from 4 liters to 4.2 liters until 2003, when Aston had the DB9 well on the way to replace the DB7... So the XKR that had almost the same outputs as the DB7 Vantage (the AJ34S supercharged, 390 BHP, 400 LB-ft) came out just as the Vantage was being phased out.

So,in conclusion these cars do share a lot of the chassis and body structure (as they are coming from the same concept car)... but not the engines...

The DB7 i6 is the most related to the XJS, since it was released first...
The XK8 (original) was less potent than the DB7, but was a more practical car, in part due to an all new engine, better budget (?), and experience.

The first, 4.0 L XKR did dwarf the DB7 i6 in most aspects... however it should only be compared to the Vantage DB7, which overall was a much more potent car...

The second 4.2 L XKR still had performance a bit below that of the DB7 Vantage and GT, however the 7 was to be phased out soon. The XK8 with 4.2 liters would have no problem debuting in 2003 also (because the i6 DB7 was not in production anymore)

There is some information that is old, perhaps some that is new. Hope this helps. Dont forget to cross reference this post :)

(Edit):
I have also noticed that on several accounts, tuners such as BBR claimed to raise the output of the DB7 i6 (specifically the i6) into high 300-low 400 bhp by simply tweaking the supercharger and an ECU remap (for a price of just several thousand dollars)...
As i see it, the DB7 was detuned due to fear that it would cannibalise Virage/ Vantage sales in the 90s...
I am not exactly sure of this connection, and if I may, I would like to ask you to verify/deny this

[Squid]

Well I had it under good authority that the V12 block used in the Vantage and beyond is good for upto 750Hp.

Since the same block (with some enhancements along the way) has been used in every V12 Aston to date since the DB7 would back this up.

I can fully believe the V12's are detuned, as they used the same engines in the Vanquish which went up to 520hp with a little head re-working and hotter cams with remap.

So getting more poke from a DB7 should not be too hard if you have the right guys working on the engine.

Exhaust, Induction and Remap would return a worthwhile improvement.

It would certainly make it more lively through the gears.

The GT only had a reworking of it's Exhaust and a small remap which works very well, so you can easily go further.

[DARJAC]

The DB7 GT was the car we would have engineered, had we the time, hindsight & access to other PT engineering options within a very compressed development programme that was AM702.

I was a powertrain design / development Engineer based @ Newport Pagnell & Bloxham.
I lived & breathed ( despaired) the PT development of the Walkinshaw I6 & it's undocumented shortcomings through to Job 1 on the Duratec, Cosworth V12.
I Instrumented an I6 for testing day at Milbrook in 1997. This confirmed all we had suspected about TWR & it's lack of data.
As you know, the V12 vehicle was not perfect but we achieved much in a 3 yr period. Sounds a long time ?
The I6 was a more compromised building block than we would have liked.
We looked to share rear subframe & hypoid with X100 XKR, but that vehicle had only a crude TC & no LSD back in 1997.

The first 2 yrs of the programme saw all work shop, chassis & PT development at Newport Pagnell. Our office sat next to the final build line of the V cars & our workshop was the old V car development garage to the right & the rear of the old manufacturing site that is no longer there, I understand.

When you look at a stock V12, spare a thought for the 6 powertrain engineers based @ Newport Pagnell, covering the US, Cosworth,Dana Spicer, Magnex, Milbrook, Mira, Arizona, Nardo etc & only 2 PT & chassis vehicles
( CP1 & CP2) one of which was our sign off durability car.
The 3 chassis Engineers initially led by Wheeler, then Porritt who with limited numbers managed to support what was predominantly a powertrain programme.
With an XJ unibody that required bigger cut outs & much modification, the chassis was never stiff with consequent handling compromise.

To put some perspective to this programme's Engineering staff levels,there were more Jaguar sourced parts procurement staff based at Bloxham chasing us for parts lists than there were Engineers !

Most of us are now scattered to the 4 winds to Redbull racing etc.
From that PT programme, Only Chris M & Tom W remain @ Gaydon.
All the remaining chassis guys such as Porritt are managerial.

I now renovate, tune & rebuild //M BMW's...& the odd Aston:)

Best regards.

P.S The XKR was a refined mass production car. Better for everyday...yes.
It will never have the character & soul of a V12 DB7 known to those who lived her as AM702.

[Squid]

Nice and great info there!!

What's the score with the V12 engine output's?

Was each one run on a dyno of were they more mass produced with only a handful being selected for testing?

Also what were the actual figures as I doubt they all put out very similar power.

Do yo know if any of the GT engines made it into Vanquishes? As AM hoped to sell many GT's than they actually did, this does make you wonder how many GT engines were produced and how many actually made it into production GT's (well we know the figures there).

