[ithooks]

can i get a little help on cam pic i just picked up small truck 355 gears 5speed 350chevy 650 dp air gap intake headers roller tip rockers i think 9.0.1 stock heads with good springsi did not build this truck ? it has 400miles on motor the cam in it now got the bigger is good pic its to big im sure it has the summit k1107 im looking low mid power what do you all think thanks

[hcompton]

Originally Posted by ithooks

can i get a little help on cam pic i just picked up small truck 355 gears 5speed 350chevy 650 dp air gap intake headers roller tip rockers i think 9.0.1 stock heads with good springsi did not build this truck ? it has 400miles on motor the cam in it now got the bigger is good pic its to big im sure it has the summit k1107 im looking low mid power what do you all think thanks

I think you may need a cam a little smaller and alot better designed. Do you know what kind of pistons are in the motor. Also gen1?

For a truck you usally want to be all done by 5500. That cams 3000-6500 powerband is not going to work well.

But you need to figure the cr so you can get the proper dcr figured out. The large cam may be because of really high compression.

[F-BIRD'88]

Replace with summit cam #1785 or 1788
and new hyd lifters

[ithooks]

its a91 truck block heads are 882 it runs good on 91 timming is nuts just got it have not looked in it runs good just dont pull good till way up in rpms where im not at much did test sc test was 140 psi and its 94 s10

[hcompton]

The 1788 fbird recommended looks good. Should still be good if your close to 9:1 compression. Do you have any problems with knocking and can you run 87 octane now?

[cobalt327]

Originally Posted by ithooks

its a91 truck block heads are 882 it runs good on 91 timming is nuts just got it have not looked in it runs good just dont pull good till way up in rpms where im not at much did test sc test was 140 psi and its 94 s10

Whether you keep the cam that's in it or get a better matched cam, you need to set up the distributor w/a performance timing curve.

[ithooks]

it has hei proformance distributor was thinking comp cam 268H with the big cam in how can i get the dcr of engine sc was 140 it will run on 87 if i baby it good i love the bigger cam its just not what the truck needsi do most my driving on street work and back and i like to play just dont what to get my *** left in the dust frome my 3000 to 6500 cam you know sounds bad by the time it get going it to late:mad

[hcompton]

Originally Posted by ithooks

it has hei proformance distributor was thinking comp cam 268H with the big cam in how can i get the dcr of engine sc was 140 it will run on 87 if i baby it good i love the bigger cam its just not what the truck needsi do most my driving on street work and back and i like to play just dont what to get my *** left in the dust frome my 3000 to 6500 cam you know sounds bad by the time it get going it to late:mad

Here is a link to figure your DCR.
United Engine & Machine Co. Incorporated

Wait so you put 87 in it and let it get hot and beat on it a little does it knock or ping? If so i bet you have more than 9:1 compression with that big cam it shouldnt knock with 87.

Might want to figure the dcr before you buy anything. I got a sinking feeling you will still need a strong cam.

[cobalt327]

Originally Posted by ithooks

it has hei proformance distributor was thinking comp cam 268H with the big cam in how can i get the dcr of engine sc was 140 it will run on 87 if i baby it good i love the bigger cam its just not what the truck needsi do most my driving on street work and back and i like to play just dont what to get my *** left in the dust frome my 3000 to 6500 cam you know sounds bad by the time it get going it to late:mad

It's hard to use the cylinder pressure as seen on a compression tester gauge to fiugure the dynamic CR. You need to know the actual static CR as measured by volume, not pressure.

This is because the cam timing effects the gauge pressure reading.

If the valves were closed at BDC and you got 140 psi, the approximate SCR would be about 8.5:1. But if the cam is radical, you're looking at more SCR than that.

Do us (or should I say ME) a favor and use punctuation, or at least periods. The sentences all run together and it's hard for me to read what you're saying.

Thanks.

[ithooks]

It just pings sorry i dont use key pads. Guess i can pull the heads and take a look at pistons and heads cc more than i like to do this time of year its cold

[cobalt327]

Originally Posted by ithooks

It just pings sorry i dont use key pads. Guess i can pull the heads and take a look at pistons and heads cc more than i like to do this time of year its cold

Back up a minute. You have "stock" heads- what's the casting number? If they're large chamber smog heads and you have flat top pistons, the SCR isn't going to be high at all. The 268 cam should work fine under those circumstances. It's only if you went to a small RV-type cam that you'd need to worry about the SCR being too high.

Now, if you have small chamber heads, that's another story...

[hcompton]

Originally Posted by ithooks

It just pings sorry i dont use key pads. Guess i can pull the heads and take a look at pistons and heads cc more than i like to do this time of year its cold

Yep imbetting its more than 9:1 best to leave the cam inplace until you can find out what the cr is and get the cam matched up right.

I understand the cold weather might be best to try to find out more from the engine builder or previous owner.

[ithooks]

yes 882s 76 cc im going with the 268h thanks for the help

[cobalt327]

With a 0.041" quench, 0.030" over flat top pistons, and unmilled 883s the CR will be right at 9:1.

If the decks are virgin and there's a 0.041" head gasket w/a stock compression height piston , the CR is about 8.6:1. Less if 1.54" CH pistons got used in a rebuild (~8.3:1). Much less if dished pistons are in there.

That said, that assumes a lot. Measuring is the sure way to know- but odds are good the 268 will be OK, and that the CR will not be higher than about 9.25:1.

Good luck and let us know how it turns out.

[ithooks]

I hade a bran fart thay are 193 think 64 cc.The cam in it now 488 510 292 302 cam timing intake opens 8 btdc ex 61 bbdc the intake closes 46 abdc ex 3 atdc the truck runs good just not where i need it to