Advance cam? Intake valve clearance?

[HotRod777]

I have 2 questions to see if advancing my cam is doable and worth while.

Here is all the dirty details of the combo that I put together in the middle of last summer. It’s in a 1966 Coronet, just a cruise car, never will see the strip or above 75mph. I think I picked pretty well as far as the whole combo... but I have to admit I was expecting a bit more from it.
383, 40 over. Sealed Power forged flattops, .018 in the hole. 1967 915 heads with new 2.14, 1.74 valves, bronze guides and hardened seats. Single street springs good to .520. .020 steel shim head gaskets giving .038 quench and roughly 10:1 calculated compression. I run 93 octane Sunoco pump gas. DP4B intake, new AVS2 650, HP manifolds and 2.5” TTI system. Refurbed factory 10.75” Hi-Stahl, 3.73 sure grip and 27” tire.
Timing set at 16 initial, 34 all in by 2200 with light springs and fbo plate.
Cam is the Comp 270H (.224 @50, .470” lift) installed straight up.
The car runs good but regrettably it idles smooth like a tow truck unless I slow the initial down to 5°. I wish it lumped more at idle. It seems to start to pull better after 2000rpm. Maybe this wasn’t the best cam choice...
I just checked cranking compression, plugs out and carb open... 150# in all cylinders give or take 2 or 3 pounds. Ideally I think I’d like to have 10-20# more...

Do you think advancing the cam 4° will provide a noticeable gain down low and how much more cylinder pressure could I expect? (And I know advancing “might” add a bit more exhaust note being the pressure is higher)
And, I know the big intake valve might be getting close the to flat-top... but with only 224° and .470” will I be ok? Has any one used a bore scope to see how much clearance they have?

Thanks for any ideas/insight

 

[cryplydog]

Hotrod, are your pistons machined for valve reliefs?

 

[HotRod777]

Hotrod, are your pistons machined for valve reliefs?

No, completely flat

 

[wyrmrider]

borrow or buy a bore scope and take a look
or put at tdc on overlap and take the springs off and move the intake and exhaust up and down
just make sure you are not on firing stroke
you should be ok but---
That cam is from before the XE series
more duration than it needs for the lift but it should be easy on the valve train
but what do you mean by "straight up" and did you degree it in when you installed it?
Is it not ground 4 degrees advanced so when you install it dot to dot it's already advanced 4 degrees?
It would be nice to try it an additional 4 degrees andvanced
first you need to verify if comp wants you to check from the .050 lifter rise timing or from the "down from the nose" method
IDK if that old grind is asymmetrical or not

 

[451Mopar]

You could put checking springs on a cylinder to check P-V clearance.

The engine sounds a lot like my old 383. Forged flat tops, no valve reliefs, milled 906 heads, similar 220 ish duration cam.
The cam was nice for a driver, but just a bit big for the stock converter. Get a higher stall converter and it will be happy.

 

[khryslerkid]

What rear gear?

 

[HotRod777]

borrow or buy a bore scope and take a look
or put at tdc on overlap and take the springs off and move the intake and exhaust up and down
just make sure you are not on firing stroke
you should be ok but---
That cam is from before the XE series
more duration than it needs for the lift but it should be easy on the valve train
but what do you mean by "straight up" and did you degree it in when you installed it?
Is it not ground 4 degrees advanced so when you install it dot to dot it's already advanced 4 degrees?
It would be nice to try it an additional 4 degrees andvanced
first you need to verify if comp wants you to check from the .050 lifter rise timing or from the "down from the nose" method
IDK if that old grind is asymmetrical or not

I did degree it at it was right on what Comp claims, 110 and 106 on the intake. Yes, dot to dot on the chain set. I’m thinking of moving the crank sprocket to the triangle mark.

 

[HotRod777]

What rear gear?

