[pggto]

What kind of vacuum are you seeing at idle with this cam? I have a E headed 455 and I'm seeing 11 inches of vacuum at idle. Thanks

[torqjunki]

E-head 462 10.5:1 with single plane intake and 850 Holley style carb, seeing 13" tuned with wide band. THis in in neutral with engine fully warmed. Running 15 Deg initial, 23 mechanical, 12 Deg from vac advance (manifold vac). THis is near sea level. Needs to idle near 13:1 AFR in neutral to idle well in gear. It will lean to about 13.8:1 or so in gear. I have run literally dozens of tuning combos. 93 octane pump fuel with no additives. Runs sweet everywhere, starts great.

[72LuxuryLeMansLa.]

Originally Posted by torqjunki

E-head 462 10.5:1 with single plane intake and 850 Holley style carb, seeing 13" tuned with wide band. THis in in neutral with engine fully warmed. Running 15 Deg initial, 23 mechanical, 12 Deg from vac advance (manifold vac). THis is near sea level. Needs to idle near 13:1 AFR in neutral to idle well in gear. It will lean to about 13.8:1 or so in gear. I have run literally dozens of tuning combos. 93 octane pump fuel with no additives. Runs sweet everywhere, starts great.

Just curious, I'm not saying you are wrong here...... Did you try ported vacuum for the advance? At idle you have 27° or so advance using manifold vacuum. What does your particular car gain from this? I'm always curious at the results people get with the whole manifold vs. ported deal.

Karl

[torqjunki]

Yes...tried it both ways. Much better idle and crisper off idle with manifold vacuum. Ported vacuum worked better before I limited the vacuum advance to 10-12 Deg because of part throttle pinging. One thing I noted that is pretty good evidence that the tune is headed in the right direction is that if you plug your vacuum advance in to manifold vacuum with engine running and the engine speed does not increase or starts to run rough, it is combination of too much initial. This happened before I limited the vacuum advance.

[ta man]

Sounds about right..mine needs a slightly richer mixture for the best idle in gear.

[78w72]

400/467 e-head engine. after 2nd startup, not fully warm, rings not fully seated, i had 12-13. 13* initial, vac adv hooked to ported per cliffs suggestion & majority of comments i read from others here.

hoping for a solid 13 or 14 after break in, tune & fully warm. but car runs great as is & power brakes work fine. i think around 13 is the average for this cam.

[jonmachota78]

I'm seeing 13-14. Manifold vac limited to 8 deg. 12 deg initial. I've tried ported but it likes manifold vac better.

[chitownTA]

I run 18 initial with KRE 295 d ports at 11:1 compression. With my qjet I can get about 14" at 900 rpm in neutral and it drops to 10-11 in gear at 800 rpm. It likes a rich idle around 13-13.5:1 AF. I use ported vac advance limited to 10 degrees.

[Cliff R]

My engine makes right at 13.5" vacuum at 750rpms. Initial timing is 10 degrees, vacuum advance limited to 10 (currently running 14 degrees but going back to 10 degrees), 20 degrees from the mechanical curve, all in by 2800rpm's.

I use ported vacuum to the advance, but have tried manifold vacuum and added as much as 15 additional degrees at idle speed. The engine doesn't really like that deal too much. Adding more timing introduces a "skip" to the idle instead of a "deep/heavy" sound. Vacuum really doesn't improve nor does the idle rpms. Reducing the vacuum advance timing to 10 degrees and using manifold vacuum it does better, but not quite as "clean" in and out of gear when I don't add any additional timing at idle.

My engine is 11 to 1 compression using 76cc KRE heads, very tight quench, and the cam is set at 109.5 ICL.

Here's a clip from Norwalk, you can hear the engine idling fine in and out of gear:

http://www.youtube.com/watch?v=6zVdoLR-VzM

I am using a 1971 factory HO intake and 1977 Pontiac Q-jet, you might say the carb is pretty well tuned for the application!....LOL....Cliff

[old66tiger]

Originally Posted by Cliff R

you might say the carb is pretty well tuned for the application!....LOL....Cliff

Who did the tuning for you? :-)

[Cliff R]

My next door neighbors third cousins sisters ex-husbands tenant who was renting a back room on their tool shed.......LOL.

Seriously, carburetor tuning is the KEY ingredient here to getting a good end result. If the carburetor isn't fully on the idle system, and has plenty of fuel available to the mixture screws, quite a bit of additional timing at idle will be required to get a good stable idle in and out of gear.

