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Member postings for Peter Seymour-Howell

Here is a list of all the postings Peter Seymour-Howell has made in our forums. Click on a thread name to jump to the thread.

Thread: Porsche 951
11/05/2021 18:34:30

A few pictures of the engine under construction, here's the ladder cradle that holds the crank, the pressed steel plate along one side is the crank scraper, this alone has a significant impact on throttle response by ditching all of the oil that sticks to the crank while running. It also solves the one flaw in this engine when racing, that being during hard cornering the oil gets aerated around number 2 rod, the scraper removes that issue.

One of the secret weapons on this engine, the two balance shafts that give this big 4 pot the same smooth running as a straight 6.

The head and cam tower now fitted, there are a number of mods done to this engine that are not visible. The pistons I have already mentioned, as stated they are full race, the rings are tiny to reduce friction and improve response.. There is also an extra groove below the compression ring to allow the piston to hold much more boost before any blow-by occurs.

The studs and bolts are aero-spec and can hold much more pressure than the Porsche originals, the steel HG ensures nothing lets go.

The cradle has an extra pin added to help in getting the crank spot on in alignment and keep it there under full load.

And the bigger turbo, this is the super 61 which is capable of developing 620 bhp at 1 Bar, not on my engine though, would need more capacity to hit those figures at only 1 bar.

The turbo is both water and oil-cooled and includes a 30-sec cooling time to negate carbon build-up after switching the engine off, which is standard on these cars.

The engine is currently running at a max of 1.5 BAR, (set via ECU overboost ), the red line is 7200 and the ECB has been set with a high duty cycle to remove most of the lag. Other safety factors have been added to tackle the resulting boost spikes from the high duty cycle. Top speed? who knows... She will red line in 5th and hold the boost all the way up there, in theory, that gives a 200 mph+ top end but of course, wind resistance has a say in such things but she does have a low drag coefficient of 0.33 and only weighs 1280KG. Cossie's have been recorded at plus 200 and they are shaped like a brick..

Hopefully, this may help answer some questions..


11/05/2021 17:50:08
Posted by Tim Stevens on 11/05/2021 17:31:50:

Head gasket thickness has no effect on the swept volume (or capacity if you like). What it does affect is the compression ratio.

And if the combustion space is decreased, the compression ratio goes up.

Cheers, Tim

Hi Tim

Hmm, I'm not sure that is correct, I mean to take things to the extreme if you had a 5 mm thick HG, that is going to increase your overall volume if everything else remains the same. We are not talking normal HG's here, I have a multi-layer steel gasket to hold the increased boost which is more than double the original, it doesn't squash when torqued down..

The figures given in my previous post stated an HG thickness of 0.7mm, this was a 3 layer steel gasket. The final HG used was a 5 layer 1.52 mm thick gasket due to the machining of the head, this is actually a little larger than required but the closest available off the shelf, well it was a special from the US but one that they could easily accommodate. The IASA full-spec race pistons have a different sized dish to the Porsche pistons which also has an effect on the cc/CR.. It's 6 years since the rebuild so my mind may be a little fuzzy but I think that covers it?



Regarding the CR, yes, if space decreases the CR increases

11/05/2021 16:57:23

Ah.. yes my son has had a few Saph cossie's too, one of which was featured in Fast Ford, I think, it was on the front cover, must be a good few years ago now.. IIRC he didn't own it at the time, bought it shortly after.. think it had 500 in the reg somewhere?

I'll keep an eye open for your other cars...


11/05/2021 15:22:35
Posted by old mart on 11/05/2021 14:54:24:

Capacity is bore and stroke multiplied by the number of cylinders, no other factors apply.

well yes but HG thickness also plays a part as well as how many times the head and block have been skimmed down... I've dug out the figures worked on at the time... the gasket was changed for thicker again later once the head had been skimmed and thus increased the cc a little further.

