Ford Crossflow Upgrades In A Vixen?
Discussion
Over the next month the Vixen engine will be taken out for a full refresh ready for the start of the new season in late March.
Current engine spec is :
Stage 3 head
1760cc
Forged pistons
A2 cam
Twin 40's
Light weight steel flywheel (4.6kg)
The rest is pretty much standard (rods, crank, valve gear etc) but properly balanced. For info, the car is used both on the road and in competitive hillclimb events.
The engine has always felt really nice for both road & track but having never driven any different spec engines, I have nothing to compare with. I don't need more power (134bhp, 131ftlb) but a wider torque curve would be good. I don't want to raise the rev range above 6,500, but strong low down torque thru to 6,000 would be perfect. I also want to 'bullet proof' it, where reasonably possible.
The items I'm thinking about include:
Steel rocker posts & shaft ?
Roller rockers ?
A more modern cam profile ? Kent 234 seems a popular choice for good power & torque across the range
Steel Maxpeeding rods ? - lighter (& stronger) so should make a more free rev'ing, responsive engine
I would be interested to hear of experience/suggestions.
Moto
Current engine spec is :
Stage 3 head
1760cc
Forged pistons
A2 cam
Twin 40's
Light weight steel flywheel (4.6kg)
The rest is pretty much standard (rods, crank, valve gear etc) but properly balanced. For info, the car is used both on the road and in competitive hillclimb events.
The engine has always felt really nice for both road & track but having never driven any different spec engines, I have nothing to compare with. I don't need more power (134bhp, 131ftlb) but a wider torque curve would be good. I don't want to raise the rev range above 6,500, but strong low down torque thru to 6,000 would be perfect. I also want to 'bullet proof' it, where reasonably possible.
The items I'm thinking about include:
Steel rocker posts & shaft ?
Roller rockers ?
A more modern cam profile ? Kent 234 seems a popular choice for good power & torque across the range
Steel Maxpeeding rods ? - lighter (& stronger) so should make a more free rev'ing, responsive engine
I would be interested to hear of experience/suggestions.
Moto
Have you got a copy of this Moto
https://amzn.eu/d/aLhJDUE
It’s very detailed if probably rather out of date
Also Burton Power has a good guide
https://amzn.eu/d/aLhJDUE
It’s very detailed if probably rather out of date
Also Burton Power has a good guide
Yes thx, I got a copy 2 weeks ago and as you say it's very, very good. Written in a style and at a level that was perfect for me. Most of my current thinking is based on it's content.
What I'd now like to know is what other Vixen owners have done and their experiences. I have a mindset that what is good for a 600kg Caterham or an Escort for example may not be best for a Vixen.
Moto
What I'd now like to know is what other Vixen owners have done and their experiences. I have a mindset that what is good for a 600kg Caterham or an Escort for example may not be best for a Vixen.
Moto
Hi Moto,
If it's a Burton head, I'd contact them to find out if they have dyno charts for an engine with a "stage 3" head in which they tested the 234 and 244 profile "back to back." (Obviously with carbs being optimised in each scenario.)
I'd also talk to them about different ratio roller rockers. You can argue roller rockers either way. The Anti school of thought says that the needles can come out of the bearings and destroy the engine. I'm of the opinion ththe reduced valve stem and guide wear makes them worthwhile.
Also, consider the ignition system. "Better" means smoother, and less unwanted vibration translates to fewer problems.
To "bulletproof" an engine, I'd go with all forged internals, including H-beam rods. Just as important, make sure that the hardware is the best available in all critical areas. SPS CARR for rods, ARP for head, flywheel, main caps, . . .
Good luck!
On edit: I'd also get someone to run the final combination through PipeMax, and make an exhaust system based on what that spits out.
If it's a Burton head, I'd contact them to find out if they have dyno charts for an engine with a "stage 3" head in which they tested the 234 and 244 profile "back to back." (Obviously with carbs being optimised in each scenario.)
I'd also talk to them about different ratio roller rockers. You can argue roller rockers either way. The Anti school of thought says that the needles can come out of the bearings and destroy the engine. I'm of the opinion ththe reduced valve stem and guide wear makes them worthwhile.
Also, consider the ignition system. "Better" means smoother, and less unwanted vibration translates to fewer problems.
To "bulletproof" an engine, I'd go with all forged internals, including H-beam rods. Just as important, make sure that the hardware is the best available in all critical areas. SPS CARR for rods, ARP for head, flywheel, main caps, . . .
