Carb size
 

I'm going to test soon with wide band, but what are thoughts on an 800 dp holley? Enough carb?

.04 over 454, 462ci
Victor junior
308 dart iron eagles, ferrea valves, 8205sp springs
Cam 231 235 and .63 lift
9.2 compression
Bore notched cylinders to match head
Gil exhaust

Looking for input on the difference to say a 850, 950 etc

800 is enough carb for your engine. I had pro systems build me a carb for an engine that probably made a touch more power than your combo. They used a Holley HP950 which flowed 830 cfm's.

Thanks, I figured it would be OK but I see small block 350s with 950s on them (not stock by any means). Also if an HP950 only flows 830, what does an 800 flow? I plan to turn this 56-5800

800 will work but imo the 850 will make more power.i tried 3 different carbs on a similar build,750 holley,850 holley and 850 barry grant demon.the bg850 made the most hp but the holley 850 made 3 less hp but 15 more lbs torque,the engine was for a street car so it got the holley 850.

Good info, for say 15 foot pounds I'd be better spending money on prop work.

I would think a vacuum gauge at wide open would tell if the carb is adequate, thoughts on a number? 1. .2 ?

if it has 2 or more inches of vacuum at wot either the carb is to small or the intake runners are too small.

If it's an old Hp500 carb do yourself a favor and use something else.

Just curious as to what is wrong with an hp 500 carb?

I'm curious also, on the 'too small intake runners' causing high vacuum comment.

They are 9022 off 420s. 76 primary 87 secondary with 6.5 power valve in the front only as it sits.

Velocity creates vacuum , I work a lot with pressurized air boxes on normally aspirated motors. they have a lot of vacuum and we get frost built up on the throat of the carb. Bigger is not always better.

Are you talking about a pressurized box surrounding the carb? That wouldn't be NA right? Not quite sure what you mean.

Yes, Pressurized through a scoop of forced speed intake

So you are saying the frost is caused by high vacuum?

High Velocity/Speed and pressure chill the air. Just like the air chuck gets real cold under volume of air rushing out

Fuel coolers :D

So the high velocity of air in the intake is what causes the carb to frost up? Hmm. So why doesn't this happen on a efi manifold at the throttle body?

water mister in the air box. LOL.

or possibly IR's with injectors over the trumphets ?

I know the temp drop in a carb is due to the venturi effect as well as the fuel evaporation (but mostly venturi effect as the air pressure drops)

Anyway, it would be nice to try some 850s or 950s but I think what I will do is get the jetting dialed in and check the vacuum under the carb at wot. If over 1 inch, I think I'll want to try a bigger one.

Thanks for the input

Apollards 461 with 496 exhaust, ovals, and vic jr oval intake with 850cfm marine holley with almost identical camshaft pulls exactly 2" at WOT.

What are your thoughts on that?

Depends if the boat will react to another 10-15hp. Oh, forgot too mention, he pulled off flame arrestor to make sure that wasn't causing it. It wasn't.

Haha, probably not, but I need all I can get. Good info. I think I'll have to drill and tap a port into the intake manifold as I don't think there is a bung for a vacuum gauge there.

SB is correct, I pull 2" at WOT with a light load. More if I have it loaded with fuel or a couple of people. However, my hull is about topped out, and another 15-20 hp won't do much. IMO, 850 cfm is too small even for a mild marine motor. I'd like a 950 or even 1000.

Theres guys who think 750 CFM, is plenty for a 6500RPM 572, and theres guys who think a 5000RPM 454 mag, needs an 1150 dominator.

If I had your combo, I'd be looking at a set of the quick fuel Black Diamond coated Marine 850's. They sell for 650 bucks each at summit, and are a dam nice carb for that money.

I wouldn't expect much in terms of power, going from that carb you have now, but you would get a much nicer running, more tuneable carb with the quick fuel M-850. The black coating on them is really nice, and stays looking good, which we all like. :D

You want to carb it for max power? Any wide-open vacuum more than 1.3" is hurting your max output.
If I'm looking for all out max for a combination, I don't want to see more than 1.0" of vacuum.

