...so what's with the Okrasa high comp heads?

Earlier I asked the readers regarding the background of the "special alloy high compression heads" that was advertised in the Okrasa price lists in the 50's.

The information I've got so far is that these heads were made to go with special Weber carburators and that only a few were ever made. Aside of the bread-and-butter Okrasa kits (16 000 made in total according to one source), they also made low volume stuff for racers. The hi-comp heads were probably in this category. If you ever find such heads they are definitely in the rarest-of-the-rare category!

The picture shows the Okrasa Ghia used at Econo motor as a demo car. From Hot Rod Magazine, April 1957. It has nothing to do with high compression heads. It's just a nice picture.

What you always wanted to know about the WW Okrasa kit

The launch of the Wolfsburg West Okrasa kit was a game changer in the world of VWintage Speed. With a complete kit to a competitive price Wolfsburg West has done a great job. Their replica is in most cases very accurate. Some things are not exactly as the original, perhaps there are technical reasons, or perhaps it is a compromise to get a decent production cost. However, those wanting to bolt-on the kit as-is on a 30/36 hp engine might want to know what effect these changes will have to their motor.

1. The venturies
   The original Okrasa kit had Solex 32 PBIC carburetors with 23 mm venturies, as opposed to 21.5 mm in the stock 28 mm unit. In the TSV1300 kit Okrasa did increase it to 24 mm. But according to the information I have seen Wolfsburg West uses venturies  with a whopping 26 mm diameter. This is what Porsche did use for their high-RPM 70 hp pre-A 1500 Super engine. Thus, the replica carb is good for those who want to further hot rod their engine. But for the bolt-on crowd using stock displacement and cam this is rather big.
   
   Bigger venturies means a lower velocity of the gasses, which results in less power at low-end rpm's. If you have a heavy full-bodied street driven car with a small 1.2 l engine this is not what you want. Thus, a replacement of the ventuires is to recommend if you want the performance to be as Okrasa intended.
2. The combustion chamber
   As recently mentioned the normal Okrasa head for the bolt-on kits had either 40 or 42 cc combustion chambers giving a compression ratio of 7.2:1 respective 7.5:1 with a reasonable deck height. Wolfsburg West claims 7.5:1 in compression when they advertise their kit, however according to two independent sources (at thesamba.com) the combustion chambers of the actual product sold is 45 cc.
   
   With a decent deck height you will then arrive at a compression not too far from the stock 6.6:1, which is rather conservative if you want the kit for more than looks. I don't know the reason why WW did chose to have larger chambers. Was it a compromise for manufacturing, an attempt to keep customers heads running extra cool or did they forget the deck height volume in the calculation?
   
   In any case, if you want original Okrasa performance it's a good idea to cc the heads to see if any machining is needed to arrive at the desired ratio.

Conclusion

Don't get me wrong, I think the WW kit is a great initiative, but as usual in the VW aftermarket world you need to check what you get and modify as needed.

Rätt rustad för rally

Den 31 juli hålls Wiking Auto Rennen i Rättvik, så det är hög tid att se över bilens utrustning. Ägaren till Speedstern i bilden ovan får ses som ett föredöme, här är det inte mycket som saknas.

Odiskret skyltad TSV1300 Ghia

Att det på 50-talet inte var helt ovanligt att utrusta Karmann Ghior med starkare motor från Porsche eller Okrasa har vi sett tidigare i bloggen. Men, en sådan här tydlig skyltning har jag inte sett på något annat exemplar. Här råder inget tvivel om vilken motor som vilar i andra änden.

Bilen på bilden togs in till Australien av den lokale Okrasa agenten Mirek Craney. Gissningsvis är året 1957 och det verkar som bilen precis lastats av båten. Mirek kom ganska snart att använda Ghian som förlaga till sin egentillverkade sportbil kallad Ascort (se tidigare blogginlägg). Denna fick givetvis också fick en Okrasa TSV1300 motor.

Var lugna. Någon oskön skyltning som denna lär aldrig dyka upp på min S-Ghia.

Karmann Ghia på Blocket

Även om jag inte har några planer på att köpa, eller sälja, någon hobbybil så är det intressant att se vad som bjuds ut på marknaden.

Ovan ser ni de Ghior som jag sett på Blocket under våren och försommaren. De är inte många och har man några speciella krav är urvalet mycket dåligt. Vill man t ex ha en körbar 50/60-tals coupé i rimligt propert originalskick, har det inte funnits mycket att välja på.

Eftersom alla bilarna ovan nyss har bytt ägare så vill jag passa på att önska de nya innehavarna ett stort lycka till!

Okrasamysteriet löst, delvis.

