Here is another thing for you to consider.
There is none of us who know your engine buiding capabilites or your tuning abilites better than you. I have learned in dealing with the public in customer's engines, that things I used to do and to get away with on my own with me talking care of it, are much different than what I will do with a customer's.
I have learned the hard way about this. Back many years ago, I had two different customers with two different engines both end up with the exact same problems with solid lift roller cams in daily street driven performance engines. I send the lifters back to Crane for an analysis and in both instances I was told that the spring pressure was too high for the amount of lubrication they were getting. The SB Chevy had 200# on the seat and the BB Mopar had only 180# on the seat and both suffered the same exact problems with lifters. Crane strongly advised me against using the solid rollers for their street engines. I disregarded them and did it again on both engines but pumped the oil pressure up a little higher and broughtthe SB Chevy down to 180# on the seat. Both engines again ended up with lifter and cam failures.
In times past In my own engines I had run as much as .680 lift intake with seat pressures of 220# and I never had any issues at all. All of my life mostly in my own stuff was either solid lift or solid lift rollers. I never had issues. A custmer application is different for several reasons. Most will not do the routine checks and maintenance that being on the edge requires. They do not watch their oil condition heavily, like I did, and they idle the engines all the time with much of the idling being in gear in a traffic jam or at a stop ligt which brings oil flow and pressure way down. Another thing customers do un-nerves me big time. If they hear something different or that they question, they keep driving it.
When a poster tells us they are street driving we try to help them without getting them in trouble. It does not matter what we can do, It does matter what the person we are trying to give good information to can do. I know that I can meet your goals if I were builing this for me. I would not try if I were building it for anyone other than me.
That AFR Head does promise to be a killer and you should be very happy with it when you get them. Joe probably nows that head and what combinations will work with it better then any of us yet.
I agree about don't use the Comp Cam that is cast. Use the Billet and ask for a cast gear n it. iF you can talk with Tim Cole there. He is pretty sharp. Comp and most mainstream cam companies valve spring recommendations touch on what is the minimum that will work, and their recomended spring pressures for hydraulics is far out. I do recommend using titanium retainers.
You can send a PM here to UDHarold. He is one of the better cam guys there is and ask him about him doing you a cam.
Consider that most things you do for performance in an engine will be like a see-saw effect. The more you do to improve top end power will result in less bottom end power and response. So if you are shooting for maximum power available in the upper end rpm and upper horsepower ranges it will result in the car being like a slow balky pig when you have to nail it for a quick low speed response. There has to be a trade off about which is the more important for you.
If you can afford it, I kile a good EFI system for street. if not I suggest to not go hog wil in carb size or intake runner sizes.
If they have one that will fit your car, the Schoenfield Headers are some pretty good reasonably priced performance headers and they are made with good quality. My other suggestion is just get the cheapest Hedman that will work.
Consider the 2004R tranny. Those can be built to be pretty strong. I prefer a clutch for me though.
Ed
Suggestions please...600hp sbc buildup
Moderator: Team
First off I'll agree with Ed on the 700r4 AND about customers can kill something in two days what you make work on your own car for years. I succesfully built my own 700r4 to run around town and 60ft 1.45 and 10.88 in the 1/4......HOWEVER it seems that every time I build one for a customer that has anything over 500 HP it winds up having to come out in favor of a Turbo 350.
I also like to run more valve spring pressure than the cam co's recommend and have been warned by many pro's to stay away from the cast core cams.....I would heed that advice in this case FOR SURE, because a 600HP street engine is going to need more (and better)spring pressure than what I have heard the cast core can live with.....ESPECIALLY with the mileage you hope to get.....
The only OTHER thing that comes to mind is some advice I recieved from more than just a few that I respect their opinions is to stay away from the 850 CFM carb on a small block......I have heard from several that dyno AND track testing has proven the 950cfm to be a much better small block carb, and not because of CFM, but because the booster to venturi ratio is poor on that 850 carb and will lack the low rpm signal needed.....several claim to have better results with the 950 cfm even on a 500HP 355 cu in motor due to this signal issue.
I agree with the standard rings, the ATI balancer and internal balancing as well.
Hope this helps
I also like to run more valve spring pressure than the cam co's recommend and have been warned by many pro's to stay away from the cast core cams.....I would heed that advice in this case FOR SURE, because a 600HP street engine is going to need more (and better)spring pressure than what I have heard the cast core can live with.....ESPECIALLY with the mileage you hope to get.....
