Cam Selection?????

[4spd350]

My 1980 vette with the L-48 is lacking just a bit of umph as you all know. Yesterday I picked up a set of 305 Torquer heads for near to nothing,. they have been modified with 1.94/1.5 valves installed, and the chambers are 58cc with Z28 springs. I know this is going to raise the 8.5 compression ratio a good bit, maybe too much, I will probobly go with a thicker head gasket to be safe. But my question is while Im replacing the heads, Im going to go ahead and upgrade the cam also. My car is a 4spd what would be your suggestion? Any help would be aprecciated. Along with the set up will be a performer intake manifold with 1.5 roller rockers. I was looking at a 280 duration with .486 lift. Is this too much? Can I go to a 292 with a .507 or do I need to go down to something like the 272 or 268????????

 

[GerryLP]

4Spd,

You'll find alot of discussion on this subject (use the search feature), but please be aware that what you want to do will most likely lead you to a complete rebuild.

How sure are you of your engine's compression health? To bump up the compression one has to be certain that the piston rings will hold up. This is how I started with my engine, and $3,500 Plus later I found myself on a complete engine swap.

Is your differential stock? If one wants to pick up the pace from 0 to 60, then a change in this area will also help you inmensely to achieve your goals.

I would suggest at least revamping the piston rings before slapping them bad boys on to the engine...:L

 

[Jack]

4Spd,
I would suggest at least revamping the piston rings before slapping them bad boys on to the engine...:L

;stupid An otherwise unmodified L48 with its dished pistons but adding 58cc heads is gonna make about 10.9:1 CR with std 0.039" thick gasket:eek ... I think those heads are iron ... octane? ... thicker head gaskets are NOT the way to go ... suggest rethinking this. However, a huge cam will get the CR down ... but it'll probably end suitable for track-only.
JACK:gap

 

[4spd350]

Well, you guys have me thinking hard here. I appreciate the info. I have 55k on the engine. Think Im going to go ahead with the install with a 280 duration cam, .486 lift. I would go to the 292 .507 lift cam but I dont think the heads will flow enough to support it. Im going to have about $400.00 in the whole job when Im done, thats including the heads. Wont be too bad of a loss. If the rings hold up that would be great. Im not the racing type person anyhow, just some more HP would be nice. If things dont hold up, guess it will give me a good reason to go buy that 420 hp crate motor. If you have anymore suggestions It would be great to hear them. Wish me luck! I can see that this is probobly going to be a bad experiance just waiting to happen. We'll see if there is any gain, or maybe a really bad loss.

 

[sscam69]

Just did a cam swap myself.

Stock heads with an even lower compression due to the fact the pistons in there have HUGE valve reliefs. I could probably run .7" of lift without having to worry about piston to valve clearance!:eek. My engine isn't exactly stock though. I think its .03 over but I will give details on that on the other thread I posted.

This was the very first time I did something like that and I was anal about everything. Chased all the threads AND I MEAN ALL OF THEM. The head prep alone took me about 1 1/2 days. Thats swapping springs, cleaning old gasket off, chasing threads (and they needed it to). I found certain things that were neglected by the mechanic, or should I say bubba, who did the rebuild.

Is this the first time you do something like this?

If you looking for more umf you should also think about exhaust thats definetly going to help.

 

[69MyWay]

They say it can't be done......but

I too have installed 305 cylinder heads on a 350 and had tremendous results. I installed a set of ported polished with 1.9/1/5 valves on a 383 small block with dead flat top pistons (four eyebrow relief).

This was also on a TPI motor for my old 85 Vette. The results were staggering. I picked up several miles to the gallon for regular city driving. I also picked up .8 in the 1/4 mile. I ran that car hard, and beat the crud out of it for about three years in that confirguration. I used a normal stock style headgasket.

It took a bit to get the timing right, and it ran best on high octane fuel (duh!).

So, you heard it from me, IT WORKS! This had also fit perfect in my budget because they heads only cost me about $350 for the porting polishing, etc, and gaskets!