Den som kommer ihåg min Okrasahistorik kanske minns mina frågetecken kring vilket kompressionsförhållande kiten gav. Importören i USA, Empi, angav 7,5:1 för TS1200 respektive 8,0:1 för TSV1300. Men, i tyska prislistor från Okrasa angavs 7,2:1 för TS1200.

Nu har jag lärt mig att Okrasatopparna kom i två varianter med 40 cc respektive 42 cc förbränningsrum. Vilken typ man har är lätt att se då det är stämplat i toppen. Räknar man på det (med en rimlig ansats på vändhöjden) kommer man mycket riktigt till 7,2:1 för en TS1200 med 42 cc toppar. Med 40 cc blir det 7,5:1 för TS1200 och 8,0:1 med TSV1300.

Så långt verkar vi kunna sluta oss till att Empi valde att tillhandahålla 40 cc toppar i USA, samtidigt som Okrasa själva sålde 42 cc i Europa. Min gissning är att man i Tyskland använde Okrasa-kiten som ett sätt att få vardagsbilen att prestera bättre på Autobahn-tjänsteresor, medan de i USA hamnade i en andrabil eller ett hobbyfordon. De Europeiska kunderna behövde helt enkelt mer tillförlitlighet och därför passade en mer moderat kompression bättre.

Detta reder ut en del av kompressionsförvirringen, nu återstår att reda ut mysteriet kring de högkompressions toppar i speciallegering som omnämns i de tyska prislistorna. Fanns de och vad var det? Någon som vet?

Enkel volymökning

Då kom den. Produkten vi väntat på. 80 mm slip-in cylindrar för trettiohästaren från AA pistons. 1287 cc rätt ur lådan med originalvev. Med 69,5 mm vev blir det 1397 cc och med 74 mm Porsche vev 1488 cc, precis som pre-A Porschen.

Men, slip-in lösningar har ofta en nackdel. Original ytterdiameter på cylinderfoten är c:a 81,8 mm, så med 80 mm borr blir det en väggtjocklek på mindre än 1 mm. Kanske tillräckligt. Kanske inte. Porsches pre-A motorer med 80 mm cylindrar hade problem med sprickor trots större borrning i blocket (förvisso var de i aluminium, men ändå).

Följ den spännande fortsättningen på thesambas vintage performance forum.

Edit 11 juni: Det börjar lukta "vapour ware" (alltså att man annonserar ännu inte existerande produkter för att kolla marknadsintresset). Ingen har dem på lager och helt plötsligt har specifikationerna ändrats. Nu är de inte längre slip-in...

Exhaust valves and the Okrasa head

My old Okrasa heads have now arrived from Danne in Västmanland, Sweden. He did do a valve job and a touch up of the mating surfaces for the cylinders. Aside from new valves, that were the only things needed to get the heads in good shape.

The exhaust valves became an interesting story. At first it seemed easy. The dimensions are the same as for the stock 30/36 hp valves. My first thought was to use stock valves. But, the exhaust valves were a source of trouble already on stock engines at the time, so a performance engine would require something better. Next attempt was to take a glance at modern replacement valves.

Looking at valve manufacturer IVAM's vast catalogue, the replacement exhaust valves offered for the 30/36 hp engine are made of a martensitic steel made for: "low stressed exhaust type engine valves". But, an aircooled engine with raised compression should not be regarded as "low stressed" in my mind. Thus, I decided to keep on looking

BBT in Belgium claimed that they had valves in a better material, but couldn't specify it more precisely. Finally I got them to at least try if they were magnetic to get some more information. They came back and said they were not. This means they are of an austenitic stainless steel, rather than a martensitic. Thus I assume they are of a quality described by IVAM as a: "steel widely used for high performance inlet and exhaust valves". Much better!

So, once again a package of valves got to travel from Belgium to Up North and then back to mid/southern parts of Sweden. For me BBT was the easiest option, but the valves for Wolfsburg Wests repro Okrasa heads are also made from a good austenitic stainless steel. Check with a magnet to be on the safe side, it's easy also for the vendors to mix them with standard valves.

Spacing the cylinders

As concluded in the last post, I did chose to use spacers under the cylinders in order to get the deck height right.

However sources for 30/36 hp cylinder spacers are not as plentiful as for the more modern engines. Wolfsburg West do sell barrel shims for the early engines up to 1.5 mm in thickness. But, to retain the deck height (69.5-64)/2 = 2.75 mm is needed on each side.

The only way to reach to this measure with WW's shims is to stack two on top of each other. Stacking means more surfaces to seal from oil leaks, thus a single one is a better choice. But, where to find someone who can custom machine a set with the desired thickness?

To my rescue came vintage VW tuner Mats from Östergötland, Sweden. He made me a set of four spacers with 2.7 mm thickness with perfect fit and finish. I now have 1.3 mm deck height, which is what I did aim for. Many thanks Mats!

Next step is to put in the Wolfsburg West extensions for the push rods.