Ok so the timing thing might be a little high but do you guys think thts robbing 100+hp? Yeah messed up on the q-jet and its long gone so i'm kinda stuck with the holley, but with the jets tuned now agian i dont see it being worth 100 or more ponies? the compression thing, i dont know what pistons were used? but they would have to be aftermarket to be at .060 right? you cant make the up with just rings? Is ther a way to check the compression ratio, eack cylinder tested ok for pressure and a leak down but without pulling the head and spec-ing the chamber is there a way? the TOTAL timing is 40 at 2100 thats vac advaance and all it idles around 26 at 800 Thanks so far guys
Total timing doesn't count vacuum advance. You probably have 26 degrees of actual total timing. An extra 5-7 degrees can make a lot of difference. Are you absolutely sure the secondaries are opening?
Umm ... not to argue with you but here it is, straight from the designer's mouth - Denny Manner talking about the stage1 Fast Foward to the 1:25:25 mark (thats 1 hr, 25 min, 25 sec.). If you want to hear his whole talk, start at 1:16 [video=youtube;GIZw05UCoJM]http://www.youtube.com/watch?v=GIZw05UCoJM[/video]
You need to disconnect the vacuum advance canister, plug the port on the carb, and re-check the timing. The vacuum advance can add upwards of 16*, which would potentially mean you are only running 24* at WOT. That will certainly cost you some horsepower. Also, I'd be willing to bet your running pretty rich with 86's & 87's, which it sounds like your plugs indicate. Your carb originally came with 78's & 82's. You might want to start there. It would also be a good idea to double check that your actually getting WOT at the carb, and that the secondaries are opening.
without the vacum advance the timing totals out around 28 at 2300 as for the compression test it was a while agou all the cylinders were pretty close less than 10% difference they were all around 250 psi on the gauge is there any way to figure the compression ratio on an assembled engine?
Jim, Vacuum advance does not function at all at wide open throttle as vacuum is at or near 0. You want initial+ mechanical to be 30-34* for best full throttle HP.
I've never ran vacum advance I'd disconnect it and leave it that way, put sum light springs in the dizzy,
First, it's my understanding that this is a chassis dyno, so this is rear wheel HP, not flywheel HP. Second, this is what Jim Weise said about the Holley vacuum secondary carburetors, "Stay away from all Vacuum secondary series Holleys, the Avenger line in particular. All kinds of issues with them, of biggest concern is an issue with casting itself- it disintegrates over time. Holley long ago decided that everyone needs a 600 on the street, based on poor intake charge velocity motors like the Cleveland Fords and rectangle port Chev engines.. and the amount of small blocks running around at the time.. and as such, they calibrate the venturi vacuum required to open the secondaries in such a manner that on the bigger cfm vacuum secondary carbs, you would need a healthy 700 inch motor to have enough airflow to open the secondary. I made an 870 work years ago, with a fair amount of fooling around, and was sorry I ever bought that carb for a customer. In fact, I replaced it with a Q-jet, and was far happier with it's power and driveablity. I think I still have that 870 in a box around here somewhere. Considering what I found out about the casting issue later, I'm glad I yanked it off the customer's car. If your going Holley, go with a double pumper, 750 is a good all around carb. No smaller. The right choice for your build is a Q-jet. That is what I would run, for an all around carb, get a good used 850 or 950 Holley if your going to go to the track regularly. The 950 is big enough to "grow into" as often happens on engine builds over time. JW" Third, most vacuum advance units will give anywhere between 14 and 18* of advance at 16" of vacuum, so your WOT timing could be less than 28* as you really don't sound certain that you know exactly where it was. I suggest blocking the vacuum advance and seeing EXACTLY what your timing tops out at. If the secondaries weren't opening and your timing was retarded, you could lose a lot.
Something is wrong. Timing might be retarded, cam might be in wrong, we are unsure of your static compression ratio.
