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please critique cam choice

7K views 27 replies 12 participants last post by  eric32 
#1 ·
Ok, here's my engine setup for my weekend warrior/mud truck

The truck is a s10 with 31" tires 4.10 rear with a locker, and a manual 5 speed.

The engine I'm looking at putting together is a 350 with Vortec heads, flat top pistons, RPM intake, retuned HEI, long tube headers, E-fan, the usual stuff...

I'm looking at one of those "IMCA" cams off of ebay. Its a solid flat tappet cam with
279/ 282 ADV dur
248/ 251 @ .050"
.531/ .542 lift
106 LSA
.016/.016 lash
2700-6800 RPM range

I know it has aggressive ramps so I'll have to be particular about springs and use special oil high in ZDDP.

also, I'll be running valves with .100" longer stem height so I won't have lift interference problems, roller rockers, and I'll angle mill the heads to get as close to 10.5:1 compression as I can with .040" quench and flat tops with 2 eyebrows on the pistons.

I really like these cam specs, but it is an "ebay cam" so I don't know if they are notorious for problems. They're also only $100 and I'm trying to build this on a budget since this is my third car that I'll have in the stable that is "just for fun".
 
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#2 ·
I don`t know about these cams either, but honestly, I would go with a smaller cam. Reason being you get into the sure enough thick mud, even so you have the advantage of a 5 speed so you can rev it high as needed, it`s going to lug the engine due to the lack of torque with that much cam and lugging it is the worst thing you can do to a engine. I would use a cam that had a power band that started at 2000 at the lowest. Summit sells the 80 buck hydraulic cam and lifter sets and I`ve used many of them without issue.
A cam with duration of around .224 @ .050 is as high as I would go. But thats just me and my opinion. being I`ve had experience playing in the mud with big cams I learned a little bit from it. If you were running a 383 or a 400 I would run the larger cam without worry.
 
#5 ·
I understand what you're saying about low end and mud, but Its more power that I'm ever had in my mud trucks in the past. I wouldn't do this for serious rock climbing or anything, but high revving engines are fun, and this is just a toy. Its basically a budget circle track engine I'm building. the only concern I really have is idle speed and running it on pump premium- I don't want to have to drive to the airfield everytime to fill up.
 
#7 ·
$100 Ebay cam??- go to enginekits.com, they sell elgin solid lifter cams for $69- there american made and good I've used them.

Or go to competitionproducts.com, they have elgin cam + oiling solid lifters with the .024 edm that lets oil spray onto the cam lobes, I think the cam/lifters is $160- dirt cheap when compared to comps edm solids and solid cam which are in the $280 range as a combo

Cam is too big, be careful angle milling heads, stuff doesn't end up fitting (headers, intakes, gaskets) decking the block would probably be better since you are just messing with pushrod length for proper valvetrain alignment.

Atleast consider something in the 230-240 range- in a 350 that should be good to 6,000-6,500

Look up Reeds Cams- he used to grind Winston Cup cams from late 70's until mid 90's knows his stuff, he'll take all your wants and make the appropriate compromises.

Best of luck
 
#8 ·
Yea, After looking into angle milling I'll probably just run a .100" dome. I know it messes with flame travel, but I figure if I knock down the edges it won't be too terrible. I'm also going to install oversized valves and clean up the port work, which I failed to mention. In regards to the cam, I actaully found it is an Elgin cam with the specs changed slightly, I'm probably going to pick one up from Midwest Motorsports. Also, with the increased compression The low end won't be soggy at all, I'll loose some effective stroke wih the larger cam but I used to run around in a different S10 with a 2.5L and a 230 cam, which was an absolute blast. I wouldn't try to pull an RV through the mountians on this cam but in a small light weight truck with a manual I'm not too concerned with power at 1,500 RPM. I just want an idle below 1,000 and for it to run on 93 octane.
 
#9 ·
I was looking through some other cam specs, and this cam is actaully smaller than the one used for the STOCK chevy 302 or the 375 horse 350... In fact the more I look at it the more I'm affraid of having too much compression. It says its best suited to around a 2500 stall speed, so it look like this setup will be just the ticket.

anyone care to guess power output? Or perhaps idle vacuum at 900 RPM? I'll be running Gapless rings so that will affect vacuum.
 
#10 ·
Anything smaller than the 254/254 .485/.485 302 cam is going in the right direction.

Find the cams specs online and watch intake valve closing @ .050, that'll tell you alot.

