Head Flows and Stroker info
02-13-2007, 11:33 AM
#1
Melting Slicks
Thread Starter
Head Flows and Stroker info
Hey all, I'm starting to research putting together a stroker, rebuilding my '91 L98/6spd coupe, and I have a couple of questions regarding head flow numbers and some stroker/crank info.
1st, head flow #s; is the number given for one cyl, one bank or all 8 cyl on a head? The reason I'm asking is numbers from, say an AFR 195 don't seem to pass enough air to fill the cylinders at high RPM, yet the seem to be one of the main types used in a lot of rebuilds... a 383 running at about 7000 RPM will pull about 750 CFM of air, while the head is specked to about 270 (depending on lift). Also, is this flow # now going to have to be reduced by 75% as the valve is closed 3 out of the 4 strokes? Or is this Per Cylinder, and multiply it by 8 and again by .25 (for the stroke count...)?
2nd, Stroker info. If I am correct to make an L98 a 383, I bore it to 4.030 and add a 3.75 crank...okay, that makes right at 383. In the current Engine Masters magazine they do a 383 on an LS engine. It must have smaller cylender bores, as they bore them to 3.905 and add a 4.000 crank. Okay, that makes just over 383 (not much, less than 1CuIn)...so it's got me thinking...If a 3.905" bore can take a 4"stroke, can I do that (easily) with my L98 bored to 4.030 and have somewhere around 406 (I did the math last night, but now am slacking at work...)
What I want to get out of this is just a ****-hot street daily driver. I'll possibly take it to a track sometime, I'd like to do some autocrossing but it won't be very often, maybe once or twice a year. I want it to have good street manners but still be a heck of a lot more than the 245 HP it was born with. And, since I live in a smog state, it will need to pass emiss testing
Thanks,
Tim
Somebody have a beer for me!
1st, head flow #s; is the number given for one cyl, one bank or all 8 cyl on a head? The reason I'm asking is numbers from, say an AFR 195 don't seem to pass enough air to fill the cylinders at high RPM, yet the seem to be one of the main types used in a lot of rebuilds... a 383 running at about 7000 RPM will pull about 750 CFM of air, while the head is specked to about 270 (depending on lift). Also, is this flow # now going to have to be reduced by 75% as the valve is closed 3 out of the 4 strokes? Or is this Per Cylinder, and multiply it by 8 and again by .25 (for the stroke count...)?
2nd, Stroker info. If I am correct to make an L98 a 383, I bore it to 4.030 and add a 3.75 crank...okay, that makes right at 383. In the current Engine Masters magazine they do a 383 on an LS engine. It must have smaller cylender bores, as they bore them to 3.905 and add a 4.000 crank. Okay, that makes just over 383 (not much, less than 1CuIn)...so it's got me thinking...If a 3.905" bore can take a 4"stroke, can I do that (easily) with my L98 bored to 4.030 and have somewhere around 406 (I did the math last night, but now am slacking at work...)
What I want to get out of this is just a ****-hot street daily driver. I'll possibly take it to a track sometime, I'd like to do some autocrossing but it won't be very often, maybe once or twice a year. I want it to have good street manners but still be a heck of a lot more than the 245 HP it was born with. And, since I live in a smog state, it will need to pass emiss testing
Thanks,
Tim
Somebody have a beer for me!
02-13-2007, 12:29 PM
#2
Racer
1) Flow is one runner/valve opened a specified amount at a specified pressure drop. Many people look too much to peak flow, which is only encountered a minimal amount of time per cycle, where mid-lift numbers are encountered twice during each valve cycle. That said, AFR's are very good heads.
2) 4.030 bore and a 4.000 stroke = 396, and is a popular setup (383 is cheaper and easier though).
Keep in mind you'll need to upgrade your cam, intake, injectors, tune, and exhaust to maximize benefit.
In CA, that means you'll need to run a Super Ram for best power (only LTR's and Super Ram are legal in CA), and LT Headers are out, though your locale may be different (check), or perhaps you know someone etc?
2) 4.030 bore and a 4.000 stroke = 396, and is a popular setup (383 is cheaper and easier though).