I saw a photo of a whole room full of engines that seemed to be the GT engines however this was where they built the Vanquishes.
The engines still had the DB7 style manifolds fitted and were all wrapped on crates.

It's a mystery and I was interested on how many engines were put with different chassis.. such as GT engines into a vanquish, Vanquish ordered engine into a GT for example.

The reason I got started on this quest for knowledge was after I had my car do about 7 Dyno runs and the output to the rear wheels was far more than should have been there.

Now either the GT has a super efficient drivetrain or the engine put's out more than the factory quoted 435hp.

FYI, the dyno runs were well scrutinised, watched, video'd and received print outs.

All the settings were spot on for air temp, humidity, barometric pressure etc.. and it was showing just over 400hp at the wheels.

Now depending on the rule of thumb you use that should put the engine anywhere between 460hp and 480hp.

I'd go for the lower of the two figures which hit's the vanquish factory figure on the nose! very intriguing indeed!

What sort of tolerances were involved with the engine specs?

5%, 10% or higher.. ?

I mean if an engine build has a tolerance of +/- 10% then a std GT engine could be anywhere between 391hp and 478hp.. probably a lower margin is more realistic say 2%?

So would the GT drivetrain only lose 43hp?


Thanks again for posting,, it's great to read something that from the proverbial horses mouth :-)

[DARJAC]

Squid
I use a rolling road as diagnostic tool primarily, but will map an engine or set up turbocharged cars etc.
One thing should be clear. Rolling roads are all different. Even same brand rolling roads. I take it that the dyno used was of the inertia type ?
If you took a stock V12 & ran it next to GT at the same time & the same day, some measure of the difference could be made assuming same tyres etc & same person strapping the vehicle down.
Drive line losses tend to work around 15%- 17% for a rear wheel driven vehicle.

But, ultimately, an engine certification dynomometer using industry accepted intake temps & parasitic loss values for the FEAD & A/C is the only true measurement.
AML & Cosworth are in the business of real repeatable power & torque numbers.
There is no doubt that some of the engines do build to a statistical top limit.
Blue print & hand selection of fit parts tighten that statistical spread...at a cost !

I can say this with a degree of confidence.
One of the CP test vehicles ( I think it was CP9) in 97- 98 had an engine that produced 440 ps.This vehicle, prior to transmission gearing changes for production touched 195.6 mph @ Nardo.
The production quoted power was 400 ps if memory serves me correctly.
Revisions to intake, compression, cylinder heads, valves & camshafts etc will ultimately raise those numbers significantly.
The engine was in a very soft state of tune in the early days.

I understand that a former poster mentioned about the I6 supercharged variant being detuned for production & a tweak being required to raise the MAP intake pressure.
I believe the quoted PS was around 360. Well, good luck finding one that actually produced that output;)
They never produced that in production & were often around 330 at best ( in stark contrast with the V12 numbers which were conservative)
The torque played havoc have with the Getrag 5 spd manual if the car was used with enthusiasm ( as intended ?)
The same transmission used in the S38B38 3.8 M5 variants also suffered from torque versus grip induced load issues, but did not suffer the same heat issues as the I6 engine & transmission which as discovered @ Milbrook were significant in the I6 vehicle.
The weight of all DB7 variants did not help either. An I6 manual Volante weighed in @ around 1800kg !
Due to the above, the move to the Tremec ( BWT) T56 was not without good reason. This transmission used in Viper & Camaro was not the most refined however, though more than capable of handling the torque & power & those sign off test required to qualify the driveline.
An improved Getrag 420 6 speed was on the wish list due to the Tremec's shift refinement & system backlash which was producing some rather unsavoury driveline back lash on torque reversals from drive to coast down.
Cost of shared development & piece cost forced the decision on the Tremec transmission ultimately.
The ratios for the AML / Ford Advanced Pre-programme powertrain team sourced Tremec 6 spd were not common with those used in Viper & Camaro.

Forced induction :It's not so difficult to increase power on any forced induction car.
However, it's measured cascade effect in terms of engine & driveline durability are not so easily percieved.

I may not have answered your questions directly or in entirety, but I hope reading this will give you some guidance.

Best regards
DARJAC

[Squid]

Thanks for that.

All great info and a source of many future conversations into the subject I'm sure.

It's good to hear about the i6 as I used to have a Jag with a similar engine and it is interesting to learn how the engine was progressed into the Aston.

As far as the V12 is concerned I am all ears as to anything regarding it's development and state of tune.

As with any vehicle they could technically go as far as they liked but most often have to settle for a comfortable middle ground in order to suit the generic end user.

