Things seem a bit slow on the forums lately so I thought I would throw this out there. I am going to replace the Chinese Pro Comp cylinder heads on my 5.0 Miata next spring. I am looking to replace them with AFR 165's and have some port matching done by Big Dogs in Chicago. Do you guys think that I should be ordering these now or wait? My concern is the quality of the heads. I might not even be able to get them for a while anyway, I don't know. All I know is that I'm hearing all sorts of complaints about lifter and camshaft failures due to poor metallurgy. What say you? -Brad

 

Not a lot of folks actively building Ford V8 Miatas these days, most are going for the cheap and easy Chevy V8 conversion, their choices, not yours or mine. Have not done a conversion in almost 7 years, since I rescued "Frankenmiata" (the white one) from Alabama and the Smurf Blue one from Naples, Fl (friend of the family) both within a month of each other. Then the move southwards...I did swap a 2.5L Ford Duratec in to SWMBO 2006 Miata GT 6 years ago, but not quite the same. I've been looking for a chassis to do another, but Laguna Blue and Tan cars are hard to come by these days As for the heads, I'd wait and let someone else see what the next batch is like. Either that, or find an early set where someone is upgrading and go from there.

Bill S.

 

Bill,
Problem is the wheels turn slowly at BigDogs. I need to get the train moving if I want things back by spring. I am assuming that all of the AFR stuff is made here in the USA. Am I wise or foolish in that regard? I'm also assuming that the heads are ProComp because there is a raised portion cast in them that says 3037. I inherited this stuff when I bought the car. The engine builder is out of business and although I have located and communicated with him, he is slow to respond. He told me that the heads were Edelbrock E Streets but the only thing that I could find with that casting were the ProComs. Edelbrock also confirmed this. Would you trust that assembled AFR's from their factory are fitted with USA springs, valves, and all of the rest? -Brad

 

Hi Brad,

AFR stuff is good and will do the job for you 100%.
Porting is optional and not absolutely necessary.

AFR 165cc will flow 260 cfm at 0.6 in lift. Porting will lift that to around 300cfm. Which is better..but again depends on your ultimate goal. If you are shooting for over 400hp then port them. OR if simply upgrade to a 185cc head (my choice). It will flow 290cfm out of ther box..bolt on. Cost to upgrade to the 185cc is minimal over 165cc version. Port speed for intake velocity will be very similar and not be detrimental to throttle response.

Depending on cam selection the only thing you might want to do is upgrade the valve spring a little. Factory spring is 140lb on seat and 0.6in max lift..its OK. But a better option is a PAC #8019 spring with 155lbs on seat and 0.65 in lift max.

For me its the AFR 185cc bolt on with spring upgrade..as the best bang for buck for street 302 head from AFR.

Cheers