I am swapping out my 305 tbi for an 1989 irocz 350 tpi this summer and i need some help. My dad is selling me these heads http://www.jegs.com/i/Edelbrock/350/60739/10002/-1 and I'm wondering what would be the best cam to use with them. "best" for a daily driver and i wouldn't mind a nice idle

Thanks
Mitch

 

This is the cam my dad said he bought for those heads http://www.jegs.com/i/Edelbrock/350/7102/10002/-1 would using this cam with those heads work just fine on a 350 tpi?

 

did i not ask my questions right?

 

There are a couple of things you have to consider to ensure that you'll get the results you're after.
The most important thing is calcualting your compression ratio. Both static (SCR) and running (DCR).
With the 70cc combustion chamber and the dished piston that comes in the 350TPI, chances are your static compression ratio will be very low.
Combined with that cam, which is reasonably large, your DCR will be so low that performance will suffer.
Somewhere in this forum is the data you need. Specifically, piston dish volume. With that a few assumptions such as piston below deck value (stock is typically .025" below deck) you can calculate what your SCR will be with various thicknesses of head gasket.
While there's more to it than that, this will get you started on a little research.
What I can't comment on is how your stock computer will react to the new cam.
There's some great tech in these pages. Perhaps that question posed in a different forum will get that question answered.
In the meantime here's an article on dynamic compression that will give you the guidelines for compression ratio and cam timing.

http://www.empirenet.com/pkelley2/DynamicCR.html

 

More info than you need here however you can calcualte your SCR and potential DCR from some of it.

These pages are strait from GM and Pontiac
Issued: 7 April 1989
Revised: 12 April 1990, 5-28-95, 7-1-99, 6-20-02
Bulletin #: CHEV-89 Page 1 of 1
Specifications for the 1989 Chevrolet engines.

R.R.
H.P. Disp. C.R. Ind. Make Model/Transmission Manifold Lifter Head cc
125/
130 173 9.14 PFI NA 10070150 1.5 H 27.3
140 307 9.24 1-4 Roch 1375x2250/1218/AV 22504068 1.6 H 59.85
170 305 11.18 TBI NA 14102183 1.5 H 53.0
195 305 10.49 PFI NA 10066015 1.5 H/R 52.3
220 305 10.49 PFI NA 10066015 1.5 H/R 52.3
230 350 10.22 PFI NA 10066015 1.5 H/R 63.2
240 350 11.53 PFI NA 14081005,10066013 1.5 H/R 53.6


Deck Piston
H.P. Disp. Cl Type Height Vol Valves Cam Lift Springs
125/
130 173 .005 Sumpted .280 20.54 cc 1710/1420 393/409 Outer w Damp
140 307 .002 Dish .072 5.42 cc 1750/1502 474/474 Outer Only
170 305 .013 Dish w/n 6.23 cc 1845/1505 350/385 Outer w Damp
195 305 .013 Dish w/n .058 8.24 cc 1845/1505 350/385 Outer w Damp
220 305 .013 Dish w/n .058 8.24 cc 1845/1505 415/430 Outer w Damp
230 350 .013 Dish w/n .060 8.87 cc 1945/1505 415/430 Outer w Damp
240 350 .013 Dish w/n .060 8.87 cc 1945/1505 415/430 Outer w Damp


H.P. Disp. Gasket Head Cast
125/
130 173 .061 10048696, 10048651
140 307 .030 22500142
170 305 .021 14102187
195 305 .016 14101081
220 305 .016 14101081
230 350 .016 14101083
240 350 .016 14101128

Issued: 28 March 1989
Revised: 6 April 1989, 9-5-95, 7-1-99, 6-20-02, 7-27-04
Bulletin #: PONT-89 Page 1 of 1

Specifications for the 1989 Pontiac engines.

HP Disp C.R. Ind. Make Model/Transmission Manifold R.R. Lifter Head cc Notes

110 151 8.50 EFI AC 25096867 10066657,10066656 1.75 H/R 50.30 A
125/
130 173 9.10 PFI Roch 10070150 1.50 H 27.30 B
138 307 9.24 1-4 Roch NA 22528212 1.60 H/R * 59.85 I
140 307 9.24 1-4 Roch NA 22504068 1.60 H 59.85 J
150 121 8.30 PFI AC/Bos 10042031 1.50 H 43.30 C
150 138 11.00 EFI Roch 17090054,17090130, 22532556,22538691 DIRECT H 47.00 G
17087259,17087260
170 305 11.18 TBI Roch 141102183 1.50 H 53.00 D
195 305 10.49 PFI Bos 10066015 1.50 H/R 52.30 E
220 305 10.49 PFI Bos 10066015 1.50 H/R 52.30 E
230 350 10.22 PFI Bos 10066015 1.50 H/R 63.20 F
250 231 9.00 SFI Bos Turbo 25505359 25525146 Upper 1.65 H 35.90 H
25507221,25525137 Lower

Cylinder Head Castings
A=10044485 B=10048696, 10048651 C=90209851 D=14102187 E=14101081 F=14101083 G=22530955,22539086 H=25533485,25539723, 25536702
I=22520142 J=22503317
* H/R Dia 0.698"


