Oversize Valves On 96 Cobra

[svt_steve_svt]

Should I go with .5mm oversize valves on B heads? Will machining be necessary if so? My build is N/A with aftermarket cams, stock bore, and a completely forged bottom end, CAI, BBK Throttle Body, catless x pipe, flowmasters, 42# inj, 03 cobra fuel pump, running on pump gas.

 

[01yellercobra]

My understanding is over sized valves don't really gain much on stock bores. The valves are already close to the side of the cylinder. Going bigger just puts them closer and causes more shrouding.

 

[svt_steve_svt]

So I shouldn’t go oversize? And should I get the heads ported? Polished? Or just leave them alone?

 

[01yellercobra]

I would still get the heads ported and polished. But I wouldn't bother with the over sized valves at this point.

 

[DSG2003Mach1]

is the motor still apart in all this? if it's a forged bottom end are you gonna throw some boost at it?

I realize B heads might be different but on my C head car the response was pretty unanimous to just up the boost a little and save the porting money

 

[svt_steve_svt]

Well I originally wasn’t going to go the boosted route, I had a boosted car before and I wanted to try something different. And yes the motor is all apart, it’s just a short block at the moment. I was just wondering about the heads because I know they already have really high flow and was wondering if porting would potentially result in less power on an N/A car. And I’m not sure if I can run boost reliably with the compression ratio I should have with those pistons.(9:1 btw)

 

[DSG2003Mach1]

Well I originally wasn’t going to go the boosted route, I had a boosted car before and I wanted to try something different. And yes the motor is all apart, it’s just a short block at the moment. I was just wondering about the heads because I know they already have really high flow and was wondering if porting would potentially result in less power on an N/A car. And I’m not sure if I can run boost reliably with the compression ratio I should have with those pistons.(9:1 btw)

gotcha. I would have to imagine you could gain something from it but I really don't know what.

9:1 is really low and would be plenty safe, if anything it might be a little lazy (especially with a centri)

 

[svt_steve_svt]

So you think it would be worth it to go back boosted? Or could I make some decent power N/A like this?

 

[01yellercobra]

If N/A is the ultimate goal I'd bump the compression up to at least 10.5:1. Local guy had his at 11:1 on 91 octane, but it was a two valve. It moved though.

My opinion is every little bit helps with N/A set ups. But you also have to be realistic. If you want more than 450 you're going to need boost. The guy that bought my old 01 Cobra had a nasty N/A engine to put in it. High compression, high rpm, lopey idle, etc. I think it made 435rwhp. But with his set up it was a mid 11's car in the quarter.

 

[svt_steve_svt]

Okay, boosted again it is then. Thanks a lot for your input man