I would guess it would have a similar personality, although without using an oscilloscope to actually measure the signals it would be a guess/crapshoot which one has greater lag numbers.

FWIW, later computer equipped cars have a calibration constant in the software that compensates (adds advance) for this lag, so this is not an issue with newer engines.

 

Yeah, that's not a lagtime issue. Four degrees in 800 RPM is a significant change. I'm interested in what you find is causing this change.

 

What kind of ignition amplifier was it triggering?

 

Just a guess off the top of my head but sometimes cam walk can change the timing, if the cam moves it engages the distributor gear at a different degree due to the way the gears are cut. Just thought I'd throw it out there

Probably happens more than you think, who has their timing light out checking the timing at 6000RPM under load ?

 

MSD box. Thinking it might be a worn dist bushing. TimAT sent me a pm saying he had a similar issue. With the advance slot issue then this, no Sun machine available and the price of parts on the MP distributor we had to look at options.
The new MSD came in today so that issue is resolved.

 

Torrington roller bearing. Cam endplay was setup right.
Me, when a 6800 RPM cam quits pulling at 5200 and the A/F ratio is good.

 

The RPM problem was spring surge. not valve float. The instability in the valvetrain is probably the issue with the MP distributor too. Gkull was right, needed more spring pressure. I was disappointed with the final peak HP numbers but all in all happy with the end result. Aldo has a nice nostalgic 427 build with all possible parts GM that should be a dependable engine that sounds like an L88 at idle, is streetable and suprisingly responsive off idle, has a flat torque curve in his cams operating range that will run pump gas and pulls to 6400 RPM. Talked to Tim this morning and decided we are going to try a 950 on it to see if that will give us more peak power. Tried everything else in tuning runs.
Here is the E-mail to Aldo.
> Late night at the shop.Done!
> Tim had some springs to fit your retainers. They were takeoffs from brand new heads, never run. The dyno only ones he had were not correct pressure. The springs are 160 on the seat and 375 @ .600 lift. 358# rate
> The Comp 930 is 153 on the seat and 383 @ .650 Lift. 365 @ .600 354# Rate.
> This is 7# heavier on the seat and 10# heavier open than the Comp spring. with a #4 difference in rate. Really close specs. They will lose a little the first time they are run. Installed the springs. The spring surge problem is gone. Made 4 pulls after changing them and readjusted them once they were hot. Pulled to 6400 peak. good valvetrain stability.
> The fuel curve is good but the carb is too small. It starts running out of breath at around 5600 and fights to gain power after that. You will see on the dyno pulls it starts getting richer there but not much. It really wants to idle at 1200. The A/F is also a little lean at idle due to the small carb with low vacuum. This does clean the idle up and it don't load up and has great throttle response. Good for street use. I would leave it. Even though a 950 would pull better peak power numbers you could sacrifice some bottom end and midrange manners. The carb required staggered jetting to equalize the exhaust gas temperatures. They were almost exactly the same on all 8 cylinders.
> The timing curve is perfect and the motor likes 38 degrees total. The MSD distributor is rock solid on timing all the way up. Put weak springs in the distributor to bring a little mechanical timing in at idle. Vacuum can won't be in until next Friday.Tuning is optimal for the combination.
> The motor did not pull the numbers I was hoping for and you will be disappointed with the peak HP. I think the combination of under 11 to 1 compression with this big overlap cam reduces cylinder pressures (DCR) especially at higher RPM. The heads don't flow the best but the smaller port size will be good in the midrange. The dual plane probably peaks out under 6000 RPM as does the carb but both again will be good in the midrange. The combination of all these reduces peak power but improves streetability, midrange and throttle response. It is all a compromise. This pulls over 450 Ft LBS of torque from 4500 to 5700 peaking at 466. This is an extremely flat torque curve for this cam. This is a wide range of high torque. The HP is over 400 @ 4600 and it pulls to 6400 where it peaks at 503 HP. The carb has been changed out three times and removed to add a spacer. The distributor and wires were changed out three times. Your MSD and wires were on it for the final pull.
> The valve springs were changed out and the valves were set cold and hot with both sets of springs. They were also checked every three runs. The valve covers were straightened at the flange before assembly and they were off 10 times. They are leaking at one corner a little now so we will straighten them again. I think you will be very happy with the sound, performance and driveability once it is in the car. Tim said if he was going for absolute power a smaller duration roller cam and bigger carb would be higher power over a more usable range. A big single plane, Big carb, Mill and port the heads to bump compression and locking out the timing would pull the biggest numbers with this cam but then you are trading streetability and may have to run race fuel.
> A ZZ502/502 runs the same peak HP with the same heads, a roller cam, less compression, better matched components and over 60 more cubic inches on 92 octane
> The 69 427/435HP was 11 to 1 and pulled 435 HP @ 5800 RPM & 460 FT LBS @ 4000 RPM with a smaller but better matched cam and similar carb CFM on 100 octane.
502 HP and 466 FT LBS is what this engine makes. Might get a little more with a carb change but it would take 4 or 5 more pulls to get it dialed in plus R&R, tuning and R&R to put yours back on and we have 18 pulls on it now. You won't get much more under 6000. I hate to pull this 5 more times. The dyno break puts more strain on it than a car ever would. His dyno is rated @ 2500 HP so it has a real heavy brake and it does have stock rods that are 40 years old. Tuning is optimal for the combination
> I have a couple videos. and the last dyno sheet. The first two videos show Tim adjusting timing (got him on camera while he wasn't looking) and the third is the last dyno run from off idle to 6600 RPM. Check out the idle, response off idle and how smooth it pulls to 6600 RPM. I think you will be real happy with the performance and streetability once it is in the car. Tim's dyno is very conservative. It would pull better numbers on something else.