Good luck!
On edit: I'd also get someone to run the final combination through PipeMax, and make an exhaust system based on what that spits out.
Edited by Slow M on Sunday 4th January 20:09
If starting again, I agree AX block being the best route. However, my 711M block was taken out to 1760 (85mm) over 40 years ago and is still going strong, so suggests it's a good block with no reason to change.
SlowM - helpful response thx. I have just spoke with Burton re any stage 3 head/cam dyno data, but alas they have nothing. I also talked to Kent - very helpful with useful advice but no dyno data. It therefore was quite subjective but they recommended the 234.
Regards roller rockers, as you note it seems to be 6 good reasons for every 6 reasons why not. They do seems to have more positives with the old cam profiles such as my A2 (low lift, gentle ramps) compared to more modern profiles such as the 234 (high lift....). Low lift cam put less stress on the rollers so less likely to fail.
Ignition is definitely something I need to think about more. as you say "better" is smoother. I'm not able to go 3D so limited to points or electronic 2d modules. Currently running Lucas 43 with Accuspark which is cheap but works OK. Maybe more upmarket items such as Aldon/Ignitor. 123 or Lumenition would be "better"?
Agree on all forged internals but as only revving to 6.5k it'll be down to £'s to be worthwhile. Maxspeeding rods 40% price of top brands and all reviews suggest OK. I do quite like OE setup if I could find a set with little wear to polish/lighten/balance etc. Just not available new anymore.
ARP definite thumbs up. Exhaust already been built for car by Maniflow.
Moto
SlowM - helpful response thx. I have just spoke with Burton re any stage 3 head/cam dyno data, but alas they have nothing. I also talked to Kent - very helpful with useful advice but no dyno data. It therefore was quite subjective but they recommended the 234.
Regards roller rockers, as you note it seems to be 6 good reasons for every 6 reasons why not. They do seems to have more positives with the old cam profiles such as my A2 (low lift, gentle ramps) compared to more modern profiles such as the 234 (high lift....). Low lift cam put less stress on the rollers so less likely to fail.
Ignition is definitely something I need to think about more. as you say "better" is smoother. I'm not able to go 3D so limited to points or electronic 2d modules. Currently running Lucas 43 with Accuspark which is cheap but works OK. Maybe more upmarket items such as Aldon/Ignitor. 123 or Lumenition would be "better"?
Agree on all forged internals but as only revving to 6.5k it'll be down to £'s to be worthwhile. Maxspeeding rods 40% price of top brands and all reviews suggest OK. I do quite like OE setup if I could find a set with little wear to polish/lighten/balance etc. Just not available new anymore.
ARP definite thumbs up. Exhaust already been built for car by Maniflow.
Moto
Hi Moto,
My 1970 Vixen S2 has a rebuilt (original) engine, because I wanted to keep it. If I had wanted more power, I could have installed a later 711M crossflow, a Pinto or even a Zetec.
But it’s an early crossflow with the 2737E block and chambered combustion chambers in the cylinder head, rather than the flat head on later 711M block crossflows. These early crossflow heads don’t flow as well, but mine is a Stage 3, with larger valves and some port enlargement, which helps. It has a Kent 234 cam and valve spring kit. A 0.040” overbore gives 1640cc. The only mods to the bottom end are ARP rod bolts, a duplex timing chain and a 3.8kg steel billet flywheel. The exhaust is a JE 4-2-1 stainless system. I could have fitted twin Weber 40s, but I also wanted low down driveability, especially with the close ratio 2000E gearbox (high 1st gear) and the light flywheel. So I decided to try electronic fuel injection (EFI).
I fitted an EFI conversion kit from DanST Engineering near Bradford. The kit uses refurbished individual throttle bodies from a Suzuki GSXR motorcycle (38mm choke I.D.), custom-made manifold and Ford Zetec twin-coil pack, all controlled by a Motorsport Electronics ECU. A crank trigger and a lambda sensor in the exhaust manifold give “closed loop” feedback to the ECU. This produces similar power to twin 40s at high revs, but a much flatter torque curve. After setting up the EFI on the DanST rolling road after the engine was run in, we got the following figures. Their rolling road's “run down” measurement estimates transmission losses, so the figures below are estimated to be at the flywheel.
