A
Anonymous
Guest
What cam ar you running with turbos? Anyone using a classic inlines cam with a turbo?
350kmileford
Well-known member
What type of engine are you inquiring about? I'd be ecstatic to see the answer to this regarding a 200ci.
We've used two different cams in Kelly's 250 powered Falcon, both were from ClassicInlines.
The first was the H-274-110. Hydraulic lifter. This one work pretty good and made for a easy driver car. But for turbo's it could be improved.
Then we tried the S-292-112. Solid lifter. For a turbo car this one is to big. Way to much duration and overlap. If running N/A or nitrous and/or high compression, this one would be great!
So we're in the process if pulling the S-292 out and installing a dual pattern cam with about 6* less duration on the exhaust side vs. the intake and a 114* lobe center. Lift will be in the range of .510". This cam will be "turbo specific" because it'll favor a restrictive exhaust.
This cam will also be a ClassicInlines cam made by Clay Smith. Clay Smith is currently checking their cores to see if they have something close in stock already.
The lesson learned here is that turbo cars like small cams. Keep the valve overlap very low if any at all, and favor less duration on the exhaust.
Hope that helps!
Will
The first was the H-274-110. Hydraulic lifter. This one work pretty good and made for a easy driver car. But for turbo's it could be improved.
Then we tried the S-292-112. Solid lifter. For a turbo car this one is to big. Way to much duration and overlap. If running N/A or nitrous and/or high compression, this one would be great!
So we're in the process if pulling the S-292 out and installing a dual pattern cam with about 6* less duration on the exhaust side vs. the intake and a 114* lobe center. Lift will be in the range of .510". This cam will be "turbo specific" because it'll favor a restrictive exhaust.
This cam will also be a ClassicInlines cam made by Clay Smith. Clay Smith is currently checking their cores to see if they have something close in stock already.
The lesson learned here is that turbo cars like small cams. Keep the valve overlap very low if any at all, and favor less duration on the exhaust.
Hope that helps!
Will
Will, I don't know if this will help, but I have modified many types of engines for turbo application and generally found 109° is about the limit for LSA when converting from NA. Retarding past this point drops BMEP too much and interferes with efficient blowdown
With the correct rod/stroke ratio a good daily drive LSA is about 105° LSA, usually 104° LCAin and 106° LCAex. Overlaps between 40° and 25° advertised.
I've found the lift is the most dominating cam event.
For instance on a stock DOHC turbo cam of say 23/51 49/17 with valve lift of 0.247" intake and 0.238" exhaust @ 75° running nominal 12 psi:
by modifying it to
24/54 59/22, 0.273" and 0.272" and running 28 psi we get at least about 2.3 times improvement in power over the 12 psi, which is a good pickup considering adiabatic lossess.
With the correct rod/stroke ratio a good daily drive LSA is about 105° LSA, usually 104° LCAin and 106° LCAex. Overlaps between 40° and 25° advertised.
I've found the lift is the most dominating cam event.
For instance on a stock DOHC turbo cam of say 23/51 49/17 with valve lift of 0.247" intake and 0.238" exhaust @ 75° running nominal 12 psi:
by modifying it to
24/54 59/22, 0.273" and 0.272" and running 28 psi we get at least about 2.3 times improvement in power over the 12 psi, which is a good pickup considering adiabatic lossess.
Something of a ramble follows..
Two valve per cylinder engines can cope with cams over 270 degrees if the ports aren't too big. I think a too big port is when it is any more than 90% of intake valve area on a wedge or canted valve engine with intakes as big as they can be. A benchmark is 2.7 sq in for a 1.96" intake valve (265 Valiant), or 3.3 sq in for a 2.19" intake valve (early 351C 4v). That's 89 to 87.6%. Any bigger, and the air speed drops, and big cams really don't help build the air speed at low engine speeds. If there is a big plip in the engine torque at about 2500 to 2800 rpm in our I6 engines, then the ports are as big as they should be for the combination, and more is to be gained by camshaft optimisation and port shape.
