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Old 02-19-2018, 04:55 PM
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Roller cam swap

I have a 1990 1 piece rear seal sbc 350 in my 78 GMC truck that I built. Before you say that my block should be machined for OEM roller lifters and I won't have to retro fit, IT IS NOT. I have checked it many times. I'm going to swap the current solid flat tappet cam (Comp XS256S) to a Comp Hydraulic Roller cam (XR258HR) this summer, and I want to see if my assumptions and ideas are correct.

Specs of cams
Solid flat tappet
XS256S 12-674-4
Lift .465/.477
Dur @.050 218/224
LSA 110, intake center 106

XR258HR 12-408-8
Hydraulic Roller
Lift .480/.487
Dur @.050 206/212
LSA 110, intake center 106

Will switching these cams give me a performance boost, a performance loss, or no noticeable difference? CamQuest says peak numbers with the solid cam is 370 hp and 448 torque, and with hyd. roller its 392 hp and 457 torque, obviously grossly overestimated, but curious if the difference is going to be that great. Also for the parts I'm going to need for the swap I'll make a list of the ones I know I'll need and I'd appreciate if anyone could tell me anything else I'll need as far as parts or things that need to be done.
Parts:
Cam
Retro fit roller lifters
pushrod length checker and pushrods
cast timing cover
cam button and shims
steel distributor gear

Recommended valve springs for this cam are the comp 981-16 springs which my heads already have so that shouldn't be an issue. Will my summit cast steel roller tip rockers work with this cam or will I need full rollers? Also on the subject of rockers, the contact patch of my rockers with my valve stems are slightly on the outboard side of center but are very narrow meaning not much sweep, is that a problem? I used an adjustable pushrod and one of those mock rocker things to check proper length and according to that it's correct

List of full specs of my motor in another thread which I'll link if I can find it, so I'm going to ask the age old newbie question, horsepower and torque estimates that are more realistic than camquest?

Here's the forum post: https://www.hotrodders.com/forum/hors...on-450802.html only difference is my carb is a 600 cfm as opposed to the 650 in the post

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Old 02-19-2018, 08:45 PM
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While there will be a gain I doubt the money spent would be worth it, hardly noticeable from the drivers seat especially in a truck where moving the torque peak up is the wrong direction unless your racing.

Guess running regular oil makes it cheaper to operate but hardly makes a lot of sense, my guess is you would get a similar torque gain just putting higher ratio rockers in and keep the current torque peak position.

I wouldn't do it unless I had another reason to tear a recently rebuilt engine apart like doing a port job to the heads to support the cam and then I would go with a more modern design cam with wider LSA and closer to 265-270 advertised duration and over 0.500" lift.
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Old 02-19-2018, 08:48 PM
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Quote:
Originally Posted by 4 Jaw Chuck View Post
While there will be a gain I doubt the money spent would be worth it, hardly noticeable from the drivers seat especially in a truck where moving the torque peak up is the wrong direction unless your racing.

Guess running regular oil makes it cheaper to operate but hardly makes a lot of sense, my guess is you would get a similar torque gain just putting higher ratio rockers in and keep the current torque peak position.

I wouldn't do it unless I had another reason to tear a recently rebuilt engine apart like doing a port job to the heads to support the cam and then I would go with a more modern design cam with wider LSA and closer to 265-270 advertised duration and over 0.500" lift.
My main concern is I have a lifter with a weird wear patter on the current cam, and I want the longevity of a roller cam. I know its probably not worth it, but personally the peace of mind is worth it to me. Also what do you mean moving the torque peak up? wouldn't the smaller duration move the torque peak down?
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Old 02-20-2018, 06:02 AM
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The new roller cam should give you a little more low end torque, especially if you are using a stock converter. I am surprised that the calculator says it will give you more total HP. If you have a higher stall converter and decent heads you may want to consider with something closer to your current cam duration. Also take a look at the roller conversion cams from Lunati and Howards.

Selection of rockers seems to be complicated for these conversions, so I don't have any recommendation. Considering the money you are spending on the roller cam conversion, I think I would go for full roller rockers also. Some of the inexpensive roller tip rockers just don't seem to have great quality.

Bruce
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Old 02-20-2018, 08:50 AM
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When I went to convert to a roller cam I was running a flat tappet cam hydraulic of course back in 2007 and just the year before I rebuilt my engine but it was with a used crank and rods and was a chevy 383 with a stock reground 400 small block crank and the 5.565 rods and I never did like the part of having used parts on the bottom while everything else was new and then starting to read on all the cams going flat I figured if I am ever going to go roller then now is the time to do so.

