B20 38.5 ventiler / porta

[Ben_Flierman]

Hello Swedish volvo guys! I heard from people at amazon.forum.bilia.se that there is a lot of knowlegde on engine performace on this forum, I'd like to ask some questions. Since I dont speak swedish, I'll try english.

Question 1:
I've currently got a late B20A head with totaly worn exhaust valve seats. So in order to be able to use it, it needs hardened valve seats put in.
The intakes on the head are the larger 44 mm ones, and look just fine. For the exhaust I could just re-use the 35 mm valves, but I started thinking I might go a bit bigger. I have some volvo 38.5 mm exhaust valves lying around, which I'm tempted to use...
My question is: would that be a good idea? Offcourse I will also work on the port, but it will not be a fully ported race head either, just some basic porting. Will the 38.5 valves work? Or should I perhaps get some 37mm valves? Compared to the 44mm intakes, 35mm exhausts seems like a small valve / ratio to me. Any opinions / experiences?

Question 2:
The early B20A heads have a very low exhaust port floor all the way to the manifold surface. The late B20A and the injected E and F-heads have a somewhat higher port floor at the valve side, which goes down to 'normal' height again at the manifold surface. The late heads therefore have -at least some- short side radius.
My question is: which one would flow best? And should you grind away the thicker port floor on the late type heads, or leave it? Do you guys have some general tips on how to port a B20 head, and what to do, and what not to do?


Thanks in advance!

Greetings from Holland, Ben

[Jens Gustavsson]

Jag ska försöka svara på dina frågor men jag gör det på svenska (tyvärr var jag inte så aktiv på engelskalektionerna).

Question 1:
I've currently got a late B20A head with totaly worn exhaust valve seats. So in order to be able to use it, it needs hardened valve seats put in.
The intakes on the head are the larger 44 mm ones, and look just fine. For the exhaust I could just re-use the 35 mm valves, but I started thinking I might go a bit bigger. I have some volvo 38.5 mm exhaust valves lying around, which I'm tempted to use...
My question is: would that be a good idea? Offcourse I will also work on the port, but it will not be a fully ported race head either, just some basic porting. Will the 38.5 valves work? Or should I perhaps get some 37mm valves? Compared to the 44mm intakes, 35mm exhausts seems like a small valve / ratio to me. Any opinions / experiences?

Det är lika bra att sätta in 38.5 mm ventilerna när du liks ska fixa säterna, B20 avgaskanaler är svåra att få att flöda för mycket.

Question 2:
The early B20A heads have a very low exhaust port floor all the way to the manifold surface. The late B20A and the injected E and F-heads have a somewhat higher port floor at the valve side, which goes down to 'normal' height again at the manifold surface. The late heads therefore have -at least some- short side radius.
My question is: which one would flow best? And should you grind away the thicker port floor on the late type heads, or leave it? Do you guys have some general tips on how to port a B20 head, and what to do, and what not to do?

Den här frågan är lite knepigare att ge ett enkelt svar på, men med snällare kammar som lyfter under ca 11-12mm så fungerar de nyare högre inner-radie-kanalerna bättre, man ska också använda mer konformade ventiler. På fullrace-toppar med mycket höga lyft, ca 13+ mm, så kan man få gasflödet att gå snett förbi ventilen på höga lyft med platta ventiler då portar man oftast bort ganska mycket i inner-radien så då fungerar gamla toppen lika bra om man har samma typ av förbränningsrum.
Men om jag var dig så skulle jag köra med en nyare topp och 38.5mm ventil och tre vinklar: 45 grader 1.5mm/60 grader 2mm/75 grader som portas/fasas mot kanalen som ska vara ca 33-34 mm under ventilen och med 3/4 borttagen ventilstyrningsknöl. Kanalen ska inte förstoras i den raka delen ut mot grenrörspackningen, inner-radien ska bara göras lite mjukare. En sådan kanal flödar ca 130-140 cfm/28tum. En lätt portad insugare med snygga säten och 44 mm ventil flödar ca 155cfm. Tillsammans blir det en fin topp med bra bottendrag som räcker till ca +160 sug hk, men fungerar också bra på en snällare 130hk motor. Lycka till!