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By ianmatt - 7 Years Ago
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Guys I am ready to push the purchase button. I have chosen a summit racing carb for my 292 .060 over, pertronix, header, mummert intake, and original heavy t-98 trans. what are your thoughts on 500 vrs 600 cfm? why? I'm ready let me know and THANK YOU
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By charliemccraney - 7 Years Ago
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Which cam?
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By ianmatt - 7 Years Ago
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Isky mild
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By charliemccraney - 7 Years Ago
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specs?
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By ianmatt - 7 Years Ago
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here are the cam specs
ISKY - Grind No./Type E-4 SOLID Low/Mid-Range performance cam. 9.5-1 compr. 3.08-3.70 axle ratio. Passenger cars and trucks. Up to 625 CFM Carb.RPM-Range 2000-5000 Valve Lift - INT .425 EXT .425PART NUMBER: 301444 GRIND NUMBER: e-4
ENGINE INFO: FORD-MECURY-T-BIRD (Y-BLOCK) V8 272-292-312 C.I. ENGINES APPLICATION:
SPECIAL REMARKS: SOLID PRODUCT USE: STREET
RPM RANGE: 2000-5000
Valve lift is calculated with zero lash and rocker ratio of 1.5
INTAKE TIMING DURATION: 260 deg.
OPEN: 22 BEFORE TDC
CLOSE: 58 AFTER BDC
CAM LIFT: .283"
VALVE LIFT: .425"
VALVE LASH: .015 HOT
.017 COLD
EXHAUST TIMING DURATION: 260 deg.
OPEN: 58 BEFORE BDC
CLOSE: 22 AFTER TDC
CAM LIFT: .283"
VALVE LIFT: .425"
VALVE LASH: .015 HOT
.017 COLD
LOBE CENTER: 108 deg. OVERLAP: 44 deg. CAM ADVANCE: 0 deg.
THE ABOVE TIMING IS CHECKED AT .020 (OPEN) LIFTER RISE
.020 (CLOSE)
The following timing is taken at .050" lifter rise and gives a more accurate determination of camshaft position.
INTAKE DURATION: 216 deg.
OPEN: 0 BEFORE TDC
CLOSE: 36 AFTER BDC
EXHAUST DURATION: 216 deg.
OPEN: 36 BEFORE BDC
CLOSE: 0 AFTER TDC
RECOMMENDED ISKY CAM KIT PARTS AND SETUP INFORMATION
LIFTERS: 302-H LIFTER TYPE: SOLID
SPRING: 6005 TYPE: dual w/damper DIA.: 1.430" RATE: 275 lbs per inch
INSTALLED HEIGHT: 1.750" SEAT PRESSURE: 135 lbs OPEN PRESSURE: 285 lbs
COIL BIND: 1.120"
SPRING SHIMS: # 2
STEEL RETAINERS: 507-ST
TITANIUM RETAINERS: 60-TI
PUSHRODS: 303 TYPE: non adjustable LENGTH: 8.187" DIA.: 3/8"
ROCKER ARMS: TYPE: RATIO:
VALVE LOCKS: VL-32
VALVE LOCKS: VL-32
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By charliemccraney - 7 Years Ago
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You get a lot for your money with the Summit carbs so I think either one will work for you. The 500 should be adequate but it is best to err on the larger side with a vacuum secondary carb, so I think the 600 will be the best choice. That gives you a little more room for future upgrades.
The most important thing, no matter which one you go with, is that you learn to tune it. Despite their claims, there is no such thing as a ready-to-run carburetor right out of the box. They all require tuning.
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By ianmatt - 7 Years Ago
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Awesome I was thinking the same thing. Now I need to dial in what jets will work best for 5000 feet above sea level for my set up. From what I have heard this engine likes a bit more gas. Any experience or thoughts on jets for the elevation? The 600cfm comes with bigger jets than the 500 as well.
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By charliemccraney - 7 Years Ago
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No idea. Start with the out of the box tune and adjust from there. There is nothing special about a Y as far as a/f ratio. It doesn't like gas any more or less than any other engine.
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By miker - 7 Years Ago
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As to altitude-Ted posted something about that not long ago. If the tuning manual for the carb doesn't address that, pull up the Edelbrock manual for a 600 or so carb. They've got a chart or reference about that. It's a pretty standard chart, should get you started.