I was also running a Crane 2040 series compucam in that motor which has about the same lift and duration, the lope seperation has to be 112 or greater to work best on a computer motor. This car run 13 flat in the 1/4 on pump gas, street tires, and full street gear (spare tire, stereo, etc).

 

[4spd350]

Thanks for the confidence builder there SScam69. When you installed the heads with the cam, where was the significant increase? Torque and HP at the bottom end of the RPM range or did it cover a pretty broad range?

 

[GerryLP]

Jack,

Sounding stupid I guess comes natural with me :L; however, I meant that 4Spd should look at his engine's bottom end as closely as he is considering changes to his engine's top end.

I tried to avoid the repetition of what had been aptly debated, discussed, or reiterated in this forum by knowledgeable folks such as 69MyWay, Stingray6974, and even yourself.

 

[sscam69]

I still have the stock heads but the intake runner has been mildly ported along with the exhaust. I used an XE268H cam and bought the springs and lifters for it. I didn't feel confident putting in a new cam without swapping springs that matched it.

I got to run the car but I have not had a chance to tune it,I am pulling ~15inHg at the moment but the timing is set just to run. Its gonna change though. I am going to tune it this weekend.

I felt a noticeable increase on the lower end and she is still pulling at the top. I only to go 6K. The car feels pretty good throughout the RPM band. The only thing that is killing me is the fact I have a 3.08 in the back. The engine does not like it much on the low end but its still driveable. The engine really comes alive about 2K. My compression ratio is really low. I would venture to guess around 8.x-1. I am also running a performer RPM intake, which I think helped the cam overall. With that cam, a better intake, higher compression and a good set of heads I think you could easily achieve 350Hp or more.

Keep in mind the bottom end of my car has been rebuilt and is not stock, to add to Gerry's point.

Frank

 

[Jack]

Jack,

Sounding stupid I guess comes natural with me :L; however, I meant that 4Spd should look at his engine's bottom end as closely as he is considering changes to his engine's top end.

I tried to avoid the repetition of what had been aptly debated, discussed, or reiterated in this forum by knowledgeable folks such as 69MyWay, Stingray6974, and even yourself.

No, No Gerry ... I meant (& still do mean) I'm in agreement with you! Too bad we don't have a "smiley" (is it emoticom?) that flags/says "I agree" rather than just "I'm with stupid" that I used. Also, when I do wish to express disagreement I usually spell it out; making clear it's not intended as a jab or flame. How about someone make/find a smiley that more clearly expresses agreement? Seems Chris has successfully done a similar head swap, although had to dink w/ timing. Now go figure ... if it can be done, Chris has done it ... look at the cool stuff he's already done ... so I shouldn't be surprized. But I still wouldn't wanna risk approaching 11:1 on a questionable lower ... nor wanna dink w/ 11:1 w/iron heads, octane, timing on street ... but I'm clearly not as industrious as some ... I think that's called being lazy. Also, while I'm no rookie ... I have a sense that sr6974 & chris have more experience than I. Anyway, I did not mean to imply you were stupid ... quite the contrary ... I apologize if it seemed that way.
JACK:gap

 

[GerryLP]

Sounding stupid I guess comes natural with me :L;

Well Jack,

I hate it when I am right about myself...:duh

But I still wouldn't wanna risk approaching 11:1 on a questionable lower ... nor wanna dink w/ 11:1 w/iron heads, octane, timing on street ...

Definetely, the compression issues are real ones. I started with the same wishes for my engine, but I was just dreaming to do all that with a 150,000 mile veteran motor as my L81.

while I'm no rookie ... I have a sense that sr6974 & chris have more experience than I.

I have certainly learned alot through this forum, and the experiences that all members share -specially Mike, Chris, Bud, and the others. This is great -isn't it?

I did not mean to imply you were stupid ... quite the contrary ... I apologize if it seemed that way.

Thanks! But don't pay me no mind. Obviously I misunderstood. I am told that this will happen to me more often (exponentially) as I age...