The only OTHER thing that comes to mind is some advice I recieved from more than just a few that I respect their opinions is to stay away from the 850 CFM carb on a small block......I have heard from several that dyno AND track testing has proven the 950cfm to be a much better small block carb, and not because of CFM, but because the booster to venturi ratio is poor on that 850 carb and will lack the low rpm signal needed.....several claim to have better results with the 950 cfm even on a 500HP 355 cu in motor due to this signal issue.
I agree with the standard rings, the ATI balancer and internal balancing as well.
Hope this helps
Sure there are many smarter than me, but at least I'm smart enough to ask THOSE GUYS for advice when needed!
I built a 406 for a s10 that we run on the street and track. We drove 35 miles one way to the next town once a month to race. Stock block, stock bolts, .030 over flat top pistons 11.3-1(pump gas motor), Brodix track 1's untouched, .670 lift roller cam with 1.6 rockers, dual plane intake, holley 850, 1.75 swap headers and it ran 11.80's not hooking to good with street tires. We changed intakes to a vic-jr and lost et big time(back into the 12's). Changed again to a weind(sp) and ran 11.20's with small slicks. Now the fun part. We put a cheater NOS kit on and started tuning it. First pass was 10.60 with a 150 and wheel spin. After many trips to the track and more NOS, our best was 9.90's at 137. (track didn't like us so back home we went) Not too bad for bolt on parts on a street s10, After all said and done and 4 yrs of street racing with NOS, a few pistons, and lotsa wins, the truck was sold. I just put another 406 together with canfield 220 heads, a nice roller, and so far it seems to be stronger than the other 406. Still tuning and trying different things.
Replace your valve springs often depending on how much you drive and check the rockers and lifters when you do. You should be able to get many miles out of this kind of an engine. The bearings always looked good when we had to replace a piston(3times). LOL
Hope this helps.
Harley
Replace your valve springs often depending on how much you drive and check the rockers and lifters when you do. You should be able to get many miles out of this kind of an engine. The bearings always looked good when we had to replace a piston(3times). LOL
Hope this helps.
Harley
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Cobra
You need to decide whether you are going to build a track car to use on the street occasionally, or a street car to use on the track occasionally! IMO, some forum members' recommendations are way more than should be used on this street car! With sticky street tires 425HP-450HP will suit your needs. More HP will require a good deal of chassis and suspension work to get the power down and fit slicks able to hook all that power. I can not in good conscience recommend a 4500-5000 stall converter for your application. A solid roller will not live in traffic conditions where you must idle motor for any longer than a short period of time. With the parts in a 600HP engine and a loose converter a simple cruise may not be a good experience. While some forum members are able to build 600HP pump gas motors that live, your experience may not be so good. I ask you to take my advice in the context it is given- from someone you do not know, over the internet! You need to decide what makes sense to you! Best of luck!
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lowflyr
It occurs to me that I should let you guys know a bit of my background so that you know where I'm coming from on this....for those who wish to skip a blog about myself, jump down below the dotted line.
I have built several small blocks now for myself and others. All have been in the 300-450hp range... I have spent a good deal of time working with a retired weekend racer of no significant fame turned carb tuner and engine builder in my late teens and assisted in several engine and carb buildups of his for his customers. Many of these engines were in the 400-500hp range. I do agree with the way you explain the difference in how an engine should be built for someone else vs for myself. I have seen engine failures due to pure stupidity on the operators behalf on a few engines which were built by myself or Robert... many people just have no concept of how to treat an engine and are only too eager to blame the engine builder for a failure.
-Bracing for the backlash- As much as I hate to admit this....I do have my mechanical engineering degree (every time someone finds this out it seems I get someone instantly assuming I have no common sense, or that I am unwilling to listen, or some other fabricated image they wish to paint me with
). Its usually best to just leave that point out....but I bring it up only to mention that I have spent hours in engine labs and I am a decently capable tuner, not to mention I am very familiar with modes of mechanical failure and the importance of lubrication. I do tend to avoid EFI due to the cost, and cost only.
Nonetheless, this is my first build of this power level, so I am bound to learn alot. I am always wanting to learn more and it drives me crazy when I see someone who is no longer willing to try something different....
I have no interest in building a motor less than 500hp again for my toy. Its time to move up. Regular maintenance is expected, lash adjustment, oil changes, spring checks, rocker arm checks, occasional teardown for inspection....and so on.
..........................................................................................................