Peak power = 119bhp @ 5850rpm and peak torque = 116ft.lb @ 4450rpm, with the soft rev limiter set at 6300rpm. But the torque curve is really flat. At least 80% of peak torque is available from 2800rpm to 6300rpm. When the engine has loosened up a bit more these figures should improve. On the road, in top gear, the car pulls smoothly from 2000rpm all the way to 6300rpm. And yes, the induction “roar” with the throttle bodies sounds great!
I’m sure that power and torque figures using a similar setup on a 1760cc, 711M crossflow would be quite impressive. If you would like more of my Vixen’s story, please see the July 2025 issue of TVR Sprint.
My 1970 Vixen S2 has a rebuilt (original) engine, because I wanted to keep it. If I had wanted more power, I could have installed a later 711M crossflow, a Pinto or even a Zetec.
But it’s an early crossflow with the 2737E block and chambered combustion chambers in the cylinder head, rather than the flat head on later 711M block crossflows. These early crossflow heads don’t flow as well, but mine is a Stage 3, with larger valves and some port enlargement, which helps. It has a Kent 234 cam and valve spring kit. A 0.040” overbore gives 1640cc. The only mods to the bottom end are ARP rod bolts, a duplex timing chain and a 3.8kg steel billet flywheel. The exhaust is a JE 4-2-1 stainless system. I could have fitted twin Weber 40s, but I also wanted low down driveability, especially with the close ratio 2000E gearbox (high 1st gear) and the light flywheel. So I decided to try electronic fuel injection (EFI).
I fitted an EFI conversion kit from DanST Engineering near Bradford. The kit uses refurbished individual throttle bodies from a Suzuki GSXR motorcycle (38mm choke I.D.), custom-made manifold and Ford Zetec twin-coil pack, all controlled by a Motorsport Electronics ECU. A crank trigger and a lambda sensor in the exhaust manifold give “closed loop” feedback to the ECU. This produces similar power to twin 40s at high revs, but a much flatter torque curve. After setting up the EFI on the DanST rolling road after the engine was run in, we got the following figures. Their rolling road's “run down” measurement estimates transmission losses, so the figures below are estimated to be at the flywheel.
Peak power = 119bhp @ 5850rpm and peak torque = 116ft.lb @ 4450rpm, with the soft rev limiter set at 6300rpm. But the torque curve is really flat. At least 80% of peak torque is available from 2800rpm to 6300rpm. When the engine has loosened up a bit more these figures should improve. On the road, in top gear, the car pulls smoothly from 2000rpm all the way to 6300rpm. And yes, the induction “roar” with the throttle bodies sounds great!
I’m sure that power and torque figures using a similar setup on a 1760cc, 711M crossflow would be quite impressive. If you would like more of my Vixen’s story, please see the July 2025 issue of TVR Sprint.
Tony,
Welcome to the PH TVR Classics forum. Good to have another Vixen owner sharing knowledge.
Your upgrade is really interesting, firstly as it's a new option to me (hadn't seen the daNST kit before) and also because my RR guy is always telling me this is the way to go and gives much better drivability throughout the rev range. Unfortunately my competition regs don't allow EFI in my class, so I'd have to compete against newer cars with ECU technology rather than the 60's & 70's machinery that is my 'thing' really. But definitely something I'll keep in mind if I ever decide to go that route.
In fairness, my twin 40's give me 80% of peak torque from 2,800 to 6,200rpm. However 80% of peak BHP doesn't come till 4,000rpm. I am curious as to whether this could be improved using a 2D ignition system such as Amethyst or 123, where you are able to program any timing advance in for any rpm. 2D systems are allowed in my historic regs. I wonder how much of your power lower down the rev range comes from your 234 cam and how much from the EFI?
Pretty car by the way - I do like the colour. How long have you had it?
I see you're N. Yorks based. If you want to come and watch us compete at Harewood, we'll be there on 6th & 7th June in the Classic Marques championship. I should be able to get you a couple of complimentary guest passes.
Moto
Welcome to the PH TVR Classics forum. Good to have another Vixen owner sharing knowledge.
Your upgrade is really interesting, firstly as it's a new option to me (hadn't seen the daNST kit before) and also because my RR guy is always telling me this is the way to go and gives much better drivability throughout the rev range. Unfortunately my competition regs don't allow EFI in my class, so I'd have to compete against newer cars with ECU technology rather than the 60's & 70's machinery that is my 'thing' really. But definitely something I'll keep in mind if I ever decide to go that route.