Setting timing turn the volume up on the videos!


Setting timing


Dyno Run 2000 to 6600 RPM


Dyno print out


Real L88 Dyno sheet. Our restriction is on the intake side

 

Nice job Kevin.The curve sounds good.I never...NEVER wanted to understand the whole compromise thing,but I think Elle will be happy,and it is a dependable build!Good job,man.
I ran around in a '69 390 horse 4-speed car w/a intake,and carb,and it would sit that car sideways in first,and second just nailing it,so Elle will be fine!

 

Talked to Tom At AMP yesterday. He said hi. Back in Illinois I hear. Glad you checked in. The cam, intake, carb and head selection was made up front by Aldo. Pump gas was required. Had to design everything else around that with streetability a priority. Did the best possible with the parameters provided. It is either a L88 with reduced compression or an L71 with a bigger cam. Power fell between the two. Beat the 11 to 1 L71 numbers by almost 70 HP.

 

Great to see/hear it running!! Sounds killer!

Using all the various OEM and nostalgia components makes it tough to hit the *big numbers*. I'm about to get involved in a big cube small block using a 283/270 2x4 setup with WCFB's and exhaust manifolds...so I'm going to be in the same boat!!

Aldo...I think in the car you're going to be happy. This is a high RPM screamer with actually a very broad TQ curve. Think of it as a big bore small block! Remember..the L-88's weren't necessarily drag motors. They were road race designed to operate at high speeds constantly. They would run up to 7000-7500 rpm....hard on brakes and downshift....and have to pull hard from the 4500-5500 rpm range. The big heads are killer above 5500 rpm on a 427...and the dual plane helps with the area below that without strangling it too bad. It's always a compromise. Look at the power curve of this motor.....that's exactly where this thing will fly. Don't be scared to push RPM well above that 6400 RPM peak so you can keep it in the sweet spot!

just for reference...many years ago I built a 396/375 with basically a stock shortblock and heads....then threw in an L-88 cam, a tunnel ram with dual 660's and dropped it into a Pro Street '68 Nova with a 4 speed and 5.38 gears (14x32" slicks). I never dyno'd it....and I'm sure it wouldn't be spectacular.....but with the headers uncapped and 7500 rpm shifts (no roller rockers either) that thing ran 10.60's in the 1/4 and walked by many a car with seemingly more power. You just have to think RPM and don't worry about it. You have a killer lower end! If you're side by side with someone and your tach reads 6800 rpm....don't be afraid of keeping your foot in it until the other guy shifts and let him fall behind!


