39 replies to this topic

[mariner]

The latest copy of Race Car Engineering has an article on the Vanwall 2.5 litre F1 car. It seems that,  like the main Autosport site, to be fililng its space with more " nostalgia" articles but this one started me thinking about how the 1950's Offy Indy car engine, a straight four with 4 valves per cylinder, compared to tis F1 4 cylinder contemporaries with 2 valves per cylinder.

 

My instinct was to think of the Offy as a very out of date and  with a low bhp/litre compared to the  F1 engines but that is not quite true.

 

Firstly, it was made in much greater  numbers in the 50's than any F1 engine. About 100 in all. So, it was very much a customer engine a bit like the Climax  engines not a heavily developed works engine.

 

To compare the Offy to F1 engines in the 50's requires choosing F1 engines which ran on Methanol/ Nitro methane up to 1957 as the Offy never ran on petrol. That leaves out the Climax 4 but leaves the Vanwall and BRM engines. Interestingly if you add back the Climax, Ferrari and Alta engines the "big Four" was the most popular 2.5 litre formula engine .

 

The best way to compare engines is BMEP but as that requires torque details not always available, I used a surrogate of BHP per litre per 1,000 revs which is roughly BMEP at peak power not peak torque

 

On that basis the big Offy is within 2% of the BRM engine , using data from Tony Rudd's autobiography and within 8% of the Vanwall engine. All three engines were run on nitro methane mix at times . There the Offy is within 4% of the BRM and 5% of the Vanwall engine.

 

The Offy power is quoted as 400 bhp on methanol only at 6,500 rpm rom both from Offy dyno sheets and from the dyno testing Ford did to benchmark their 1963 Indy pushrod V-8. It did 415 bhp on 10% nitro.

 

The Offy was a much slower revving engine due to its long stroke -and the need to survive 500 miles not 250 miles per race. Its bore/ stroke ratio was 0.97 vs 1.12 for the Vanwall and  1.37 for the BRM 4.

 

That allowed the Vanwall to run at 7,200 rpm and the BRM  at 8,000 rpm versus 6,500 for the big Offy.

 

It’s true that the Offy made a lousy 3 litre or 2.5 litre petrol engine, but  I doubt the Vanwall or BRM fitted with a longer stroke to reach 4.2 litres would have made a very durable Indy engine so horse for courses.

turbo charged 

Obviously the Offy wasn’t as good , not surprising as it was originally designed in the 1930's but it surprised  me how close to contemporary F1 specific power outputs it got - and it was still winning at Indy in the 1970's, reduced to 2.8 litres, running at 10,200 rpm  and  developing 1, 200 BHP for qualifying.

Edited by mariner, 06 November 2022 - 11:17.

[mariner]

I think I meant " How did the" - sorry 

Edited by jcbc3, 06 November 2022 - 10:56.
Edited

[BRG]

How do they compare weight-wise?

[Collombin]

Ludvigsen's Classic Racing Engines puts the Vanwall at 163kg. Gordon Eliot White in Offenhauser says the initial 4.2 litre Offy variant was 205kg.

Ludvigsen also has a chapter on the early '70s 2.6 litre turbo Offy, giving a weight of 216kg.

Edited by Collombin, 06 November 2022 - 12:01.

[mariner]

About 360 - 370 lb for for the 255 cubic inch engine. There were so many deck height etc. variations it could vary. Incidentally  whilst Drake Engineering built  few new Offy engines in the 1970's they made 400 to 500 blocks  blocks as the turbo boost consumed them rather quickly.

 

The Vanwall engine is quoted as 358 lbs here http://8w.forix.com/...ifications.html

 

 

I am not sure on teh BRM engine, maybe one of Dug Nye's BRM books  has that data?

[mariner]

I think one of the problems with engine weights is whether

the clutch is included. 

[D-Type]

How similar were the 2.7 litre [?]  Offy Midget and 3-litre engines to their larger brother?  In particular the power, weight and power/weight ratio.
Were these totally different engines or did they use the same block and/or general architecture?
The other factor is the shape of the power and torque curves.  The Offy was essentially a constant speed engine without the flexibility required of the F1 engines.