Its always a great sign in a turbo engine if the cam is too big...it most likely means your cylinder head is flowing too much
.
Wasn't it Sam Blumstein from Chevy Off Road and Marine who said "There are no wrong cams, only wrong engine combinations!
The 292 degree cam would work fine only if the ports were restrictive, and the turbo was sized to suit. A free breathing head creates problems with 'cammyness' compared to a log head. With a great cylinder head, you always have to come down on cam duration compared to an optimized turbo combination with a poorer flow.
When the cam is larger, and you
a) Reduce capacity
b) OR Increase VE (head flow, improved inlet intercooling air flow efficiency, improved manifolding with better apprach and larger ports, , or more efficent exhast, or go to port on port carburation)
c) OR Reduce lob seperation
d) the rocker ratios are increased (SOHC Fords have aggressive ratios up in the 1.8 to 2.0, much above the 1.5, 1.6 or 1.73:1 used in I6's.. while 4 valve per cylinder DOHC machines are much milder and this means they have to have much less duartion and lift)
these cars always get cammy earlier.
The duration issue is based on the way in which the above factors conspire against the turbo charger graph.
On Pinto 2000 cc engines, the point at overcamming for a turbo is often right at 292 degrees at 12 psi with a large T04 turbo and where the LSA is less than 110 with a stock 2-bbl intake...any more, and the engine falls flat and fails to build bost. Camming up just a little to over 300 degrees results in a bad surge, and awfull transitional response.
The wrong cam with just a smidgen too much duration and too little lobe centre angle, and the car is a dog. Backing off the cam helps massively.
On an I6, VE is lousy with a stock 1-bbl head, much better with a 2V head, and out-of-sight with the CI head. As soon as you improve VE, the car instantly goes cammy. This is always the case with a freeer breating cylinder head, as the air speed drops, and messes up transitional response.
As for the DOHC Ford, take a cruise in an F6 verses the XR6 Turbo. Stomp on anyone of these mutthas out of a corner at 1500 rpm, and the F6 has lots of turbo lag, yet the XR6 Turbo has none. That's because of the improvement in volumetric efficeincy , and it always hurts low speed off boost to boost transition.
In the case of the CI alloy head, a 292 cam will be a problem because of the port sizes. The stock Iron or 2v heads can run largers cams than a freer breating head.
This is a rule found by Rob McGavin's land mark book Modifying Your Mini for Modern conditions. After Mc Gavin poored over Vizards air flow theory, he found that BMC allways undercammed there high performance 998, 1071, 1275 engines whenever the better high flow Weslake designed heads were used. That's because a 'cammy' engine is where air speed goes subcritical and produces a drivability problem. So cars like Aussie Minis with 1098 cc twin carb plodders, or 1275 MG Metros had quite aggressive cams, but the Cooper S variants only had really mild cams, seamingly hardly worth the effort. BL race cams were off the planet, but seldom did the hot 648 profile cams ever yield the goods unless the lobe separation was special. The sucessfull ones were hybrid blends.
Same with the beloved Cleveland 351. First versions with the little 2V head had like 256 degree cams just like the cooking Windsors yet had massive wide open throttle power with awesome low end torque, and then the big port 4V HO ones with too much duration, like the early 310 degree Phase II GT, with 10.7:1 compression, were absolute hairy beasts to drive. As soon as the duration was dropped just 10 degrees to 300 degrees, the engine became wounderfully elastic. By the time hydraulic cammed 280 degree 1973/74 Cobra Jet 351 4V versions with a paltry 9.1:1 compression, they were very tame, and ended up being the standard Pantera engine for a while.
So if you have a stock log head, a wild cam will surfice. If its a better flowing head, a wild cam will screw it up a bit. The critical point for non turbos comes when you are over 270 degress with a great head, and about 280 with a small port head. For a turbo, you can add 10 degrees to these, and still have good streetable combination.
