Help!! Better flowing heads and a better intake and less speed!!
 

Got my dads SBC running good today and I am still yet to see the 6000 RPM we use to get out of the old chevy heads and the obsolete holley strip dominator we ran last year. The old heads were GM angle plug Bowtie cast iron with 2.05" intake valves and 1.60 exhaust. These heads have 180 CC intake runners with no porting. The flow numbers are as follows on these.
.2 124 119
.3 176 149
.4 216 163
.5 230 171
.6 236 179
.65 236 179
We are now running some 200 CC Pro Topline heads. I will post the flow ratings later since the numbers are in the shop. These heads have 2.02" intake valves and 1.60 exhaust. The new intake is an Edelbrock Super Victor #2925 and is supposed to be about way better than the old strip dominator. In the Edelbrock catalog they claim a 43 HP increase from the intake alone on a similar engine. The cam we are running is a 246/254 @.050 on a 112 + 4 install with .592" int/.555 exh. and is the same stick as last year. One thing I noticed is the runners on the new intake are quite a bit smaller than the old Strip. Also the motor has a stronger midrange and seems to pull harder to about 5500 RPM than last year. So do I need more cam? Maybe I should prop it down and try to turn 5500 and see if it is faster there. The boat did 82 MPH at 6000 last year pretty regularly. So far 5900 RPM is about all I can muster with these new hi-flo parts. Let me know your thoughts.

Here are the Pro #'s
 

.2 134.32 100.99
.3 191.63 156.94
.4 235.96 176.85
.5 260.98 186.34
.6 268.51 190.13

The motor is a 358" SBC with 11.5:1 compression. Both heads have 64 CC comb chambers and are iron. We run a Holley 800 DP that has worked great for years and is unchanged from last year. The only change- BETTER heads and intake and so far no more power or speed.:( Thanks for your replies.

You may have better flowing heads & intake but it probably moved your HP peak higher

Maybe the heads and intake are not the limiting factors. ( cam or exhaust)

Glad to see you got it up and running. Sounds almost what I am doing. My peak hp moved up and to get that I have to go down a pitch or two to get my rpms needed. Still have to find a prop.. Right now I am only spinning a 24" at 5000 rpm. Hopefully a 23 or 22 will get me around 5500. I didn't gain much with this high $$$$$ motor, I am guessing around 6-7 mph as of now. Just enough to go by my dads boat and my uncles boat... :D I am still not to happy with it. I thought it would spin my 25 mirage over 5500 and it would barely turn it over 4400 :(


With those 200cc heads and that cam.I would think it would have to be spun up to around 6500 to get max hp.


Just my 2 cents bro..

What about carb jetting?

Possibly a different flow characteristic is giving you a leaner mixture. I have seen this on an automotive engine after switching to an exhaust with better scavenging.

Thanks for the replies. I also thought the HP would move up a bit. I just hoped to be able to spin the same prop 6200 or even 6300 as opposed to 6000 RPM last year with a nice speed gain. The motor has CMI E-Tops for exhaust. I haven't yet gotten into jet changes, but from initial plug readings it looks pretty close. What is boggling to me is the low end and mid range are far better than last year. The motor pulls hard out of the hole and is to 5000 RPM much quicker than the last year. All of our tests have been with the same prop we ran last season. So this creates the conflict for me. Bigger ports and better flow and the same or less top end and more mid range to low end??? Well before we do anything drastic we are going to try some larger props to see if there is more speed at lower RPM's. If not we will put a bigger stick in there. This current solid roller is like a ***** cat idleing and cranking pressures are 200 PSI. Keep the thoughts coming!!! Hopefully I am just missing something simple.:D

Forget HP and think about what you did to the TQ curve, If you didn't move the TQ curve higher you won't go any faster.

Yeah Vette!----what a dummy!!! :crazy: :rolleyes:
You have been officially bared from the OSO club!




















;) :p :)

It sounds like your flow velocity has changed due to the updates. This is giving you more torque at lower rpms. However at some point the velocity slows and you run out of torque. You might have better results with a bigger pitch prop and turning the lower rpm number, but that carb will not take advantage of all the velocity you are making, it's kind of big for that engine.