Looking for opinions on my timing curve
 

Sorry this post is going to be a little long.

1970 Judge 3.90 gear, m21 close ratio, and 275/60 -15 tires

.060" over 400
Autotec 25cc dish pistons
RPM H-beam rods
Factory N 3.75" crank
"0" deck height
56cc Whitmore ported #614 RAIV heads - flow approximately 280cfm
Approximately 10.25:1 compression
Crane "041" copy cam installed 2 degrees advanced w/ Johnson R series lifters
Harland Sharp 1.65 rockers
Dave Bisschop ported Holley Street Dominator intake
OBX stainless Dougs copy headers
Luhn oil pump
Idle RPM 800 and 9.5" vacuum

Ignition:
MSD 8528 RTR distributor
MSD 6AL
Pertronix coil
AC Delco R43S plugs gapped at .050"
Taylor Spiro Pro wires

Initial timing is set at 18 degrees
Mechanical advance has the black 18 degree bushing installed and has one light silver and one light blue spring
Vacuum advance is hooked up to ported vacuum, and set to the maximum of 10 degrees

So it should have 36 degrees total all in by 2100ish RPM.

Motor runs strong from 3000 rpm up. I have the rev limiter set at 6700 rpm and it pulls hard right to it. I have not heard any detonation anyplace yet, but I've also been running a 50/50 mix of VP110 and 91 pump. The motor also starts great when warm, but starts a little hard cold (very cold blooded).

I'm going to be installing a Holley Sniper kit and would like to get this thing to run on 93 octane so I'm not killing the O2 sensors. I've been told it shouldn't be a problem by a few respected members.

I guess I'm just wondering if the pro's think I'm in the ballpark or not. I don't want to hammer this thing to death.

Thanks, Nate

sounds okay but that's a really fast curve. If it works, it works though. I'd be more focused on your total timing, you may not need that much. If you can get it on a chassis dyno or out to a test & tune day at the track I'd try backing it off two degrees at a time and see what happens. For pump gas you might want to slow it down a bit too. Try pushing the total all in point back to 3000-3200 RPM.

My last engine with 061 heads that have chambers which vaguely resemble the 614 chambers didn't pick up any power with more than 34 degrees and I ran into detonation running it at 38, which I only did because the curve was too long and it was more responsive with more initial timing.

I think you have everything set up good for starters. Just need to dial it in either at the track or on a dyno. Read the plugs for A/F and timing and you're done....

Sounds like a nice combination.. Good luck..

You need to check what the actual advance versus rpm is rather than go by the theoretical, only takes 5 minutes to check.

Even with a Street Dominator, the vacuum seems a little low for that camshaft and compression ratio especially with 18 degrees initial. I'd expect closer to 12-14in-Hg.

What carburetor are you running? Did you do a vacuum check and look for leaks? When your turn the idle screws does the engine respond in kind? Did you verify the balancer is reading zero with #1 at TDC? I'd check all the basics first before even messing with the timing. I'd regap the plugs to 0.045".

As far as your timing goes, you can still lose power without hearing knock. Starting the ignition too early could be causing negative work as the piston is coming up. By 3000rpm, the timing is probably right where it wants to be and suddenly it picks up. With that short a curve (again assuming you've confirmed the marks are showing correct), I'd slow it way down. Put it the stiff springs and try to get it to not come all in before 3000rpm.

Holley #6213 800cfm 4165 on it right now. Turning idle screws in will make the motor stumble, I did adjust them for best vacuum. The vacuum gauge in the car may not be completely accurate, at idle the motor runs the 9” dual diaphragm booster fine. After cam break in I used a known good vacuum gauge to set idle and I’m pretty sure I remember it being 9.5” at that time also tho. ( It has been almost two years since I built this motor.

The new Powerbond balancer lined up dead on when I installed it.

Nate

These guys saved me a lot of typing.

Centrifugal curve too fast. May or may not have the optimal "total" advance. Spark plugs gapped too wide.

I might play around some with the vacuum advance, but not until the rest is sorted out.

Sounds like a nice combo!
I gap everything I ever worked on between 0.035~0.040"(go/no go) with MSD box.
IDK, manifold vacuum for the VA may make life a bit easier on your starter, if it cranks hard. My 400 liked a lot of initial timing lead too.

Very similar to what I'm (re )doing, you have much better heads. I didn't run numbers, but I'm thinking you may have more static CR than you indicated.

Is E85 widely available near you?

VP110 is an excellent leaded fuel, pump gas will be a far cry from that in many ways.

Something I learned from first hand experience is when a fuel station gets a load of fuel, and they order "too much" cheap unleaded, they drop the balance in their premium tank, great for profits, terrible for your ride.... It happens a lot.

I'd try some straight pump fuel with your carb before making the big jump to the Sniper and fuel supply system.

Your main goal is to be able to manage pump premium correct?

BTW>>>>>Dug up some old posts of yours, love the thump from the trunk.

Too much timing, coming in too fast. I suspect you've got the base timing jacked up to give it some idle vacuum. I'd think that a 10.3:1 motor would like 12-16* base timing better. For total timing, 31-34* at 3000 should do the trick. Use the two blue springs in the MSD kit, that brings the timing all-in by 2800-3000 RPM.

