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Cam Selection

4K views 41 replies 8 participants last post by  bygddy 
#1 ·
i currently have the comp xr288hr 236/242 @.050 duration with 110 lobe seperation.... 3500 lb car...3.73 gear automatic.2800 convertor.406 sbc 10.5:1 compression ratio. car made 322 at the wheels before having the heads ported and polished with rpm performer intake. i have jegs aluminum heads being ported and polished as we speak. going with rpm air gap intake with holley 750 carb. just wondering if you thought this cam was a good match for this set up or if i should go with a bigger cam? any thoughts or suggestions would be appreciated.
 
#2 ·
Well what size rockers are you running? With a 750 carb you should probably look into your cams duration more than its actually lift. If anything put in some bigger rockers add anywhere from .3+ of lift. What size is your crank? In fact, with a 1.5:1 rocker ratio, the solid's duration at 0.050-inch reads as if the duration was taken 0.033-inch lifter rise in hydraulic terms. That's a significant difference. A solid cam will behave like a hydraulic with duration at 0.050-inch spec. of approximately 10 degrees less duration
 
#6 ·
4.00 is stock piston size for a 350
+0.030 are 383 piston size
3.75 stroke crank is a stock 383

If you really wanna get drastic bore it to .060 over and run a 388, Maybe even put a 4.00 crank in it. Which will make easy 550 ft/lbs easy. But you'd need different rod size and piston height. And also depending on the base block your using.
 
#11 ·
Which Jegs heads? Who is porting them?
Air gap intake is an excellent wallet lightening device
Carb is too small
Needs a 3000-3500 stall

IF the heads are being ported by a reputable head guy that knows what he is doing,
I would
1.6 rocker
850 Carb and play with different spacers
3000 stall
Get the timing and tune on the money.
This is all assuming the bottom end is high dollar exotic parts that won't explode the second you hit 6000+rpm.....
Oh wait, sorry.....disregard that last part.
:D
But do confirm your compression is what you think it is.
 
#18 ·
Yes, we got that part, now read post #11 and fill in the blanks for us.
Wow in deed.What in the world are you guys doing to this poor O/P??.He provides info tons more than most and you guys tear him a new one :nono:!!!. Stop and think not every poster that comes on here doesn't know what they are talking about you know. Some just want to confirm their build plans and trade ideas.Gezzzz man!!!.

My two cents fifty:

Airgap a waste of money???. Hummmm??.

850 vs a 750 when he owns already a 750.Yeah I do think he could get the 750 to work.

Never been a huge supporter of 1.6 rockers on a street driven vehicle.After all he needs not go through all the B.S.with valvetrain geo and after all why compensate for a cam when he is asking about a cam choice in the first place??. I'd bet money his seat of the pants dyno would never know the difference.

3,000 stall T/C??.Well kind of left out all the associated parts that comes along with that.Tranny cooler,400 and the need to a really good cooling system..................maybe some valve body work.................holy cow!!.
 
#26 ·
Oh Gar.....
Air Gap when he already has a performer RPM...yep, absolute waste of money....play with some Carb spacers, more power to be had then the intake swap and a hell of a lot cheaper.
1.6 Rocker on a hyd roller Cam, cheaper then the proposed cam swap and were talking fine tuning and finding power with the current set up....the OP is reasonably new and has stated he is on a budget, a roller cam isn't cheap.
850 Carb, sure, his 750 will work, its a fairly large cube with a bigesh head, I suspect he will see a good increase with the 850
And the 3000 stall? OP has a 2800 now lol, I was saying "at least a 3000 stall" and I would gowith a quality 3500 myself. Im willing to bet its a generic 2400-2800 converter in it now, and I would hope it has an aftermarket trans cooler in it at this point.
The flow and port velocity of the Jegs head will make incredible power if compentently ported.
I'm not beating up the OP at all, in think either himself, or someone he trusts has put together a solid package street/strip motor that with a little work, and not a bunch of money, will pick up significantly from where he is now.
 
#24 ·
As long as the head port person you picked is cognizant of shape as it equals to volume and velocity (IE. a pro that reworks heads and checks his work on a flow bench keeping in mind what you are doing with them) the cam you have is plenty. Can't stress enough......dial in the carb and timing.
 
#28 ·
Nope, your not turning the motor hard enough to justify it. The basic performer RPM will match it until 6000+ rpm where the single plane will take off...but your not going to need or be turning it any harder then 6500max anyways.
Save your money, keep the performer RPM and try a 1" and 2" spacer and see where they get you.
We have a poster here that has a big cube SBC and loves his single plane and has the cam and heads to support lots of power to 7000+rpm...even tho he is getting old and has it chipped for 6k ;) (hi Vin!) Lol.....
You didn't answer, or maybe I missed it, what's on it for exhaust?
 
#32 ·
The headers work, I would step up to a full 3".
I'm a huge fan of the flowmaster sound myself, but they don't have the flow to back up the sound. On a street motor that isn't concerned about every last HP I would leave them alone.
In your case where were trying to find power without braking the bank I would swap them out for something free flowing, I like an X pipe with dynomax race bullet's to full tailpipes. 3" pipe from header back. The X pipe mellows the sound enough to make the Bullet's comfortable and promotes exhaust scavenging. You will see a solid gain from the 2.5" and flowmasters you have now.
 
#37 · (Edited)
Just a shot in the dark projection re-reading this thread,I would expect a 450 hp output at the flywheel with the planned mods.(head/intake)When the dyno runs where made what heads where on it at that time that you are replacing??

If not for nothing,our experiences with 400's giving it is a 400 we when dealing with a 400 go back to the basics when we have one that is laying down.What that means is leakdown our 9.90 cars with 400's often.

What I get from your first post is this is a build that has had sometime running before the intake/head mod.So how old is the build??.

Do think Vinnie's questions are very important.

Not knowing how old the first build was and for that matter if the original build was ever leaked down leaves you not knowing if you building from a sound foundation.If a issue is coming from that,mod's compound those issues making it worst.

Guess the Jeg's not ported where on it when the dyno pull was first done??.
 
#39 ·
Yes Sir.Thank you for your reply.

Do think for you follow what Vinnie suggested is important.

Establish the foundation I suggested with a compression check and leakdown is my suggestion as well.

When you from the dyno test had 210cc intake runners already,not sure how much you would realize with the port work or exhaust improvements.Yes maybe the exhaust improvements will help some,but Vinnie's approach questioning the tune might reap more.
 
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