It sounds like I will have to focus on the solid roller lifter lubrication if this engine is to survive street duty. Knowing what to expect is half the battle on this engine. I will have to see what I can do to to minimize the chance of failure with the cam. ie billet cam good, cast cam bad. Solid rollers will need help to survive, particularly at idle.
The 950 carb a better choice?? Wow, I did not see that coming. I figured a 750 would be suggested... But that's why I'm here asking questions. perhaps a Bg race demon RS will be my carb of choice. That way I can try several different cfm combinations.
Titanium retainers may not be necessary with the new AFR's 8mm valvetrain (like gen III sbc), but at this level why risk it....titanium retainers it is.
I will mention again, the 700r4 is more or less expected to fail. And I am fully aware that my chassis will not be anywhere close to optimized for this combination. The 200 4R is an interesting option that I had not looked at, but a standard trans is really my ultimate goal. A 600hp standard shift street car running plain street tires will in no way be competitive at the track, but it sure makes for a fun toy!
Ed, Harley, Wolfplace, Silverfox, Cobra, Joe, Alex, Eric, 69RS502 ad Longrodsbc thank you all for helping me out with the suggestions and comments. It's really got me thinking. Please do not hesitate to give more feedback. I guess cam selection is my primary area of focus now, along with making it survive street duty.
I have built several small blocks now for myself and others. All have been in the 300-450hp range... I have spent a good deal of time working with a retired weekend racer of no significant fame turned carb tuner and engine builder in my late teens and assisted in several engine and carb buildups of his for his customers. Many of these engines were in the 400-500hp range. I do agree with the way you explain the difference in how an engine should be built for someone else vs for myself. I have seen engine failures due to pure stupidity on the operators behalf on a few engines which were built by myself or Robert... many people just have no concept of how to treat an engine and are only too eager to blame the engine builder for a failure.
-Bracing for the backlash- As much as I hate to admit this....I do have my mechanical engineering degree (every time someone finds this out it seems I get someone instantly assuming I have no common sense, or that I am unwilling to listen, or some other fabricated image they wish to paint me with
). Its usually best to just leave that point out....but I bring it up only to mention that I have spent hours in engine labs and I am a decently capable tuner, not to mention I am very familiar with modes of mechanical failure and the importance of lubrication. I do tend to avoid EFI due to the cost, and cost only.Nonetheless, this is my first build of this power level, so I am bound to learn alot. I am always wanting to learn more and it drives me crazy when I see someone who is no longer willing to try something different....
I have no interest in building a motor less than 500hp again for my toy. Its time to move up. Regular maintenance is expected, lash adjustment, oil changes, spring checks, rocker arm checks, occasional teardown for inspection....and so on.
..........................................................................................................
It sounds like I will have to focus on the solid roller lifter lubrication if this engine is to survive street duty. Knowing what to expect is half the battle on this engine. I will have to see what I can do to to minimize the chance of failure with the cam. ie billet cam good, cast cam bad. Solid rollers will need help to survive, particularly at idle.
The 950 carb a better choice?? Wow, I did not see that coming. I figured a 750 would be suggested... But that's why I'm here asking questions. perhaps a Bg race demon RS will be my carb of choice. That way I can try several different cfm combinations.
Titanium retainers may not be necessary with the new AFR's 8mm valvetrain (like gen III sbc), but at this level why risk it....titanium retainers it is.
I will mention again, the 700r4 is more or less expected to fail. And I am fully aware that my chassis will not be anywhere close to optimized for this combination. The 200 4R is an interesting option that I had not looked at, but a standard trans is really my ultimate goal. A 600hp standard shift street car running plain street tires will in no way be competitive at the track, but it sure makes for a fun toy!
Ed, Harley, Wolfplace, Silverfox, Cobra, Joe, Alex, Eric, 69RS502 ad Longrodsbc thank you all for helping me out with the suggestions and comments. It's really got me thinking. Please do not hesitate to give more feedback. I guess cam selection is my primary area of focus now, along with making it survive street duty.
Imho,
I would not use the scat cast crank and expect it to live 30000 miles in this engine.
You will probably have to find some way of increasing the oil system capacity-either a larger pan/accusump system or some form of external oil pump and tank. In order for the lifters,rockers,etc. to live you will probably need more oil. The stock pan will not supply it.
It would be a good idea to hook up a knock sensor ignition timing retard system. Todays pump gas varies and it will eventually save you some problems.
Sounds like fun but if you run the et calc's it makes no difference if you have 500 or 600 hp on street tires-they just smoke. I am building a similar hp engine for an older gal's '73 'Cuda, but with 512". I talked to all her relatives to make sure they knew that I really wasn't trying to kill her and they said build it! Should be alot of fun to drive!