I guess for someone such as yourself an unlimited budget and a free hand would be a dream come true. Especially if it were to follow through to production.

[Serega91]

Thank you very much for the information!
I had a very hard time with getting information on specifically that time period.
Very interested on the transmission aspect of it, my guess they used the T56 in the 98' Project Vantage/the V12 prototypes during the testing, fairly sure Ford Motor Company(who themselves started using the transmission just several years later) would be willing to supply them. After that it seemed rather economical to put it into production on the DB7 and the Vanquish.
I will try to get back to this discussion once I get some more time on my hands...

[solardone]

I have been on seminars for both the xjs and the xk8 with the jec(a very good ,hands on club).There are no common parts xk8 to db7 but an enormous amount xjs to db7

[Serega91]

I have been on seminars for both the xjs and the xk8 with the jec(a very good ,hands on club).There are no common parts xk8 to db7 but an enormous amount xjs to db7

Do you mean the first or the second generation of the Xk8? I really thought that the earlier XKs had the chassis only slightly different from the DB7/XJS

[DARJAC]

I concur with Solardone.
Bob Dover, our MD resident @ Bloxham was X100 Jaguar Cheif Engineer.
And a fine Engineer he was too.
You would not build a modern unibody with all the Finite element analysis tools available & copy all the significant flaws the XJ chassis then 20 plus yrs old already had.

When you look at the two unibodies (XKR & DB7) naked next to each other, the fact is, a blindman would soon see the differences.
The X100 was 30-40% stiffer than the DB7 / XJS platform.

Aprototype DB7 with X100 rear end was built.
If we had persisted with using X100 rear subframe & hypoid, the rear axle tunnel would have ended up looking like the Jaguar to fit it cleanly.

Ultimately, the requirement for an LSD ( what there was of it !) & timing / budget contraints took the X100 rear end off the table.

[solardone]

The chassis may have been only slightly different but all suspension components are different,front and back,electrics,heating and air cond.In fact i could not see any common parts even hubs although i think on the early xk8s that the stud pattern is the same so possibly some wheel swaps may be possible.This all refers to early xk8s,later ones might have parts in common with db9s?

[AMG]

DARJAC,
I read with great interest your recollections of the time you spent with Aston Martin on the development of the DB7 V12 variants, so much so it prompted me to sign up to this forum in the hope that you could so kind as to pass on a some more of your unique knowledge.

I wonder if you could expand on the problem you highlighted with the "back lash on torque reversals" from the Tremec T56, and what was the cause / remedy.

Also I would be interested in any information regarding the modifications done to the Vantage rear suspension for the GT. I.e. changes to the wishbone, dampers, springs etc.

And lastly, how was the reduction in ride height accomplished on the GT.

Sorry for so many questions but I, like others, find this type of information invaluable.

Best Regards

[MyCarQuest]

At my blog My Car Quest I have written about my visit to the DB7 factory in 2000 here:

http://mycarquest.blogspot.com/2010/12/aston-martin-db7-part-1-of-2.html

[Pudelspringer]

I have the 1996 DB7 I6 & my Dad has the 1990 5.3l V12 XJS. My observations are;

They share the aircon, ABS and chasis. The rear suspension is completely different despite what the media state.

The DB7 I6 engine is a supercharged 3.2l straight 6. The 6 cyl. XJS was 4.0l and never available supercharged. A supercharged XJR 4.0l sedan was available. The DB7 engine is a modified Jag 3.2l & outperforms the Jag 4.0l supercharged engine in power, torque & weight.

The DB7 I6 is a better drive (Sorry Dad), but the V12 XJS sounds better. I'm sure the V12 DB7's especially the GT version are substanially better again. IMHO the DB7 remains the best looking car ever built. (OK, the current DB9, DBS, Vantages look ok as well).

[Squid]

The GT is only lowered by 3mm, hardly noticeable to the naked eye but obviously results in aerodynamic improvements and handling.

They revised the bump stops to allow a lower ride as I have read.

The GT had the steering rack repositioned and all bushes were upgraded to stuffer items, generally I think they used the red polybush items and the front subframe mounts (six shooters) had an additional snubber inserted which was a large fat plastic washer to further compress the bush.

The GT was 20% stiffer than the V12 vantage.. how much stiffer the V12 vantage was over the i6 I do not know.

also the rear lip on the boot lid, under tray and wheel arch extenders help to add almost an extra 50% down force, which as you can imagine increases stability and road holding at higher speeds.