You'd be suprised just how much compression it takes run a cam that's good to 6,500 so to much compression isn't an issue unless you aren't running 100+ octane with an iron head.

I've got a 327 with 9.75:1 with a comp xtreme solid 230/236 and it really should have around 10:1.
 
#11 ·
ap72 said:
I was looking through some other cam specs, and this cam is actaully smaller than the one used for the STOCK chevy 302 or the 375 horse 350... In fact the more I look at it the more I'm affraid of having too much compression. It says its best suited to around a 2500 stall speed, so it look like this setup will be just the ticket.

anyone care to guess power output? Or perhaps idle vacuum at 900 RPM? I'll be running Gapless rings so that will affect vacuum.
Just because chevy put a combo together stock doesn't make it a good match. My factory LT1 has 10.5:1 compression and a 191/196 cam, and they also do a crate engine with 8.5:1 and a 224/224 cam. You also can't compare those engines you mention. First of all, the 302 was made to rev, so it needed that much cam. It was a race engine that trickled down to the Camaro. The 375hp 350 was gross HP back in a time when gas was darn near free, compression was king, and HP ratings were inflated. If you wanted power (since you didn't have the head and cam ramp technology to get it) you just had to go nuts with duration. You're also comparing two combos that are 40 years old.

If you really want to run this combo, go for it. We are trying to tell you it will suck big time. If you want to believe that it will work fine, that's up to you, but you have a buttload of experience at your disposal on this board and you asked for our help. We're telling you that you have a mismatch.

And no, you won't have too much compression. With that much duration and a 106 LSA, you could run 13:1 on Vortecs and probably not have too much compression. Of course, you'll need 110 octane :) Also, gapless rings or not, you'll be pulling maybe 8" of vacuum. Power guess? I'd give it 390 hp/375 tq as simulated on Desktop Dyno. The cam won't start making power until 3600 and the heads will be done by 5500; especially with that 106 LSA. That cam is going to really shine at 6500 RPM or higher and stock vortecs won't breathe that high.

Now, contrast that with something more reasonable like a 224/224 duration cam on a 110 LSA you're still going to be making 380 hp, but well over 425 lb-ft of torque, and you'll be able to access that torque all the way from 1500 rpms and up instead of having to rev to 3500 like with the cam you've chosen.

Do what you want, but we're only going to tell you so many times... that cam will suck with your combo.
 
#12 ·
I do respect a lot of the guys on here, but as an engineer I also have a great respect for data and facts. Most of the people on here who are the "expierenced" ones haven't commented in part I think because this such a well rounded package. Idealy I would step up to 4.56 gears, but 4.10's will work, and they were cheap. It won't have the best gas milage but for a weekend toy its a damn hard budget combo to beat. Sure its a solid cam and will need more work than a hyd. and sure it'll have a little rough idle but as an updated version of the 375hp 350 It's going to be sweet.

I'm going to guess 460/420 for hp/tq. That could vary some with my carb choice, and it'll be on roller rockers which I don't think I included before... Actuall street tune will probably be 430/400. That's flywheel too, at the wheels I'd probably say 380.
 
#13 ·
I can say I am rather experienced. Especially in mud racing. We mud raced for a total of around 6 years. And during those 6 years we used the same 1979 high sierra with 38 inch tall tires and 3.08 gears. it was the full truck not cut up or modified. During those years we learned alot about engines and how they respond in the mud. We didn`t race in the little ankle deep skim mud, the track we raced at used deep thick clay mud. We started out with a 350, and in the first year won most of the races held, even against big blocks. The next year we did well again with a 383, but not as well as we did with the 350. The year after we got our butts handed to us, we only placed once, but, we made a mistake and that mistake was a 372, 400 block, 350 crank combo. even with a 3000 stall, we put too much cam in it. The cam was 234/244 duration at .050 and it had no low end power whats so ever. It would rev to 7200 rpm but no matter, the heads we used ran out of breath at 5000 and it didn`t make any more power after that point which is the same thing Curtis has already mentioned. If the head can`t flow it, it can`t make anymore power. Years later we returned to mud racing when another track opened. this time we used the same combo as the 372, same cam, same heads only we used a 400. the first 2 years we kicked butt and took names. Then my brother in law, the owner of the truck, got ambitious and wanted to step up, so he installed a massive solid lifter cam, duration of around .255, and a set of 200cc runner dart II heads. I was against this idea, the heads I agreed with, but the cam I warned him was way too big. He chose to use it anyway. Now this is a 400, 50 cubic inches bigger than your combo and the cam size is close to the same, but the dart II heads were made for upper RPM power. The thing sucked, it was lazy and didn`t make any power until the revs reached 4000 rpm, from there on it screamed. Once it hit the deep mud and engine lugged below the power band the game was over.
Sorry, but I don`t call your package well rounded, I can tell you from experience it`s not going to work as well as you think it will. When your trail mud riding you need control, and you can only have that with low rpm torque, you don`t have that control when you have to rev it to the moon to make it move.
Lastly, It wouldn`t matter to me if you have 40 years as a engineer, there is no substitute for experience. Curtis is well respected on this site and is very very knowledgeable. And myself I just listed my experience in this. But, if your age is stated correctly then I will say respectfully you have a lot to learn, and your only going to learn it with experience. And that type of experience is build it then get out there with it and see what happens.
Were only trying to tell you before you do it you have a mismatch.
Good luck. Let us know how it works out.
 