Can't wait to hear of your first driving impressions!

JIM

 

Jim Moore, "The temptor".
I would put a 6500 RPM chip in the rev limiter. I really don't want to do this over.

BTW Jim recommended a 1000HP carb for this when I asked him in a PM.

This is what theskunkworks said "I've run as much carb as a 1050 cfm Dominator (progressive) on a moderate street 427, and would probably be taking a serious look at something along the lines of an 825 Mighty Demon myself (which should "flow" ~890 cfm, dry)."

 

here I am...

the engine as dynoed now is the "street" version. a dependable , pump gas (I will run vacuum advance too), mid-rpm engine with which I can enjoy both "road racing" and quiet rides. divided plenum , small carb , 11:1 were mandatory.

but I wanted a strong low end for future possible "race track " conversions.

I look forward to see the dyno pull with a 950 cfm carb on a 1" spacer, just to have an idea of what it could be. I know , i would need a different intake too, etc...

in the future , this engine is a good start for an high rpm motor for vintage racing events. let's see...

I agree with Kevin-63mako that Tim's dyno seems a bit on the conservative sides (or other dynos are too optimistic). earlier in this thread I posted an l88 build that put out big numbers on my same dual plane intake...and similar build.

I look forward to drop it in my car soon and have fun, after many months of troubles and forced stop. then will see...

p.s. Jim , gimme time to be accustomed again to the motor and the car, then we'll see if I'll need higher rpm...it was an hard task to drive it on the street already as it was before engine decided to leave me...I felt a bit safer only after fitting the Avon soft tires

 

I'm never scared to put *too much* carb on one.

Do you still have all that stuff I sent you on carb throat and throttle bore sizes? If so, post that up so folks get an idea of what carbs can really do what.

Dual planes LOVE bigger CFM carbs.

I'm using the same 1050 Dominator on my 540 as I did when I had the 427 in it. Ran great on the 427....much stronger than 750's and 850's. You want more airflow capabilty from the intake and carb than the heads need. The restriction should be the heads, not the intake tract before them.

6500 RPM???? C'mon.....what are you doing? Pulling into a parking lot???

JIM

 

You got it!
Tried a Barry Grant that was flowing 950 CFM. It does give a couple more HP up top but it was just because it did not go richer at higher RPM. Only did a baseline run and a run after a close jet change. It wasn't making a big change. It also has 4 corner idle so it idled a little better. I like the 800. It does drop on the A/F ratio up top costing a couple HP but a touch rich is safe at high RPM. I think the restriction is the intake. 40 year old design dual plane. This was originally installed on 396/375 HP and 427/425 HP copo. The L72 425 HP had a 780 vacuum secondary carb same as an LS6. Less than 1 HP per CI and peak RPM @ 5800 RPM. The holley 800 matches the intake pretty well. That is right where our pulls seem to flatten out on power. They do still make them so it is a pretty good 40 year old design. Just not an ideal match for high RPM operation on this bigger motor. A big single plane and a 950 would probably wake this up upstairs but streetability would suffer a little. There is that compromise thing again. No sense in pulling this past peak HP on the dyno. It will probably do ok at 7000 but why go there. This one woul pull higher. http://cgi.ebay.com/ebaymotors/38850...item5acfa689fd

 

63 Mako, nice thread on a great motor. I have just rebuilt my 71LS6 and blueprinted it to NHRA specs (11:1)with the 074 alluminum heads, and 569 low rise intake to race in the pure stock muscle car drags. I read the dyno sheet and assume the stagger jetting is 76 for the left primary, 72 right primary, 74 left secondary and 70 right secondary, is that correct?? You did have a power valve in the primary and secondary?? I have an LM1 meter and have gotten the AF ratio at wot correct, Now i am wondering how many tries it took to get this break down correct? CAn you talk about this stagger jetting and if it would be the same with the different intake. What carb was that dyno sheet running. I nelieve there is alot of power in stagger jetting