I saved up my cash and ended up buying a hydraulic roller cam and the parts necessary to do the whole conversion and while I was at it got a new crank and rods and re freshed my bottom end and was happy spending the extra. To me even just converting over to the hydraulic roller cam is worth it to me as it gives a piece of mind as far as not having the high risk of the cam going bad over time and filling the engine with all its junk and then having to end up rebuilding it again anyways which would cost even more in the long run. If you can go for it then do as in the end it will be worth it anyways and on the cam part I would bump the hydraulic roller cam up one size comparable to your flat tappet size cam and being the cam would be a hydraulic roller and a modern grind to boot it would make more power in my opinion with less friction etc.

As mentioned above the lunati voodoo hydraulic roller cams are some good grinds and are slightly better then the comp cams extreme energy grinds and Howards make some really good grinds as well. I based my recent hydraulic roller cam custom grind off of a Howards roller cam and two other from comp and lunati but the Howards was the main grind. Howards has the kit where you get the cam and the lifters that will also go with it.

One thing you did not mention on your block I know you stated it does not have the machining for a oem roller setup but does your block still have the bosses in the lifter valley where a spider tray would get bolted and also the taller lifter bores compared to a 86 and earlier block? If so that will make a difference on the lifter roller wise on what you would use and also does your front of the block have the two spots for a cam lock plate?

I have only dealt with the once piece rear main seal blocks that have the oem roller setup machined in the block but I know the truck blocks had the bosses but were not drilled from reading on articles but the cam plate are should still be drilled so you can use an oem step nose camshaft and use the locking plate to keep it in place and in that part you would use an oem 87 and up hydraulic roller cam oem style and you would need the lifters and I recommend the howards ones which would come with the cam kit would be a drop in deal with the link bar being .300 taller and clearing everything.

That is the way I am going for my dart shp build even though I could use oem hydraulic roller lifters and the spider tray but my cam has a higher lift rate then what the factory style lifters are made for so I am using the howards link bar style lifters and they are .300 taller then the retrofit style ones which are shorter and won't clear an 87 and up block with the taller bores.

Also just for a recommendation on a roller cam swap I run a lunati 270/278 219/[email protected] 515/530 lift 106/112 voodoo hydraulic roller cam with a turbo 350 and a 2000 stall converter with 3.42 rear gears with a 650 holley and that cam is a really good daily driver cam that is nice and tame for cruising around while also giving some very nice throttle response and starts to pull really strong after 2500 rpm and I even get 19 mpg in my 96 s10 with it. It has a very faint lope at idle but really hardly even noticeable and is similar to the comp extreme energy 218/224 @ 50 roller version.

Last edited by eric32; 02-20-2018 at 09:00 AM.
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Old 02-20-2018, 09:24 AM
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I don't see much of a difference but my gut says the flat tappet you have is better, which flies against your calculator.

This is mostly a lift against duration trade where the cam you have has less lift but more duration than the roller cam you're proposing. Since your engine is induction limited by the carb size more duration (thus time open) is more effective than more lift. This also speaks to the exhaust system as well where flow rate is always an issue that responds better to more cam time than lift. Engine modeling on an engine dyno is a better situation than when the engine is installed thus is often optimistic from the standpoint of what parts would be preferred upon installation for best power.

All that said a roller is costly in a non roller block but does away with the flat tappet wear issues that arrive at the cost and effort of replacement. The roller also lets you dry out the bottom end with effective windage control that would get you into trouble with a flat tappet cam unless other steps are taken to oil it.

I like to use a 2 or 3 piece cast aluminum timing cover with these cam's as it is strong and doesn't deflect under thrust loads so the clearance you set is the clearance you get. The other thing you get is it is removeable for inspection and adjustment without having to disturb the gasket seal with the pan. Plus they don't leak oil like the stamped metal versions that also require external reinforcement for he cam button. The roller bearing thrust button offers less wear against the cover than solid version whether aluminum or nylon. But the roller is messy if it ever comes apart which is very rare but can happen.

Bogie
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Old 02-20-2018, 10:36 AM
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Quote:
Originally Posted by EragonSuperH View Post
My main concern is I have a lifter with a weird wear patter on the current cam, and I want the longevity of a roller cam. I know its probably not worth it, but personally the peace of mind is worth it to me. Also what do you mean moving the torque peak up? wouldn't the smaller duration move the torque peak down?
Sorry didn't look at the cams that closely, they are basically identical. The 0.050" duration looks different but thats due to the faster opening ramp on a roller cam.

If you wanted to upgrade to roller this will get you there without changing much in the power curve.
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Old 02-20-2018, 10:39 AM
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Quote:
Originally Posted by 4 Jaw Chuck View Post
Sorry didn't look at the cams that closely, they are basically identical. The 0.050" duration looks different but thats due to the faster opening ramp on a roller cam.

