stacey
New Member
Posts:28
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| 08 Mar 2008 06:28 AM |
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I'm on a role with ?'s this morning. 2nd cup of coffee ya know.
My engine is new, been bored and stroked to 492, merlin heads, hooker headers, roller rockers, edelbrock intake and I just put a 800 edebrock carb on it. Aso have the gear vender OD. Runs unbelievable and I'm now pulling 13 at highway speed on vacuum instead of 10 with the old quad jet. I tried rebuilding the quad but just couldn't get the take off stumble out or the fall on it's face four barrel from opening up. Anyhow, love the new carb but wondering if it's on the large side. Stacey |
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Balrgn
Moderator
Advanced Member
Posts:801
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| 08 Mar 2008 12:02 PM |
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Sounds like alot of motor! NICE |
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1977 Argosy 20
454 V8 Gas
Southern NH
Maintenance Analyst
www.balrgn.com |
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new-to-rving
New Member
Posts:36
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| 09 Mar 2008 09:11 AM |
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I would say maybe on the bigg side, but not by much. adjustments can be made, with the overdrive you want low end torque,and not really top end cubic feet per min. of flow. but that thing must get up and jump when stumped on!  check out summit racing or jegs and check out oxygen sensor in stall kits and thet would help with checking for performance and gas mileage, with this info. you can adjust jetting and advance if needed |
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Gon Mad
New Member
Posts:20
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| 09 Mar 2008 08:39 PM |
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If you use this formu;a You wll be switching to a 650 thunder series.
cubic inches x max RPM=total divided by 3456 (a constant) equals total CFM at whatever rpm you choose as a cutoff point.
example 454x4500=2214000 divided by 3456=640.62 CFM.
If you figure that the overdrive generally keeps the engine under 3000 & usually cruising at or close to 2600 the need for a carb that size would satisfy my 10 second street car. And if you wish to go a step further try knocking off 10 or 15 0/0 for parisitic losses the CFM drop even further.
The carb you have is a very good one & try resrtting the secondary thighter to slow down the back barrels opening too soon. |
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Jim Elliott
New Member
Posts:80
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| 10 Mar 2008 09:12 AM |
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Posted By Gon Mad on 03/09/2008 9:39 PM
If you use this formu;a You wll be switching to a 650 thunder series. cubic inches x max RPM=total divided by 3456 (a constant) equals total CFM at whatever rpm you choose as a cutoff point. example 454x4500=2214000 divided by 3456=640.62 CFM. If you figure that the overdrive generally keeps the engine under 3000 & usually cruising at or close to 2600 the need for a carb that size would satisfy my 10 second street car. And if you wish to go a step further try knocking off 10 or 15 0/0 for parisitic losses the CFM drop even further. The carb you have is a very good one & try resrtting the secondary thighter to slow down the back barrels opening too soon. V/E on that formula is missing....Usually everyone considers their engine at 100% V/E but thats not so.....If we reach 85% that is/would be a strech.
Jim |
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Gon Mad
New Member
Posts:20
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| 10 Mar 2008 05:36 PM |
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My Bad . I meant That!? Even 85 percent relates to mostly race engines.
Thanks; Steve |
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stacey
New Member
Posts:28
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| 10 Mar 2008 06:21 PM |
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I kinda thought I was over carbed. This tranny is govned to shift really early and we all know the MH's aren't race cars, they're torch monsters. I have a friend that has a wide band o2 senser that I can barrow and use the laptop to dial in a good jetting but think a smaller carb is the best route.
Shifting gears here.... What about high altitude. Planning on a trip to the Rockies this summer. How to jet for the mile high? Stacey |
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Gon Mad
New Member
Posts:20
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| 10 Mar 2008 08:42 PM |
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Try installing a RED stripe adjustable vacuum modulator. I have mine turned to shift at a higher rpm.
Jetting for high elevation is not my forte. Try googleing for the info & dont be hesitant to refine your search a couple of ways to get what you can be happy with. Been a sea level dweller most of my life, I like an A/F ratio around 14.8. ( I like it not quite frying the valves & not killing pulling power).
I personally like lots of carbureters on my engines like TWO Predators on a tunnel ram on my street car but its for a little extra if needed. In reality only one more than adequate.
Keep up what your doing & enjoy the results C YA Strve |
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Jim Elliott
New Member
Posts:80
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| 10 Mar 2008 09:56 PM |
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Posted By stacey honn on 03/10/2008 7:21 PM
I kinda thought I was over carbed. This tranny is govned to shift really early and we all know the MH's aren't race cars, they're torch monsters. I have a friend that has a wide band o2 senser that I can barrow and use the laptop to dial in a good jetting but think a smaller carb is the best route.
Shifting gears here.... What about high altitude. Planning on a trip to the Rockies this summer. How to jet for the mile high? Stacey Stacey, The carbs are a pita to dial in most of the time......My Quadrajet is now with 73 jets and the idle jet circuit is leaned out....