This has been copied from my build page on the official Porsche forum


Displacement = 101 x 78.90 (10,1 x 10,1 x 3,1412 / 4 * 7,89) = 632.05cc ( considering deck as 0) per cylinder with a total displacement of 2,528.2cc... nice..
Head = 55cc (standard approx)
Piston volume dish= 26.0cc

101x0.70mm gasket = 5.6cc (aprox)
CChamber = 55 + 5.6 +26(piston dish) = 86.6cc

Therefore: 632.05 +86.6 ) / 86.6 = CR 8.26:1(using a 0.70mm gasket)

End Quote>

Note, in this calculation, I used measurements from a standard head, the stage 2 head chambers were measured later once it had been stripped down and rebuilt.

Also as I recalled, the CR is slightly higher than the 8:1 on a standard car., or should I say 'lower'



11/05/2021 10:36:05

here you go steve, my son's 'Cossie'



11/05/2021 09:20:12

Lovely cars Steve, I thought that I had it bad but you have clearly been bitten by the modified bug far worse than I....🙂

The Beetle/911 is very convincing...very impressive sir..

My son's are worse than me, I have no idea where they get it from..son No.2 is the worse, he's had a number of Fast Fords over the years, he's just bought himself an RS Focus with 350bhp, he was going to leave it alone but evidently a 911 showed him it's heels last week so he's now going to boost it a little. He's always telling me that his cars will beat mine but after being beaten by this 911 he knows the Focus isn't as he's seen mine leave 911's, including turbo's and recently a new GT3 for dust.

I used to be an avid follower of the 951 on the race track admiring just how quick it was in the Porsche Cup series. Alas after watching some great racing in the late 90's early 2000's Porsche banned the older cars from the series as they kept beating their brand new models. After trying many things with handicapping Porsche then entered the fray with the then brand new 996 GT3. In the last season the field included 13 GT3's with not many 951's or older 911's still in the series. The final straw came when the championship was one by an old RS 911. Interrestingly the car with the most wins was Chris Heeley's 951, it also had a lot of DNF due to mechanical failures so only got 3rd overall. At this point Porsche had had enough of 25 year old cars beating their brand new models and made the series GT3's only.

The most impressive thing about this is the engines had to remain standard, just goes to show how good the 951 is and why Porsche themselves when a current model rated it as the fastest car in the fleet, at that time this included the 928 GT and 911 turbo

Going back to my son, he may have been outdone by this fat 911 but if he had been in his other car it would have been a different story altogether. His real pride and joy is his Ford Escort Cosworth which has a lot more power then my 951, IIRC around 600bhp and it is in mint condition having been fully restored and painted by my eldest son's business partner who is superb, hopefully, the same chap who's painting my car this year.

I'll try to post a picture of the cossie later..



10/05/2021 18:20:11
Posted by old mart on 10/05/2021 18:12:21:

No mention of the actual engine size?

ah, sorry about that...

originally 2,479, now IIRC 2,532 ( i would have to dig out my calculations). This is due to the larger bore, deeper dished pistons, and thicker multi-layered steel head gasket. Again, IIRC, this keeps the compression ratio close to its original of 8:1, perhaps slightly higher?

10/05/2021 18:04:34
Posted by Ady1 on 10/05/2021 17:44:03:

Nice to seeing you using her as intended, great engineering is made to be used and enjoyed

A neighbour of mine worth millions has an e-type stashed in a garage somewhere doing nothing, going nowhere, wasting away its existence as an investment I presume

thank you, IMHO a garage queen is only good for one thing, sitting in a garage. Start driving it and it will soon break down. I love the E-type, perhaps the most beautiful car in the world, I put the 951 right behind it in looks. A good friend/old work colleague of mine has an E type which he fully restored, it was he who got me into Porsche when he persuaded me to drive his own 951. Up until then, I had been a fast Ford man. Today he builds Bugatti's, not replica's per se but real cars built to the original drawings, the coachwork has been a challenge as no drawings exist. Last time I visited he was building a Bugatti Royale, an enormous car which IIRC has a locomotive type Bugatti engine in it? I recall seeing the engine castings sitting on a pallet ready to be shipped to holland for machining... no cylinder head, all built-in one with the block.

