Pesky SHP Problem (?)

[Joe C.]

This has been going on for quite some time, and I'm about ready to throw in the towel. Here is a summary, which some of you might remember.

Car is 1965 with close ratio, 3.70, new Borg standard diaphragm type, 365 SHP. Everything on the car is new or rebuilt--car has a total of 57 miles since completion. Just got carb back from Jerry Luck, who did an outstanding job. Distributor rebuilt with new shaft, bushings, etc--end play set to .004, zero wobble, no discernable plate wobble, special hi perf points as per Duke's recommendation (which DID cure a high RPM breakup problem). Dist set to spec, and tested for proper vac advance/cent advance deployment--oll AOK. Delco "44" plugs, which all show dry and grey-tan after hot laps. 30-30 correctly set as per Duke/John H method. Lifters no longer clack, but "sing" sweetly. Vac @ idle (800RPM)= 10.5 in-hg. Valve springs new, measured at 100 pounds - valves on seats. Heads pocket ported, CC'd (opened to 67 cc's), intake gasket matched/ports polished. Carb stock, and as delivered by Jerry Luck. Compression tested @ 195psi +/- 5, across all 8.

The car screams at high RPM, shift points @ 6200 RPM, no breakup, still pulling hard. THE PROBLEM IS that I've got to slip the clutch to get the car rolling from a dead stop. If I don't slip it enough, the RPM's drop, and it will stall unless I pump the gas. Is this normal, or am I expecting too much.

Sorry for the lengthy post, but I tried to give you all a clear picture.
Appreciate any help here.

Joe

[Jim T.]

Re: Pesky SHP Problem (?)

I have a 68 327/350 with the M21 and 3:70. The street from my drive way is driven just about half block before I have to stop and it is a up-hill takeoff from the stop sign and the engine is cold and I have to slip the clutch to get going, but for only to get the wheels turning. Have one more stop like this before getting to work. Its all technique. My wife had driven this car since it was new and I had to replace the clutch in 73. The clutch disc was almost like new on one side, the other side was really worn from slipping the clutch. Still using the replaced clutch in this car today with me putting mostly all the miles on it.

[Larry E. Howard]

Re: Pesky SHP Problem (?)

Joe,
I would expect to see the problem you describe for 2 reasons. The combination of close ratio tranny and 3.70 gives a pretty tall take off ratio. Larger tires on the rear than original equipment would even compound the problem more. Second, you don't say what cam you are running, but my guess is it is ground for HP at high RPMs thus not much bottom end and easy to stall. Some 65 HP engines used the 097 Duntov cam which is solid lifter. I have that cam in my 57 and even with the wide ratio tranny and 3.55 rear (a better take off ratio than you have) I have to sip the clutch to take off. I don't have much experience with the HP hydraulic cams of that era but I would guess thay had no bottom end either. If you have the solid lifter cam check the clearance the lifters should clack.

[Wayne W.]

Re: Pesky SHP Problem (?)

Every time that I have had that problem it has been related to an incorrect vaccum advance. It needs to be activated at a very low vaccum. For instance a 350HP with 300HP advance will fall on its face every time when the clutch is released.

[Joe C.]

Re: Pesky SHP Problem (?)

Larry:

I have the original type Goodyear 7.75-15 tires. As I said, the engine is a 327/365, running the original type 30-30 cam. The Duntov was used for the SHP smallblock thru 1963. In '64 they dropped the c/r from 11.25:1, to 11.0:1 (ADVERTISED -I calculated my actual c/r based on the chamber mods, head gasket thickness, etc, etc, @10.55---10.75, which is probably a lot closer than the factory variation, considering that I carefully cc'd the chambers), and changed to the 30-30, and bumped the ADVERTISED horsepower from 340 to 365.

Thanks for the input. Yes, this is strictly a top end motor. I never owned one "in the day", so I just might be too used to modern manual trans V-8's.

Joe

[Joe C.]

Re: Pesky SHP Problem (?)

Wayne:

Vac can is a 236, and, as I said, operates as it should (base timing set to 12 @500,weights tied, when vac advance is reconnected, total advance jumps to 38, which means the vac advance is adding 16 at idle, per spec).

Joe

[Joe C.]

Correction

Vac advance adds 16 degrees at idle, NOT 26 degrees, for a total of 28.

Joe

[Duke W.]

Re: Pesky SHP Problem (?)