Keep in mind you'll need to upgrade your cam, intake, injectors, tune, and exhaust to maximize benefit.
In CA, that means you'll need to run a Super Ram for best power (only LTR's and Super Ram are legal in CA), and LT Headers are out, though your locale may be different (check), or perhaps you know someone etc?
Hey all, I'm starting to research putting together a stroker, rebuilding my '91 L98/6spd coupe, and I have a couple of questions regarding head flow numbers and some stroker/crank info.
1st, head flow #s; is the number given for one cyl, one bank or all 8 cyl on a head? The reason I'm asking is numbers from, say an AFR 195 don't seem to pass enough air to fill the cylinders at high RPM, yet the seem to be one of the main types used in a lot of rebuilds... a 383 running at about 7000 RPM will pull about 750 CFM of air, while the head is specked to about 270 (depending on lift). Also, is this flow # now going to have to be reduced by 75% as the valve is closed 3 out of the 4 strokes? Or is this Per Cylinder, and multiply it by 8 and again by .25 (for the stroke count...)?
2nd, Stroker info. If I am correct to make an L98 a 383, I bore it to 4.030 and add a 3.75 crank...okay, that makes right at 383. In the current Engine Masters magazine they do a 383 on an LS engine. It must have smaller cylender bores, as they bore them to 3.905 and add a 4.000 crank. Okay, that makes just over 383 (not much, less than 1CuIn)...so it's got me thinking...If a 3.905" bore can take a 4"stroke, can I do that (easily) with my L98 bored to 4.030 and have somewhere around 406 (I did the math last night, but now am slacking at work...)
What I want to get out of this is just a ****-hot street daily driver. I'll possibly take it to a track sometime, I'd like to do some autocrossing but it won't be very often, maybe once or twice a year. I want it to have good street manners but still be a heck of a lot more than the 245 HP it was born with. And, since I live in a smog state, it will need to pass emiss testing
Thanks,
Tim
Somebody have a beer for me!
1st, head flow #s; is the number given for one cyl, one bank or all 8 cyl on a head? The reason I'm asking is numbers from, say an AFR 195 don't seem to pass enough air to fill the cylinders at high RPM, yet the seem to be one of the main types used in a lot of rebuilds... a 383 running at about 7000 RPM will pull about 750 CFM of air, while the head is specked to about 270 (depending on lift). Also, is this flow # now going to have to be reduced by 75% as the valve is closed 3 out of the 4 strokes? Or is this Per Cylinder, and multiply it by 8 and again by .25 (for the stroke count...)?
2nd, Stroker info. If I am correct to make an L98 a 383, I bore it to 4.030 and add a 3.75 crank...okay, that makes right at 383. In the current Engine Masters magazine they do a 383 on an LS engine. It must have smaller cylender bores, as they bore them to 3.905 and add a 4.000 crank. Okay, that makes just over 383 (not much, less than 1CuIn)...so it's got me thinking...If a 3.905" bore can take a 4"stroke, can I do that (easily) with my L98 bored to 4.030 and have somewhere around 406 (I did the math last night, but now am slacking at work...)
What I want to get out of this is just a ****-hot street daily driver. I'll possibly take it to a track sometime, I'd like to do some autocrossing but it won't be very often, maybe once or twice a year. I want it to have good street manners but still be a heck of a lot more than the 245 HP it was born with. And, since I live in a smog state, it will need to pass emiss testing
Thanks,
Tim
Somebody have a beer for me!
Last edited by doug_dayson; 02-13-2007 at 12:31 PM.
02-13-2007, 12:42 PM
#3
Drifting
#1...The flow numbers are for each individual port. The AFR heads flow very well; the best for their size as far as I know. The size to flow ratio is important on a streetable motor.
#2... The LS blocks do have smaller bore, but this has nothing to do with it's ability to take a 4" crank. That is in the design of the block. A 4" crank can be used in an OEM block but, it requires someone who knows what they're doing. Some block fill, reduced base cam, and lots of grinding for clearence is required.
#3...Do a search as this has been discussed a number of times over the years.