10/05/2021 16:39:53

Thanks, Dave

I know what you mean about getting in and out, I also find it difficult these days. No problem with the cockpit being tight though, lots of room in these cars with their fairly modern design. The earlier 944 was more difficult as its steering wheel sat much lower making it difficult for taller gents. This was corrected for the 86 model year when what's known as the 'oval dash' model first appeared.

I used to also believe that the 944 engine was basically half of a 928, recent reading has changed that view a little but the jury is still out.. There are a lot of similar parts though, IIRC they have the same stroke too. I've had 5 adults in my car, the result of giving 3 girls a lift home from a night club late one night, with my mate sitting on the tunnel in the rear with his head through the roof... he didn't complain, he had two beautiful girls to sit between.

Having been in the back of a 944 I would say it's only for very short people, I say that as someone who's under 5' 8"... This was while at Le Mans when a group of us decided to go to the pub in one car, never again....


10/05/2021 16:03:52
Posted by roy entwistle on 10/05/2021 15:55:36:

Apologies, I hadn't realised that there was a Vehicle Restoration Page. Sorry

Roy blush

No apology needed Roy, I didn't realise that this thread existed until recently either..


10/05/2021 15:49:21
Posted by Michael Gilligan on 10/05/2021 15:10:00:
Posted by Peter Seymour-Howell on 10/05/2021 13:31:27:
Posted by roy entwistle on 10/05/2021 13:21:11:

Model engineering ?

Is ithis not the 'vehicle restoration page?


Very well said, Peter ... and congratulations on the beautiful work.


Thank you, Michael, I hope that I didn't come over as rude as that was not my intention.


10/05/2021 15:47:51
Posted by KWIL on 10/05/2021 15:36:29:

A very nice model 951. Certainly a labour of love.

thank you,


10/05/2021 15:47:12

Ok, so that's the 368bhp covered, now onto the beast.

Block: bored/skimmed out to 101mm *
Con-rods to remain unchanged although will be checked for balance, whilst researching the options the general consensus is that you can't beat the original Porsche forged items as used for the Turbo cup cars.
Pistons: IASA 101mm full race spec forged pistons with extra machined grove below the first ring, this allows a far higher boost without risk of blow by past the rings.*
IASA gudgeon pins*
Crankshaft machined undersize 0.25mm , both main and rod journals*
Raceware Head stud kit*
Raceware Main stud kit*
Raceware rod stud kit*
Genuine Porsche 0.25mm oversize Main/rod bearings*
Crankshaft scraper*
replaced water pump/belts/tensioners/pulley's
Lindsey Turbo super 61 rebuilt
Vitesse + V-flex MAF for ignition timing
3" custom made Magnaflow free-flow exhaust including the all-important turbo downpipe*

Of course, a lot of what was already on the car was reused after a good clean or rebuild where needed.

Recently I have also added...

80lb injectors

race-spec high temp fuel lines

map adjusted and the Vitesse chipboard now switched to a more aggressive ignition profile, I still have one more setting for what the creator describes as an extreme setting... Basically, the chipboard has 8 jumper switches, some are written to run the smaller 55lb injectors which I used when running in the freshly rebuilt engine. The other setting gives a more aggressive ignition of for when running on race fuel. Everything is controlled through the piggyback via laptop.

The air filter has now been moved to just behind the lower front apron, it's the biggest filter that K'N produces. The last 6" cone which had been fitted higher up inside the wing was sucked too hard and collapsed a number of times so clearly couldn't handle the amount of intake force being produced. Not the first time as the earlier Piper ram air intake had it's bonded foam filet within sucked out and damaged the turbo and destroyed the intercooler. Porsche originally designed the intake to run via a snorkel which takes cold air from the passenger wing, this hole is 3-inch dia and so I have now run 3-inch reinforced ducting throughout the intake system. down to the air filter. produces a lovely roar which when added to the burble from the exhaust on overrun and the whoosh when changing gear from the dump valve makes it a real head-turner long before they actually see the car.