When I get back home I'll produce the "Chevy high performance" carb site that shows the idle circuit remains in play up to and around 2500 RPM then the mains really kick in, I dont mind a 15.2 lean burn but when the throttle is pushed up against the wall I want a 12.8 climbing those hills........
I started a "Ignition section" with NO follow up as of yet but IMHO that where the greatest gains are and once set and locked down then it's on to the carbs and fuel injection.......Gon Mad is correct about the V/E 85% being a dab high but my GUESS with the small heads (even the L-29 heads) the numbers are about 80% at best.
Jim |
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Gon Mad
New Member
Posts:20
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| 11 Mar 2008 06:17 AM |
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Very good on the fuel ratios, I'm concidering an Edelbrock Diirect port RAIL system. I saw one closley at a car show here in Ft. Myers & the owner couldn't speak more highly about it. Kinda pricey though.
Tignition is the most misunderstood part of an engine. I was fortunate to work with & knew very well Dr. Chris Jacobs of JACOBS Electronics when it was located in LA I got firts hand Knowledge of how important & how difficult proprer timing curve & initial timing are. I use nothing but Jacobs equipment on everything I own. Also Jacobs sells the best book on ignitions I've ever read. Not only does it explain electricity, it gives a better understanding about ignitions. Chris (at the time) has 9 phds. in electronics engineerring a really super guy. Pick up a copy & be delighted with the info it provides. C YA! Steve |
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Jim Elliott
New Member
Posts:80
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| 11 Mar 2008 11:18 PM |
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For those readers who like to crunch numbers, there is a commonly used formula for determining carburetor size, but it provides only a rough starting point as all the engine's variables are not taken into consideration. This equation assumes 100 percent volumetric efficiency (VE) and can be worked out using the following equation: VE = (displacement x rpm)/3,456. For example, if we were to run a 350ci engine at 6,000 rpm through this equation, the formula would tell us that a 350ci engine requires a 608-cfm carburetor. However, most 350ci engines do not produce 100 percent volumetric efficiency, even at peak torque. They more likely produce around 85 percent as a strong street/strip engine. The same 350ci engine with 85 percent VE would require a much smaller carburetor (516 cfm) using this equation. As you can see, compression ratio, bore and stroke ratio, combustion chamber design, and much, much more are not even considered. In this case, a good street/strip engine would probably work best with at least a 600-cfm carburetor, and the same engine dedicated to the dragstrip would use every bit of a 650-cfm unit and sometimes more....
Jim |
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Jim Elliott
New Member
Posts:80
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| 13 Mar 2008 05:39 PM |
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Lets try the formula on a 8.1 engine (496) and I'm NOT going to push it over 4500 RPM.
496 X 4500 = 2232000
/3456 = 645.83333
X 0.85 V/E =548.895833 CFM
So a 600 carb would work fine, In fact I have installed a Edelbrock (1400) smog certified carb 600 CFM
on a Chebby 454 with excellant results...Now if the person would quit messing with it everything
would be fine..................
Also the 0.85 V/E was a dab generous IMHO and the only heads that come close to the 100% are AFR heads
but I'm NOT a fan of aluminum heads on a motor home.......
Wanna play more? Since the head gaskets are rather thick (stock) zip over to the Chevy house and purchase
some stock steel shim head gaskets that are 20 thou thick, With the 20 thou gaskets and with the pistons
down below the top of the block about 22-25 thou that will give you almost a perfect quench and end the
ping and detonation problem mucho plus the compression ratio will increase a dab also.
