• When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.

Stroked 383/438" on the dyno

Good story.

The two big win-win takeaways.......
It didn’t eat the cam...... no rear seal leak.
Power seems commensurate with the combo.

Dyno sheet critique.......

Imo, the dyno carb isn’t all that dialed in(at least not for that combo).
Big lean hole in the middle.
Builds like that rarely respond favorably to a/f ratios in the 15’s.
Fuel flow between front/rear isn’t balanced that well.

Up towards the top of the pull the a/f ratio is getting more normal, so it’s doubtful a different carb would have yielded drastically different power.

Checking the uncorrected power from the fuel flow and bsfc numbers....... the uncorrected power was actually higher than the corrected power.
You don’t get air like that very often.
At 5400, 94.5 + 88.5/.404 = 452.9hp uncorrected.

Cool! Guess the air was pretty good!

I forgot to mention that he used a wooden, tapered four hole spacer. It wasn't anything trick.

He did offer to duplicate his carb recipe for us for a small fee if we bring him a double pumper with adjustable air bleeds. Jury is still out on that. I would like to see if that vac. sec. carb can be made to work.

This engine would probably be a good candidate for EFI but that's not in the budget right now.
 
What I want out of a dyno mule carb is one that isn’t very fussy about what’s under it.
I want the jetting safe, and a pretty flat fuel curve.
It doesn’t have to be anything special in terms of power...... but it can’t be a dud either.

This is a pull with my dyno mule Holley 4779(750DP):

F76CEC13-A271-4E6E-A45D-7AA574475972.jpeg

I rarely ever have to adjust anything other than the idle speed.
I often use this on stuff in the 350-475hp range.
I prefer to start out with my carbs....... especially for a new build.
Usually eliminates issues during start up and cam break in, etc.
 
Cool! Guess the air was pretty good!

I forgot to mention that he used a wooden, tapered four hole spacer. It wasn't anything trick.

He did offer to duplicate his carb recipe for us for a small fee if we bring him a double pumper with adjustable air bleeds. Jury is still out on that. I would like to see if that vac. sec. carb can be made to work.

This engine would probably be a good candidate for EFI but that's not in the budget right now.
I have read that a double pumper is not a good choice for a car that will mainly be street driven? Nice thread on the work and results of your dyno pull.
 
That's cool, you got the same torque and 60 more ponies as the 440 magnum out of your B block! Should be fun!
That plug though, new and only a couple dyno runs? Threads look cooked to me...

Here's a Champ out of one of my big block builds after about 1000 miles.
20201004_094009 (2).jpg
 
What I want out of a dyno mule carb is one that isn’t very fussy about what’s under it.
I want the jetting safe, and a pretty flat fuel curve.
It doesn’t have to be anything special in terms of power...... but it can’t be a dud either.

This is a pull with my dyno mule Holley 4779(750DP):

View attachment 1198064

I rarely ever have to adjust anything other than the idle speed.
I often use this on stuff in the 350-475hp range.
I prefer to start out with my carbs....... especially for a new build.
Usually eliminates issues during start up and cam break in, etc.

We used his carb for the break in and the first few pulls before we tried the vacuum secondary and he didn't touch anything on it. We futzed with mine for a while but it was getting later in the day and we threw in the towel when it sputtered on start up; it started instantly with his. Frankly I did not really trust mine from the start anyway and specifically requested we use his for break in. Turned out to be the right move.

I was going to bring my Proform 750 double pumper but the goal was to see what the 3310 would be like since we intended to use it in the car. The Proform works but it's probably nowhere near as sharp as the dyno carb. Perhaps it would have been more forgiving though.

We discussed carb options at the end, the dyno operator saw no reason for us not to use a D.P. for this combo but I'm not so sure about that. I get it - throttle response would be perceived as "better" but my friend does not need his rickety, 4,000 lb. boat jumping off the line from every stop light in Queens.

Now that the motor is broken in and has good ring seal we can try to get my carb running and not have to worry about wiping the cam.
 
