Cam selection for 350 chevy small block

[BigBlockMopar]

Since the current timingchain-set is of unkown age and quality, it would be a smart (and cheap) move to just replace it with one with at a least 3-way crank sprocket, and maybe put some advance on the cam rightaway. I think this would be the most noticable change for the least amount of money.

[kikkegek]

I get the impression kikegek doesn't want to do a full rebuild or raise compression /torque converter or any of that, just cam it for what he has now. 8.5:1 compression. Whatever intake manifold not so big an issue as that. Rams horns would be perfect for the exhaust. Pure guessing what that compression would react right to, I'd go real small on the duration 252? 110 - 112 spread, mild but a bit of lift. Advance that cam a bit? Give him a ball park what sort of cam may work without any other major changes. Can't be any worse than advancing the stock smogger cam. jmo

I find several info on my heads...here http://www.bolt-on-performance.com/?p=19 it says they can get you 9:1 compression. But that is on a corvette I believe. Probably a little differently build sbc350 then mine.

my heads have a date code G246 = July 24th 1976


I just had the converter that came with the tranny revised. So dont want to change that.

and no dont want to do a full rebuild (yet). I am researching what simpel things I can do to optimize my current engine.

[kikkegek]

Since the current timingchain-set is of unkown age and quality, it would be a smart (and cheap) move to just replace it with one with at a least 3-way crank sprocket, and maybe put some advance on the cam rightaway. I think this would be the most noticable change for the least amount of money.

that might indeed be the best way to go. We have driven is about 40-50.000km in the netherlands and dont know the history of the engine. But since it was sold, they probably hadnt done any big service lately.

[kikkegek]

Since the current timingchain-set is of unkown age and quality, it would be a smart (and cheap) move to just replace it with one with at a least 3-way crank sprocket, and maybe put some advance on the cam rightaway. I think this would be the most noticable change for the least amount of money.

that might indeed be the best way to go. We have driven is about 40-50.000km in the netherlands and dont know the history of the engine. But since it was sold, they probably hadnt done any big service lately.

so would something like this work?

http://www.summitracing.com/parts/sum-g ... /chevrolet

Summit Racing Part Number:SUM-G6601-B

Timing Chain Style:Double roller
Maximum Advance/Retard at Camshaft:4 degree
Maximum Advance/Retard at Crankshaft:8 degree

its $68,- at Summit

[MLGPropane2]

the double row "roller" chain and sprocket set when tested at 500 rpm on a SBC 350 gives 15 free "reduction in friction"
horsepower compared to the factory "link" chain. Est 5 horsepower benefit at 2000 RPM. Of the 4 events controled by the cam, intake open intake close exhaust open exhaust close....Intake close has the most signifigant effect on the
powerband of the engine. Next most important is Intake open, next is exhaust close and last is exhaust open, For
best low RPM (idle to 2500 RPM) efficiency the intake needs to close before the upward movement of the piston
reverse pumps the incoming charge into the intake manifold. Advancing the stock cam 6 deg will increase the cylinder
pressure (compression gauge test) from 120-130 psi to 170-180 psi. The horsepower penalty at 5000 RPM is 21 hp
measured on a superflow engine dyno. LPG fuel economy on 33 Chevy vans with 350 ci V8 (8600 lb gvw and always fully
loaded) improved from 9 MPG to 14 MPG (fleet average for a year) using 6 deg cam advance. Also the exhaust gas
temp changed from 1500 deg F to 1250 deg F

Best Regards

Roger Wheeler

[kikkegek]

the double row "roller" chain and sprocket set when tested at 500 rpm on a SBC 350 gives 15 free "reduction in friction"
horsepower compared to the factory "link" chain. Est 5 horsepower benefit at 2000 RPM. Of the 4 events controled by the cam, intake open intake close exhaust open exhaust close....Intake close has the most signifigant effect on the
powerband of the engine. Next most important is Intake open, next is exhaust close and last is exhaust open, For
best low RPM (idle to 2500 RPM) efficiency the intake needs to close before the upward movement of the piston
reverse pumps the incoming charge into the intake manifold. Advancing the stock cam 6 deg will increase the cylinder
pressure (compression gauge test) from 120-130 psi to 170-180 psi. The horsepower penalty at 5000 RPM is 21 hp
measured on a superflow engine dyno. LPG fuel economy on 33 Chevy vans with 350 ci V8 (8600 lb gvw and always fully
loaded) improved from 9 MPG to 14 MPG (fleet average for a year) using 6 deg cam advance. Also the exhaust gas
temp changed from 1500 deg F to 1250 deg F

Best Regards

Roger Wheeler

he thanks Roger. that sounds like exactly the thing I am looking for and in the range I currently suspect I am missing power/torque.

so something like this?
http://www.summitracing.com/parts/cca-3 ... /chevrolet

[gottago]

It is pretty well the same amount of work to advance the cam as replace it if the intake manifold is going to be changed anyway. Advancing any cam is a cheap enough way parts wise to change a pwerband caused by improper cam selection in the first place. Don't get me wrong, I've done it and liked the results of advancing some cams in some cases but really that same lobe advance and duration obtained by advancing the stocker cam can be ground into a new cam and still retain the proper coordination with crank/piston position.