250 psi compression for a compression test? Does that sound like a lot to anybody? Advanced cam maybe?
timing is the foundation of all other tuning. The first thing you do when you get a new motor running is set the timing. It may not be all of your missing hp but it is the first place to start eliminating variables
September 8th is the next race for the Chicagoland GS club. We will be at Byron Dragway. Come on out and we can take a look.
As you said your chassis numbers actually match your strip time pretty well. Not good for either. Having chassis dynoed my car multiple times with many changes I'd say if you reached 250+ HP/300 TQ you are about there. You should post up a pic of your dyno run. My guy gives it to me in a file that I can bring up any time. We need to see the curves. If everything is right you should peak out around 5000 rpm. My 4250 lb '76 ran high 12's and was only in the "sad" low 300's and <350 torque. I had about the same cam and a good amount of headwork and all the other usual stuff but nothing too fancy. That being said I'd say that you are off the mark by about 50+ HP and about 1 sec/10 mph on the track. Easy 13's with that setup and 250 HP. Torque should be around 50 numbers better than the HP number. You never mentioned TQ. As far as my testing goes the Holley 870 will give close to the same HP number as the Q-Jet on the dyno but won't work as well on the track because of the slowness of the secondaries opening as mentioned. As was said that Holley setup for opening them is really bad compared to the Q-Jet. I do remember running it at the track and you could feel the secondaries close up a bit between shifts and then reopen. It is not worth 50 HP though unless something is drastically wrong. Wouldn't hurt to have another carb on hand. A Q-Jet would be nice but per Larry a nice 750 DP would work great on your setup in a pinch. No need of 850+ DP's at this HP level. My '65 ran well into the 11's with a lowly 800 DP on an Edelbrock. I'm not saying it would't go slightly faster just that it can be done w/o it. If you do another dyno run have them put a probe in the tailpipe to check a/f mixture. If you go again get the timing set. Disconnect the vacuum advance. You don't need it on the dyno. Start at 30 and add 2 every time until it starts to drop off. You could do the same at the track. What kind of fan do you have? If it is a clutch fan and it is locked up it would soak up a chunk of power. The same goes if it doesn't have a clutch. Aaron said it. If your compression is actually that much then that cam is overadvanced way too much. Recheck your compression. No guessing. The cam needs to be degreed in. If you used a billet +/-8 set and you didn't degree it you're probably off. I can tell you how to do a minimal fuss jury rigged degreeing in of that cam if you know somebody that knows their way around a dial indicator. Going by the 2400 stall speed your converter shouldn't be giving away too much HP on the dyno. At the dyno your guy should be flooring it around 2500 and surely by 3000 rpm and it should rev to 5500 rpm fairly smoothly. Did he have you disconnect the downshift cable so it doesn't DS into 2nd when floored? If not that's what needs to be done so you get a smooth run without downshifting. Lots of stuff to play with.
i'm gonna double check that just going of memort on that i will put those up today ---------- Post added at 11:34 AM ---------- Previous post was at 11:28 AM ---------- cam is in striaght up, how much work is that do dgree any more than a timing belt change, never done it before, the secondaries were actually a little loose, on the street with the air cleaner on they opened a bit too soon and had a little stumble around 1500-1800 so i went up a notch in the spring for street driving. as far as the hp number that sounds better i could see a few of these things adding up to 50 hp 50 lbs this thing will not make any power after 5000. i;m gonna scan those run sheetes now and put them up.
You "think" or "assume" the cam is installed straight up because you lined up the dots and called it good. What you can't assume is that every machining process from the crank snout to the timing gears to the camshaft were all machined precisely at the nominal (zero) position. In manufacturing, this simply doesn't happen. There will be tolerances on all machining operations, and those tolerances stack up between components. You have to check cam installation and possibly offset it based on what your measurement tells you. There is always the possibility that something was machined outside of tolerance or just plain wrong. There's no way to know unless you check. http://www.v8buick.com/showthread.php?220945-Camshaft-degreeing-101 Devon
