Cam questions

[Spoonbill]

I have an 87 c10 305 tbi 700r4. The question I have is that when you look up cams on jegs or summit it will show some cams for my truck they have ones that you would normally see like 234 / 238 and then they have a bunch have numbers like 296/304. I thought numbers that high was only for race cars. These weren't unknown cams. This is companies like edelbrock and comp cams so you know the numbers are real. I had an 82 a few years ago and checking them out in jegs and summit. The high numbers back then were like 240's & 250's. How are they so high now. Would roller setups have anything to do with it??

[Rattler12]

The lower #'s are at .50 lift on the cam and the higher with 0 lift.  Go by the #'s at .50. Anything higher for a small block than 224 int/ 230 exhaust especially on a 305 makes for an unruly street machine...imho......ie less vacuum for power brake booster, need for a higher rpm torque converter, rough to a lopey idle etc. The higher the CI of the engine the less "unruly" IE the above cam in a 350 or 400 would be tamer......overlap makes a big difference also. 107 degrees = lopey idle, 110 to 112 rough idle. 114 and up pretty much unnoticeable. You're passing gas from the intake and out the exhaust the lower the overlap until the rpms get up then you're getting more combustible gas to air mixture and that= more power......but less mpg. Depends on what you want and what you're willing to put up with

[Spoonbill]

These numbers are 0.50, I have found one that is probably ok, it is 234/238 @.050. Let me ask you this. Truck is all original 87 305tbi 700r4, it only has 66,000 original documented miles. We have had it since we picked it up from the dealership. I don't like this efi crap. I know exactly nothing about it don't want know, grew up with carbs I want to take all of the efi off and get heads, cam, intake and carb. When you look up my truck on anyone's website it will tell you that it has vortec heads but they aren't. They are swirl port heads. So since I am changing it over to carb at that point would I maybe just put in that it is an 86 model or is the block just machined for that type of swirl port head??

[Rattler12]

Some one else may want to chime in but I think the only difference  in the early model (pre 87 ) and the 87 heads is the angle of the four bolts in the middle of the manifold. Most aftermarket mfg have  manifolds that can fit either with the use of provided spacers. I have a pre 86 305 carbed engine with the "old style heads" and an 87 350 TBI engine with the heads drilled to the different angle for the 4 interior bolts. The 2 manifolds I have will fit either........the 85 w/o spacers, the 87 with. I think the intake to head mounting holes changed from 86 to 87 along with the small block going to a single rear main seal instead of the 2 piece. Should be an easy swap going from a tbi to carb

[SkinnyG]

234/238@0.050 is still pretty big for an otherwise stock 305.  You will want a high-stall converter (2500 for sure, maybe 3000), and you ~should~ raise the compression significantly.  If the lift is over 0.480", you will need to machine the heads for more clearance. That cam should ~start~ making power around 2500 or higher on a 305.

I would encourage staying around 218° or smaller.  a 218° will still have a noticeable idle, but a lot less "snowball" effect of changes that you need to do to make that cam work.

There are EFI cams that you can put in, that will make considerably more power and still be able to keep the TBI, which is hands down better than carb for driveability and economy.  I know carbs very well, I know EFI really well.

[Spoonbill]

I think I might just stay with efi then. That way I won't have to change everything. Since you lined me out with numbers what about I think it is the runners number. I see everything from 170 to 225 what do I need on those numbers to work good with the 0.50 you gave me??

[SkinnyG]

I don't know what you mean by "runners number."  Can you elaborate?

[bd]

Intake runner volume

[SkinnyG]

Is this intake runner in the manifold or in the head itself?

If you're looking at buying aftermarket heads, look for 305-specific heads.  The combustion chambers are very small so that you can have good compression.  60cc or less, likely.  I think Edelbrock among others have a 58cc head.  Once you pick your combustion chamber size, then see what intake volume they offer in that size.  Smaller volumes keep the port velocity high which benefits torque - desireable on the street, and in a truck.

BIG cams will want BIG volumes, but BIG requires a whole fleet of other mods to make work - usually at the cost of low speed torque.  Err on the side of small, and you will be a lot happier.

[Spoonbill]

Thanks a lot for the help guys. Answered all questions about that whole part of the engine

[Spoonbill]

When looking at heads you see numbers like 180, 190, 195. I think it is maybe the volume number but not sure. Maid up my mind and I am going to stay with the tbi but I still want to get heads, cam, intake and Holley has a new tbi system that has more than the stock tbi so I will replace the factory one and keep of course. Anything I do to this truck will be bolt on and I will keep all the original parts. By doing it this way it won't take anything away from the originality. So with all that in mind what heads should I look for. Already got me figured out on what cam do I just need some help now on what heads I should be looking at

[bd]

Which cam have you decided to install?  Be specific.  Same question regarding the Holley injection system.

[Spoonbill]

The Holley injection is just a tbi replacement. It has 670 cfm which has to be bigger than stock because if you went with a carb and did the numbers deal it comes out to 516 cfm so I figure the stock tbi has to be close to that 516 number. As far as the cam that I have in mind is an edelbrock 22046 rolling thunder hydraulic cam & hydraulic lifter kit which is a complete roller setup for 87 and later sbc chevy 283-400. I want a 1500-6500 setup and I figure this will all get me to that. Not only is this setup all 1500-6500 but the Holley efi intake is that range too. I'm just sure on what heads will work good with this setup. Any ideas??

[SkinnyG]

That's a big cam.

Unless you're also going to upgrade the rods and rod bolts and valve springs, you will never see 6500.  More than once.  Not sure how long the pistons will last at that rpm either.  You WILL have to modify stock heads to run that much lift.

Don't do this.

[SkinnyG]

Cam with the same specs (prolly the same cam, less pushrods and such):

https://www.youtube.com/watch?v=8HKlFOJZ0sk

S-n-o-t-t-y.