I called about ordering a cam for my set up and the people at comp cams say that the AFR 227 will be too much for my set up.
Is it possible that a set of AFR 227 will NOT help me????


396 ci LT4
ATI D1 w12 psi
195 AFR heads
and...............................................

 

F-bud: I would not recommend AFR 227's for a street blower application. If you are building a race motor that will occasionally see the street, it's one thing. In that case, get a big solid roller and hang on! But if you want something less exotic, stick with the 195's. You can make big power with even a small cammed SC car and these heads. You need the big intake ports to make hp on an NA car, but this is not as important with a blower. So why put up with the potential disadvantges and the cost?

Rich Krause

 

i agree with Rich. fully ported 227s are easily 235-240cc when ported.. too much for a sub 6500rpm smalll cube motor.

The 195s will go to 220 pretty easy, and flow around 300cfm with out too much fuss. that would be where I would spend my money- good porting on your heads.

 

Wouldn't having such big ports hurt velocity and lower lift flow, needing such a big cam to offset it??

 

big ports willl probably flow more at lower lift also. however velocity will be very low, and you won't get as good cylinder filling.

 

This is a "RACE" car that will see the street, but i have absolutly NO concern about drivability and "LOW" end power. What will the loss of velocity do??? He also said that a larger runner will lower my boost levels, but my question is that the amount of boost that reads on the gauge is actually back pressure, and increasing the runner size and valve size should increase the flow and lessen the back pressure ??????, BUT does that automatically mean MORE power ?? I am struggling to understand this issue and how it will effect the power.

Also, is a 396ci motor considered small?? and i shift the car at about 6800 to 7000 rpm....does that matter??

396ci
solid roller cam
ATI D1
T56 w/ Mcleod
58mm NOS TBI
AFR 195 (or AFR 227's) LT4
9" rear 3.70:1

 

In the sbc world a 396 is mid sized but with the LT1 bore size max it is pretty large. With the use of bore sizes in the 4.125 and larger it can really take heads with 2.10 valves better as to not shroud the valves.

I go on the same thinking as you do with the heads though. If it takes less pressure to force the air in then it will inherintly make more hp (more air+more fuel has to =more power) I had choosen afr 220's With the use of 2.08/1.60 valves for my combo thinking this as well as talking to people i respect on this issue. I look at it like this. If small heads are so great why would anyone run anything but a stock casting with some mild clean up? Now i know that is an over generalization but still. I feel if you don't go overboard on the valve size you will make more power. cause of the lack of back pressure.

Of course this is just my .02.
Steven

 

To a point.....increasing the runner size and valve size only increases the flow of a head marginally. To really see the gains in flow you need a good porter to do that

Yes, if you port your heads and get more flow out of them your reading on the gauge should be less because your motor is efficiently using that airflow and not backing up into the intake registering as "boost"

 

To take advantage of a set of ported 227cc castings you should consider a "high rev" setup. Big cam and a blower setup to give the desired boost in the 6,500+rpm range. Off boost at low to medium rpm, this combo will not run very well. But you can make big hp with boost at the right rpm.

Rich krause

 

Yes.. Yes.. to Richard Krause you listen...

That is why I chose the 190's... I know that they should be around 205's cc. I saw a well ported stock heads and they dont look as good as my badly ported AFR's.

Anyways...

The thing with such big runners is that at low piston speeds the engine will create less vaccum inside the cylinder to actually fill correctly the cylinders thus not having enough speed with such big runners... That is why in part throttle and off boost it will not run as good... There is an advantage though with such a long stroke as the 3.85, since it provides more piston speed.

If it is a race engine, then I see why go upstairs in the rpm range and not care about the driveability...

I think choosing a right cam is criticall (well, always) to make the best out of the heads.

 

This forum is GREAT because of guys like YOU ALL, you take the time to help others in need (like ME ) and i always appriciate it, THANKS.........................



So lets continue....cause it looks like it is too late to change my heads (already being done by AFR). So i have to make sure that i make all my other decisions RIGHT!! So i am back to the question about the cam...should i go with the one that krause suggested or should i make some changes????? There is another post is this forum that has this topic with all the info.

I hope i am not being too much of a burden, i just dont want to put this thing together and find out i should have done something different.

thanks again to all those that offered their opinion!!!!!!!!

 

go with a solid roller that will shift around 7k, and pulley the blower accordingly.. and you will probably be ok. not 100% optimum, but it wil be fast

 

James, how much compression will you be running with this setup? What gear ratio do you think will be necessary to put you where you want to be with the kind of mph you will possibly be seeing? (140+ is my guess) What about finding an appropriate location to mount the chute???

 

The advantage of smaller volume runners/high velocity is that even after the piston stops generating any noticable depression (dependent on piston velocity and area) the inertia of the air column will continue to force air into the cylinder - the intake valve will typically stay open to even a bit past BDC, so there is always opportunity for this. If you had a flow sensor hooked up to your intake valve seat you would want to keep the valve open as much as possible until the air velocity goes to zero, then slam it shut - this would be maximum cylinder filling.


Now with a blower the positive manifold pressure is normally a good bit more "potent" than the inertia of the airstream, so volume isn't as critical - though especially on the bottom end - or any point where you aren't at significant boost, the car will run much worse - but once you have significant pressure flow becomes probably more important.

If you already have the heads ordered and spec'd setup your blower so you are making as much boost as soon as possible - this will overcome lower end problems


Chris

 

I agree with Jordan.

What engine management system are you going to use? Keep in mind the limitation of the stock PCM (<7,000rpm). You are in a kind of conundrum with the parts you want to stand up to boost (strong, but heavy) and those that like high revs (light, but strong). The best solution to this is $$$$. How long is ok between rebuilds?

Rich Krause