WETTE VETTE

Good things to ponder as we continue to look for more. Just to be the devils advocate is it possible the motor wants more carb? Let us say the heads and intake are flowing better, and that is why I have noticed more low end and mid range punch, even with larger ports. Now when the motor gets to say 5500 the restriction is actually at the carb. I know an 800 sounds large for a small block, but the boat comes out of the hole with a Ski Nautique until about 35 MPH where we leave the Nautique in the dust. As for the torque curve moving most cam experts say more head or better flowing heads will generate the same peaks with less cam. I know AFR says this in their head catalog. Basically with the cam being the same and the flow increasing I figured the peaks would also increase slightly up in RPM. Maybe I am mistaken. Keep the ideas coming.

Turbojack

I went from merlin VR heads to AFR heads this year. Only change, in running desktop dyno with the better flow heads the torque curve followed the old one but continued on up 500 rmps past the old one before peaking. The HP peaked 1000 rpms above where the old peak was. I just changed desktop dyno from forced induction to single plane manifold & the torque & HP peaks did go up. So I will say your torque peak & HP peak has increased.

Now for your problem. Gas from last year? Timming right? Plug gap to big now with the more air flow? Carb to small, I would say no but ??? While I was typing this I was thinking about the carb being the main restriction & then it hit me. What about your exhaust. If you can not get the air out, it does not matter what you do to get it in you still got to get it out.

WETTE VETTE

All good points Turbojack. The fuel is fresh 110 octane leaded, which is the same type we always run. Plugs are gapped at .035" and the exhaust are CMI E-Tops. I moved the timing everywhere from 34 to 42 in 2 degree increments and 36 and 38 perform the same and better than the other settings. I am really wondering about the intake manifold. The old Holley had larger cross sect to the runner which leads me to think the new Edelbrock is more restrictive. This could possibly explain the good low end and mid range. Anyway we are gonna try some things nd if need be I will put the holley back on.

JimV

iTrader: (1)

Are the new heads modified as far as port work?

WETTE VETTE

JimV
The Pro heads are out of the box and the flow nombers are from their website. We are really leaning toward the new intake as being a factor to the lower top end. As I stated the Edelbrock 2925 has noticeably smaller and longer runners than the Holley Strip Dominator we ran last year. This may be the reason for the stronger mid range and low end, despite the larger runners on the Pro heads. The bigger runners in the Holley manifold may be beneficial at 5500 plus RPM's. Anything else anyone has to add is certainly welcome. A cam change is in the future, but only when I see the performance at the same levels or better than last year.

Turbojack

I would put the old manifold back on. Then see if there is a difference. At least changing manifolds is a lot easier than changing heads or cams.

mopower

Take any given cylinder at any give speed , and it will require a certain amount of air flow.OK? Now , if your heads and intake ports are bigger and flow MORE than the engine is pulling , the velocity will go down. By sizing down the ports to match the flow requirements of the cylinder you will increase the velocity of the incoming charge and can actually overfill the cylinder. By increasing the velocity to an optimun rate , what happens is the incoming charge backs up against the intake valve while it's closed due to its momentum, and when it opens it's forced in(almost like mini super charging it).
This way you can get more charge in the cylinder than you would if you had a port twice the size and with less velocity.
The result is less power

I'm not called "mopower" for nothing

Case in point , I had a 540 Ford with Trickflow aluminum heads. The engine was cammed for 5000 rpm ( round .600 lift) and the ports were WAY big. On a flow bench , you could open the valve to .600 and fill close to the bottom third of the port with clay and not effect flow numbers. The results were increased velocity.
Now if this was a drag engine and got spun 8000 rpm it would be a whole different story. Then those BIG ports with BIG flow numbers would come in to their own and make power

Hope this is a help

WETTE VETTE

Mo,
I totally agree but then why does the motor have such good low end torque with the new heads and intake and is only lacking on the big end? If anything I would think the lower velocities would really hurt the bottom and mid range more than the top end, especially at 6000 RPM with still relatively small 200 CC runners. That is why I think the new intake, which actually has longer and smaller runners than the old is hurting the top end power and helping the low and mid, and now the heads are not the restriction at WOT so there is no gain from the better flowing heads. Good thought and you may be correct. The old intake will go back on with the new heads and we will know for sure.

mopower

Wette,
The longer , smaller runners could be giving you the good bottom end by increasing velocity down lower and also hurting the top.
There's a lot of home work to be done to get just the right combo.
and bigger isn't always better.
I'm running dominators on my 540's which are worth more power upstairs but I know they hurt my low and mid range response. I could do better with a little less carb , but lets face it , my Formula is no drag boat

Besides...they look neat

WETTE VETTE

Yea I know what you are saying about the Dominators. I run one on my 498" BBC in my boat. Actually it is a stage 5 1050 that flows like 1175 on the bench and I run ported 325 CC heads, both of which most people on the board would say is to much. My boat with the dominator and big ports does everything well with no noticeable effects of being over carbed or to large of heads. My dads SBC on the other hand has the right runner size in the heads I am pretty sure, but the smaller intake runnere are actually hurting top end despite a 45 HP gain on top end CLAIMED by Edelbrock over the Strip Dominator, which is what we ran before. I will test this theory soon and let everyone know. If it does turn out to be the new intake holding this little mouse back Edelbrock will be black balled from my pits for false advertising.