I have read that a double pumper is not a good choice for a car that will mainly be street driven? Nice thread on the work and results of your dyno pull.

Thanks.

My friends car certainly fits into the vacuum secondary carb category described below but that does not mean it will be optimal. It's a trade off like everything else.

From Holley:

"For high performance engines a carburetor with mechanical secondaries has
an inherent advantage over a carburetor with a "controlled" secondary
system (air valve or vacuum diaphragm). This is possible because a
controlled secondary carburetor, until it reaches wide open throttle, will
not have as great a pressure drop below the throttle plates as would a
mechanical secondary unit. The greater the pressure drop below the
throttle plates the more dense will be the fuel/air charge to the engine
and, hence, the more output."

"As a rule of thumb, vacuum secondary carburetors work best on:
Relatively heavy vehicles
Street gearing
Automatic transmission
Engines built more for low-end torque

Conversely, mechanical secondary carburetors seem to work best on:
Relatively light vehicles
Strip gearing (4.11 or numerically higher)
Manual transmission
Engines built more for top-end horsepower"
 
That's cool, you got the same torque and 60 more ponies as the 440 magnum out of your B block! Should be fun!

Thanks. My friend is stoked.

That plug though, new and only a couple dyno runs? Threads look cooked to me...

Maybe it's the picture but the plug is not cooked. I've had wasted plugs on either side of the spectrum, the one I posted shows no signs of any damage - it's not white/chalky (lean) or carbon fouled/sooty/wet (rich), no crater marks on the porcelain (detonation) ... it's OK!
 
All good Ramcharger!

13 (AFR) is supposed to be unlucky?
But for me its 'the right number' for an engine of this calibre!

Carb choice is a minefield, nearly as big as the camshaft spec...:realcrazy:

My Moparmates 915 headed 452ci ran like POO with a stock Edelbrock manifold and a proform 750.

We went to another build to see if we could improve on our skills?
511ci with Edelbrock heads and Edelbrock performer intake.
Did we use that proform err no, he phoned up some guy who hand builds HP Holleys.

He suggested a 950cfm for a street car 'WHAT', the guy is on drugs methinks:fool:
Just 'bolt it on and go' yeah right, we spent a year trying to dial in that awful Proform (and failed).

YEP approx 500 hp and 15mpg to the English gallon, no tweeks...:rofl::usflag:
 
Last edited:
Just to say it look's a little rich on the fuel mixture. Too much black on the plug. Should be more a tan color. Just my two cent's.
 
More comments from the peanut gallery.......

If the Stealth heads didn’t get the seats done and some bowl work....... I think that was an opportunity missed to grab some low hanging fruit from the HP tree.

Frankly I did not really trust mine from the start anyway and specifically requested we use his for break in. Turned out to be the right move.
:thumbsup:
 
Cool reply PRH!

How do I get in the peanut gallery?

Guess my 50 year old B&D vibro centric, had already got me there lol...:rofl:

800px-Have_a_Good_Seat,_Mr._Valve,_Vibro-Centric_(NBY_7983).jpg Black-Decker-Valve-Seat-Grinder-Vibro-Centric.jpg
 
If it were me, and on a budget, maybe check out the Brawler series of carburetors from Holley (750 / 4150-series). Start out with a 6.5"-8.5" PV in the front, block the rear PV, add rear jet extensions with a notched float if it doesn't have one. Purchase a pump cam kit from AED or Holley to tune the pump shot, and you may need to go up to a 33 or 35-squirter F/R which is fairly common. If it doesn't idle without relying heavily on the curb idle screw, uncovering the transfer slot, you'll want to drill (1) 3/32" hole in each of the primary throttle plates to add additional airflow. If the cam is large enough, you can drill additional holes in the secondary throttle plates or open them up (square with the front) to add additional airflow at idle. Fine tuning the fuel curve can be done with air bleeds, but most of the time, it's close enough to not worry about.

I wouldn't run a vac secondary on a performance application, but if it's just a cruiser, they work perfectly fine, but will still require some tuning.
 