[Sterzo]

Fascinating subject. I suppose one question is, how much development would have been required to produce a 2.5 with a torque curve suitable for mid-fifties road racing? Would it have taken much more than different cams? Also, how much of the extra weight was in the block, and how much in components which could have been replaced with less robust ones?

[Bloggsworth]

Scarab anybody?

[D-Type]

Scarab anybody?

The Scarab engines were built by Offenhauser, but I think they were a totally different design.

[Lee Nicolle]

How similar were the 2.7 litre [?]  Offy Midget and 3-litre engines to their larger brother?  In particular the power, weight and power/weight ratio.
Were these totally different engines or did they use the same block and/or general architecture?
The other factor is the shape of the power and torque curves.  The Offy was essentially a constant speed engine without the flexibility required of the F1 engines.

AFAIK midget engines never got over 2.5litres. That was the maximum allowable  world wide. And where a lot of the Holden 6s were.  And even then it was to try and keep up with the VWs, Sescos and Chevy11s. Originally they were limited by OHC to be around 1.8 litre?

But as I have seen on here there is Offys and Offys. Most midget engines had the intakes on the left side of the engine ingesting all the mud!!

Yet few used airfilters!!! Though I have seen them with the intakes on the right as well.

The big Indycar [and Sprintcar] Offys I believe are the same basic design but are taller and longer to get the capacity.

The Scarabs I beieve are a normal big Offy though maybe with detail differences.

[Tom Glowacki]

The Scarab F-1 engine was designed by Leo Goossen, who was chief engineer at Meyer & Drake.  It was not an adapted Offenhauser, as the head was not integral with the block as on the Offy.  It featured desmodromic valve actuation.  That design was "borrowed" from the 300SLR at the Henry Ford museum by Jim Travers and Frank Coon, soon to become known as Traco.  Somewhere, I have a copy of an interview with Chuck Daigh, who continued, for years, to play with the engine.  In it, he says that he found that, back in the day, a mistake was made in reading Goossen's plans and the valve system was never correctly assembled.  When he corrected the error, the output went up considerably.

[GregThomas]

The undersquare layout is at least partially due to the need for a compact combustion chamber in order to use high compression ratios for methanol. The need for a flat torque curve to suit both banked sealed ovals and dirt mile and half miles comes into the equation too.
Given that the design has roots in the 1913 3 litre Peugeot - incl what would now be called excessively wide valve angles - it doesn't do too badly. It's rugged - reliable both at Indy and on the dirt miles. The barrel crankcase with bolted in bearing bulkheads could obviously be made quite easily on available machinery - and at an affordable price.
Maintenance appears to have been easily done between races. A factor often overlooked in F1 engines.
Midget versions - 91cu/in I believe - ran competitively around the world till at least the early '70s.
Memory says there was a version - Sparks/Goosen/Drake ? - with a modern Cosworth style 4 valve head which offered a lifeline to keep it going longer.

I can remember the last Offy Midget running local to me. It made a very nice noise, A high pitched howl audible above the Holdens.....the Cosworth BDP just wasn't the same.

[Henri Greuter]

It has always a kind of surprise for me that within the 50's the 3 liter centrifugally blown Offies never were much of a success against the 4.5 liters.

 

But perhaps that was because of that engien being more for Indy only while the 4.5 literes were at larges useful over the entire AAA & USAC Season and therefor the moviation to develop the centrifugally blown Offy not that big: there was an alternative that was good enough for the job.

 

Herb Porter had some successes with one in the second half of the 50's but other then that.

Edited by Henri Greuter, 07 November 2022 - 09:49.

[mariner]

To answer an earlier question o teh output of the Ofy Midget engine Drake Engineering ,( who took over the Offy design) published a dyno chart showing 175 bhp at 8,000 rpm. 

 

That was from 114 cubic inches or 1.85 litres. That is  94 bhp/litre on methanol. At the time a Lotus twin cam was at about 140 bhp or so for 1.6 litres so 87 bhp/litre. 

 

Given a 10% benefit from the Offy's Methanol fuel that puts a 4 valve Offy midget about level with the 2 valve Lotus twin cam but well below the  4 valve Cosworth FVA. 0f 1966 - which makes sense I think

Edited by mariner, 07 November 2022 - 12:17.

[mariner]

Going back to the bigger Offy it was really old fashioned in many ways but it had one "old fashioned" feature which made it ideal for the era of unlimited boost at  Indy.