If you wanted to upgrade to roller this will get you there without changing much in the power curve.
Another concern of mine is that the current cam has a huge rpm drop when I put the truck in gear, from 800-850 rpm in neutral to about 550-600 in gear. Will the roller cam have that same problem, or will it pull more vacuum? I don't want to do a band aid fix like a stall converter either, so I'll either live with the drop, or try to tune it out.
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Old 02-20-2018, 12:30 PM
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On my roller cam I mentioned above I get 18 inches of vacuum in park and I run a 800 to 850 rpm in park. My cam runs very well and I only have a basic 2.5 inch exhaust with plain jane turbo mufflers with dual exhaust and it runs fine for me wise as I honestly would go roller especially if you have the chance to do so and I do recommend an aluminum cover over any stock or old steel type cover as they are not as good as any aluminum ones that i have seen over the years
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Old 02-20-2018, 03:26 PM
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Quote:
Originally Posted by EragonSuperH View Post
Another concern of mine is that the current cam has a huge rpm drop when I put the truck in gear, from 800-850 rpm in neutral to about 550-600 in gear. Will the roller cam have that same problem, or will it pull more vacuum? I don't want to do a band aid fix like a stall converter either, so I'll either live with the drop, or try to tune it out.
Pretty typical for cams in this zone, they are an the top of livability with a stock stall converter not a big deal. To get more vacuum with these kind of cams you either have to select a cam with a wider LSA which reduces overlap or put advance in to the cam with adjustable or multiple installation positions of the timing set then select 2 to 4 degrees of advance. This moves the events sooner which cuts down both on the overlap effects (but not the overlap) and closes the intake sooner so there is more trapped cylinder pressure at lower RPMs which brings the torque up making life with a low stall converter simpler.

Bogie
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Old 02-20-2018, 03:38 PM
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Quote:
Originally Posted by EragonSuperH View Post
Another concern of mine is that the current cam has a huge rpm drop when I put the truck in gear, from 800-850 rpm in neutral to about 550-600 in gear. Will the roller cam have that same problem, or will it pull more vacuum? I don't want to do a band aid fix like a stall converter either, so I'll either live with the drop, or try to tune it out.
Thats a function of converter stall speed, not much you can do about except run a looser converter. Depending on your trans I believe the 4.3L converter from certain years has a slightly higher stall speed (2000rpm or so) which would help.

Your rpm drop is typical of using a stock converter.
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Old 02-21-2018, 10:04 AM
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Quote:
Originally Posted by BogiesAnnex1 View Post
Pretty typical for cams in this zone, they are an the top of livability with a stock stall converter not a big deal. To get more vacuum with these kind of cams you either have to select a cam with a wider LSA which reduces overlap or put advance in to the cam with adjustable or multiple installation positions of the timing set then select 2 to 4 degrees of advance. This moves the events sooner which cuts down both on the overlap effects (but not the overlap) and closes the intake sooner so there is more trapped cylinder pressure at lower RPMs which brings the torque up making life with a low stall converter simpler.

Bogie
My timing set has the option of 0 advance, 4 deg retarded, or 4 degrees advanced, should I switch to the 4 degrees advanced when I swap cams or will the roller have a small enough duration to idle fine in gear?
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Old 02-21-2018, 11:24 AM
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Almost all off the shelf cams have 4 degrees advance built into them when you put them in the straight up position which is what I always put mine at. You would have to have it install it retarded 4 degrees just to have it in the traditional straight up position of where its not advance or retarded timing wise.
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Old 02-21-2018, 06:06 PM
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The big RPM drop is because of the high idle RPMs... the new shorter duration cam should idle with more vacuum at lower RPMs... or you could have used a vacuum cannister to save high vacuum and idle with lower RPMs with the old longer duration cam... Part of the low vacuum may also be a too low compression ratio for a 218/224 cam... GM tended to use 11:1 for that duration cam...

Yes, I see almost similar HP between the two cams... as Bogie says, wouldn't expect the new cam to have more HP, but expect the torque to hit harder at low to mid RPMs, so it may seem stronger in most usage... and better MPG if you have stock low compression ratio...
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Old 02-21-2018, 06:42 PM
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Quote:
Originally Posted by BuzzLOL View Post
The big RPM drop is because of the high idle RPMs... the new shorter duration cam should idle with more vacuum at lower RPMs... or you could have used a vacuum cannister to save high vacuum and idle with lower RPMs with the old longer duration cam... Part of the low vacuum may also be a too low compression ratio for a 218/224 cam... GM tended to use 11:1 for that duration cam...

Yes, I see almost similar HP between the two cams... as Bogie says, wouldn't expect the new cam to have more HP, but expect the torque to hit harder at low to mid RPMs, so it may seem stronger in most usage... and better MPG if you have stock low compression ratio...
My compression ratio is 9.3 to 1. I would definitely like a better idle and more mpg, with more torque to boot.
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