This combo would likely be more fun on the street with a RPM intake and a spacer.

https://youtu.be/N9b7Nca0Rdo

https://youtu.be/W48L3-kOMpY

https://youtu.be/g3trldmid2I

My plan was to buy 55 gallon drums of non ethanol 93 from a local supplier. Most stations around here only have 91 now.

Nate

That was the initial plan, however; the rpm would have taken some welding to get it to seal on my heads. The ports are very tall at 2.350”.


So the general consensus is slow down advance rate, possibly back off total a few degrees, and tighten up plug gap. I’ll play with it before I pull the carb off. I want to get this set right before I go injection. I won’t be using the Sniper to control timing at first. I’ll be taking it one step at a time.

Nate

Compression is a bit low for the RAIV size cam and high ratio rockers so it's not going to be real fussy about a lot of timing and getting it in quickly. It will EASILY manage your 91 octane pump fuel with correct tuning with that much overlap, so no worries there.
18 degrees initial timing to only see 9.5" vacuum at idle speed tells you the cam is PLENTY for the CID and compression ratio. It's also going to need a lot of fuel to be happy as well, especially at idle and right off idle.

I really don't see any flaws in the set-up and it's probably fine with that much total timing with 25cc dished pistons. Even so I like to start out somewhat conservative and sneak up on the optimum settings. I've only did a few Pontiac engine builds with dished pistons in them. They came up a little short on power on the dyno compared to the same build with flat tops and larger chamber heads, and they took a little more timing to make the best numbers.

To date all of the engines we've done with .035-.039" quench have liked 28-32 degrees total timing to make best power, with the vast majority of them like 30 degrees the best. This does not include builds using the early "bathtub" chamber Edelbrock heads, those come in 37-41 degrees. The last 455 I did with dished pistons (pretty sure they were around 20cc) liked 35 degrees total timing. That engine also made less power than a nearly identical 455 build with flat top pistons and a little larger combustion chambers.

Overall the engine build sounds fine, will make great power, and it should be fine on lower octane pump fuel with close control of timing/fuel curves.....IMHO......Cliff

Did you install the Cam advanced as a need called for from degreeing it?

Yeah, Cliff, unless I'm doing something wrong, the SCR for me is coming out in the 9.12-9.28 range. On a .039 gasket, .006 deck, and a true 72cc head, I even get 8.87. Max with the planets aligned correctly I get 9.42.

A .027 gasket would help if it doesn't already have that.

Agree pump gas and current tune seems all fine, and expected for the combo. I can see where it would like more lead, and the lower vacuum.

I like the car & combo though, no fuss, drive and have fun.

.

He lists his heads at 56cc. They are highly worked heads to flow 280 and were likely decked to achieve 56cc

Do Autotec pistons have a D dish or full round?

56cc in the chambers plus 25cc in the piston dish is still over 80cc of squish area not taking into account deck height and head gasket thickness. The .060" overbore sure helps here, so it's probably just a big over 10 to 1 as the OP mentioned. Still pretty "low" for a RAIV cam in a 400 build. They are simply OK around 10 to 1 compression and really start to shine about 10.6-10.7 and higher.

The original Crane version of the RAIV cam was advertised as "computer smoothed" so they took out some duration/overlap. Even so I've worked with 455's using that cam and it makes the grade acting very much like an original 041 grind, about the same idle characteristics, dyno numbers, etc.

I don't think a 2 degree advance is going to hurt it at all in a 400 build either.

My first 455 was 9.97 to 1 compression and EASILY managed any grade of pump fuel I felt like putting in it, even in really hot/humid weather, and it used the Crower RAIV grind part number 60919. Vacuum at idle was just over 10" w/o Rhoads lifters and 12.5-13" with them.

For the 400 build in question here it will want and need more idle fuel from the carburetor (assuming factory Q-jet), and more fuel for "normal" driving as well. Far as timing goes I'd start out around 32 BTDC and do some drag strip runs, or chassis dyno, with 91 octane and start putting timing into and stop when it quits making more power or running quicker, then back off about 2 degrees and enjoy it. Of course IF you hear any audible detonation along the way, retard the timing till it quits............Cliff

I missed the 56cc thing, my bad.

.

Yes cam was degreed and set at 2 advanced.

Full round on these... dang things look like swimming pools! Lol!

Yes heads were milled excessively before I got them. The intake port was opened up to 2.350 tall which also limited my options for intake.


Nate

Yep, you aren't going to get 25cc of volume in the dish in a "D" shape. You won't get enough volume that way to keep your compression where you have it.

Those cams are ground on about a 113.5 lsa or so. You installed it 2 degrees advanced at 111.5 ICL ??

Personally I would have moved it a little more. Usually those cams work nicely around 109ICL, and it may have helped your low vacuum situation and likely would idle a little better, and possibly not need the extra initial advance (although I don't see the initial being an issue) Would also bring the power down a pinch more so you aren't shifting at 6700 lol.

Would still run fine on pump with only 10.25:1 compression. These are pretty healthy cams for a 400.