Jim
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Gon Mad
New Member
Posts:20
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| 13 Mar 2008 09:36 PM |
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Let me share some personal experience with the 600 carb. It's OK for driving & NOT towing anything BUT when you hook up a heavy trailer it wont pull a fat girl off a tricycle. I switched to the 650 Thunder series (it has an adjustable secondary) & it pulls better than the 750 carter carb & the 600 edelbrock. The mileage stayed the same for the 650 as the 600. Not to mention the factory uses 650 Quadrajet carbs stock . The 600 (I dont think) is as well engineered as the AVS or Thunder series whereas the 600 is the AFB.Both work & I own about 10 of them currently My experience is that the larger will pull harder & the 600 wimps out passing or steep hill climbing. Too bad Predator doesn't make a street conifugured variable venturi fuel metering device. I guess fuel injection would be better but more expensive. Gotta go now CYA! Steve |
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Jim Elliott
New Member
Posts:80
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| 13 Mar 2008 11:59 PM |
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Posted By Gon Mad on 03/13/2008 10:36 PM
Let me share some personal experience with the 600 carb. It's OK for driving & NOT towing anything BUT when you hook up a heavy trailer it wont pull a fat girl off a tricycle. I switched to the 650 Thunder series (it has an adjustable secondary) & it pulls better than the 750 carter carb & the 600 edelbrock. The mileage stayed the same for the 650 as the 600. Not to mention the factory uses 650 Quadrajet carbs stock . The 600 (I dont think) is as well engineered as the AVS or Thunder series whereas the 600 is the AFB.Both work & I own about 10 of them currently My experience is that the larger will pull harder & the 600 wimps out passing or steep hill climbing. Too bad Predator doesn't make a street conifugured variable venturi fuel metering device. I guess fuel injection would be better but more expensive. Gotta go now CYA! Steve Steve, I'm toooo cheap and hate spending the money on the AVS or Thunder series carbs  There is two different Rochester carbs stuck on those units.....750 is the average carb but the 800 CFM was also on the books............ One of the big reasons I love a (properly setup) Rochester 750 is the primarys are smaller on that spread bore and the square bore carb are 300 CFM VS the 275 or so on the spread bore......As long as my foot is out of the the back 2 toilets the milage is good. Jim |
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stacey
New Member
Posts:28
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| 14 Mar 2008 05:24 AM |
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EFI... Man if I only had the money tree in full bloom. Almost bought one on ebay called a "mega squirt" last fall but shyed away when it hit over 400.00
Here is what I'm up to. I have the 800 Edelbrock sitting on an adapter plate that funnels the 2 front barrels down to the little peanut 390 cfm barrels on my Edebrock Performer 2.0 intake. Old intake, I know. Probably not the best idea funneling down a Big 800 either. But hey, that's what I'm working with. I just welded a O2 senser in and I'm borrowing a wide band air/fuel ratio meter that will read idle, cruise, and wot. I'll probably never need to nail the trottle but I might get an itch at a street light if a mustang pulls up next to me.
If all fails I'll put the quadrajet back on and try and tweak that with the wide band. I bought the 800 cheap enough to horse around. I do notice I don't have my foot into the carb now as I did with the quad and my vacuum is a about 2 #'s higher at cruise. Does that mean anything? Probably not. In the end a 492 even with a Gear Vendor is going to have a very personal relationship with Exon.
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duct-tape
New Member
Posts:1
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| 14 Mar 2008 07:29 AM |
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I have built 3 megasquirt cars you can find it cheaper here: http://www.diyautotune.com/ I lOOOOOve my 454 with megasquirt and throttle bodies, it's responsive it's ridiculous. (this isn't a spam, I was trolling when I saw your post) |
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Jim Elliott
New Member
Posts:80
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| 14 Mar 2008 01:31 PM |
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Posted By duct-tape on 03/14/2008 8:29 AM I have built 3 megasquirt cars you can find it cheaper here: http://www.diyautotune.com/ I lOOOOOve my 454 with megasquirt and throttle bodies, it's responsive it's ridiculous. (this isn't a spam, I was trolling when I saw your post) Duct tape, I looked at the web site.....No help cuz I'm a carb guy  For the carb folk's I'll dig around for the modifications for carbs on the Chebby high performance web site...... Jim |
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Capt.Dan
Basic Member
Posts:126
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| 14 Mar 2008 11:49 PM |
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Hi, When i was thinking about getting rid of the Q-junk I went with the thunder series and 650 cfm and that really helped mine as it was a gutless wonder and now, I can race for the camping spot! With the vacumn gage I am using less pedel and getting more power and also a higher vacumn. That later means it is getting more power for less gas and that is Always a good thing!! I love that thunder series!!! The one I have has bigger secondarys as it was made for a thermoquad for Dodges like the 440! I needed a plate but there is not much on the primarys, only secondarys. I am getting around 8-10 mpg, somewhere in that range. Mine is small though at 25 feet.  |
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stacey
New Member
Posts:28
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| 15 Mar 2008 03:31 PM |
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Update on the wideband o2 censor hooked up to the engine!
My idle is easily adusted to get a 14.7 readout but my wot and my cruising air/fuel is a way too lean 16.
Now this is a 800 edelbrock dumping down into a 492 BB. I have a calibration kit for the carb and I'm spending the day tuning. I guess I'm shooting for a mid 14? |
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Jim Elliott
New Member
Posts:80
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| 15 Mar 2008 10:33 PM |
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Posted By stacey honn on 03/15/2008 4:31 PM
Update on the wideband o2 censor hooked up to the engine!
My idle is easily adusted to get a 14.7 readout but my wot and my cruising air/fuel is a way too lean 16.
Now this is a 800 edelbrock dumping down into a 492 BB. I have a calibration kit for the carb and I'm spending the day tuning. I guess I'm shooting for a mid 14? 14.9 on a light cruise would be nice, 16-17 inches of manifold vacuum would support the air/fuel ratio.
12.8 or a dab richer hill climbing with a vacuum of 5 or less inches would be safe also.....
I use a "Snap-on" smog test machine (old) to dial mine in but the (LM1) wideband is looking real good for the price.
Jim |
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