Good luck,
Please report the results.
P.S. I also have an engineering background(B.S.Electronics Engineering Technology).
I would not use the scat cast crank and expect it to live 30000 miles in this engine.
You will probably have to find some way of increasing the oil system capacity-either a larger pan/accusump system or some form of external oil pump and tank. In order for the lifters,rockers,etc. to live you will probably need more oil. The stock pan will not supply it.
It would be a good idea to hook up a knock sensor ignition timing retard system. Todays pump gas varies and it will eventually save you some problems.
Sounds like fun but if you run the et calc's it makes no difference if you have 500 or 600 hp on street tires-they just smoke. I am building a similar hp engine for an older gal's '73 'Cuda, but with 512". I talked to all her relatives to make sure they knew that I really wasn't trying to kill her and they said build it! Should be alot of fun to drive!
Good luck,
Please report the results.
P.S. I also have an engineering background(B.S.Electronics Engineering Technology).
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lowflyr
Interestingly I have not had any crank failures in any engine up to 450hp with stock cast iron cranks, no NOS of course. The scat cast steel crank is much stronger than stock, but for the cost difference, I should probably look for a forged crank. Now to dump that scat cast crank.....
The knock sensor is something I was looking at in the summit catalog this morning...MSD has a nice looking setup there for about $190. Good insurance for a pump gas motor of this level. Good call Cogburn.
With regard to the oiling system, I have an idea
.....this is always dangerous, but where else could possibly be better than here to discuss it.
Here it goes.... Since my car does not have A/C I was thinking of mounting an auxilliary belt driven oil pump in its place. Hold, on contain the laughter for a sec guys....what if I were to use a similar setup to drive the oil pump as an A/C compressor, i.e. a clutch setup, but rather set to engage below a certain rpm. Say I use a normally closed relay to keep it engaged below 3000rpm than use an rpm activated switch from my MSD ignition to shut it down above 3000rpm. This pump could be fed from the same oil pan, maybe not, haven't worked that out just yet. But, disregarding that for the moment I could use this (filtered of course) auxilliary oil supply to keep the lifters, rockers, springs (hey they need to keep cool too!), etc oiled very well. While I'm at it I can use the excess to spray the underside of the pistons and keep piston temps down to help ward off that pesky knock problem, along with keeping those wrist pins oiled. Now to keep excess oil from ruining ring seal and to keep the oil temps where they need to be.... this is really starting to sound like an engineers car isn't it?
The cost of this project it starting to climb thats for sure...I will get it finished, but to have it together before the summer is gonna be tough if not impossible financially. Anyway, I will keep you all posted as the results come in.
Cheers
By the way, that cuda sure sounds like it would be a blast as well. Good call on the whole contact the family first thing...
The knock sensor is something I was looking at in the summit catalog this morning...MSD has a nice looking setup there for about $190. Good insurance for a pump gas motor of this level. Good call Cogburn.
With regard to the oiling system, I have an idea
.....this is always dangerous, but where else could possibly be better than here to discuss it.Here it goes.... Since my car does not have A/C I was thinking of mounting an auxilliary belt driven oil pump in its place. Hold, on contain the laughter for a sec guys....what if I were to use a similar setup to drive the oil pump as an A/C compressor, i.e. a clutch setup, but rather set to engage below a certain rpm. Say I use a normally closed relay to keep it engaged below 3000rpm than use an rpm activated switch from my MSD ignition to shut it down above 3000rpm. This pump could be fed from the same oil pan, maybe not, haven't worked that out just yet. But, disregarding that for the moment I could use this (filtered of course) auxilliary oil supply to keep the lifters, rockers, springs (hey they need to keep cool too!), etc oiled very well. While I'm at it I can use the excess to spray the underside of the pistons and keep piston temps down to help ward off that pesky knock problem, along with keeping those wrist pins oiled. Now to keep excess oil from ruining ring seal and to keep the oil temps where they need to be.... this is really starting to sound like an engineers car isn't it?
The cost of this project it starting to climb thats for sure...I will get it finished, but to have it together before the summer is gonna be tough if not impossible financially. Anyway, I will keep you all posted as the results come in.
Cheers
By the way, that cuda sure sounds like it would be a blast as well. Good call on the whole contact the family first thing...
