Porsche 951

[Peter Seymour-HowellParticipant @peterseymour-howell39349]

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?

[SteviegtrParticipant @steviegtr]

Stunning car you have there. Way back i did quite a bit of mods to porsche cars. My 1st was i built a Covin fibre glass replica of a 911 turbo flatnose. The kit cost me £3000 from Covin in south woodham ferrers . It used a Beetle platform which i cut 6.5" from its wheelbase. Then welded it back together. Not happy with that i made a 25mm x 25mm chassis of which was welded to the underside of the Beetle platform. I bought a wrecked 911 2.4 litre flat 6 engine & rebuilt it. This was grafted to a Transporter gearbox. I kept it for a while & sold it & bought a 924. Which i fitted 944 wings at the front & replica glass fibre ones to the rear. Will try & find some pics of it. Dissapointed at the lazy 924 audi 2.0 engine i sold it on. Later i bought a 911 carrera 2 3.6 litre 231 hp . But was dissapointed again as i had a Nissan Sykyline GTR33 vspec running nearly 700 BHP. So the Porsche was a bit flat. Unfortunately i at the time could not afford a 911 turbo which was my aim. Many cars since i now have my dream car. When i was in my early 20's i had an Etype 4.2 series 2 drop head. So when the Ftype came out i prommised myself one when finanaces allowed. Now i have one the Dam Coved has stopped me enjoying it for nearly 18 months now. This is the 575 Bhp v8 which was chipped with the SVR map. I have it booked into Appleby engineering who are going to change the Supercharger pulleys to get the most from the Eaton charger. They are also going to fit the 200 cell race Cats. So hoping for around 630BHP. Still way short of my Skyline , but instant power over the Nissan twin turbo's. Some pics here.

Steve.

Edited By Steviegtr on 11/05/2021 01:01:00

[Peter Seymour-HowellParticipant @peterseymour-howell39349]

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..

Regards

Pete

[Peter Seymour-HowellParticipant @peterseymour-howell39349]

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

regards

Pete

[old martParticipant @oldmart]

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

[Peter Seymour-HowellParticipant @peterseymour-howell39349]

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

Quote:

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

101×0.70mm 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'

Regards

Pete

[SteviegtrParticipant @steviegtr]

Lovely Cossy escort. The nearest i got to one was my 1988 Saphire Cosworth. It was the 1989 Pace car for Brands Hatch. But was no where near your Sons power. I think from memory it was running 22psi with grey injectors. Around 300 BHP. I will post some more pics of cars i have had , but rather than spoil your thread i will put them in my Albums. So keep having a look . It may take a while as they all need scanning from Photo's. I think one of the nice things about the Porsche you have is that they seem to be timeless. Always fancied an S2 soft top. Never happened.

Steve.

[Peter Seymour-HowellParticipant @peterseymour-howell39349]

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…

Pete

[Tim StevensParticipant @timstevens64731]

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

[Peter Seymour-HowellParticipant @peterseymour-howell39349]

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?

Regards

Pete

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

[Tim StevensParticipant @timstevens64731]

I wonder if you are confused by the term 'capacity' ? Engine capacity is really a confusing term, as engine size is measured as the volume of mixture which would be taken in under ideal conditions, in one full rotation. Swept Volume (swept by the moving piston) is a much clearer term. It doesn't matter how thick your gasket, or how much you plane off the head or block, the swept volume does not change. Honest. I'm not a betting man, but I'd put money on that statement.

Cheers, Tim

[Ian Skeldon 2Participant @ianskeldon2]

Wow what a stunning car, nice work done on the restoration Peter.

[Peter Seymour-HowellParticipant @peterseymour-howell39349]

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..

Pete

[Peter Seymour-HowellParticipant @peterseymour-howell39349]

Posted by Tim Stevens on 11/05/2021 18:07:34:

I wonder if you are confused by the term 'capacity' ? Engine capacity is really a confusing term, as engine size is measured as the volume of mixture which would be taken in under ideal conditions, in one full rotation. Swept Volume (swept by the moving piston) is a much clearer term. It doesn't matter how thick your gasket, or how much you plane off the head or block, the swept volume does not change. Honest. I'm not a betting man, but I'd put money on that statement.

Cheers, Tim

Interesting Tim, perhaps I should bring this up on the Porsche forum next time I post, those guys know their stuff although none of them pointed this out when the build was current. I can easily get confused though, especially these days….

Cheers

Pete

[Peter Seymour-HowellParticipant @peterseymour-howell39349]

Posted by Ian Skeldon 2 on 11/05/2021 18:27:53:

Wow what a stunning car, nice work done on the restoration Peter.

Thank's Ian, very generous of you to say so, sir..

Pete

[JasonBModerator @jasonb]

You can only increase capacity (displacement) by increasing bore and/or stroke, using a thicker gasket will just lower your compression ration

Edited By JasonB on 11/05/2021 20:57:06

[Peter Seymour-HowellParticipant @peterseymour-howell39349]

Hi Tim and Jason, my apologies chaps, you are of course, correct which is a bit worrying for me as clearly my mind is worse than I thought? That's another story which I don't want to bore you guys with my health issues.