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By ianmatt - 7 Years Ago
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Just got my summit carb. next day shipping is amazing. One thing I know I had to do with my set up when I was messing with an older holley carb last summer was change the power valve. I ended up seeming to have the best success with a 5.5 power valve. While I am in there I want to pick the right jets. Any suggestions? I know the stock jets for sea level are not going to be right for colorado. The stock jets are Primary Jet Size:67 and Secondary Jet Size:73. I might go down just a tad to start. Thoughts?
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By charliemccraney - 7 Years Ago
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Start with the baseline, out-of-the box settings and see what it needs. Don't make any guesses.
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By miker - 7 Years Ago
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I'd go with Charlie on this. See how it runs, check the plugs, then go to the tuning manual. It did come with a tuning manual, didn't it? It's your best friend.
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By 57RancheroJim - 7 Years Ago
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Somewhere in my stash of info I had the factory listed jet sizes for different altitudes that always showed slightly smaller jets for 3000-5000 ft and then smaller again for 5000+. Naturally I can't find it now.
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By charliemccraney - 7 Years Ago
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Jet sizes for any carb other than the Summit carb will not be applicable. It should follow the same trend. That is it.
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By 57RancheroJim - 7 Years Ago
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Thats all I was suggesting, regardless of carb make the jetting will be smaller at higher altitudes in most cases. Just using the factory specs as an example.
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By ianmatt - 7 Years Ago
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Been running the summit 600cfm and love it. lots more power and smoother. One problem I am having is if I blip the throttle reall quick it revs nice but then the idle will drop really far and want to die. Any thoughts? i have checked the float levels and fuel pressure is right around 5. so close to perfection if I can just get this one thing dialed. thanks
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By Outlaw56 - 7 Years Ago
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Who makes the carbs for Summit?
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By ianmatt - 7 Years Ago
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Ported vacuum fixed it. weird but it likes that way better than manifold vacuum
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By Ted - 7 Years Ago
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Outlaw56 (2/12/2017)
Who makes the carbs for Summit?
That would be Holley. Here’s a picture of the 600 and 750 cfm carbs when Holley was selling them.
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By Outlaw56 - 7 Years Ago
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One of my Yblocks is a 292 that is eventually going to be built to the max. I got an edelbrock for that one already. I have another 272 that will forever be tame while I have it, and no plans for much over stock. Would the 600 still be a good choice just in case? Maybe Im better off sticking with Edelbrock so I dont have to figure out tuning on two different carbs?
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By charliemccraney - 7 Years Ago
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For something that is pretty much stock, 500cfm will be fine. However, for your 292 that will be built to the max, 600 is too small.
Carburetors are more or less the same as far as tuning goes. If you know how to do one, then you pretty well know how to do any other. You just have to understand how items on one carb are applied differently on another. A good example of that with Edelbrock is the power valve. Edelbrocks use a plunger, spring, and metering rod to perform the same function as a power valve. Different method for the same goal. If you simply understand the basics of how that works, then it applies to any carb. You just have to know what the analog is for the particular carb you are working on. I wouldn't shy away from another carb just because it functions slightly differently.
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By Outlaw56 - 7 Years Ago
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Thanks guys, definitely something to consider both ways. Im 68 years old and only have two Y blocks to every work on and probably will never get into the tuning aspect more than just getting them running good and staying tuned. My brother in law is a retired mechanic so I have a good teacher to get them set up.
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By Canadian Hot Rodder - 7 Years Ago
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Not sure if this will help anyone, but I am running a Holley 570 Street Avenger, bolted on, as is out of the box. Runs great with no lag from primaries to secondary's, and does not run out of fuel at top end. Running a Mummert intake & 284S cam, 30 over 292, 10.5 to one compression and un-ported 57 G heads.
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By ErnieL - 4 Years Ago
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let’s revive this one and call it Lazarus
I’m running a sleepy and stock ‘57 Turnpike Cruiser 312 in my 56, and I’m taking the leap to improve drivability. A Mummert intake and Summit 600 carb, plus I picked up a distributor for a 60s 292. It’ll get a Pertronix, and after that, I’m done. It should wake that thing up, because right now it’s like it’s asleep.
Comments?
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By Joe-JDC - 4 Years Ago
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A Summit 750 will help with about 8 more horsepower, all else being equal, over the 600. Joe-JDC
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By paul2748 - 4 Years Ago
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I disagree on the 750 CFM carb - much too much carb for a basically stock 312.. Even 600 CFM is pushing it.