 

That was the combined head and block, like a Bugatti.I t eliminated the head gasket and allowed free coolant flow up from cylinder area to the valves. With very high boost levels every bit helped.

 

It's also amazing that a basically 1930's engine of 2.8 litres and just 4 cylinders could rev to 10,000 rpm.  am not an engine expert but I have read that very high bost presures actaly reduce the strees on rod bolts.

[rl1856]

The Scarab F-1 engine was designed by Leo Goossen, who was chief engineer at Meyer & Drake.  It was not an adapted Offenhauser, as the head was not integral with the block as on the Offy.  It featured desmodromic valve actuation.  That design was "borrowed" from the 300SLR at the Henry Ford museum by Jim Travers and Frank Coon, soon to become known as Traco.  Somewhere, I have a copy of an interview with Chuck Daigh, who continued, for years, to play with the engine.  In it, he says that he found that, back in the day, a mistake was made in reading Goossen's plans and the valve system was never correctly assembled.  When he corrected the error, the output went up considerably.

 

An article entitled "We could have run with them"  in Motor Sport (?) was about the Scarab and the missing HP.  I read the article, but do not have access to it.   

 

From 8W site:

 

"Daigh had access to all of Leo Goossen's drawings and notes acquired from Kellogg and found that during the 1960 F1 foray, Traco had not been setting up the engine's desmodromic valve gear to Goossen's instructions. Daigh had never seen the drawings and set up specifications before and had always been in the field with the team during the 1960 campaign and the engines came to them ready to go from the engine shop. Goossen's instructions called for a valve clearance of 0.002 inches, but the engines had been built with a valve clearance of 0.012 inches. Daigh reasoned that following the valve breakage on the first dyno test of the desmodromic engine the engines had then been purposely set up with a little more valve clearance to keep the valves from breaking when things heated up and expanded, relying on compression to keep them shut, but this caused problems with the engine's breathing on the intake stroke, with the exhaust valves not fully seating.

 

"Interestingly, the Mercedes Benz M196.I engine upon which the Scarab's desmodromic valve gear was modelled had valves almost as big (50mm inlets and 43mm exhausts) in cylinders of half the swept volume and it operated very successfully using valve clearances of 0.008 inches for the inlet opening cams and 0.013 inches for the exhaust opening cams.

 

"Daigh studied Goossen's drawings and instructions and then spent time experimenting with the valve gear of the Scarab engine. Finally, he settled on a reduction of the valve clearance to 0.0015 inches (slightly less than what Goossen had specified) which let the valves seat properly and boosted compression significantly. In the autumn of 1999, the engine was put on a dynamometer and with no other changes it produced 267bhp at 6,500rpm, almost 50bhp more than they raced with. The power curve indicated that 280bhp could have been developed at the 7,500rpm designed peak. This vindicated Leo Goossen's design, representing a very high bmep of 218.3psi at the tested engine speed of 6,500rpm. If raced in this form, the engine power would have been more than competitive, although that would have been tempered by the outstanding engine reliability problems and chassis deficiencies."

 

As for the original Post, Reventlow, Daigh, Travers and Coons attempted to adapt the 3L Offy to 2.5L use, and were extremely disappointed with the results.  This was a factor in their decision to design their own engine.

Edited by rl1856, 07 November 2022 - 14:50.

[mariner]

The desmo Scarab engine was a case of too much with too few I think. As I understand the story Leo Goossen was given very detail access to a MB 300 SLR owned by Ford and based his design on that - without one presumes the MB technicial know how which was behind it.

 

One thing pussles me - teh Scarab is now very successful in Historics , but what actual engine and size doesit run? 

 

It isn't the desmo design I presume.

[D-Type]

The desmo Scarab engine was a case of too much with too few I think. As I understand the story Leo Goossen was given very detail access to a MB 300 SLR owned by Ford and based his design on that - without one presumes the MB technicial know how which was behind it.

 

One thing pussles me - teh Scarab is now very successful in Historics , but what actual engine and size doesit run? 

 

It isn't the desmo design I presume.

The engine was enlarged to 3 litres for the 1961 Intercontinental Formula.  I assume that is the engine it now has.  As described above, Chuck Daigh finally got the desmo engine working properly.
Alternatively it might be running a 3-litre Offy.