 

Had 3.5 power valves in both. Your right on the 76 L primary ect. The exhaust gas temps were staggered. Need a probe in each exhaust port so it is done on an engine dyno with the 8 sensors. You can see them in the video. Might be able to see it with an IR gun in the car if it is off as much as this was. After the stagger jetting EGT were almost dead on across the board. We had 18 tuning runs. Probably 10 were fuel curve runs. You get the AF right with the same jetting on both sides but if the EGT is higher on one intake plane side than the other with the dual plane you bump the jet up one size on the primary and secondary on that side to fatten it up. If it isn't enough you go down one size on the other side. This build needed to be 2 jet sizes bigger on both primary and secondary on the left side to get even exhaust gas temperatures on the cylinders connected to that plane equal to the other plane. Runs smoother and has more uniform A/F ratios in each cylinder hence more power. That sheet was running the 800 carb, Some would not need stagger jetting. If it is needed there is power there.

 

Been looking back at the intake, and tho I'm certainly not a fan of drastically compromised dual plane intakes, I'd really consider opening up the plenum divider a little to drop isolation to no more than ~80% from what appears to be nearly 90% isolation between the two sides (as measured on the high plenum side of the divider). My thinking is that with this particular intake it may possibly yield a little more in top end benefits than it should cost in drivability penalties (especially when compared to the later "open" version of it which Chevy made).

FWIW, from observations, I've noted that quite a few of Edelbrock's dual plane manifolds seem to fall into the 80-85% isolation ballpark. Of course, it all falls back to which end more priority is being placed, and such change would no doubt affect idle, but thought I'd share anyway...

As my curisity is up, I might just "run" this combo on my EA Pro simulator this weekend to see where it lands.

 

Here is your PM.
I never was a giant fan of the 800's out of the box. There's about a gazzillion versions of them...but the fuel curve always seemed a little fat overall. They did run well though.

The 800's pick up airflow over a 750 with a 1/16" larger sec venturi.

The 850's have a pri venturi 3/16" larger and a sec that is 1/8"" larger than a 800. The throttle is 1/16" larger too.

The 950's are a little goofy with a 750 venturi and an 850 throttle bore. But they work very well and this is typically how folks like Braswell size their custom carbs. They like to open the throttles and speed up venturi speed. So you can see the 950 has same pri venturi as the 800 and a smaller sec..but it has larger throttle bores on both sides.

The 1000's have the same throttle bore as the 850/950 but have a larger venturi that is 3/16" larger than the 950 and the same as an 850.

All that said, it's going to have a dual plane intake so it can stand some more CFM. It sounds like he likes to *road race* play so throttle response is going to be real important. That's where the 950 might do well on a single plane. If it was mine..and I was running a dual plane, I'd put the 1000HP on it in a heartbeat. Those carbs work very well out of the box. If you look at dimensions it's identical in venturi and throttle as an 850...so it's not a problem, but the fuel curve on them is great.

For a 427 size motor I might pick the 80514 annular one to make it more responsive. But even the regular boosters would do fine.

Just for comparison, I can tell you my old 427 loved a 1050 Dominator vs a 750Dominator on the street and track.

See ya,

JIM

 

The L88 and ZL1 both had either an open plenum or a drasticaly milled down divider. Would love to see your dyno projection. This was designed to be an 11 to 1 build but it did end up with a .010 thicker head gasket than the original plan due to having to massage pistons and chambers a little to get everything to clear. Wanted to make sure we had at least .040 quench everywhere and avoided a custom gasket. If you need build specs let me know.
ZL1 intake

 

Just to add to Jim's comments, I've run a 1050 on a moderate street 427 before, and were it not for the difficulty of mating that monster up to the L88 type hood CAI and for the availability of the AirGap manifold, I may well have chosen to run another one on the 427 I'm working now. As Jim can tell you from our past conversations, I've really struggled with reaching that decision, and every time it comes up I can't help but think about reconsidering that C454 intake I have stuck away...




edit - Yes, if you'd PM those specs to me, I'd have to do less guesstimating...