I have just reread my notes and yes I did state that it's the CR that is affected not displacement…sorry about that and thanks for putting me straight.

Pete

[SteviegtrParticipant @steviegtr]

Peter as promised , put a few of my past cars in my cars album.

Steve.

[Peter Seymour-HowellParticipant @peterseymour-howell39349]

Posted by Steviegtr on 11/05/2021 22:07:27:

Peter as promised , put a few of my past cars in my cars album.

Steve.

Thanks Steve… I saw them…didn't know how to acknowledge.. should have just said so here..lovely cars.. I'm intrigued..what's the story with the Tesla?

[SteviegtrParticipant @steviegtr]

It's a guy on youtube who buy's write off tesla's. He then makes other cars electric. That one was at Copart, i might say a place where i have bought over 100 motorcycles & scooters to repair. Plus quite a few cars & camper vans. I digress. He was at Copart looking round & came across that one. What i never knew was the whole floorpan is the battery store. Thousands of them. The whole lot had gone up in smoke. I believe the early batteries used were terrible for catching fire.

Steve.

[Russell EberhardtParticipant @russelleberhardt48058]

Posted by Peter Seymour-Howell on 11/05/2021 18:34:30:

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.

 

Not much of a secret. Lanchester used that idea back in the 1930s they even used it with the shafts geared up to remove vibration harmonics on six cylinder engines.

Russell

Edited By Russell Eberhardt on 12/05/2021 10:03:46

[Peter Seymour-HowellParticipant @peterseymour-howell39349]

Posted by Steviegtr on 12/05/2021 00:59:18:

It's a guy on youtube who buy's write off tesla's. He then makes other cars electric. That one was at Copart, i might say a place where i have bought over 100 motorcycles & scooters to repair. Plus quite a few cars & camper vans. I digress. He was at Copart looking round & came across that one. What i never knew was the whole floorpan is the battery store. Thousands of them. The whole lot had gone up in smoke. I believe the early batteries used were terrible for catching fire.

Steve.

Ah.. yes electricity, has its own issues, safety is one although perhaps not as bad/often as fuel. EV's are the future, there's a video on YT of a guy who's converted his IIRC 951 (could be a normal 944?) to electric and then put it up against the latest McClaren on the dragstrip. Well, let's just say that not only did the 944 win but evidently it won by a bigger margin than any car before it against this brand new McClaren. I don't think that we will see the end of IC engines though, certainly not Porsche who have teamed up with Siemens to produce their own zero-emissions fuel to keep all old Porsche's on the road. IIRC they will be testing it either later this year or early next and have invested other £1 billion into new factories/plants to produce this new fuel.

They are also very much into electric and again have joined a partner (can't recall who although could be Seimens again) for electric flying cars which on being developed as we speak.

Pete

Pete

[Peter Seymour-HowellParticipant @peterseymour-howell39349]

Posted by Russell Eberhardt on 12/05/2021 09:49:54:

Posted by Peter Seymour-Howell on 11/05/2021 18:34:30:

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.

Not much of a secret. Lanchester used that idea back in the 1930s they even used it with the shafts geared up to remove vibration harmonics on six cylinder engines.

Russell

Edited By Russell Eberhardt on 12/05/2021 10:03:46

True, sorry I didn't mean 'secret' per se, just that not many people know of this feature and it does mean that the engine can be pushed far more than most others. IIRC Porsche paid royalties to Mishibusi who held the patent at that time?

Pete

[SteviegtrParticipant @steviegtr]

Hi Pete. some of the bhp figures you have given are extreme. Are you sure of these figures. We can all say our cars have this much power, but is it real. The Skyline i had was already very powerful when i imported it from Japan with 1000cc injectors, a forged & balanced crank to 9000rpm & twin turbo's with steel impellors & 360degrre cut back blades. The bearings were roller with oil & water cooling. This with a lot of electronics & high octane fuel gave around 700 BHP. This was using a RB 26 DET block with strengthened main bearings. The most powerful 2.0 cosworth engines were good for around 450 bhp with a lot of work. The Colins & Routh motors with the 2.4 litre conversion could reach around 600 unreliable bhp.

Steve.

[SteviegtrParticipant @steviegtr]

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…

Pete although i have done the Le-mans trips many times myself, in A Bentley arnage black edition. A Bentley arnarge red edition A few Tvr variants. A 911 Turbo . A 993 RS. . It would be impossible to record 174 mph from 282 bhp. Do the math. My skyline registered 193mph at Elvington in 1998. That was with 700 BHP. I think your figures are maybe just what you think they were. Not actual. I ran a 9.8 sec 1/4 at Melbourne raceway in 1999. I have the ticket. But the point is a Nissan Skyline can be tuned to over 1000bhp. I do not think an old 944 2.5 inline 4 could ever be that good. I wish you were right but it's only a pipe dream . Even my old Ultima gtr with the 350 ci ls6 engine could only manage 182 down the Mulsane straight. Sorry.

Steve.

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