[10kDA]

One of the Scarab F1 cars is now running a laydown Offenhauser, as in this pic:

 

 

Tapered coolant line between the cams; single magneto. I doubt if it is a 3 liter Offy. I've never heard of an Offy sized at 3 liters. When the laydown Offys were running in the late 50s I believe the displacement limit was 255 cu. in.

 

This one was shown "for sale" and it has a real Scarab F1 engine installed - whether it's "running" in vintage races or not, I don't know. All I have seen are the showroom pics.

 

 

Coolant line connections below intake ports, dual ignition with two Lucas mags, middle intake ports closer together than typical on an Offy..

[Tom Glowacki]

One of the Scarab F1 cars is now running a laydown Offenhauser, as in this pic:

 

 

Tapered coolant line between the cams; single magneto. I doubt if it is a 3 liter Offy. I've never heard of an Offy sized at 3 liters. When the laydown Offys were running in the late 50s I believe the displacement limit was 255 cu. in.

 

This one was shown "for sale" and it has a real Scarab F1 engine installed - whether it's "running" in vintage races or not, I don't know. All I have seen are the showroom pics.

 

 

Coolant line connections below intake ports, dual ignition with two Lucas mags, middle intake ports closer together than typical on an Offy..

There was at least one 3 litre Offenhauser.  Briggs Cunningham had it in his 1955 LeMans entry  C-4R.  

[RonPohl]

When making the pilgrimage east to the Indy 500, I always spend a little time in the excellent museum. A few years ago, they had a “Petting zoo” Display of a disassembled Offenhauser. You could pick up the various parts, which were of course secured by some sort of cable so souvenir hunters didn’t walk off with their piece of Offenhauser. I am not sure exactly which version of the Offie this engine was, and I am not an expert on engines,. The only engines I had much familiarity with was the  formula ford Kent engines and what struck me about the Offie was the similarity to the Kent engine. It was a very simple engine consisting of four cylinders and the parts were really only slightly bigger than a 1600 cc Ford.

[Collombin]

There was at least one 3 litre Offenhauser. Briggs Cunningham had it in his 1955 LeMans entry C-4R.

White's book lists 2 other 3 litre Offys from 1954, as well as 4 made in 1950 that were just under 2.9 litres.

[Henri Greuter]

White's book lists 2 other 3 litre Offys from 1954, as well as 4 made in 1950 that were just under 2.9 litres.

Those 1950 engines could be the ones that eventually were supercharged. Andy Linden used such an engine to qualify on the front row in 1952.


Adding to the stat that during the 50's in 1952 the Indy starting grid had the largest varieties in kind of engines used by the top 4 Qualifiers. 4 different kind of engines. (Turbocharged Straight-6 Diesel, supercharged 3 liter Offy, 4.5 liter atmo Offy, 3 liter supercharged Novi V8)

[Collombin]

Adding to the stat that during the 50's in 1952 the Indy starting grid had the largest varieties in kind of engines used by the top 4 Qualifiers. 4 different kind of engines. (Turbocharged Straight-6 Diesel, supercharged 3 liter Offy, 4.5 liter atmo Offy, 3 liter supercharged Novi V8)

Surprisingly this holds true whether you look at the top 4 on the grid (Agabashian/Linden/McGrath/Nalon) or the fastest 4 qualifiers (Miller/Vukovich/Agabashian/Linden).

[Henri Greuter]

Surprisingly this holds true whether you look at the top 4 on the grid (Agabashian/Linden/McGrath/Nalon) or the fastest 4 qualifiers (Miller/Vukovich/Agabashian/Linden).

 

 

And then one other exotic within Indy history engine didn't make it into this bizarre stat. But 1952 saw of course yet another unique engine in the starting field:  Ascari's V12 Ferrari

 

enginewise, 1952 was by far the most interesting year within the 50's, considering the fact we also had years with 33 Offies....

[Roger Clark]

The engine was enlarged to 3 litres for the 1961 Intercontinental Formula.  I assume that is the engine it now has.  As described above, Chuck Daigh finally got the desmo engine working properly.
Alternatively it might be running a 3-litre Offy.

Did the Scarab have a 3-litre engine in 1961?  I’m not saying it didn’t but I’ve never heard that it did. If it did, was it an enlarged Scarab engine or an Offenhauser?