What you report is somewhat the nature of the SHP beast. Consider that I am pulling a 3.08 gear through a CR trans on my '63 L-76 (76 MPH @ 6500), and the 30-30 cam is more radical than the Duntov or LT-1 cam.

My startup technique is sometimes to just ease the clutch out at idle until the engine almost stalls. This just gets the car moving, then I declutch, blip the throttle and dump the clutch. This is probably easier on the clutch, but not particularly smooth. If you've ever seen a racer drive from the paddock to the couse, you'll probably see the same technique.

What happens is that as the revs drop you lose manifold vacuum, and since fuel is metered on the basis of manifold vacuum at idle and below if revs drop too low the engine will lean out and stumble. Also, some heat under the manifold plenum is necessary to evaporate the fuel. If the fuel doesn't evaporate it cant' get to the cylinders and the engine will stumble. I tried blocking my heat riser once and the driveability was just unacceptable. Wiring it open is okay, but blocking it completely with shim stock covering the passages is not. So what's the status of your heat riser?

Richening the idle mixture might help, and if the problem is bad during warmup, indexing the choke a bit richer might help. Beyond this it sounds like you have an excellent setup and have sweated the details. I have no doubt your engine runs like gangbusters other than the launch problem. The only thing I would have recommended is to replace the original 30-30 cam with the LT-1 cam since it makes considerably more low end torque at the cost of a bit less power in the 6000-up range, and it should be no tougher to launch than a Duntov cam. I also prefer Delco heat range "5" plugs or equivalent as they are more resistant to fouling than fours. Give them a try the next time you buy plugs.

One other question. Do you have the OEM 30 pound flywheel? I don't recommend a light flywheel on these SHP/FI engines as a light flywheel will just exascerbate the launch problem.

Talk to John Hinckley. His '69 Z-28 has the 30-30 cam, but he has a 800 CFM carb and is pulling a 3.55 gear.

Duke

[John H.]

Re: Pesky SHP Problem (?)

Joe -

Your combination is similar to my '69 Z/28 (stock, 30-30 cam, M-21, etc.); it came originally with a 4.10 axle, which I swapped out for a 3.55 (3800 at 70 finally got to me). Between the 3.55/M-21 combo and the poor low-end torque of the 30-30 in the little 302, slipping the clutch from a dead stop is just part of the "recipe". On the other hand, my '67 327/300 3.36/M-20 is much slicker from a dead stop, and just takes off - the stock "929" cam is very happy at low rpm, and makes good torque - the 30-30 is NOT happy at low rpm, and makes poor low-end torque; just the "nature of the beast".

[Craig S.]

Re: Pesky SHP Problem (?)

Joe - you are getting the best advice you can on this board as always, so all I can add is how long is Jerry Luck's turnaround running? I need to make a decision on my 3247 and have used Jerry in the past, but may use MacNeish if he is still half a year...thx!...Craig

[Everett Ogilvie]

Fuel and Vacuum Issues (long)

A recent experience with a big block car that had trouble moving away from a stop prompts me to post this info. A big block with 3.70 gears should not have any problems and you may be experiencing something similar with your small block. I have been considering posting this for big block owners specifically, but because your issue could be similar (although the root causes may not be the same), here goes - sorry for the long post.

In addition to Duke's info, there is another set of problems that can cause a similar symptom, but due to a rich, rather than a lean condition. We just spent 50 or 60 hours setting up a '65 396 car that would bog and load up when letting the clutch out from a stop. You did not mention if your car loads up, but if so, that is the key to a rich condition. Here is the problem we had and what we found; the car would bog when moving away from a stop. Once you got it going it would clean up and run fine and it was extremely strong in the mid and upper range as it should be, with no missing, etc. At idle we observed some smoke coming from both sides of the exhaust, and found it to be fuel (not oil). The carb had been worked on extensively in the past and we found many issues inside it - the work had not fixed the root issues and had indeed created new issues.

1) the flat surfaces of both metering blocks had been worked (presumably because they were not flat), along with the corresponding surfaces on the main body). The metering block surfaces had not been worked enough, and you could see a "low" section that allowed a fuel path from the main fuel slot to the idle slot on the metering block. This meant the idle circuit was way too rich, all the time. Clue - if your idle mixture screws have little impact when you turn them, and if it actually idles better with them closed all the way, fuel is getting into the idle circuit via some other path. You have to find this path (this troubleshooting took a great deal of time). Hours of hand work were required to flatten the surfaces so the fuel would not cross-talk from the main to the idle slots.