Most issues with carb size, turbo and camminess due to duration were expounded very clearly in the two SOHC Ford/A-Series Vizard books, and they are noticed much earlier on small 1.0 to 2.3 liter engines with Holley and Weber series carbs and turbos than on our big old iron lumps 1.1 to 5 times the capacity.
Two valve per cylinder engines can cope with cams over 270 degrees if the ports aren't too big. I think a too big port is when it is any more than 90% of intake valve area on a wedge or canted valve engine with intakes as big as they can be. A benchmark is 2.7 sq in for a 1.96" intake valve (265 Valiant), or 3.3 sq in for a 2.19" intake valve (early 351C 4v). That's 89 to 87.6%. Any bigger, and the air speed drops, and big cams really don't help build the air speed at low engine speeds. If there is a big plip in the engine torque at about 2500 to 2800 rpm in our I6 engines, then the ports are as big as they should be for the combination, and more is to be gained by camshaft optimisation and port shape.
Its always a great sign in a turbo engine if the cam is too big...it most likely means your cylinder head is flowing too much
. Wasn't it Sam Blumstein from Chevy Off Road and Marine who said "There are no wrong cams, only wrong engine combinations!
The 292 degree cam would work fine only if the ports were restrictive, and the turbo was sized to suit. A free breathing head creates problems with 'cammyness' compared to a log head. With a great cylinder head, you always have to come down on cam duration compared to an optimized turbo combination with a poorer flow.
When the cam is larger, and you
a) Reduce capacity
b) OR Increase VE (head flow, improved inlet intercooling air flow efficiency, improved manifolding with better apprach and larger ports, , or more efficent exhast, or go to port on port carburation)
c) OR Reduce lob seperation
d) the rocker ratios are increased (SOHC Fords have aggressive ratios up in the 1.8 to 2.0, much above the 1.5, 1.6 or 1.73:1 used in I6's.. while 4 valve per cylinder DOHC machines are much milder and this means they have to have much less duartion and lift)
these cars always get cammy earlier.
The duration issue is based on the way in which the above factors conspire against the turbo charger graph.
On Pinto 2000 cc engines, the point at overcamming for a turbo is often right at 292 degrees at 12 psi with a large T04 turbo and where the LSA is less than 110 with a stock 2-bbl intake...any more, and the engine falls flat and fails to build bost. Camming up just a little to over 300 degrees results in a bad surge, and awfull transitional response.
The wrong cam with just a smidgen too much duration and too little lobe centre angle, and the car is a dog. Backing off the cam helps massively.
On an I6, VE is lousy with a stock 1-bbl head, much better with a 2V head, and out-of-sight with the CI head. As soon as you improve VE, the car instantly goes cammy. This is always the case with a freeer breating cylinder head, as the air speed drops, and messes up transitional response.
As for the DOHC Ford, take a cruise in an F6 verses the XR6 Turbo. Stomp on anyone of these mutthas out of a corner at 1500 rpm, and the F6 has lots of turbo lag, yet the XR6 Turbo has none. That's because of the improvement in volumetric efficeincy , and it always hurts low speed off boost to boost transition.
In the case of the CI alloy head, a 292 cam will be a problem because of the port sizes. The stock Iron or 2v heads can run largers cams than a freer breating head.
This is a rule found by Rob McGavin's land mark book Modifying Your Mini for Modern conditions. After Mc Gavin poored over Vizards air flow theory, he found that BMC allways undercammed there high performance 998, 1071, 1275 engines whenever the better high flow Weslake designed heads were used. That's because a 'cammy' engine is where air speed goes subcritical and produces a drivability problem. So cars like Aussie Minis with 1098 cc twin carb plodders, or 1275 MG Metros had quite aggressive cams, but the Cooper S variants only had really mild cams, seamingly hardly worth the effort. BL race cams were off the planet, but seldom did the hot 648 profile cams ever yield the goods unless the lobe separation was special. The sucessfull ones were hybrid blends.
