Strange SBF problem ...

[Cfin]

I have a strange SBF engine problem I would like to run past you guys, its a long story ... will touch on the highlights to keep it short.

The engine started out as an owner freshened road course 302W, very basic build 165cc AFR heads, custom solid flat cam, headers,intake, carb etc.
It was delivered to us to break-in and then do some basic tuning, but had a "problem" (piston to valve clearance) so we pulled it down, re-cut valve reliefs and re-assembled. It went ok for what it was, but always had some blow-by.
A year later the owner decided it needed a piston and rod upgrade which we did .... broke it in and did some pulls on it, near identical numbers as you would expect. Owner installs in car, does a few practice laps and it picks up on two piston skirts (thrust sides). He tells me he's running 50W racing oil and I assumed probably lack of warm-up was the cause.
We rebuild with new pistons, break in and do a few power pulls ... send it back. He changes to 10-40, does a few laps and it does it again .... picks up 3 piston skirts this time ?? We get it back, go thru everything and don't find a definitive answer why.

After talking with the owner the decision is made to get a another block (last oversize) and build a 331. This time we get sent his custom made stepped headers, 4 into 1 design ... which were used in the two prior "upgrade" failures, but not on the very first freshened engine. They are space limited in the engine bay and as such the headers wind round/over/through each other .... a fabricators nightmare so to speak.
Anyway we break-in the engine but it just appears harsh, even with little/no load on it. We continue on and do a power pull .... its down a bit of what was expected, but the graph is full of small peaks throughout its rev range and pretty "untidy" looking.
The headers are unbolted and some old dyno headers put on, harshness seems to diminish/disappear and the engine makes more power virtually everywhere ??
Over-laying the graphs shows smooth curves with these headers on too and we thought the trouble may be related to the new headers and the fact the plugs leads run very close to some primaries creating spark issues ? We that in mind some heavily heavily insulted, sleeved, leads were tried but no improvement. The final nail in the coffin is the plugs ... a real mix of rich/lean on the new headers and much more even spread with the dyno headers.

To me the writings on the wall as to the cause ... but the owner doesn't like my answer.
Has anyone had any similar experiences ?? Anyone got any answers/theory to what is going on here .... the dyno headers are about the same length and diameter as his new ones but have no step.

[mag2555]

Back in this section you need to find the post headed “ Jon Kaase tips and tricks”and watch his video .

What he show’s about the first start up of a new motor with headers that have sat around a while was eye opening, at least to me!

The difference your seeing in plug readings could be due to smaller header tube ID at the flange to head allowing for more reversion, or rust scale in the header tubes making for such.

[rustbucket79]

Almost sounds like the collector merge is a mess, with the various exhaust pulses fighting each other.

My question to the owner is how can he argue with the results?

[Cfin]

mag2555 - Headers are stainless and are "new", so no rust issues.

rb79 - Yes I would agree that its something to do with the collectors, but it looks like a commercially made merge collector has been used ... which generally work well. However there is no reducing cone "venturi" after the collector that you generally see on those systems ... potentially the problem ??

IMG_20211006_201706.jpg

[EDC]

Crazy "looking" headers...

Interesting forward facing then rearward exiting configuration.

[BillK]

it picks up on two piston skirts

Just curious what you mean by that ?? I have never heard that term.

[Cfin]

Sorry Bill .... meaning gall's the skirts. No visible signs of detonation on the pistons though.

[Ericnova]

I bet Calvin Easton would tell you "too many bends, especially tight radius and more than 90° is the problem", and I could see that being a factor.

Lets see a pic of the dyno headers?

that's a crazy looking monstrosity of a header, got to be a better way than that.

[Cfin]

Yes Eric .... they are a monstrosity of a setup alright, apparently you can't even get the plugs out when they are in the car ....