#14 ·
I'm not running mud bogs, 3.08 gears is what killed your ability to use the high RPM power, and people said the same damn thing when I put a 11.5:1 a 2.5L with a 232/235 cam in the first s10, which was one hell of a blast to drive.

I'm not saying this will be a torque monster, it won't be. But it will be plenty streetable, pull above 2500 like a freight train and be more than enough to get my truck through anything.

Also, because of the changes in the automotive world I am slow to take anyones years in the bussiness as evidence- recent build in the past 10 years sure, but more often than not, old timers (which Im' not saying you are) have clouded judgement of what is and is not possible because 20 years ago things weren't possible that are today. As such I follow the numbers on most aspects of engine building. Numbers never lie, nor are they opinionated.

calculate the DCR adn the effective displacement on the engine I'm building adn you'll see that even with the big cam the low end stomps the 4.3L which came in the truck along with 3.23 gears and a 700R4...
 
#16 ·
DoubleVision... let's just let him build it how he wants and learn for himself. He's not listening to experience, fact, or reason. He wants that cam, period.

AP72, if you seriously think that a cam with 250 degrees duration at .050 and a 106 LSA is what you call streetable with 31" tires, then you are deluded. That's not what most people call streetable in a 2300-lb stripped Nova with 26" tires and 4.56s.

I'm 34, I've built just as many "new" engines as I have old ones, and VE theory is the same regardless.

You're right, numbers don't lie, but dynos don't race. You can guess and hope and simulate torque figures, but unless you are a master tuner, you're not going to get anywhere close to the torque that you guess will be down below 3000 rpm. You also probably don't understand that VE below the peak falls off at a much faster rate with anything less than WOT. So all of this torque you speak of in the lower range is ONLY there at WOT. If you've never driven a combo like you talk about on the street, it gets absolutely tiring.

Oh... you can also skip the electric fans. They might work on a stock output engine, but you're talking the need for absolutely serious heat, and you'll be doing it while thermally punishing the engine at anything below 3000 RPMs.

Even at its most fundamental, you have to see the major mismatch between a cam that is larger than some NASCAR cams, and a factory iron street head that flows 230 cfms.... or do you just not want to look at the numbers in that case.

The worst part is, you're going to build this engine out of stubbornness, put it in, then a week later you're going to post the following threads:

"350 overheats all the time - I have electric fans"
"More mileage from 350 - I'm only getting 4 MPG"
"Carb running super rich - It burns my eyes"
"Can't get 350 to idle below 1200 - I've already tried 30 degrees initial"
"No power brakes - why do I only have 6 inches of vacuum?"
"350 not as powerful as I had hoped - I used Vortec heads, but..."

Mismatch. Big time. Have fun tuning it. It will take an absolute master. I'm out.
 
#17 ·
I really don't understand why everyone is getting so miffed over a little duration. Here's a setup very simmilar to what I'm building except he has heads that were ported better than mine will be, and a cam with MORE duration that is still streetable.... Wow, imagine that... There's a lot of people running bigger cams on the street. hell my hp peak will probably end up around 6,000 or maybe a hair under. And that's not streetable? Granted its not a deisel, but what's the point of building this stuff if you're just going to stick with stock, or near stock parts?

and yea, I know I'll be getting around 14 MPG, but I'll live with it.