Same with the beloved Cleveland 351. First versions with the little 2V head had like 256 degree cams just like the cooking Windsors yet had massive wide open throttle power with awesome low end torque, and then the big port 4V HO ones with too much duration, like the early 310 degree Phase II GT, with 10.7:1 compression, were absolute hairy beasts to drive. As soon as the duration was dropped just 10 degrees to 300 degrees, the engine became wounderfully elastic. By the time hydraulic cammed 280 degree 1973/74 Cobra Jet 351 4V versions with a paltry 9.1:1 compression, they were very tame, and ended up being the standard Pantera engine for a while.
So if you have a stock log head, a wild cam will surfice. If its a better flowing head, a wild cam will screw it up a bit. The critical point for non turbos comes when you are over 270 degress with a great head, and about 280 with a small port head. For a turbo, you can add 10 degrees to these, and still have good streetable combination.
Most issues with carb size, turbo and camminess due to duration were expounded very clearly in the two SOHC Ford/A-Series Vizard books, and they are noticed much earlier on small 1.0 to 2.3 liter engines with Holley and Weber series carbs and turbos than on our big old iron lumps 1.1 to 5 times the capacity.
xecute":2vyij0hq said:
One of the hallmarks of a twin cam turbo exhaust port is it's size = big. The inlet really responds to siamese or bifurcated runners.
Of course DOHC has it all over single valve heads:- shorter valve travels, larger Valve/Bore ratio (so it can breath and rev), pent roof, reduced bounce, etc.
I tend to subscribe to larger runner area than the curtain area of the valve (and therefore the corollery that the valve curtain shouldn't exceed the available port area). This gives second tier authority to the valve, after the throttle plate.
I am using a Classic inlines 264 duration cam, nothing crazy, someday I may step up to somethign bigger but I need to get the car back on the road again. Trying to save any paying bills and such is killing me and I seem to have a major problem keeping a stock daily driver, its now faster than my 6 which I would have never imagined.
In a sitation where an engine in indepedent runner (EFI or carb, and 4 v per cylinder and a turbo) you have something very special with specific torque and off boost characteristics the envy of us all. Sierra Cosworth and Lotus Espirit Turbo type stuff, cars as tame as a the cooking model vairant of a Cortina or Vauxhall 2300. As soon as the engine is no longer battling a wide variance of different runner lenghts, the cam required to do the job comes down in duration.
Getting back to it, Unlike a V8, with the stock carb log unequal runner I6's have a variable port area to curtain area, mixture variance from cylinder to cylinder, and consequently valve event, lobe center and individual spark advance is all up the Kyber. Add a cam with too much duartion, and you'll run into problems. The use of larger runners with better concentration helps peak power, but has to use less duration to get the same results. Improving swirl and mixture motion will help the engine come on the cam, but won't improve gas speed in the port.
So the better the cylinder head flow, all else being equal, the less the cam duration to get the job done. And on our sixes, port area to curtain area variance requires a scatter pattern cam to even get close to an optimized package.
tjnavyblue
Well-known member
Keep us informed Will. I'm sure there are more of us interested if that works out.
xecute":3tq3e8qr said:
Man Xecute! You nailed this exactly!
Obviously we're not at 300 degrees, but with the 292 cam in our application, I can't ge the car to move or come up on boost below 4000rpm or so. Once it's get going to runs OK. But the transition from the idle circuit to the boosters is horrible. I've tried a bunch of different PVs with virtually no difference.
Thanks!
Will
A
Anonymous
Guest
Thanx, guys. This is what I was wondering about. I need to reread all this once I get some sleep.
I am workingon several things all at once to get it done including fabing a new oil pan and the turbo header. I read an older book on turbos about three times over the last 8 years. The one thing that seemed to be needed was a proper cam so some of fuel charge is not blown out the exuast ports.
