Effects of too much cam advance?February 11 2018 at 7:15 PM
|Chillymerc (Login chillymerc)|
Way back in 2000 I had a 390 rebuilt, going in my F250 at the time. Machine shop asked if I wanted it advanced, knowing it was going in a truck. What I didn’t know back then was many cams are ground with 4* or so advance included
So that motor ended up in my 63 Marauder, runs ok but I was never really happy with it, chassis dyno’d right at 300rwhp, so a 350-360hp combo. Seemed weak for performer rpm intake, bowl blended edelbrocks, headers, 270H....but Barry dynod almost the exact same combo and his numbers and peaks jived with mine so I lived with it.
Tearing it down to repaint and get gaskets in it as it’s leaking from every possible junction, picked up a set of BBMs and a small roller as well. I degreed the cam tonight just out of curiosity and to brush up on using the wheel as it’s been a long time. So it’s advanced 8* to a 102ICL. My understanding is this would generally help a low compression deal, but is there a point of diminishing returns? My guess is this is like carb spacers, lots of variables and you have to experiment to determine what’s best. I think I’m sticking to running the roller at 110LSA 106 ICL, any thoughts?
4° ahead is a safe place to go.......n/m.
|February 11 2018, 8:18 PM |
more low end, peak hp down 14
|February 11 2018, 8:35 PM |
I had your combo in the Gonkulator database already.
Gonk says, at 4 advance or 106 ICL
Torq 340 at 2000
Torq 444 at 3800
Powr 409 at 5200 gross, 350 net, 312 rwhp, close to what you saw.
8.61 at 82.2
13.41 at 103.6
Geez, I'd be happy with that from a 2-ton street Merc!
Ok now lets advance it 4 MORE degrees to 102 ICL
Torq 349 at 2000 +9
Torq 438 at 3700 -6
Powr 395 at 5100 -14
8.65 at 81.6
13.49 at 102.8
So yes, it was advanced "too far", but I'm not sure I would feel that with the buttmeter, less than a carlength diff.
Mainly with that much advance you risk more spark knock down low.
Run the compression numbers and see....
|February 12 2018, 2:35 AM |
If the compression will allow it, I'd run that thing 6-8 degrees advanced and not think twice about it.
On a lot of my street combos, I have the cams ground 6 degrees advanced and I have not seen horsepower suffer because of it. Sometimes it's quite the contrary and you can tell that an engine is more efficient as you will keep pulling fuel out of it in comparison to other similar combos. In lower compression engines, DCR will go up, which means power goes up.
Honestly, I don't think you'd lose any horsepower at all (and may gain), but would definitely gain some low-end snap and throttle response.
Take a few minutes and take some measurements. I believe those were my BBM heads, so the build sheet should have a chamber volume on it. Should be easy to measure how far the pistons are down, get the volume off the pistons, and go from there.
My custom camshaft too, right? Post the specs and I'll help you sort the combo out.
|February 12 2018, 3:03 AM |
The pistons average .018” in the hole, specs on the 2291s show a 10cc volume, I had it at 9.14:1 with a 1020 gasket. Brent they are your heads, CC wasn’t listed on the spec sheet. The cam, I believe, the guy got from Barry, it’s a 224/230 110lsa .563 Comp. The guy I bought it from had mixed up some of the parts and who they came from so took awhile to sort it all out, he had another cam from you so that’s what you’re thinking of (good memory)
Was it written on a deck surface?
|February 12 2018, 3:08 AM |
I'll see if I can look through my notes and find it. I usually write it in Sharpie on the deck surface and then record it on the build sheet.
Do you have advertised duration numbers on the camshaft?
With pistons .018" in the hole, I wouldn't use a 1020 gasket. The resulting .060" quench distance will hurt you more than anything else.
|February 12 2018, 3:15 AM |
I didn’t see it but I’ll double check. I have another thread below trying to find some thinner HG, agree it needs to tighten up the quench. It ran fine and never pinged with the advanced cam and loose quench but I’d like to optimize what’s there
|February 12 2018, 10:02 AM |
I checked again, it wasn't written anywhere. They've passed through a few hands so could have been cleaned off. If you happen to have the CC in your notes, great, but if not no worries.
Well, I've dropped the ball on this one....
|February 12 2018, 12:44 PM |
Just checked head sheet on them, didn't write it down there either.
You got a way of cc'ing a chamber?
That camshaft you have is not too small, especially not with a 290 cfm cylinder head. It will be fine and you can probably roll her on ahead and help things out a good bit.
Re: Well, I've dropped the ball on this one....
|February 12 2018, 12:57 PM |
I don't have the tools required to CC but I can get them easily enough, it'll be good to check them out.
I think this'll be a nice little combo with the BBMs and roller. Not at all apples to apples but I'll spin it up on the chassis dyno and see how it compares to the old combo. I'm also going to flow the Edelbrocks (have some porting in bowls and port entry) to see where they land vs the BBMs on the same bench.
Too small a cam and it will dog out over 3500 rpm.
|February 12 2018, 9:16 AM |
Prob great off idle, but if you were using an automatic trans, you would not notice the benefits. That smallish cam would give better dyno numbers straight up. Cam is a little small for a performer RPM in my view. Would work ok, but would have been a stronger midrange motor with a regular performer and running the cam at 106 where it was supposed to be.
Not sure what roller you have, but undoubtedly it will give bigger bites of air and actually use the volume of the Performer RPM intake. Probably will find 60 HP with your changes.
|February 12 2018, 10:03 AM |
224/230 .563/.563 Hydraulic roller is going in it. Definitely "street" oriented for a heavy car with O/D
|February 13 2018, 9:41 AM |
My neighbor (E B Porting) should be able to CC your heads, or The Shop is about 8 minutes down the road.
|February 13 2018, 10:16 AM |
Thanks, might just do that. Had a guy flow my BBMs here in town but got somewhat odd numbers, not a big deal as I'm looking for relative comparison but they're far enough off known that not sure I want to continue with that bench.
Email me with the results...n/m
|February 13 2018, 11:13 AM |
E B Porting also has a flow bench...
|February 13 2018, 3:06 PM |
The Shop has one too, but I think Lewis was working on it recently.
How heavy? That is a big cam compared to factory.
|February 14 2018, 10:35 PM |
It's 10* bigger than a CJ cam for comparison.
I wouldn't call that big, but
|February 15 2018, 4:41 AM |
I do agree with Brent, in a 390 with big heads, crank that baby forward as much as you can. It'll drive part throttle response up and those big heads should carry you through.
Also remember, about 15 years ago, we all started talking .050, but advertised duration matters too. My hunch is that the roller has quite a bit more .006 duration and therefore overlap, so it should be a little more rowdy than the .050 numbers indicate. Not saying that to indicate it's too wild, but, to avoid you getting concerned that it advancing it will shift the peaks too low.
On another note, I am not sure on valve sizes on your BBM, but be very careful on valve clearance. TRW/Speedpros don't have a lot of room
- 70 Fastback Mustang, 489 cid FE, Victor, SEFI, TKO-600 5 speed, 4.11 9 inch.
- 71 F100 shortbed 4x4, 445 cid FE, headers, RPM intake, 1000 HP series Holley, 4 speed