I hope you don't think you are going to get a large HP increase with the mods you mentioned. While they will help, your not increasing the HP that much over stock.. As far as the intake, your are just as well off with a "B" manifold.
If your going to start a new posting, always start fresh. Using an old posting is not the way to go.to get good responses.
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By Ted - 4 Years Ago
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There are so many misconceptions when it comes to carburetor sizing. While double pumper carbs or those with mechanical secondaries can be and usually are sensitive to over carburetion issues in the lower rpm ranges, vacuum secondary carbs present a completely different scenario. When dealing with vacuum secondary carburetors, it’s suggested to always oversize intentionally so that the carburetor is never in a position to be too small or ‘under-carbureted’. When the vacuum secondaries are properly set up which is the case much of the time when using them out of the box, the secondary actuation only opens the amount required based on the demand from the engine. If the carb is on the big side which may be the case when flooring the throttle from idle or at a low rpm, then the secondaries only open partially or the amount required. As the rpm increases, air flow through the venturies increases thus giving the carb the signal to open the secondary blades appropriately. Because most driving with a vacuum secondary carburetor is performed using only the primary side, it’s the primary side venturi sizing that important. A 750 cfm carb is essentially the same as a two barrel carb in this respect.
I have a basically stock 272 in a ’55 Ford with nothing but a Isky E4 camshaft and it currently has the Summit 500 cfm carb on it. That carb is too small which becomes obvious when running the engine past 5000 rpm but it’s a good driver otherwise. The key here is I likely don’t need a larger carburetor as that engine really doesn’t need to be wound much tighter than 5000 rpm. But to prove a point to customers, I have had a 1050 cfm Holley Dominator carb on that engine and it runs just fine abeit just not flooring it a low rpm. There is an obvious bog in that instance. For dead stock Ford Y engines or those with just a small camshaft upgrade, I’ll typically recommend a 600 cfm carb. For those Y engines with modifications that improves the air flow (camming, porting, intake manifolds, improved exhaust, etc.) I will recommend a 750 cfm carb. If top end performance is not a factor, then a smaller carburetor will suffice.
A case in point is a 330” Y that was dynoed yesterday with a Summit 750 cfm carb. With this particular carb, the engine is under carbureted but will still be a spirited driver in the ’57 Ford it is slated to be dropped into. It has the normal mods such as a 228/238 Isky cam ground on 110° lobe centers, Mummert aluminum heads and intake manifold, and a MSD ignition recalibrated so all the mechanical timing is in by 3000 rpm while the vacuum advance provides up to 48° total timing while in cruise mod. If cruising at less than 3000 rpm, then the total timing will obviously be less than 48°. Total timing under full throttle drops back to 36° at 3000 rpm and greater. The manifold vacuum at 6000 rpm is 1.5” Hg which is a strong indicator that this engine would like a larger carburetor for maximum performance. But it will be a daily driver so a 750 cfm vacuum secondary carb it is.
Here’s the link to a past Y-Block Magazine article where a 304” Y with iron heads uses a 750 cfm carb. Prior to the Covid-19 pandemic, the owner of that engine visited regularly and made it a point to remind me how good that engine starts and drives.