Deck Piston Dish/Dome
HP Disp Cl Type Height Vol Valves Cam Lift Gasket Springs

110 151 .036 Dish .160 15.80 cc 1720/1500 248/248 .044 Outer Only
125/
130 173 .005 Sumped .280 20.54 cc 1710/1420 393/409 .061 Outer Only
138 307 .002 Dish .072 5.42 cc 1750/1502 474/474 .030 Outer Only
140 307 .002 Dish .072 5.42 cc 1750/1502 474/474 .030 Outer Only
150 121 .010 Dish .020 18.70 cc 1690/1430 430/430 .050 Outer Only
150 138 .010ab Dish .118 4.50 cc Note a 424/424 .037 Outer Only
170 305 .013 Flat/notches 1842/1505 350/385 .021 Outer w Damper
195 305 .013 Dish .058 8.24 cc 1842/1505 350/385 .016 Outer w Damper
220 305 .013 Dish .058 8.24 cc 1840/1500 415/430 .016 Outer w Damper
230 350 .013 Dish .060 8.87 cc 1940/1500 415/430 .016 Outer w Damper
250 231 .020 Dish .190 25.23 cc 1750/1500 438/438 .060 Outer Only

Notes
a-This is a 4 valve head In 1.400 & 1.437 Ex 1.176 & 1.240

 

So armed with the following:
Combustion chamber volume 70cc
Piston dish volume (from the spec sheet) 8.24cc(+/-)
Bore 4.000" (unless it been rebuilt to the next oversize)
Stroke 3.48"
Gasket thickness. Variable. Thinest .015". Thickest .051"

I calculate your static compression ratio to be a bout 9.25:1 with the thinest head gasket at .015". That's good.
Using that cam, your running or Dynamic compression ratio will be less than 6.5:1.
That motor will fall on it's face plain and simple.
A cam with less duration is definitly going to improve things. Perhaps something along the lines of this.
http://www.compcams.com/Cam_Specs/Ca...?csid=195&sb=2
That will allow the engine to build some compression pressure.
I believe it will also be more computer friendly however the comp cam spec says custom chip.
In any event, stay away from that huge cam.

 

You sure know your stuff I'm new to this stuff and this is my 1st engine swap so all of this is kinda hard to grasp. So with that comp cam I should have no problems? I'm having the 350 rebuilt next month so any tips before i go up to the shop spending more than I need to.

 

That's just a bunch of math.
There are people here that REALLY know this application. I'm not really up on TPI and computers.
What I did see on the Comp Cams web site is that the cam mentioned above WILL need some kind of computer upgrade to allow the basic engine functions to perform properly.
The next cam down the list, the XR264HR, can be installed without any reprogramming. At least that's what Comp says.
My experience says that when choosing between two cams, choose the smaller one. Generally the results are better with respect to throttle response and drivability.
If you're doing a total rebuild, that is a rebore and new pistons, be sure you know what's being installed. If the block gets decked, then you will need to know by how much and how far the piston sits in the bore at TDC. These are all elements that determine your final SCR. The cam you choose MUST match the compression you arrive at.
More precisely, you should choose a cam (with heads to match) and then build the engine to give what the cam needs. Bigger cams need a higher compression ratio and vice versa.
If you end up with 9.5:1 with the 70cc Edelbrock heads and a stock type piston then the XR264HR (I assume you have a roller cam block) would be your best choice. Certainly there are others (different brands as well) however this is just an example.
You can juggle the final compression ratio a little with various thicknesses of head gaskets however that affects things like piston to head clearence and quench so you have to be careful.

 

I mostly agree with Skinny Z. However, I'd go with a 212/218-110 cam and have the heads milled 0.030"

 

After a few days of thinking I don't think those 70cc edelbrock heads are a good idea. How about these heads http://www.jegs.com/i/Edelbrock/350/60859/10002/-1 with this comp cam http://www.compcams.com/Cam_Specs/Ca...?csid=207&sb=0

I'm having to get a custom chip anyways to disable vats and the fact that the ecm I have has the 305 tpi prom in it

thanks guys

 

Question: This also pertains to my potential build as I'll be getting the same 70cc Edelbrock heads. Compression ratio notwithstanding, is it better to have a smaller combustion chamber in terms of efficiency and power production? Example: 64cc vs 70cc provided a domed piston isn't needed to arrive at the target compression ratio.

 

Those heads are a better idea, but that cam is a poor match. consider a 12-000-8, 3013/3034-111 as a far torquier choice.

 

For N/A builds I prefer to always run flattops then order chamber volume to match the desired compression. The OP running dished pistons kind of renders the question moot. when dished pistons are required, which is mostly with boosted strokers, then I'm NOT in the camp of symmetrical dish. It's better to have the dish the same shape as the chamber. They talk of getting the pistons cocked in the bore. But their way promotes detonation.

 

Could you explain these numbers so I can better search for a matching cam of those specs. Sorry, I'm still not all that familiar with this

 

When you order a custom cam from COMP cams, the part number is 000. If you're using a pre-'87 SBC, the prefix is 12. For '87-up SBC blocks, the prefix is 08. And the -8 suffix means it's a steel core for roller lifters.
The 12 prefix can be used in '87-up blocks, while the 08 prefix cannot be used in earlier blocks. Not knowing what block you have, I played it safe and used the 12 prefix.
Now, the 3013 number is which COMP lobe for the intakes, while the 3034 is the exhaust. 111 is the lobe separation angle.
You can't order this from Jegs or Summit Racing, you have to order directly from COMP.
This spec will easily pass emissions and make good vacuum.

 

I get it now. How will the idle sound with these specs?

 

very mild. not dead stock, but really close to it. This spec is a perfect match for the rpm range of a stock L98, and will make it feel like a 383 stroker.