3.73

 

[RJRENTON]

IMO....
Follow the suggestions for checking valve /piston clearances, as previously noted. The most critical dimension is the exhaust valve to piston as the piston is coming up as the valve is oprning. As far as advancing the cam....advancing the cam improves the bottom RPM band; conversely regarding the cam improves the the top RPM band.....limited to the initial cam profile's degrees and lift. Is what you hsve adequate??? It sounds like you want or need a "little more" cam. I suggest you talk with several suppliers: Comp Cams (especially, since this is what you have ), Edlebrock, Crane, Hughes and explain EXACTLY what you seek including all aspects or your car and your intended use...or....ask your next door's neighbor's brother-in- law's cousin's best buddy's friend's sister-in-law's husband, who will have the definitive answer for your issue. Just my opinion of course.
BOB RENTON

 

[Kern Dog]

You could put checking springs on a cylinder to check P-V clearance.

The engine sounds a lot like my old 383. Forged flat tops, no valve reliefs, milled 906 heads, similar 220 ish duration cam.
The cam was nice for a driver, but just a bit big for the stock converter. Get a higher stall converter and it will be happy.

The OP's combo actually does sound pretty decent. It should be a decent performer with a bit more stall speed.
Back when I was dealing with my detonation problems, a few helpful members commented on how it is so common to see spark timing curves that come in so early. My own MP electronic distributor is "all in" at around 2000. Why ? What is the point of having all the advance in at such a low rpm? Mine knocked at WOT despite all sorts of band-aid fixes. It is off topic but I just wonder why these fast advance rates seem to be so common.

 

[wyrmrider]

you can feel a quick curve in the seat of your pants
compare a MP computer to the stock FI computer
unfortunately I get pinging that even premium will not make go away
better check your timing RJ
advancing opens and closes the intake earlier
opening the intake earlier means that it is further open when the piston is closest (not usually at exactly TDC)
Isky gives the valve opening at different intake centerlines. so do a few other grinders
hope you have the clearance to try the advance
problem is it also opens the exhaust early which cuts power and mileage
trade offs
let's see what you find
and a new compression check
how much did you gain
cheers

 

[HotRod777]

I got a bore scope on its way, I’ll give it a try next weekend and see what I can see. I’ll post a vid if possible.

 

[HotRod777]

Well I advanced the cam today. Took about 3 hours start to finish. I’m going to try to attach the video from the bore scope. The ones I’ll try to attach are the “after shots”... showing intake valve/ piston clearance with the cam advanced 4. The first vid shows the overlap... the second I got closer under the intake valve and backed it up showing the clearance.
I did start it up and give it a quick time with the light... they idle is defiantly more “strong” sounding... which is good. I’ll be taking it for a drive tomorrow... fingers crossed that it runs strong.
(Just realized i can’t attach Vids... I’m going to send them to YouTube and then post the links)

 

[HotRod777]

Overlap

Intake

 

[Don Frelier]

3 Hours is pretty good time for that job.

 

[wyrmrider]

great work
looking fwd to results
did you work from timing or nose?

 

[HotRod777]

All I can say is WOW. It’s like a totally new car/cam. Before I was really a bit disappointed with the performance of the combo of parts. It was “ok” but it seemed to be no better then a bone stock 383 w/log manifolds/ stock cam/ etc.
After advancing the cam it really came alive... sound/ power/ idle are all noticeably better. I did not check the new cranking compression, I might, but I’m so happy with what I got there is really no reason too... especially being I pick up no detonation that I can detect.
(I timed it at 17int / 36tot in by 2400)
It might not work for ever parts combo out there... but it surely worked on mine.

 

[oldkimmer]

That’s great. Glad ur happy. How much lifter preload do u have? Kim

 

[HotRod777]

Just wanted to tie up one loose end, I re-checked the cranking compression. All cylinders gained between 10-15 pounds, all tested in the low 160's#

 

[oldkimmer]

Sweet. That’s why it important to degree the cam. Kim