Well, I think that covers most of the details, there is bound to be something that I have forgotten, will it now stay at this level? now there's a question, I'm over 60 now and too old for boy racer antics, even my wife says that I drive like an old man these days. This is a very fast car, not much out there to bother it, it will fly past 180 mph with ease and who knows where it stops when finally restricted by the wind. In the USA with similar power levels, they have seen 200+mph. The fastest that I have driven her is a recorded 174mph on one of my trips to Le Mans, back then she only had 282 bhp...recorded by sat nav, not my speedo which at the time was bouncing off its 170 mph pin and still accelerating hard until the column of cars backed off a little...

She is a beast, I would guess the 0-60 time is safely under 4 secs, in standard form auto road tests of the day cars managed 5.9 secs, and according to one auto mag the fastest speed at that time of any car roadtested on the autobahn in 1986 at 159 mph. The best thing about these cars, is they are just as planted on the road at 140mph as they are at 40mph, I can attest to this having driven much faster and never feeling light at the wheel.

Ok, I think that covers it, you can perhaps see now why I still have this car after so many years of ownership, it would be a very hard act to follow and it's 35 years old?...


10/05/2021 15:46:52

Some details on the engine, luckily most of this was already written on the PCGB forum so I could copy/paste most of this. Part 1 as the forum won't let me post in one go.

First mod (1999) was a Lindsey boost Enhancer, not a real power gain but it felt quicker

Next (2000) was a Lindsey dual port wastegate with a manual boost controller, this was then mapped on a dyno by Wayne Scofield, resulting in power 282bhp/282torque.

Followed by (2007) 368bhp/382torque

So what do you need to make a reliable 368 bhp from a 220bhp engine?

Block remained standard, it's an 86 car which means forged internals and originally designed for over 500bhp, ( under the 924 GTP guise an engine based on this raced at Le Mans coming in at 7th overall and having spent less time in the pits than any other car in the field, IIRC this engine was detuned down to 420bhp for longevity in the race. later cars used the same crank but not forged components.
Lindsey Stage 2 Head with ceramic exhaust coating and machined valves for greater flow, all ports polished and map flowed.
Cometic head gasket
Lindsey Super 61 Turbo
Siemens 55lb injectors
Lindsey Dual Port wastegate
New standard Hydraulic Tappets
Manual boost controller
NGK Iridium Plugs
Magnecor 8.5mm Red Leads
150mm K&N cone filter
Vitesse MAF with piggyback system
Intercooler: standard
Bailey Motorsport DV30 re-circulating valve
Exhaust: standard
silicone vac lines
Innovate Air Fuel Ratio meter/gauge
Adjustable fuel regulator
8 Hours mapping on a dyno at Chip Wizards Rochdale by the maestro himself Wayne Scofield. The car was set to run on 95 RON ( for safety) at 17psi. For those not in the know for every extra RON grade used you can safely increase the boost by 2 psi, so if I had requested the car set for 98 RON the boost could have been safely increased to 21psi and be just as safe, or so the theory goes, of course, the power would have been a lot higher, Back then I was a little scared of going too far, so played safe, today I'm far more confident in the capabilities of the engine although I still do not intend to use all of the boost available.
Note: If I've forgotten anything I'll add it later

Now before I get started on the new build some things were added to the old spec but never put on a dyno to remap.

Janspeed twin rear exhaust section
Piper Ram intake system, custom install
Apex-i AVC-R electronic boost controller
Engine loom fully rewired using Lindsey components and covered in 1200 degree sheaving.
All sensors renewed
Dump to atmosphere Cosworth type dump valve
Stepper motor boost gauge with record
89' Turbo gearbox with LSD

I think that's covered most of it, I haven't gone into brakes and suspension, I think this intro is long enough I don't want to bore you guy's on the first page now do I... I will add though that as far as bodywork is concerned the car remains standard.

Part 2 coming up

10/05/2021 14:33:18

Thank you Peter.. a Porsche as a company car??.. it's I who is envious, all I got was a VW golf...