396= 4.030 bore+3.875 stroke
#2... The LS blocks do have smaller bore, but this has nothing to do with it's ability to take a 4" crank. That is in the design of the block. A 4" crank can be used in an OEM block but, it requires someone who knows what they're doing. Some block fill, reduced base cam, and lots of grinding for clearence is required.
#3...Do a search as this has been discussed a number of times over the years.
396= 4.030 bore+3.875 stroke
Last edited by Curveit; 02-13-2007 at 12:44 PM.
02-13-2007, 01:14 PM
#4
Melting Slicks
Thread Starter
Thanks
Thanks Guys,
The info about the flow makes a little more sense. 2 recent mags both made 600+hp 383's with AFR's, one with 195's the other with I think it was 210's. (195 on carbeurated, the other on the LS, injected). NOT looking for that much, but it's nice to know the exreme possibilities
I don't want to get into too much modification...block fill, reduced base cam is too much... a little clearance ginding to make the stroke work is one thing (if needed) but I'm not going to try and eek out every last little HP I can with it.
As for "legal" parts...the only part they check for is cat, the rest is just a sniff-test, so as long as the parts burn it clean enough, I'll be okay.
Injectors, heads, cam, intake, headers/exhaust will all be figured into the build...I'm not going into this with blinders on! This is down the road a little so I'll have plenty of time to do more research.
Tim
The info about the flow makes a little more sense. 2 recent mags both made 600+hp 383's with AFR's, one with 195's the other with I think it was 210's. (195 on carbeurated, the other on the LS, injected). NOT looking for that much, but it's nice to know the exreme possibilities
I don't want to get into too much modification...block fill, reduced base cam is too much... a little clearance ginding to make the stroke work is one thing (if needed) but I'm not going to try and eek out every last little HP I can with it.
As for "legal" parts...the only part they check for is cat, the rest is just a sniff-test, so as long as the parts burn it clean enough, I'll be okay.
Injectors, heads, cam, intake, headers/exhaust will all be figured into the build...I'm not going into this with blinders on! This is down the road a little so I'll have plenty of time to do more research.
Tim
02-13-2007, 01:54 PM
#5
Burning Brakes
As for "legal" parts...the only part they check for is cat, the rest is just a sniff-test, so as long as the parts burn it clean enough, I'll be okay.
I forgot to look at your state before this, so forgive me
if I am talking the wrong state....Ca also does a visual. This takes out tube headers as okay on a car that came with pre cats. AFR 195's do have an EO#
I do not think our gen blocks can take a 4" crank. I thought 3.875" was max.
I forgot to look at your state before this, so forgive me
if I am talking the wrong state....Ca also does a visual. This takes out tube headers as okay on a car that came with pre cats. AFR 195's do have an EO#I do not think our gen blocks can take a 4" crank. I thought 3.875" was max.
02-13-2007, 09:38 PM
#6
Safety Car
#2... The LS blocks do have smaller bore, but this has nothing to do with it's ability to take a 4" crank. That is in the design of the block. A 4" crank can be used in an OEM block but, it requires someone who knows what they're doing. Some block fill, reduced base cam, and lots of grinding for clearence is required.
3.875" stroke ==> 396cid
4.000" stroke ==> 408cid
This can be done fairly easily in an OEM block (not a whole lot of clearancing) if high quality parts are used. I have a 408cid in my street car, and run with a std base circle cam.
Aaron
02-13-2007, 09:52 PM
#7
Racer
Quite right, my bad, sorry about that.
02-14-2007, 05:19 AM
#8
Melting Slicks
Thread Starter
...something to think about
Aaron, thanks for the info. As for "quality parts", I don't intend to do this on the "cheap"...I hate having to pay twice for something because a cheap one wasn't quite up to snuff! I have a tendency to "over-build" things, make them stronger than they need to be. On the other hand I can't afford, and won't need to build it with all-out race parts either. I'll definitely start delving more into the data when I get back from my "vacation" in the desert.
Thanks again, everyone, for respoding.
Tim
Thanks again, everyone, for respoding.
Tim