In fairness, my twin 40's give me 80% of peak torque from 2,800 to 6,200rpm. However 80% of peak BHP doesn't come till 4,000rpm. I am curious as to whether this could be improved using a 2D ignition system such as Amethyst or 123, where you are able to program any timing advance in for any rpm. 2D systems are allowed in my historic regs. I wonder how much of your power lower down the rev range comes from your 234 cam and how much from the EFI?
Pretty car by the way - I do like the colour. How long have you had it?
I see you're N. Yorks based. If you want to come and watch us compete at Harewood, we'll be there on 6th & 7th June in the Classic Marques championship. I should be able to get you a couple of complimentary guest passes.
Moto
Hi Moto,
Thank you for the welcome. I've been reading PH for a while, but this is the first time I've posted. I bought my Vixen in 1975, when I was 21, so I've owned it for over 50 years now. The last 5 or 6 years were spent on the complete rebuild, which it really needed. As I said, if you'd like the whole story, please see the July 2025 issue of TVR Sprint magazine. If I can figure out how to upload photos to PH, I'll post some photos of my EFI installation.
I think you're right about the low-down torque, the Kent 234 cam is amazing in giving good torque throughout the rev range. But when I was running the engine in, it still had a very old Weber 34DCS twin choke carb. Although I'd rebuilt this carb, it still had a bit of a flat spot off-idle (I could never get the "progression" setup right) and would not idle below 1400rpm. The EFI cured all that - it now pulls well at any revs and will idle at 800rpm. Although fuel economy for this car is not a huge issue for me, it regularly achieves 35mpg, so I reckon the EFI is running the engine quite efficiently.
Also thank you for the offer of tickets for Harewood in June, I'll contact you if I'll be going there.
Cheers :-)
Thank you for the welcome. I've been reading PH for a while, but this is the first time I've posted. I bought my Vixen in 1975, when I was 21, so I've owned it for over 50 years now. The last 5 or 6 years were spent on the complete rebuild, which it really needed. As I said, if you'd like the whole story, please see the July 2025 issue of TVR Sprint magazine. If I can figure out how to upload photos to PH, I'll post some photos of my EFI installation.
I think you're right about the low-down torque, the Kent 234 cam is amazing in giving good torque throughout the rev range. But when I was running the engine in, it still had a very old Weber 34DCS twin choke carb. Although I'd rebuilt this carb, it still had a bit of a flat spot off-idle (I could never get the "progression" setup right) and would not idle below 1400rpm. The EFI cured all that - it now pulls well at any revs and will idle at 800rpm. Although fuel economy for this car is not a huge issue for me, it regularly achieves 35mpg, so I reckon the EFI is running the engine quite efficiently.
Also thank you for the offer of tickets for Harewood in June, I'll contact you if I'll be going there.
Cheers :-)
TB-L said:
I think you're right about the low-down torque, the Kent 234 cam is amazing in giving good torque throughout the rev range.
I have a 244 on twin 40's, when I bought the car it had supposedly been 'set up by a RR engineer' but was flat over about 3000rpm and it was struggling to achieve 100hp. On investigating I found the cam timing was over 5 degrees out (amongst other things) and setting it up all correctly liberated about 25 additional HP but its still a bit of a dog below 2500rpm which is just the cam profile - so I was thinking about the 234.I haven't heard anyone say the 234 is poor at high revs before, or that they needed to improve it by changing to EFI. Do you think this was because of your head/pistons or the early block?
I'm quite happy with 119bhp at 5850rpm (maybe 120 once it's loosened up a bit). The soft rev limiter is starting to operate about then, with the hard limiter coming in at 6300rpm and I don't really want to rev it any more than that. I've been told that my early Crossflow chambered head doesn't flow as well as the later flat head ones because of the port design and that the valves are more shrouded. The top end power is about what I'd expect if I had used twin 40s, but my experience with them is difficulty in setting up, staying in tune and reduced low down torque. So the EFI seems to give me the top end power that I wanted, with greatly increased low down torque. If need be, the car pulls strongly from 2000rpm in top gear.
The Vixen only weighs about 720kg, so almost 120bhp equates to about 170bhp/ton. That's good enough for me :-)
The Vixen only weighs about 720kg, so almost 120bhp equates to about 170bhp/ton. That's good enough for me :-)
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