I am building a 4x4 offroad and daily driver. I dont care to have a 10 second truck. I am looking for power off idle to 5500. I have two transfer cases and a four speed tranny. So i am hoping to turn 35'' tires with 16 gears to choose from. The 289/302/351 boys do this and even larger 37'' tires. I am hoping the 250 with a little boost will do fine. The 170 did great with 28 inch tires NA. The torque from the little 6 did fine but I need more power for the tires that i need with my added 5.5" Rock crawler lift.
It sounds like the first post from does10's says it all for my application. RV type cam ehh?
I was wondering if their would be dual patterns coming for the sixes. Thatll be good news.
From what execute is saying, I would probly be better off with my log head.
I am workingon several things all at once to get it done including fabing a new oil pan and the turbo header. I read an older book on turbos about three times over the last 8 years. The one thing that seemed to be needed was a proper cam so some of fuel charge is not blown out the exuast ports.
I am building a 4x4 offroad and daily driver. I dont care to have a 10 second truck. I am looking for power off idle to 5500. I have two transfer cases and a four speed tranny. So i am hoping to turn 35'' tires with 16 gears to choose from. The 289/302/351 boys do this and even larger 37'' tires. I am hoping the 250 with a little boost will do fine. The 170 did great with 28 inch tires NA. The torque from the little 6 did fine but I need more power for the tires that i need with my added 5.5" Rock crawler lift.
It sounds like the first post from does10's says it all for my application. RV type cam ehh?
I was wondering if their would be dual patterns coming for the sixes. Thatll be good news.
From what execute is saying, I would probly be better off with my log head.
gravelrash
Well-known member
Xecute,
mate i love your in depth replies, must take you hours to write up.
mate i love your in depth replies, must take you hours to write up.
I have to say, Xecute either really knows what he is talking about or is completely full of shit. I haven't quite figured out which yet...
There are a few things that I do disagree with him on, but I think that may be more of a case of talking past each other than anything else...
There are a few things that I do disagree with him on, but I think that may be more of a case of talking past each other than anything else...
A
Anonymous
Guest
Well what cam do ya have bort62 ? do you like it ? any problems?
I agree. That era was not interetsed in good engine design... fuel was cheap, the environment of no consequence and mods were more follow the leader rather than knowledge based engineering. Then along came the Japs with more precision, better geometry, better materials..... the rest is history.
Absolutely.
You will always make more power, turbocharged or otherwise, with a better flowing head.
Assuming you have the intake, cam, and exhaust to match. It would be possible to bolt a great head in w/ a crappy intake, exhaust, and factory cam and make LESS power than you had before... but you would have to be talking about a pretty huge head.
And frankly, while the CI head is a big improvement for us, it's not like it's a LS-6 head or something - it doesn't flow THAT Much. Throw that head on w/ a stock exhaust manifold, 2bbl carb, and stock cam, and you will probably still pick up a few hp.
And I am using the stock cam. My car isn't exactly what you would call fast...
You will always make more power, turbocharged or otherwise, with a better flowing head.
Assuming you have the intake, cam, and exhaust to match. It would be possible to bolt a great head in w/ a crappy intake, exhaust, and factory cam and make LESS power than you had before... but you would have to be talking about a pretty huge head.
And frankly, while the CI head is a big improvement for us, it's not like it's a LS-6 head or something - it doesn't flow THAT Much. Throw that head on w/ a stock exhaust manifold, 2bbl carb, and stock cam, and you will probably still pick up a few hp.
And I am using the stock cam.
My car isn't exactly what you would call fast...With a stock cam I would assume the LSA is more moderate, which amongst other things will mean you won't be prone to elevated engine temps and burnt exhaust valves.
One good thing about unleaded fuel is that you can increase the size of the valves and thus the ports. In the old days the lead fuel had a low combustion swirl and the contact faces would build up with carbon and lead oxides regardless of spring tension.
One good thing about unleaded fuel is that you can increase the size of the valves and thus the ports. In the old days the lead fuel had a low combustion swirl and the contact faces would build up with carbon and lead oxides regardless of spring tension.
350kmileford
Well-known member
I mucked up on the cam selection, ignore this.