Newer chevy cams separate the intake lobe from the exhaust events- lobe phasing accomplishes the same as what advancing a cam does. Intake close /and exhaust close degree determine the rpm band in combination with overlap derived from the duration of each. It all works together. There is likely a far superior cam for any desired condition than just advancing the stock one especially given the specs in this case aren't known imo.

chevy article- re: performance orientated but the same rules apply. You can purchase a cam with a 6 degree advanced intake centerline ground in and with the exhaust events spread more towards the retard side and install straight up to keep with ideal crank position timing events. There are many possibilities to consider and if Kikegek isn't in a big rush, may pay added dividends including the compression. Perhaps if Kik knew the specs of the cams in Rogers chevy vans, he could make some better informed decisions? Short of using a degree wheel and dial guage its tough to tell what Kik is running for a cam and too much work to just advance that cam without knowing exactly what it will do first. IMO..

The most important point in the four-stroke cycle is the intake closing point. While this is not part of overlap, the timing of intake opening and closing determines total duration. The intake closing point is a big determiner in where the engine makes power. A later intake closing point improves top-end power. Combine that with more overlap and you have a cam designed to make power at high rpm. However, it’s possible to decrease overlap by using a shorter-duration intake lobe and retard the intake centerline (which spreads the lobe separation angle) to improve midrange power.

We should also look at cams with a short duration and a wide lobe separation angle. All late-model Chevrolet engines use extremely wide lobe separation angles to improve idle quality. A late intake centerline combined with an early exhaust centerline and short-duration lobes creates very little overlap, yet the new LS1 and LS6 Gen III engines make great overall power without having to rely on large overlap periods. This is something to think about.

Read more: http://www.chevyhiperformance.com/techa ... z2GNK2jpT4

[gottago]

Lots to compare in the way of cams but they all sort of come down to the same variables for consideration. Any cam timing chart even one as simple as comp cams sales info gives a good idea what you can expect from any lobe combo.

like this 1000 - 5000 rpm cam - a 107 degree intake centerline on a 111 spread cam creates an exhaust centerline near 114 degrees. The lobes are spread differently from each other giving a different effect than you get just by advancing a cam. This one goes more for the low end power side increase but others do the same for economy etc.. Its the lobe phasing numbers on the chart that determine what sort of power and mileage you get and where in the rpm band. If you aren't in a big rush, well worth looking at.

http://www.compcams.com/Company/CC/cam- ... id=95&sb=2

[MLGPropane2]

The Chevy vans were model yeay 1985 & 1986. GM used the same cam from 1976 until 1988 for the truck version
of the 350 ci smallblock. some of the "Smog" versions used a factory 6 deg retard (UGH) on the cam.

best Regards

Roger Wheeler

[kikkegek]

good stuf guys.

love 4x4 cam

and what is UGH?

I got a smog engine I think. it had the air pump and charchoil canister and stuf

[MLGPropane2]

UGH is about the 6 deg retard. Quick and ineffecient pre computer emissions compliance. Chrysler and Ford did it also
some crankshaft keyways were offset 6 deg (EPA and CARB antitampering rules) You will need a degree wheel and find
true top dead center,,a positive stop in the spark plug hole rotate engine mark pllley rotate opposite direction until hit
positive stop...mark pulley...exactly halfway between the marks is true TDC. The Summit componants can do 4deg plus
8deg minus the factory six deg = six deg advance. Be careful make sure you advance the Cam...not the Crank

best Regards

Roger Wheeler

[gottago]

Where I live, we had the same smog standards as the California cars. Most of our 350 cu in trucks running on propane didn't respond all that well no matter what you did to them. We are in the mountainous region and they get a work out here. Ugh as in ugly with the stock smog cam in those years. The older models did way better even with just a distributer recurve and very little else. Maybe advancing that cam will do the trick butt...

I think a compromise over a stock or a total mileage oriented cam could make the combination work better. Concentrate the power even if in a narrower band in the desired rpm range and that jumping back and forth effect between gears may completely go away or at least get minimized. Makes it much more pleasant to drive. I had one doing that and it gets to be a pain to drive on the highway . Sacrifice a little mileage to add a bit more torque at a lower rpm is best you can do without adding compression etc.. imo ..You may not need all that much of a change to make it come together. A cam is a relatively cheap part compared the labour required to change it. May as well shoot for your best chance at the all round best combo right off the bat.. maybe go to the trouble to degree the old one first and if not that happy with it, or want more of that effect can still change it out when the intake gets swapped?

There are lots of other semi similar cams at comp, even a slightly smaller 4x4 style one that may do ya well.. Choices choices...

[kikkegek]

Ryan from Comp Cams came back with a cam selection:

Xtreme Energy™, XE250H
Very Strong Torque, Smooth Idle
http://www.compperformancegroupstores.c ... Code=HFTXE

still not sure if I will just swap chains to double true roller and advance the cam 4 degrees or if I will also while I am at it also swap the cam for this one?

I will check engine compression first this weekend to see if this baby is still fresh enough for this upgrade.

will report back here.

[BigBlockMopar]

If your current timing chainset has a lot of play, the change to a new set will have a significant effect on lowrange power.

[kikkegek]

If your current timing chainset has a lot of play, the change to a new set will have a significant effect on lowrange power.

I'll be checking compression this saturday morning at Riks place. While the plugs are out of the engine I might as well check how play there is in the timing chain.