[Roger Clark]

Did the Scarab have a 3-litre engine in 1961?  I’m not saying it didn’t but I’ve never heard that it did. If it did, was it an enlarged Scarab engine or an Offenhauser

The programme for the 1961 Lavant Trophy gives the Scarab capacity as 2900cc so that answers part of my question.

[mariner]

The engine in pictures 1 and 3 above is definitely an Offy, but 2 and 4 look like the Scarab desmo. engine. As noted by others the desmo. engine has uneven inlet port spacing which is also clearly seen in period pictures.

 

The two " real" Offy's are the laydown type developed for the Indy 500 to lower the CG, cut frontal area, and give left hand weight bias.so the original lay downs would be 255 ci/ 4.2 litres.

 

The sports engines developed at 180 c.i. / 3 litres for Cunningham were upright engines fitted with Weber carbs. and Lucas distributor unlike the magnetos in these pics.

 

So if the historic engines Offy engine above is at 3 litres it must be mix of parts. 

 

As Offy's seem to come in many combinations that is quite possible.

 

 

 

e sports 

[DCapps]

I must be missing something as usual, but would not the better comparison be with the 1948/1953 period cars? After all, the engine was within the F1 specs and so were the cars equipped with it. Or is that not relevant?

[mariner]

The Offy gave around 380 - 400 bhp in 1952 at 4.5 litres as did the Ferrari 4.5 V 12 - so I think they were a close match. Their relative performance in Indy qualifying tends to confirm this.

[Henri Greuter]

The Offy gave around 380 - 400 bhp in 1952 at 4.5 litres as did the Ferrari 4.5 V 12 - so I think they were a close match. Their relative performance in Indy qualifying tends to confirm this.

 

Offy was much more driveable than the Ferrari.

Offy had so much more torque that it could stay in high gear and accelerate out of the corners to top speeds again.

Ferrari V12 never matched that acceleration.

From what I have found out, Top speeds at the straight were about identical but the Offy powered cars reached it quicker and hence were faster.

It is rumored that Ascari actually dropped a gear before the corners in order to enhance acceleration in the lower gear before going back to high for top speed.

But I am not 100% sure this is true.

 

 

That was indeed one of the underrated qualities of the Offy by many non-USA onlookers: it's torque figures made it a very flexible and drivable engine.

Edited by Henri Greuter, 10 November 2022 - 08:41.

[Collombin]

It is rumored that Ascari actually dropped a gear before the corners in order to enhance acceleration in the lower gear before going back to high for top speed.
But I am not 100% sure this is true.

Johnnie Parsons complained about having to downshift for the turns.

[Roger Clark]

That's very interesting about the flexibility of the Offenhauser engine.  An Offenhauser in a suitable chassis could have saved Formula 1 in 1952.

[Roger Clark]

It was in Vintage Racecar magazine that Chuck Daigh talked about the error in the Scarab's valve gear that had such an effect on the power.   He says thet the Scarab was designed with starter motors and reverse gear because RAI believed they were compulsory.  It was only after a conversation with Bruce McLaren that he learned that Cooper had not had either for two years. He also said that in 1961 they reduced a 4.2-litre Offenhauser to 3-litres but it wasn't successful. I would infer from this that it was done by or for Scarab, not an existing 3-litre engine.

 

An article in Motor Sport November 2017 describes some of the work done to Julian Bronson's Scarab to make it competitive in Historic Racing.  The magneto system did not provider a spark below 8,000rpm; power was about 220bhp.  The chassis was described as a very good basic design, not fully developed.  Handling was vastly improved by firing stiffer springs and anti-roll bars and reducing ride height.

 

Motor Sport February 1973 contained an article about Leo Goossen.  It said that Drake engineering was not a research and development oriented company.  Any changes to the engine originated from outside and were passed to Goossen to draw and then to Drake to make.  It described his frustration that he rarely received any feedback as to how the engines were performing.

Edited by Roger Clark, 10 November 2022 - 12:02.

[10kDA]

Offy was much more driveable than the Ferrari.

Offy had so much more torque that it could stay in high gear and accelerate out of the corners to top speeds again.

Ferrari V12 never matched that acceleration.