As far as expierence goes, no one who commented ahs tried anything like this- just the same with the last engine build that I did with a "cam that was too big" as it turned out my milage was twice what they speculated and the torque curve was damn near flat with a peak around 6k RPM again. Oh, and as far as the numbers go I had it down to the exact jetting before I even put it together. I underestimated my milage by 2 MPG's last time (I got an easy 25- 27 on the highway) and I was off on the timing with 1 degree too much advance. Before I even turned a bolt.

I really just wish you were here for the big "I told you so." I guess the only people that can really comment on this would be budget oriented roundy round racers, since they actaully do have expierence on setups very close to this.
 
#19 · (Edited)
ap72 said:
Okay, I conceeded, I decided to step down a bit on the cam and am going with an ISKY grind.

http://www.iskycams.com/timingchart.php?product_number=201524

which has only 244/248 duration @.050" and .524/.534 lift... I figure buying from Isky is proably a safer route.
OK, assuming 1.94/1.50 valves, 10.5:1 c.r., 750 carb and Performer RPM manifold, 1 3/4" headers with mufflers and the Isky solid lifter cam, here's how it works out on my software....(1 5/8" headers will drop power, any smaller carb will drop power)....
rpm tq hp
2000 355 135
2500 360 170
3000 385 220
3500 435 285
4000 460 350
4500 475 410
5000 475 450
5500 460 480
6000 435 495
6500 390 485
7000 345 465
Retarding the cam timing 2* will make 500 peak hp @6200 and 475 peak tq @5000..... 2* retard and 850 carb will make 505/480.
 
#20 ·
if your off roading my friend did his 79' prospector up with a edelbrock performer cam, 750 carb, and performer intake. the summit cam is .420/440". the heads were magnums converted for a LA block. gears were 4.88's with 31's.

made a powerfull combo.
 
#22 ·
ap72 said:
I really don't understand why everyone is getting so miffed over a little duration. Here's a setup very simmilar to what I'm building except he has heads that were ported better than mine will be, and a cam with MORE duration that is still streetable.... Wow, imagine that... There's a lot of people running bigger cams on the street. hell my hp peak will probably end up around 6,000 or maybe a hair under. And that's not streetable? Granted its not a deisel, but what's the point of building this stuff if you're just going to stick with stock, or near stock parts?
First of all, my problem is not that you want to use 250* on the street... its that you want to do it with 4.10s in a truck with 31" tires. You also just said what many of us said days ago... "except he has heads that were ported better than mine will be". You have to match everything together. You are planning to use a cam that will shine from 3500-7000 with heads that shine from 1500-5500. Streetable also has A LOT to do with the rest of the car. If its a 3000-lb Camaro with a 3500-stall and 26" tires and manual brakes, great. If that is your idea of streetable, then do it.

and yea, I know I'll be getting around 14 MPG, but I'll live with it.
My guess is 10 mpg on the highway if you spend lots of time tuning.

As far as expierence goes, no one who commented ahs tried anything like this-
Uh.... yeah, because its mismatched. If we were inexperienced enough that we HAD tried this, you wouldn't be asking our advice. There's a reason why experienced people like the one's you asked DON'T do what you suggest.
just the same with the last engine build that I did with a "cam that was too big" as it turned out my milage was twice what they speculated and the torque curve was damn near flat with a peak around 6k RPM again. Oh, and as far as the numbers go I had it down to the exact jetting before I even put it together. I underestimated my milage by 2 MPG's last time (I got an easy 25- 27 on the highway) and I was off on the timing with 1 degree too much advance. Before I even turned a bolt.
Then you, sir are a master. I retract everything I said. Can you build me one of those 6000-rpm torque peak 4-bangers that gets 27 mpg? I'd love to have one for a rock crawler with 40" tires with a 3.08 rear.

I really just wish you were here for the big "I told you so." I guess the only people that can really comment on this would be budget oriented roundy round racers, since they actaully do have expierence on setups very close to this.
Firstly, no. Roundy-round racers wouldn't build this for a race. Secondly, they are restricted by very specific rules. They are building a purpose-built engine to run at an insanely specific RPM range. You are building a street engine for a large-tire mud truck. Those two couldn't possibly be more different.

Secondly, I WILL be here for the big "told you so." I've been here for years and I plan to stay. Post your numbers after you get it dynoed... or can you just magically predict that like you predict jetting and torque curves?

Is your combo terrible? No. Could it be worlds better? Yes. I just have to laugh that the TITLE of your thread is "please critique my cam choice," then you have spent the last three days insulting us and defending your original choice while citing a 4-banger that was a "blast to drive" as your last build.