2) engine vacuum at idle was quite low and highly variable (7 – 9”, although it sounds like your vacuum is slightly better at 10.5”). Here was our issue - the standard power valves for the 396 carb are 8.5. With our poor vacuum, the power valves were fluctuating at idle, adding fuel in addition to the issues described above. The lifters were fairly quiet, and we knew they were set too tight because of the lack of noise and the poor/variable vacuum. They ranged from 013 to 020, with all of them set too tight. We set them to a spec half way between the 396 and the 427 spec (022/026 - this works great for any 396 or 427). This gave steady vacuum of 11 – 12” at idle, well above the 8.5 of the power valves. After confirming that the 8.5 valves were no longer opening at idle, we went to 6.5 power valves anyway because of the high altitude here.

There were some other problems with the carb that were corrected, but they were not contributing as directly to the problem as the items above. Before all this work the car ran perfectly on the main system, but it had a poor idle and it would bog terribly moving away from a stop. Now it takes throttle better than any car I have personally driven, and it will literally idle away from a stop (note - I am not claiming that a small block with the big cam will do this). Hopefully this will offer some items to confirm on your setup, and maybe it will help a few big block owners out there.

[Joe C.]

Re: Pesky SHP Problem (?)

Craig:

I sent Jerry my carb on 1/2/03, and got it back on 3/24. I would expect his turnaround time to be less at this time of year, as most folks now have their ducks in a row for the 2003 show season.

Joe

PS: His promised turnaround time was 6-8 weeks, which turned out to be more like 11----but it was worth it.

[Joe C.]

Re: Pesky SHP Problem (?)

Duke:

Thank you, as always. Your response is encouraging. Here is some more data:

1. The heat riser passage in the intake, is open, per spec.
2. Heat baffle/shield on underside of intake was removed, and all surfaces were cleaned (very little carbonization was found, so heat transfer was never an issue. Shield was reinstalled, of course.
3. Heat riser is NOT wired open, and works as it should. As I remember, exhaust pressure blows it open, and it operates freely.
4. The flywheel is a GM "021" unit, which I believe is 12.5" OD and 153 teeth. I removed an incorrect, 172 tooth flywheel (14"OD?) This also necessitated a new bellhousing and starter.
5. The flywheel is solid nodular iron, with the GM part number cast in. I did not weigh it , but it was pretty goddang heavy, with no cross drilled holes.
6. The idle mix screws are both set @ 1 1/4 turn out, with no afterfire on closed throttle coasting. Spec calls for 1 1/2 turns each. Do you think that the extra 1/2 turn will richen it enough to do me?

Duke, so far you have been right on the money. Believe me, it takes a HELLUVA lot to gain my respect. At this stage, I now believe that I can expect no more.....and that I have perfected it!!

Best,
Joe

[Duke W.]

Re: Pesky SHP Problem (?)

If you can rustle up Joe L on this thread he can probably tell us the original application of that flywheel and maybe give us an idea of the weight. I have the original in my '63 L-76, but I didn't record the casting number. I expect it is gray iron. I did weigh it and recall it was over 30 pounds. I considered replacing it with the 18 pound L-88 flywheel, but figured it would just make the launch driveability poorer, so I retained the heavy original. The less rotational energy, the more recalcitrant a SHP engine is going to be to get going in normal driving.

You should play around with the idle mixture to see if richer, or even leaner helps out. One thing about Holleys is that some use an idle air bypass screw so turning the mixture screw in actually richens the mixture. The AFB and some Holleys use the needle valves to control the area of a passage that passes an emulsion of fuel and air, so turning the screw in leans the mixture. Be sure you know how the idle mixture screw on your carb works.

The SBs with the 30-30 cam were probably the most high strung engines ever built by a domestic manufacturer that were intended for street use (by this qualification I do not include the L-88 or ZL-1), and I think even Chevrolet Engineering realized they went a bit overboard, and that's why they developed the LT-1 cam. Part of the visceral quality of SHP/FI engines is their "race engine demeanor", which is one reason why most of us love 'em, but it does come with a price.

Duke

[Craig S.]

Re: Pesky SHP Problem (?)

Thx Joe...I misplaced his phone number, posted above for help, do you have it handy? Thx, Craig