But, if you carb it for less than 1" of vacuum, it will not behave as well when nursing the sticks in rough water since the signal thru the venturies is weaker at real low vacuum. You can make up for it with the accel pump cam, but then you end up squirting the heck out of fuel in there. If you commonly run wide open in rough water where you have to be constantly on the sticks, then stay above 1.5" of vacuum wide open.

Tapping for a vacuum gauge? if your intake doesn't have a tap, most carbs either have a port on the baseplate OR many are spotdrilled in the correct location for you to install one there.

Having a vacuum gauge hooked up also helps you get your idle mix and static timing figured out. Sometimes hotrod boat motors end up with way too little initial timing, and too much centrifugal advance with soft springs that end up with "hunting" off idle around the docks. It's not just a supercharged thing.

Intake manifold restrictions will not show up on a vacuum gauge. The gauge is on the wrong side of the manifold to mean anything if you suspect your intake of being a problem.

M

Good conversation here....... I have a 555 CID AFR 335 cnc heads, Edelbrock Victor, 4500 flange, 9.7 CR.... 255/262 .722/.702 solid roller with a 1050 Holley modified by BG way back when 6300 rpm target.
It's sitting here on the dyno, it should be at 750 hp... ran shy of 721 hp with mufflers on exhaust, torque was 683 @5100. Ran without mufflers torque jumped to 693, HP dropped 703 @6100. AF went from 12.8 to 12. I took fuel away no change... I data logged with a Daytona CD-1 made my pull from top down on de acceleration from 6200
MAP dropped from 100 to 75 ? my dyno data showed 1 ". I have a 1200 cfm coming tomorrow to try, then go from there..
It's a strange issue, I can build a 540 hydraulic roller, use a 2000 cfm TB and make 740 hp @ 5900 and the MAP will hold 98-99 Kpa until i get out of the throttle.

How was the exhaust set up in your shop. Meaning, where the mufflers connected directly to the header collectors or how long of pipe before mufflers ? Was pipe same diameter as collectors ?

Without heavy thought, sounds like an exhaust wave tuning issue where the mufflers had you at a better length.

You sure your throttle was opened all the way? :D

I hear ya. If I were to do it what do you think of the carb you suggested vs a 950 holley? With a future ci increase in nind?

This was a good read. I'm looking at options and will run it to get a baseline first. I don't need every last bit of power like a drag car, but don't want to leave a bunch on the table. 25 x 2 is 50 horse so it can add up..

Wrong post

I think you should be close, tuning with a wide band a big plus...you can be shocked sometimes, also the newer carbs, I like quick fuels, are very adjustable thru out the RPM range, another note the prostock engines do pull vacuum at wot for max HP so not sure where the figures come up with runners/carb being to small...theirs sure are not...

I agree, there will always be some vacuum no matter what, or air wouldn't flow in. I hope to get some baseline AFR numbers soon.

YES JOE .....not a mistake I make...

Mufflers are 6 feet away 4" inlet 5" outlet there is a 90 degree elbow at end...Mufflers are truck style.

So one side is running mid 12s and the other mid 13s. Because of this I didn't push it too hard into the 4 barrell. Need jets but not sure why the difference. Can float level do this? Motors are both strong and I never would notice this difference without the gauge.

Sometimes, it just works that way. I would treat them as individual engines, and tune them that way. Float level can have a slight effect on that as well. Typically, the higher the float level, the more head pressure there is, and more fuel will flow per a given jet size, the higher the float level is.

Ok, I need to get a jet kit and get them tuned in, but they definitely have a lot more power.

I think the old 800 holleys are worn out. One is reading rich and the other lean. When I switch carbs the problem follows so it's not the engines. They are not reacting well to jet changes.

So now is it quick fuel 850s or holly hp950s?