Also the brakes on the GT are phenomenal and very good by today's standards back in 2003 must have been like throwing one of Titanic's anchors out of the window.. :-)

[DARJAC]

AMG
The torque reversal / system backlash was an issue on the Man trans variant.
The stated initial gear set back lash from input shaft to output could be as much as 12 degrees.
At higher speeds in the upper gears, this was not a problem but low speed low gears, it could be unpleasant, read unrefined.
Some of this driveline lash was damped by throttle pot calibration irrc.
This lessened the tip in top out throttle movement making less aggresive or immediate.
It worked to some degree ( no pun intended)

The spring & damper rates of the GT are / were somewhat of marketing game.
The rates were actually close to those of the original ride & handling Confirmation Prototype Vantage cars that Richard Parry was test driving to sign off the car.
After driving the car over unmade roads in Bedfordshire on hie way to Milbrook test facility, the handling was revised & softened.
I think this was also to give the Traction control a helping hand which does not work so well if the unprung mass is mostly not keeping the tyre contact patch on the road.
Some wag in powertrain who will remain namless, suggested the car was a 2 metric ton go kart:)
So, in some respects the GT was more focused, but was what was always intended.

The reduced lift.
This improvement sounds alot. It's all relative to just how much there was to start with;)
I drove the cars beyond 180 miles per hr. They were a very stable high speed platform.
Reducing axle lift would help somewhere like the Nordschliefe when big sweepers such as Flugplatz, Bergwerk & Kesselchen would make high speed crest / compression & direction changes a potential clenching moment:D

Have a good day.
D.

[Boxer]

Jag made one XKR with a manual gearbox and a limited slip diff. Anyone know what happened to it?

[DARJAC]

Jag made one XKR with a manual gearbox and a limited slip diff. Anyone know what happened to it?

Development car.
If not hidden away in storage, almost certainly chopped up.
Would not have been sold on.

[Boxer]

Development car.
If not hidden away in storage, almost certainly chopped up.
Would not have been sold on.

Anyone have a contact at Jag who might know what happened to it?

[AMG]

DARJAC
Many thanks for the reply, most interesting. It’s great to have an insight into the reasons behind some of the development decisions.

I did some searching into the T56 backlash issue and even found a GM TSB on the subject, basically saying that this can be a normal characteristic with this type of box.

I am now just trying to decide if using Mobil 1 ATF Synthetic will be better than a Dexron III. There’s a lot of discussion on this subject in various forums. It all seams to boil down to what material was used in the blocking rings and year of manufacture.

Best Regards…

[DARJAC]

Good morning AMG.
Some thoughts on manual transmissions
Fill for life = Nonsense. A stupid cop out I was never happy with in 20 yrs of powertrain developmen
My views based on test & experience got me considerable static from my Chief Engineers & programme managers:rolleyes:

The advantage with synthetic oils is somewhat moot with what amounts to quite an old transmission generically.
Mostly, these synthesized lubricants are used in race or fill for life application.
Race use brings more frequent inspection & change typically.

From my early days in strip & inspect / oil analysis, I suggest that those claims for higher temp resistance to shear & better
thermal stability at higher temps are forgetting several factors, but lets stay with the Tremec in the V12& Vanquish etc.

1. It has auxilliary cooling. The pump on / off calibration was speed & temp dependent & I'm pretty confident
that I nailed this.
The I6 was a cooker on the powertrain & would easily hit 150 deg C trans bulk oil. Only in high ambients ?
No, you would be shocked at what alt & what ambient we got thoese figs..!
Vmax in Arizona in an I6 is NOT recommended on a regular basis:)


2. Whilst syn oil resists shear etc, it should never get to that condition.
The weak point with many hypoids & transmissions is often the seal material.
Many do not go beyond 150-160 Deg C before breakdown occurs over X number of heat cycles.

3. Particulate contamination. Often overlooked.
My view is that engine & trans oil in particular should be changed @ 1200 miles from new & then,
trans & hypoid should see 3yr / 24k mile changes.
An oil analyisis would show much to concern even the average owner.
Meshing gears produce heat but what else ?
Extending oil service intervals & fill for life strategy helps 2 parties.
The first owner in warranty. After this, the loser is always the subsequent enthusiast owners.
The winner is the manufacturer. Do they really want a transmission to last 200k miles ?
Thats not a spec for durability signoff so most PT parts see 100-150k miles if lucky on the this kind of hardware.
Some of the wear & major service can be prevented.

My own Getrag equipped M5 is now approaching 200k miles run on ATF Dexron 111. The box is silent & has seen hard use,
but regular oil change.
To qualify hard use, that 10 yrs of intermittant Autobahn & track use ( Nordschleife) though now retired from that kind of life,
she remains a demonstrator for the business.

Cheers.