10/05/2021 13:57:01
Posted by Henry Brown on 10/05/2021 13:49:35:

Very nice Peter, a friend has had a few of these, one hard top, the rest convertibles. Well built and as you say very reliable, I think his only real issue was with the electric hood but that won't bother you! Looking forward to seeing more form you and wondering what year the car is?

Thank's Henry, she's an early '86' model year, the only year that was homologated as a Group B race car, IIRC there are currently 5 left on the road with a few SORN.. They are approx 100kg lighter than the last in the range.


10/05/2021 13:53:41
Posted by Old School on 10/05/2021 13:40:17:

It is see top left.

What a nice looking car it’s the Porsche I would like to own. Interested to here about the engine it’s amazing what you can get out of an old block.

Thank you.. I thought I was losing the plot for a minute there...

yes, the engine even in standard form is more or less bulletproof if serviced correctly.. The car now has nearly 220k miles on the clock, since engine rebuild it's covered approx 25k so I must have got something right during the process..

Original output was 220bhp, the first round of mods back in 2000 saw this rise to 280 bhp, next round in 2007 bumped it up again to 368 bhp (she was then the 5th most powerful 951 in the country) , today she is close to double the original 220. A lot was changed during the last round and it cost me a pretty penny in parts alone, substantially more than the original cost of the car back in 1999.

I'll write an update soon to give more details for those interested, it could be a long write-up though..

Thanks for the kind words on the car, I hope that you do get the chance to own one in the future, they are something very special and it's getting more difficult to find a good one these days.


10/05/2021 13:31:27
Posted by roy entwistle on 10/05/2021 13:21:11:

Model engineering ?

Is ithis not the 'vehicle restoration page?

10/05/2021 13:06:37

This car has been an ongoing development, in both power and general maintenance for the over 22 years of my ownership. Power has been steadily increased to twice what it was today. Being an '86' model year it's light, very light when compared to today's models, and the lightest of the range. I have driven many powerful cars in my lifetime, none have impressed me as much as this and it brings a big smile to my face each time I drive it.

This car is my daily driver for the simple reason that I am a car fan and no other car delivers what the 951 does and thus feels boring in comparison, it's ultra-reliable too even when highly modified. 951 is the factory model number which is used in Porsche circles to easily identify the model, it's also much easier to type than 944 turbo.. the true number is 952 which means it's an R/H drive variant but in general, we just settle with 951 for both.

I have created a new album for the car to show more images but will add more to this page as things change.

Currently, I have been working on the interior, this included a retrim to the dash and centre console, the dash had developed a few cracks which is common for these cars, I had got away with it for a long time so wasn't really surprised when cracks began to show a couple of years ago.

I have now covered the dash and console in stitched black leather replacing the original vinyl. This picture gives some idea of the cracks that had developed on the top of the dash near the windscreen. The cracks here have been cleaned up and opened before filling

Here we see the dash after being filled and sanded, for this job I used a flexible plastic bumper filler which does this particular job very well.

The dash now covered in a stitched black leather kit which I purchased some 6 years ago, only now finally getting around to fitting. 6 years ago is when the car went through it's last round of mods which this time involved removing the engine and doing a complete rebuild, I'll give more details on this at a later date.

And the last picture for the dash showing it refitted to the car.

Lastly for now a couple more general views of the car

engine bay

And those sexy hips which fill the door mirrors when driving

Parked at the famous Ace Cafe for one of the monthly Porsche meets, pre lockdown of course

Some of the images seem to have distorted a little, sorry about that, I have no idea why?

Hopefully, she will be going in for a full respray this June, the second respray in my ownership, the first was over 20 years ago. This time she will have modern paint and a good few coats of ceramic clear coating which means she should still be looking good long after I've fallen off my perch.

Next time I'll give some details on the engine.


Thread: Don Young's 'Doncaster'
18/04/2021 10:49:59

Oh, I best add that the photo above although it has the same lubricating system and crosshead, it's from a different class. This is a picture of a V2, the drop arm is different to the A1 and this also has the later grease nipple for the union link rather than the oil reservoir found on the A1..


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