Just to clear up that part of my post.......................I have never tried a 750cfm on anything over 520HP......The 750 may indeed be okay for your combo......my advice is to NOT use the 850.....use either the 750 or the 950 as EITHER one of those will have a better low speed signal over the 850......lowflyr wrote:The 950 carb a better choice?? Wow, I did not see that coming. I figured a 750 would be suggested... But that's why I'm here asking questions. perhaps a Bg race demon RS will be my carb of choice. That way I can try several different cfm combinations.
Sure there are many smarter than me, but at least I'm smart enough to ask THOSE GUYS for advice when needed!
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lowflyr
Thats what I thought you were getting at silver. Just kinda surprised me to hear 950 vs 750...I was unaware of any issues with 850's...I was running a 650cfm vacuum secondary speed demon on my last build, also a 400sbc, albeit I shifted it at 5500rpm. I will be pushing my limits trying to tune this engine to run well on the street. Thanks for the heads up on the 850's cause that is what I was going for.
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bigjoe1
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600HP on the street
A Holley 950 is just a 750 main body on an 850 base. It is not any better than a 750. The last time I did a back to back, the 850 beat out the 950 by 23 HP on a 600 HP engine build up.850 should drive as good or better than the 750 or the 950. JOE SHERMAN RACING
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OldSStroker
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Re: Suggestions please...600hp sbc buildup
A 600 fwhp ~400 inch driver can be done. A recent build I saw did that, but it was a US$14k engine. LOTS of money was spent with a top name head porter, along with a super shortblock. The castings were not what you plan to start with.lowflyr wrote:Hi everyone,
This is my first buildup of an engine with this power level....so suggestions/critics are welcome. My goal is a 600hp pump gas (91 octane here in NS, Canada) engine which will see regular street use and weekend dragstrip duty likely on 5-6 weekends a year.
Thanks guys
I think listening to Joe Sherman is a very good idea, especially about rethinking your goals.
[i]"There are some people who, if they don't already know, you can't tell 'em."[b]....Yogi Berra[/b][/i]
[i]"Being able to "think outside the box" presupposes you were able to think in it." [b]--Bob Lutz[/b][/i]
[i]"Being able to "think outside the box" presupposes you were able to think in it." [b]--Bob Lutz[/b][/i]
Big Joe is dead on. That is why we always used an 850.
Not that I recommend a cast GM crank, but the first 406 was ran with factory cast crank, gm 5.7 pink rods, stock oil pan, pump and ross pistons. Now was this engine on borrowed time, well maybe, but it ran good and turned more rpm's than you would dream of. The cast crank took many bottles of a 200 hit hooking pretty hard( front wheels 6" high) right out of the hole at Gainsville Raceway. As for the 750 carb, it will work but your upper end power and rpm climb will be down a little. I have a 750 race Demon because I had it on my new 406 and it is holding it back although for a street car would be fine. Too small for a race car or high rpm mud truck. I have only built 6 or 7 engines and have never spun a bearing or broke a crank and all of them have turned way over 7000 rpm's.
Not that I recommend a cast GM crank, but the first 406 was ran with factory cast crank, gm 5.7 pink rods, stock oil pan, pump and ross pistons. Now was this engine on borrowed time, well maybe, but it ran good and turned more rpm's than you would dream of. The cast crank took many bottles of a 200 hit hooking pretty hard( front wheels 6" high) right out of the hole at Gainsville Raceway. As for the 750 carb, it will work but your upper end power and rpm climb will be down a little. I have a 750 race Demon because I had it on my new 406 and it is holding it back although for a street car would be fine. Too small for a race car or high rpm mud truck. I have only built 6 or 7 engines and have never spun a bearing or broke a crank and all of them have turned way over 7000 rpm's.
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lowflyr
Well, the carb choice is obviously a debated issue right now, and I have no problem testing a few different carbs on the dyno...so I'll leave the carb choice to a later debate. It will be an interesting comparison when the time comes.
As for rethinking my goals, absolutely not. If I NEED so spend $14kUS to do this, then I will take two years to build it. But I still do not see the need to spend that much yet. From what I can tell, my current expected total is around $9000 Canadian ($7650 US approx) and I do not see any reason to double my costs yet. I'm sure I can rig up some kind of oiling system to help the lifters, rockers, etc live. With the forged crank, and splayed 4 bolt mains, forged rods and piston, along with the adequate cylinder wall thickness, I have no reason yet to believe this engine will be a grenade on the bottom end. My top end with Jesel shaft mount roller rockers and a good solid roller lifters I think I have a fighting chance at least on top.