It's not about setting up a super-rich carburetor, they will do the job but be pretty "stinky" at idle speed. It's a combination of idle fuel and idle airbleeds that will give the engine a good mixture so it's efficient at idle/off idle/low rpms with a big camshaft.

I've tried to tune 455's with the OF camshaft and less compression. They ALWAYS want more initial timing and more idle fuel than what my engine requires. We are still able to get a great end result, and have never once had to resort to adding 15-20 degrees of timing from the vacuum advance with manifold vacuum. That deal is just a "crutch" for poor carb tuning, IMHO.

I've built 455's with both iron and ported KRE heads, at compression ratios from 9.90 to 11 to 1, and there is a considerable difference in what is required to tune them from one extreme to the other.

The OF cam is a great cam for the 455 street/strip engine. It's really happy the closer to 11 to 1 compression that you get. Going below 10 to 1 compression it still works fine, but idle quality and vacuum produced suffer considerably. Instead of making 13-13.5" vacuum at 750rpms like they do at 10.5 to 11 to 1 compression, the engine is hard pressed to make 10" vacuum at 900-1000rpm's, which is marginal for power brakes.

For the lower compression engines we start adding timing and fuel, to get a stable idle in and out of gear (auto trans). They are going to be happier with 14-16 degrees initial timing, plenty of idle bypass air, and fuel to the mixture screws, etc........Cliff

[torqjunki]

Torque converter characteristics will play a big role in idle quality in gear for automatic trans cars. I went with the tighter version of the Jim Hand tight 10" converter and it makes it a little harder to get the idle in gear just right especially with the Holley style carbs with large primaries. Love the converter, but considering having it loosened up a tad more similar to Cliffs converter. Like to get about 3800-4000 flash and feel confident after hearing from Cliff and others that it is still very tight for driving and cruising with the overdrive. I will add a large trans cooler just for insurance.

[Skip Fix]

I agree with Dave on convertor. My Hand 10" in the 78 now is also a tad tight. Big clunk shifting to drive and lugs motor down in gear changing the AFR considerably. So tight even on the replay tach don't see it "flash" just a steady pull from foot brake rpm. Looser wouldn't be loaded as much in idle and be a little better.

One I had years ago a Trans King you could see the rpm go up as you went up a steep overpass on the freeway.

[Cliff R]

+3 and a good point to make as it relates to this topic. My converter doesn't drag real heavy on the engine when the trans is placed in gear. It does lower the rpms from 750 to about 700, you can hear this in the video above. A "stock" type converter would be a poor choice for this cam right to start with, and it most likely would create more difficulty in tuning for good idle characteristics in and out of gear.

Also, as it relates to this topic, the distributor timing curve must be rock solid at idle speed. If any of the curve is in and some timing falls off when you place a load on the engine, idle tuning will be difficult, if not near impossible.

I see this all the time in my business, folks have distributor issues and think that they have a carburetor problem. In a high percentage of cases, someone has installed one of those el-cheapo aftermarket recurve kits...FWIW....Cliff

[old66tiger]

Originally Posted by Cliff R

My next door neighbors third cousins sisters ex-husbands tenant who was renting a back room on their tool shed.......LOL.

I know that guy....he also likes XE cams! I digress.

Yea, tuning is everything. I see a ton of cars at the local shows with those Edelbrock carbs (Carter clones) and the thing is running like crap and the guy doesn't seem to care. The carb is pretty and shiny.

[old66tiger]

BTW...mine is around 12" which was NOT enough vacuum for a 9" booster in my GTO. The factory 9" booster don't work with anything else than factory covers which I didn't care for. I am running a Hydratech booster which could care less about what vacuum I am running.

[oville]

Speaking of carbs I assume a quadrajet with dual plane intake would produce more vacuum than say 850 holley on same intake? Due to smaller primaries?

[oville]

Just asking because I am buildind an E-head 455 with the OF cam also, and was thinking the q-jet/dual plane would have better street manners than the holley/torquer II setup I was intially planing

[ta man]

Originally Posted by old66tiger

I know that guy....he also likes XE cams! I digress.

Yea, tuning is everything. I see a ton of cars at the local shows with those Edelbrock carbs (Carter clones) and the thing is running like crap and the guy doesn't seem to care. The carb is pretty and shiny.

I would guess 90 percent of the cars at cruise nights and car shows could use a good tuneup..

[ta man]

Originally Posted by oville

Just asking because I am buildind an E-head 455 with the OF cam also, and was thinking the q-jet/dual plane would have better street manners than the holley/torquer II setup I was intially planing

Either will work fine properly setup..I run a Holley /Torker 2 intake with mine and it drives like a 301 car...