Don Terrill’s Speed-Talk

May be I can do a better job of explaning what I mean here.
I have had two peticular motors where this that I will describe took place.

Motors I had built came back for a freshen up which entailed nothing more then a re-hone / re-ring and I valve job.

The valve job increased the low lift flow on both heads from when they first went out the door on these motors ,but the peak flow did not change, but it came in at .050" lower lift.

On both motors peak power was a just a tad better, like within the accuracy range of the dyno, but also it was very clearly seen once back in the car that the rpm point of peak power came down 200 to 250 rpm from what it had been even though peak port velocity had not changed.

Both of these motors where able to make use of the added low lift flow, if perchance your motor can not make use of greater low lift flow or let's say too much curtain area at a given rpm then the end result is to move the power band up more .

This was before and after testing on an engine dyno ?
This test was done to 2 different engines ?

You said within the accuracy of the dyno, but rpm was down in the car ?

Or was this on a Butt dyno ?

Randy

mag2555 wrote:Many times you just have to see what the motor wants in regards to where in the rpm range you want the power band to have the most girth!
Have more low lift flow Intake port wise will always drop the rpm where the port becomes velocity blocked because your already moving more air thru the port earlier at a lower lifts, that is if the motor can make use of the added low lift flow.

Excess air flow available before the descending piston gets to within 75% of its peak FPS down the Bore can at times buy you nothing power wise!

A couple questions here regarding the above post and then your post about the two engines that lost 200 rpm after the valve job.

1. Have you questioned if those two engines want a little less port velocity since the increase in port speed from a sooner peak flow (.050) took 200 rpm off the top?

2. Did the ssr play any part in these two engines by beginning to develop flow problems around the max lift area, as in is it possible on both engines with increased flow sooner they began to let go and that's why it stopped .050 sooner than before even though the numbers were higher and max flow was the same.

3. For the quoted post above, I'm not saying it's wrong, but I think that when when the intake valve opens its good to have as much flow available as you can to help get the cylinder filling going. Also, on the other side of the mountain when the valve is on its closing ramp why wouldn't there be a benefit to good available flow potential there as well? I do realize these lower points are not where the majority of filling is happening and are not as important on high lift engines but to say sometimes they buy you nothing is hard for me to imagine. So, can you explain how it could have no effect on the time at which the intake valve first opens and how on the closing side these numbers can add up to zero hp? Again, I'm not saying your wrong, I just want to understand how this is possible in the engine assuming the cam events were correct?

Edit: I see you're talking about fps getting too high sooner in the cylinder filling causing no power gain. Sorry I did not catch that the first time.

The good flow numbers at low lift and good air speed and its inertia allow the piston to move upward on the compression stroke further before the flow into the cylinder drops. Of course if a cam with too much over lap is selected a lot of power can be blown out the exhaust.

turbo2256b wrote:The good flow numbers at low lift and good air speed and its inertia allow the piston to move upward on the compression stroke further before the flow into the cylinder drops. Of course if a cam with too much over lap is selected a lot of power can be blown out the exhaust.

Yes, when comparing results for heads with 'good' low lift flow vs. 'poor' it's easy to overlook the interaction with overlap. If valve events are well matched to head 'A', they may be sub-optimal for head 'B', leading to mistaken conclusions re LLF effects.

Many negative comments on milling out the guide boss made me work on leaving it in. Stalled at 166 cfm down about 15 cfm from my first design.

66 289 exhaust port since these are a bit down on intake flow they need all I can give them as far as exhaust flow. So mill em out. Lost.1" guide support to 2.1" but gained .1" roof to ssr height. Roof still .2" thick!

I should mention with guide boss at .7" lift and 1 5/8" pipe 190.5 cfm and same lift with 1 7/8" pipe 201.4 cfm. Hopefully new flows today. Input welcome. Thanks, Charlie

These are the 65 289's with 1.85"/ 1.6" valves I keep goofing that up. Sorry

65 289 exhaust not finessed. This is actually a bit different than my first exhaust ports on the 66 heads. Taking a lesson from Bill C's cnc head it has a smaller bowl which during testing was much stronger than my exhausts in the mid range and gave up a small amount of high lift flow. Thanks, Charlie

229.1 cfm .7" lift intake 1.85" Manley with single backcut
174.5 cfm .7" lift exhaust no pipe back cut and rad. Face
192.6 cfm with 1 5/8" pipe .7" lift
204.4 cfm with 1 7/8" pipe. .7" lift
Calling it done.

Good job!

Thanks Bill. Terrified of cutting that ssr too thin so gave up a bit for durability. Started to separate at .75" lift.

After those heads make their way to David.. you getting them back Charlie? Since they were original heads on my 289 boat motor.. maybe they can end up going back on.. that would be cool... nice work you did there Bud..

Old as Dirt wrote:After those heads make their way to David.. you getting them back Charlie? Since they were original heads on my 289 boat motor.. maybe they can end up going back on.. that would be cool... nice work you did there Bud..

That would be pretty cool. There is a list of people who wanted these ported heads after the competition I can add you on.

Old as dirt, that little boat would be some fun with a near 450hp 347 cube smallblock! Thanks for the kind words.