If you think a 4-banger with a 6k torque peak is a blast to drive on the street, then enjoy your overcammed 350 that is built with a no-name Ebay cam.



Done.
 
#23 ·
curtis73 said:
Then you, sir are a master. I retract everything I said. Can you build me one of those 6000-rpm torque peak 4-bangers that gets 27 mpg? I'd love to have one for a rock crawler with 40" tires with a 3.08 rear.
Well thank you for the compliment, and I'd love to help you buidl an engine like the one I had, it won't do well with that gearing and tire combo in a full size truck though. Mine was with 30" tires in a 5-speed S-10 with 4.10's. 3.08 gears with 40" tires needs nothign short of a big block. To match the displacement/revolution of the tire you'd need a 600 inch big block to match me putting my 350 in this S-10. A 262 would be about comparable to my origianal 2.5L...

Oh and Tech Inspector did a dyno sim of my engine combo... I don't think it looks bad at all- 495 hp, 475 tq... 355 ftlb at 2000 RPM... That's big block territory (not a well built big block, but still impressive for factory heads and NA on pump gas with stock displacement.)

I know what you'll say next- its a SIMULATOR... yes it is and its as valid on this combo as any of the other ones.

As far as critiquing, I was looking for suggestions on simmilar cams... running something like a 262H cam compared to this one would be as close as running a solid roller... And to risk sounding like a ******* I actaully like arguing about things like this, if nothing else it forces me to reconsider and evaluate my own opinions... even if I decide to still stick to them.
 
#24 · (Edited)
Hey guy's don't mess with him, he's an ENGINEER. Not to be a @$$hole, but you fit the profile of an engineer (I have worked with TONS of them). No matter what anyone suggests you still think your way is the best, and that's fine because most things are learned through trial and error (unless you heed peoples advice). Just like the Guy who lived next to me with a 327 Chevy that he built, and him & his smart buddies knew that it was over 600 hp. That thing sounded nasty & was pretty cool in his 72 nova, but too bad he got his ***** kicked by my mild 383 in a 3700# 72 Chevy pickup which sounds decent but not radical like his beast (hahahah :) ).
These HotRodders on this forum are very smart and have information that CANNOT be ignored. It pisses me off when someone gives you good advise and you don't listen because you know better. If you are so set on this combo, build it, but don't keep asking for advise and then blatantly turn it down. :nono:
(No Offense to any Engineers who aren't bull-headed, I actually am one but a piece of paper with your name on it doesn't give you the right to be stubborn).
 
#26 ·
jbvcw71 said:
Your best cam selection is one that you initally feel is WAAAAAY too SMALL.

NO REGRETS!
Well, going with a cam that is too small leads to detonation problems, especailly with high compression- which is one reason why I'm going with a unusually large cam.

As far as the bull headed engineer thing, I'm actaully fairly quiet when it comes to giving suggestions, when it comes to work I only speak up when they need the right answer. :mwink:

Seriously though this thing is not meant to set records on the track nor on the mud runs. Its built to be a fun toy to drive. Some people like cruising in an automatic od car with a torque curve as flat as a pool table and an idle speed at 500 RPM... If I wanted that I would buy a diesel.

To me running with a 4500 RPM torque peak, banging gears on a stick shift, and the absolute nasty sounding idle that comes with engines like these is a good time.

The only thing I'm worried about is running it on 93 octane VS having to switch to E85 because of too much effective compression, and an idle speed over 1,000 RPM (just a number I set as my own standard), and wearing through springs (which with modern designs isn't more than a little more initial capital investment).

My effective displacement is still about 276 ci, and compared to a stock 4.3L which comes in around 237 ci I'm still coming out ahead on power with the big cam- even at idle! (I'm comparing it to the largest enigne that came in the S-10 for reference- also the one many people use with stock gearing, auto transmissions, and 30" tires- factory size tire is right around 28-29")

Oh yea, effective compression is up too... along with intake and exhaust flow...

Are there ways to build engines that idle lower and pull more vacuum and can run on watered down gas- yes, hell you can even buy one from GM for a fairly low price. But where is the fun in that.

Lastly, don't blame relying on the numbers as a fault since they don't support your opinion. I understand your opinion- I really do and there's nothing wrong with it. I just don't like being that conservative when its not at all needed.

Techinspector posted the numbers- to me they look great. 6,000 RPM hp peak is my idea of ideal for this project.
 
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