can I use a 405 head?

[canadiangt]

I am getting all of the final parts together for a megasquirt installation. Since I am going to change the head gasket anyways, I am wondering if I can use the 405 head I have laying around. It is a BCP, but I am wondering if anyone is using one and if they have had the problem with the head cracking or breaking. I know that it is 1.5mm larger bore and 2cc larger. I figure that you would have to cut the head .017" to yield the same c/r, but the head FAQ states that a cut head is very weak. is this under boost or under detonation? I would probably be running it with an A cam, advanced 4 degrees and the turbo exhaust valves. Would the reduced height and incresed lift make it an interference engine? How about if I used a K cam. I think I would only have the head shaved .010.
Any help would be appreciated.

 

[GTJordan]

Is this on a B23 or a B21? Which pistons are you using?

I plan on using a 405 head when I turbo my B23E, I'm going to use the K grind, and a set of B23FT pistons.


Of course I'll be using megasquirt, I"ve got a good 16000Km on it so far, and everything is going a-ok.

Jordan

 

[canadiangt]

I will be using a b21ft with a stock shortblock. Do you have 16000kms on megasquirt?

 

[GTJordan]

yes 16000Km on megasquirt.... down to -20, and upto 38degrees tempature range... Starts everytime, except sometimes it doesn't like to idle after start up, but thats because I havn't messed too much with after start warm up...

If you don't do somthing to increase the compression ratio, its gonna be very low. I don't know if I personally would like driving a car with that low of a ratio. you should maybe try a set of B21A or B21F pistons in there?

Jordan

 

[Canuckvolvo]

Matt Dupuis ran that set up for a while (405 on B21FT). I don't think he minded it, means you can run more boost!

 

[Captain Bondo]

I actually don't think Matt was convinced the 405 was a great idea on a street driven b21ft- if at all. i won't put words in his mouth though. Perhaps that will instigate a post or PM or somethnig from him.

I personally don't think a 405 is a good match for a B21ft if for no other reason than that the chamber diameter is larger than the bore diameter which is not ideal at all for many reasons (well 2 reasons- flow and squish).
I also thought we had put away the "let's lower the compression ratio way down and run MEGA BOOOST" theory to rest...

I would find an SCP head from a late turbo car and cut it 40-60 thou or run different pistons.

 

[Canuckvolvo]

All too true Kenny. All I was saying is, yes, it can be done and has been done. I'd tend to go the SCP route myself anyway- the tradeoff in CR using a 405 lose more power than any gains from the better flowing head.

C'mon CGT, might as well pull the block out and get it decked quick! Bring up the CR while getting better quench/squish...

 

[Guest]

If I did use a 405 head, I would have the coolant passages welded up slightly to stiffen the surface, machine o-ring grooves or use a CE gasket, do extensive porting on the exhaust and fit larger exhaust valves. The intake to exhaust flow on a stock head needs to be improved for turbo use and on the 405 head the imbalance (for turbo use) is even worse.

 

[Tuff240]

I'm running a b23ft with bcp 405 and so far (approx. 1500 abused miles) I love it. I o-ringed my block and all seems to be going well so far. It is still a bit early to tell if I'm going to have problems at higher boost levels though. I currently at 14psi.

You can see see all my specs on my website. ( www.tuff240.com )

Patrick D.

 

[mikep]

C'mon CGT, might as well pull the block out and get it decked quick! Bring up the CR while getting better quench/squish...

I agree, unless it starts an avalanche of spending.
As far as the lower compression idea, it does hurt off boost driveability, but it is the ticket for ultimate power(racing). I personally would never go below 8.5:1 on the street. Hmmm...wonder what my WRX has?
I guess you just need to ponder it a bit more, lots of good thoughts here.^

 

[Captain Bondo]

ON a B23ft I would say go for it- but the bore is bigger, the piston is larger and makes a larger squish area, and the edges of the chamber are not misaligned to the cylinder wall.

I would really think about those 2 points before proceeding.
Sorry to reiterate but they're fairly keynote issues.

 

[mikep]

ON a B23ft I would say go for it- but the bore is bigger, the piston is larger and makes a larger squish area, and the edges of the chamber are not misaligned to the cylinder wall.

Well stated

 

[canadiangt]

The question I originally asked was also if the cut head was signifigantly weaker than an uncut head. I figure that the head would need to be cut in the nieghborhood of .017" to yeild the same compression ratio. The combustion chamber is only 2cc larger and 1.5mm larger bore. if you cut the head or even .020, you would be decreasing the bore as well because of the taper. Tuff 240, have you done any mods to your head to run it on your car. I think that I would take the advice of porting the exhaust side of things. When you put the 405 head next to a b21 head you can see the huge difference in the intake runner size.