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-   -   please critique cam choice (http://www.hotrodders.com/forum/please-critique-cam-choice-145864.html)

ap72 09-29-2008 05:24 PM

please critique cam choice
 
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".

DoubleVision 09-29-2008 05:32 PM

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.

curtis73 09-29-2008 05:37 PM

I'll second that... too much duration. You could get by with it in an automatic with a 3500 stall, but you need gobs of low end torque to move those 31" tires with 4.10s.

I'm in complete agreement with the 224 degree recommendation

RippinRon 09-29-2008 05:42 PM

You would probably be better off with a performer intake opposed to the rpm version for your application.

ap72 09-29-2008 05:45 PM

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.

DoubleVision 09-29-2008 06:02 PM

Run it how you like it`s your ride. However, circle track engines have there place and it`s not in the mud.

GenYnNC 09-29-2008 08:14 PM

$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

ap72 09-30-2008 06:14 AM

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.

ap72 09-30-2008 07:24 AM

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.

GenYnNC 09-30-2008 09:46 PM

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.

curtis73 09-30-2008 10:54 PM

Quote:

Originally Posted by ap72
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.

ap72 10-01-2008 06:39 AM

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.

DoubleVision 10-01-2008 08:09 AM

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.

ap72 10-01-2008 10:07 AM

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...

GMC boogie 10-01-2008 11:32 AM

Seems like you have it all figured out, contrary to what everyone else has to say.

Experience is often gained the hard way.


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