jspeeddemon

ttt

tomcat

Smitty: I didn't read your post carefully enough. But even so I think you're losing HP. I would expect about 625 HP with 4 psi boost. You needed 5 psi. I pulled out the dyno sheets I was referring to and read 844 HP and 806 ft-lbs @ 5500 with 8.5 psi boost. For you to get lower HP with higher boost just means that things are restricted after the intake plenum. I like your cam, so my money is on the heads not flowing as well as you'd like and the stock intake runners. If you look carefully at the lower intake you can see that the cross sectional area of the runners is reduced quite a bit below the flange. A single plane intake and some head porting would get you a lot in this case. I don't know about 100 ft-lbs, but a lot.

If you used the Holley EFI, you could eliminate a lot of intercooler plumbing pressure losses and get the same intake boost with a lower compressor RPM, lower temp, less parasitic loss etc. This is all good.

How good did you build the short block? You know if you get everything connected you're knocking on 1000 HP don't you?

WAGS382

To all looking for some good head,
I will be running my 1998 gen VI HP 500's (carb) on the dyno before I tear them down, they are stock except I removed the choke horn. They have 250 hours on them not too many at wot. They are in a 382 Fastech formula weighing 10,450# dry approx 12,000# with fuel and people. It now turns un-labbed 28" bravo one four blades at 5,000 rpm at 75 mph. I will post before and after dyno results. Jeff

cstraub69@comcast

Smitty,
Cam is part of the problem, you don't want any advance in a blower camshaft. . you don't need to open the intake valve early because you have a power adder. You need to retard the cam 4 degrees.

Chris

cobra marty

I have a brand new Hirel/Holley manifold, fuel rails, and 1000cfm throttle body. Is it worth $1000 to you?

articfriends

iTrader: (1)

Marty,i'm interested,sent you private message,Smitty

JimV

iTrader: (1)

Hi Jim:

Good point about venturi and valve size. I was trying to visualize this idea. When you have time could you comment on the following:

There are two ways to reduce resistance to airflow and they apply to cylinder heads like anything else.

1) Make the hole bigger. The hole can be venturi area or the area between the open valve and the seat. For lots of reasons we don't want a bigger hole than necessary, so the second method is usually the one we want.

2) Reduce losses through the hole. In my business we call this reducing the loss coefficient. In practical terms it means preventing flow from detaching from the wall and going turbulent.

Nowhere is this more important than between the valve and the seat, and in the area immediately before and immediately after the seat. Correct me if I'm wrong but isn't this where it's at for lower lift numbers and the main benefit of porting?

.......Yes, the area's closest to the valve/seat are the most sensitive. As far as low lift numbers (below .200) I don't believe they are as important because of piston position and cam overlap. There isn't much pressure in the chamber when the piston has moved a few degrees after TDC or BDC.

Once the valve to seat area is wide open at high lift, then maybe the "small" venturi becomes the restriction.

One thing I don't understand; do smaller venturis always give better low lift numbers than large venturis? Is this because the larger venturi creates a sharper radius into the valve seat on the floor of the port?

........Dealing in cylinder heads, usually the smaller venturi will flow more air because there is more distance between the valve and cylinder wall.

I like the idea of your wedges because raising the floor makes the short radius bigger. I never understood why Edelbrock/GM didn't raise the floor of the "square-oval" aluminum heads. If you're going to keep port volume small it makes sense to do it by raising the floor vs lowering the ceiling of the port.

........I don't understand that either. It shouldn't cost any more to make a high port oval port head. Thanks Tom!