I would be interested in seeing what article you read that had $14K into it to make 600hp. Sounds like it could leave some good clues.
As for rethinking my goals, absolutely not. If I NEED so spend $14kUS to do this, then I will take two years to build it. But I still do not see the need to spend that much yet. From what I can tell, my current expected total is around $9000 Canadian ($7650 US approx) and I do not see any reason to double my costs yet. I'm sure I can rig up some kind of oiling system to help the lifters, rockers, etc live. With the forged crank, and splayed 4 bolt mains, forged rods and piston, along with the adequate cylinder wall thickness, I have no reason yet to believe this engine will be a grenade on the bottom end. My top end with Jesel shaft mount roller rockers and a good solid roller lifters I think I have a fighting chance at least on top.
I would be interested in seeing what article you read that had $14K into it to make 600hp. Sounds like it could leave some good clues.
I am currently involved in a very similar build up, much the same goals as you. Mine is going in a mid 80's Iroc as well. I am going with a Dart little M, forged internals and a 4" stroke, 4.125" bore. I had been hearing too many horror stories with stock 400 blocks cracking on the thrust wall, so I decided to go the Dart route. I am impressed with the thickness' you measured with your stock block. I will be running a mighty Denom 850 on a super victor or bowtie manifold. I believe there would be too much restriction with a Holly 750. I am running Dart Pro 1 230's ported by myself with CC around 73cc. Shooting for 11:1 CR. My cam is quite a bit more of an aggressive profile and is 259 @ .050 intake. I am shooting for 600 hp+ also. I am going to run a Rockland gear prepped T56 manual trans., along with a 12 bolt or 9"(haven't decided yet).
I think the two biggest problems we need to worry about for a street motor is valve spring and lifter failure. I am going to run the pro shaft rockers from T&D because they have pressurized lubrication to both the rocker bearings and the valve springs. They are the only ones that do that, that I know of. I haven't decided on which lifters, but they will have to have the pressurized oiling system like Comp cams endure-x or Isky redzone. A check up on valve lash every now and then should show if there are signs of lifter wear or failure. The springs will just need changed every so often like a maintenence thing.
If I am off base on anything, any of you guys on the forum may feel free to correct me. Just my .02, ARN
I think the two biggest problems we need to worry about for a street motor is valve spring and lifter failure. I am going to run the pro shaft rockers from T&D because they have pressurized lubrication to both the rocker bearings and the valve springs. They are the only ones that do that, that I know of. I haven't decided on which lifters, but they will have to have the pressurized oiling system like Comp cams endure-x or Isky redzone. A check up on valve lash every now and then should show if there are signs of lifter wear or failure. The springs will just need changed every so often like a maintenence thing.
If I am off base on anything, any of you guys on the forum may feel free to correct me. Just my .02, ARN
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Troy Patterson
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Re: 600HP on the street
I agree with Joe.bigjoe1 wrote:A Holley 950 is just a 750 main body on an 850 base. It is not any better than a 750. The last time I did a back to back, the 850 beat out the 950 by 23 HP on a 600 HP engine build up.850 should drive as good or better than the 750 or the 950. JOE SHERMAN RACING
If it were my engine, I'd run a 1000 - 1100 cfm 4150 HP, modified of course.
The 950 is kind of a bugger'd carb combination because people think their getting a larger carb, when from flow bench results I've seen indicated the 850 base on the 750 was worth about 20 cfm, not 200. I'll admit I did not check this info myself, but the 850 has a larger venturi alone with the larger base of the 950 - it MUST flow more air.
An important distinction here is that if your budget is limited and you are dealing with "stock" carbs, the recommendations made are safe, but proper tuning is still necessary for best performance and engine life. If you've got more money to spend, you can easily surpass performance levels of stockers!
I've seen .5 reductions in 1/4 mile times over conventionally modified and sized carbs - no problem. Think about it this way; if you build an engine that runs 12.0's, and you want to go 11.50's, you can do a bigger cam loosing driveability (to some degree) with stiffer valve springs (due to increased lift) or cam types with limited life (mech. rollers), bigger heads, bigger intakes, bigger stall converters and so forth in pursuit of faster 1/4 mile performance, all reducing the life and reliability of the engine, or you could make the investment into a carb that delivers greater performance, improves driveability, throttle response, fun, hp & tq and engine life. Boy that was a long sentence!
I used 11.50 as an example, but it holds true at any power level.
Just to let you know all carbs are not created equal.
Troy Patterson TMPCarbs.net TMP Carbs