Dyno headers are nothing special, but a much more friendly design -

IMG_20211010_184716.jpg

[Cfin]

I have a new theory on whats going on here ....
Talking with the owner again and he tells me they cut the outlet ends back on the merge collectors as they needed to room to turn the end pipes downwards.
After doing some measurements, the end of internal merge part of the collector is only an inch or two ahead of where the collector outlet pipe's down-turn starts .... if you look back at the pic you will see what I am getting at.
I am thinking that maybe the two upper pipes of the merge collectors are "seeing" a larger area/void at exit (the outside radius of the down-turn) whilst the two lower pipes of merge collector are "seeing" a much smaller area (the inside radius of the down-turn) .... due to the collector and down-turn being so close together ??
Think I will try cutting that down-turn off and putting a straight pipe on there and see what happens ...

[mag2555]

The old tried and true practice that has served me well of painting a collector extension with cheap enamel paint and then cutting the collector shorter 2 inches passed where the paint has started to burn off will put you well in the ball park of the overall length that is needed.

A major key to getting this right is to fire and run the motor while the paint is still wet!

If the motor is to make its peak power above 5500 and run mainly above 5500 also then cut the extension right where the paint first starts to burn.

[Cfin]

Just a follow-up post to this problem.

We got the pieces sent to us that were cut-off the merge collectors .... they were reverse cones and around 5" long. Cut the down-turned collector pipes off, tacked the cone back on and put a straight piece of collector pipe on that.
Gave it a warm up and engine appeared to be happier .... so we gave it a trial pull. It picked up 15 - 20ft/lbs everywhere and the pig rich/white lean coloring on the plugs appears to be fixed.

Prior to this little lesson, I wouldn't have believed headers could have such a dramatic effect on the running/tune of an engine .... you get "good/bad" headers output wise, but they don't threaten to destroy the engine itself !! Lesson learned ....

[Walter R. Malik]

I have a strange SBF engine problem I would like to run past you guys, its a long story ... will touch on the highlights to keep it short.

The engine started out as an owner freshened road course 302W, very basic build 165cc AFR heads, custom solid flat cam, headers,intake, carb etc.
It was delivered to us to break-in and then do some basic tuning, but had a "problem" (piston to valve clearance) so we pulled it down, re-cut valve reliefs and re-assembled. It went ok for what it was, but always had some blow-by.
A year later the owner decided it needed a piston and rod upgrade which we did .... broke it in and did some pulls on it, near identical numbers as you would expect. Owner installs in car, does a few practice laps and it picks up on two piston skirts (thrust sides). He tells me he's running 50W racing oil and I assumed probably lack of warm-up was the cause.
We rebuild with new pistons, break in and do a few power pulls ... send it back. He changes to 10-40, does a few laps and it does it again .... picks up 3 piston skirts this time ?? We get it back, go thru everything and don't find a definitive answer why.

After talking with the owner the decision is made to get a another block (last oversize) and build a 331. This time we get sent his custom made stepped headers, 4 into 1 design ... which were used in the two prior "upgrade" failures, but not on the very first freshened engine. They are space limited in the engine bay and as such the headers wind round/over/through each other .... a fabricators nightmare so to speak.
Anyway we break-in the engine but it just appears harsh, even with little/no load on it. We continue on and do a power pull .... its down a bit of what was expected, but the graph is full of small peaks throughout its rev range and pretty "untidy" looking.
The headers are unbolted and some old dyno headers put on, harshness seems to diminish/disappear and the engine makes more power virtually everywhere ??
Over-laying the graphs shows smooth curves with these headers on too and we thought the trouble may be related to the new headers and the fact the plugs leads run very close to some primaries creating spark issues ? We that in mind some heavily heavily insulted, sleeved, leads were tried but no improvement. The final nail in the coffin is the plugs ... a real mix of rich/lean on the new headers and much more even spread with the dyno headers.

To me the writings on the wall as to the cause ... but the owner doesn't like my answer.
Has anyone had any similar experiences ?? Anyone got any answers/theory to what is going on here .... the dyno headers are about the same length and diameter as his new ones but have no step.

The reality is ... getting full time oiling with no drastic fluctuations, which many road race wet sump systems will not accomplish, can become a nightmare.
This is not Ford related.

Also, header length and tube sizing can make a huge difference in power and the application of that power ... intake manifold design also can make a huge difference and the way they work with each other can make a huge difference