From what I have found out, Top speeds at the straight were about identical but the Offy powered cars reached it quicker and hence were faster.

It is rumored that Ascari actually dropped a gear before the corners in order to enhance acceleration in the lower gear before going back to high for top speed.

But I am not 100% sure this is true.

 

 

That was indeed one of the underrated qualities of the Offy by many non-USA onlookers: it's torque figures made it a very flexible and drivable engine.

 

Right, Offys were not engineered to be steady-state engines in that time frame. The typical Indy Big Cars had 2-speed transmissions - Low to get out of the pits, and High for racing speeds. The engine was flexible enough that more gears weren't necessary. This was another one of those factors that resulted in some opinions that the Indy cars were "archaic".If everybody was running this setup, the field was more or less equal. If somebody added more gears to get up to speed quicker, they were adding more weight and complexity. Would it pay off? At the time, a 500 mile race was most definitely an endurance contest.

 

Given that most of the drivers raced dirt tracks during Indy's 11 month off-season, their driving styles were oriented to flexible power characteristics. Bobby Unser, who was pretty darn good on low traction surfaces like dirt tracks and Pike's Peak, once said he preferred a "long" throttle, meaning the range of throttle travel occurred over a large range of motion at the gas pedal. He said many drivers who came to Indy cars from a road racing background preferred a very short throttle, more like On-Off. Road racers typically match engine torque and power delivery to available traction (including corner radius) by selecting appropriate gears. The wide torque curve of the Offy allowed this to be done with throttle position, and on dirt, no shiftable transmission at all, just an in & out box. Bobby said the long throttle setup was a huge advantage when picking his way through traffic on fast paved ovals.

 

Edit: Typo - PiKe's Peak, not PiLe's Peak nor Pike's Pile.

Edited by 10kDA, 10 November 2022 - 12:43.

[mariner]

The lack of any in house development team at Drake etc. seems to be common theme. They seemed to have excelled at materials , machining and assembly but reacted to the ideas tried out by the racing mechanics. The lay-down idea was from a team for example but machined up by Drake then asembled in their shop by hte team.

 

 

Also the teams only spent May at Indy, they were often based in California but travelled everywhere. That required the teams to do trackside rebuilds of engines. Interestingly in his book Pete Bryant describes often re building Climax 4 cylinder engines in the field in the 590's and very early 60's but the advent of the V 8 Climax stopped that as CC took over all maintainance. 

[10kDA]

The lack of any in house development team at Drake etc. seems to be common theme. They seemed to have excelled at materials , machining and assembly but reacted to the ideas tried out by the racing mechanics. The lay-down idea was from a team for example but machined up by Drake then asembled in their shop by hte team.

 

 

Also the teams only spent May at Indy, they were often based in California but travelled everywhere. That required the teams to do trackside rebuilds of engines. Interestingly in his book Pete Bryant describes often re building Climax 4 cylinder engines in the field in the 590's and very early 60's but the advent of the V 8 Climax stopped that as CC took over all maintainance. 

 

Meyer-Drake Engineering, the source of Offys in the time frame being discussed, was located in the greater Los Angeles California metro area.

[Michael Ferner]

To answer an earlier question o teh output of the Ofy Midget engine Drake Engineering ,( who took over the Offy design) published a dyno chart showing 175 bhp at 8,000 rpm. 

 

That was from 114 cubic inches or 1.85 litres. That is  94 bhp/litre on methanol. At the time a Lotus twin cam was at about 140 bhp or so for 1.6 litres so 87 bhp/litre. 

 

Given a 10% benefit from the Offy's Methanol fuel that puts a 4 valve Offy midget about level with the 2 valve Lotus twin cam but well below the  4 valve Cosworth FVA. 0f 1966 - which makes sense I think

 

4 valve Offy midget? Is that four inlet valves, or four exhausts? Or did you mean to imply it had four per cylinder? No such thing exists. To even only mention the midget engine in this discussion is like assessing a Cosworth DFV engine by analysing the performance of a Sierra Cosworth.

[Jim Thurman]

Meyer-Drake Engineering, the source of Offys in the time frame being discussed, was located in the greater Los Angeles California metro area.

Los Angeles proper. Within the city limits. The building, which was Harry Miller's before that, still stands. Unfortunately, with the build-mania going on, one wonders for how much longer.