https://www.eatonbalancing.com/2015/05/01/unported-iron-heads-can-still-make-over-a-hp-to-the-cubic-inch/
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By capelo - 4 Years Ago
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Ted (8/16/2020)
There are so many misconceptions when it comes to carburetor sizing. While double pumper carbs or those with mechanical secondaries can be and usually are sensitive to over carburetion issues in the lower rpm ranges, vacuum secondary carbs present a completely different scenario. When dealing with vacuum secondary carburetors, it’s suggested to always oversize intentionally so that the carburetor is never in a position to be too small or ‘under-carbureted’. When the vacuum secondaries are properly set up which is the case much of the time when using them out of the box, the secondary actuation only opens the amount required based on the demand from the engine. If the carb is on the big side which may be the case when flooring the throttle from idle or at a low rpm, then the secondaries only open partially or the amount required. As the rpm increases, air flow through the venturies increases thus giving the carb the signal to open the secondary blades appropriately. Because most driving with a vacuum secondary carburetor is performed using only the primary side, it’s the primary side venturi sizing that important. A 750 cfm carb is essentially the same as a two barrel carb in this respect. I have a basically stock 272 in a ’55 Ford with nothing but a Isky E4 camshaft and it currently has the Summit 500 cfm carb on it. That carb is too small which becomes obvious when running the engine past 5000 rpm but it’s a good driver otherwise. The key here is I likely don’t need a larger carburetor as that engine really doesn’t need to be wound much tighter than 5000 rpm. But to prove a point to customers, I have had a 1050 cfm Holley Dominator carb on that engine and it runs just fine abeit just not flooring it a low rpm. There is an obvious bog in that instance. For dead stock Ford Y engines or those with just a small camshaft upgrade, I’ll typically recommend a 600 cfm carb. For those Y engines with modifications that improves the air flow (camming, porting, intake manifolds, improved exhaust, etc.) I will recommend a 750 cfm carb. If top end performance is not a factor, then a smaller carburetor will suffice. A case in point is a 330” Y that was dynoed yesterday with a Summit 750 cfm carb. With this particular carb, the engine is under carbureted but will still be a spirited driver in the ’57 Ford it is slated to be dropped into. It has the normal mods such as a 228/238 Isky cam ground on 110° lobe centers, Mummert aluminum heads and intake manifold, and a MSD ignition recalibrated so all the mechanical timing is in by 3000 rpm while the vacuum advance provides up to 48° total timing while in cruise mod. If cruising at less than 3000 rpm, then the total timing will obviously be less than 48°. Total timing under full throttle drops back to 36° at 3000 rpm and greater. The manifold vacuum at 6000 rpm is 1.5” Hg which is a strong indicator that this engine would like a larger carburetor for maximum performance. But it will be a daily driver so a 750 cfm vacuum secondary carb it is. Here’s the link to a past Y-Block Magazine article where a 304” Y with iron heads uses a 750 cfm carb. Prior to the Covid-19 pandemic, the owner of that engine visited regularly and made it a point to remind me how good that engine starts and drives. https://www.eatonbalancing.com/2015/05/01/unported-iron-heads-can-still-make-over-a-hp-to-the-cubic-inch/
I also have a summit 750 cfm in my Y-block 302 and for the moment both the operation and the consumption are fine, no complaints
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By Florida_Phil - 4 Years Ago
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This is an interesting thread. The way I see it, a vacumn secondary carburetor is a two barrel with extra cfm available on demand. When street driving, 90% of the time you are running on the front of the carb. If my thinking is correct, the size of the front venturis is what determines the drivability or lack of such. My TBird has a .060" over 292 engine with stock 1957 312 heads, iron intake and distributor. The only modification is an Isky 301333 cam which has a noticeable lope at idle. I have an out of the box Holley 1848-1 465 cfm carburetor with a 1" spacer on the top of the iron manifold. I chose that carburetor because it's a copy of the stock 1957 312 carburetor. I like the stock look and I figured if it was good enough for Ford, it's good enough for me. My car has a stock manual transmission with O/D and a 4.11 gear. Throttle response is instantaneous with no bogs or hesitation. My engine idles at 600 rpm, my plugs are perfect and my tailpipes are clean.
The question I always have is, Would my car perform better with a larger carb? Would a 600 cfm make a noticeable difference? How about a 750 cfm? When I stab the throttle, the back barrels open like they should. While my TBird is never going to blow away any late model muscle cars, it's faster than many would think. I think the question of carb size depends upon so many factors it's hard to make generalizations. I am sure I could easily over carb my 292. If I did, it would run like a light switch, either all on or off. I prefer drivability over top end performance.
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By charliemccraney - 4 Years Ago
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Assuming it is not significantly under-carbed. and as long as the mixture is correct with the smaller carb, you will not gain a whole lot with a larger carb, for street use. In the dyno info I've seen where carb cfm was the only change, the larger carb will tend to show improvements below the peak of the smaller carb but it's usually at such a high rpm that it is useless for most street driving. For instance, if the smaller carb peaked at 5000rpm, the larger might start to show improvements around 4000rpm and peak higher.
Lower end, entry level carbs tend to be geared toward a particular performance level so it is possible for a smaller carb to provide a less than ideal fuel mixture because it is just not set up for a higher performance engine. They can usually be modified to work but the modification is beyond the ability of the average person. This can result in poor overall performance with the smaller carb. This is one of several areas where the Summit carbs shine because they have adjustable air bleeds, which are not usually found on a carburetor at that price point and those allow you to tailor it to a wider range of performance.
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