I've got enough parts and pieces to build any variety of carburetor. Again, our intent is to run the 750 vacuum secondary carb. I know the carb works because it ran for thousands of miles on my old D100 before I sold it. I even managed to get 13 MPG out of it on a 8:1 400 with a too-big cam and no vacuum advance. We won't be needing to drill holes in the throttle blades, plenty of vacuum with this combo.

Problem was the 750 sat outside for a couple years and it got kinda crusty. Before we went to the dyno I did a quick "rebuild" on it. I've had the thing apart many times before but whatever I did this time didn't work out so well. No biggie, just have to find the problem (if there is one) and try again.

Or maybe we try one of my Thermoquads...
 
A few years ago I had the idea of testing just what kind of power differences there were by swapping out a stock 750DP main body for one of the HP bodies.
So I bought one(I had previously built several new carbs out of the Proform bodies with good results, but never compared to the stock body).

Then I thought....... maybe I could test some billet metering blocks too.
When I got done buying parts....... I basically had everything to put another carb together.
So...... that’s what ended up happening.
Never did the test. In fact I’ve still yet to try this carb on anything.
It cost as much(or more) to build it as to just buy a new Brawler 750 now.

D0780C40-6512-42AF-86EC-10EEBD3427DC.jpeg
 
You mentioned snapping off the dipstick. After building my 440 and using Doug's headers I couldn't get the stock dipstick tube to seat properly and it wept oil at the base. Wound up installing a Lokar flexible dipstick. Its a nice product with O-rings at the base and secures on top to one of the exhaust bolts. No leaks since.
GMVortecInstalled.png
 
You mentioned snapping off the dipstick. After building my 440 and using Doug's headers I couldn't get the stock dipstick tube to seat properly and it wept oil at the base. Wound up installing a Lokar flexible dipstick. Its a nice product with O-rings at the base and secures on top to one of the exhaust bolts. No leaks since.
View attachment 1199418

I'd like to use the Lokar piece and it might even be a necessity with some combinations. However, we used a specific length dipstick to work with the larger capacity 440 Source 6 quart pan. Like you mentioned, the Lokar is a completely different design with o-rings so I don't think we'd be able to use the flex tube with the existing OE-style stick.

The dipstick is turning out to be kind of a PITA actually to the point of considering a block off plug. Generally, you put 6 quarts in and unless there is a severe leak there should be 6 quarts in the pan when it's time to change the oil. Even if there are drips you're not likely to be a quart low just not sure I trust my friend with that situation. We'll probably just order a new tube. Believe we just need to grind down the block end more before putting it in. Also probably best to wait to install it until the headers are on.
 
A few years ago I had the idea of testing just what kind of power differences there were by swapping out a stock 750DP main body for one of the HP bodies.
So I bought one(I had previously built several new carbs out of the Proform bodies with good results, but never compared to the stock body).

Then I thought....... maybe I could test some billet metering blocks too.
When I got done buying parts....... I basically had everything to put another carb together.
So...... that’s what ended up happening.
Never did the test. In fact I’ve still yet to try this carb on anything.
It cost as much(or more) to build it as to just buy a new Brawler 750 now.

View attachment 1199399
Have you ever tried playing with the emulsion jets on the dyno?
..surprised you haven't tried your creation yet..
 
Have you ever tried playing with the emulsion jets on the dyno?
..surprised you haven't tried your creation yet..

I haven’t messed with the E jets on the dyno.
I can see where that could really eat up some time though.

As for the new carb....... I just haven’t needed it for anything yet....... and since it’s untried at this point, it’s not quite ready for use as a dyno mule.

If the right build comes along, and time permitting....... I’ll try it at some point.
I’d prefer to try it out on something like a SB with a fairly rowdy cam making around 500hp.
 
Thermoquads now we are talking lol.

I got a shed full of 'em and I want to make at least on of them work on my 71 GTX manifold...:praying:
 
Auto Transport Service
Back
Top