Mortorq

Hello all
What are your thoughts with the following engine combination?
1988 IROC vert presently equippedwith a T5, 3:08 posi, catless 3” Hooker Aerochamber exhaust with Hooker 2055 headers, Factory L03.

Considering swapping in a used L98 350 or L05 passenger car TBI 350 short block using
#059 58cc heads with clearanced guide bosses, LS6 springs,
Chevy SP350/357 cam #12677151, 215*/223* @ .050” & .473”/.473”, 108LSA,
Performer intake,
Holley #6210 650 CFM mech sec spreadbore, Mallory 4340? Press reg
Comp ratio with stock dished pistons & 58cc heads ok for pump gas?
Thank you ahead of time!

AlkyIROC

Well just going from a 305 to a 350 engine alone will make a big difference to start with.

059 heads are a very good head for a 305 but you're going to be feeding a 350. Not sure what the air flow is but it will probably be a restriction compared to a good 350 head. Doesn't really matter if the combustion chamber size bumps up the compression if you can't get enough air flow into the cylinder to feed the bigger engine. 305 heads also have small valves and for a bigger engine, you also want bigger valves to utilize the increased displacement. If you start restricting a lot of options which will limit the potential of a bigger engine, the 350 may not make any more power than the 305.

GM never put a T5 behind a 350. The transmission will probably survive as long as you don't beat on it.

dmccain

iTrader: (2)

The 059s flow really well.. they say over 200cfm. We ran a set "because they were free" on a 350 L05 short block with a Doug Herbert flat tappet cam 218-218 465 lift. 650 Holley DP. Ran great, very very strong lil engine

skinny z

What defines a "good engine combination"?
Do you have a HP goal? An all around cruiser with a broad flat torque curve? Is fuel economy a concern?

As for compression ratio, if the inputs posted below are accurate then at less than 10:1 you'll be pump gas friendly. Some of that will depend on the cam chosen. Not too sure about the factory cam suggested though.

Mortorq

Thanks for the reply DM & Skinny.
Yes, just a cruiser with maybe some spirited on ramp driving.
That compression calcumalator is a help too.
I think Dr Vizard would approve of the #7151 cam, 108LSA & all?

skinny z

Well, that's the thing. Vizard approved no doubt. But it raises a question that I've tried to get answered by DV but the information isn't forthcoming. That question being what are his specs aimed at? Is he looking to make the most torque at peak or the most torque as an average?
Case in point: My 357 that's recently been put together. I had all of the architecture in place. Intake, heads, shortblock, compression ratio etc. with the only thing not sorted being the cam. I had used Vizards's Torque Master program (many times via trial offers) and it would produce a spec that is DV recognizable as it had a 108 LSA. In fact, when inputting a compression of less than 10.5:1 (which is a DV target for his formula) and using 10:1, the LSA tightened up further still to a 107. Vizard bases his specs on a 10.5:1 CR and generally a 2.02" intake valve with an average coefficient of discharge. So no trick valve jobs or oversized valves in general.





The above was for a 10:1 Vortec headed 355 that I had. Notice the minimum required port flow at 210 CFM and where the peak HP RPM falls (5140). A 107 LSA as well due to the lower CR and smaller valve.

Now to further explore the LSA in developing the 357 with a 10.25:1 CR and better heads (255 CFM with a 2.02" valve but a small port similar to Vortecs) I used TM to see what would be developed.




No surprises really. 108 LSA.

Now, I approached Jones Cams for a spec as I intended to use his cam and lifters (and did).
First spec as per his cam recommendation form was a street/strip deal. Targeting a peak HP RPM around 6000. He produced this:



By way of explanation, the upper rows in the chart are the profiles as taken from his catalogue. The lower rows are the result of those profiles being tweaked (by Jones) to suit my application.
Notice the 110 LSA.
I then asked for another recommendation with the application more suited to drag racing. That came about as a result of a converter stall that was about 4500 RPM. That meant that TQ below that RPM wasn't considered as it would be in a street car with less stall.



Much shorter in terms of seat timing but notice the the tighter LSA. And also notice how close it is to what Vizards's cam spec'ing program churned out.
My conclusion here is that DV may be building more towards greater torque but perhaps at the expense of a broader curve. A a truly street car spends a lot of it's time below peak TQ RPM so it's preferable to have a little more down low as opposed to up higher in the rev range.

Anyway, that's my take on it. If you'll be buying a cam, compare Jones' prices ($541.64) to something you might get from Summit (GM PN posted above $524.15 ). With Jones you'll not only get something perfectly suited to your intended use but excellent customer service as well.

Mortorq

Skinny
Fascinating treatise on your 357. Thank you!
I do not have personal experience with any sbc hyd roller with less than 110LSA.

That said, with quite a few different various forum comments & owner’s opinions regarding 108LSA cams with a milder Chevy #7151-type duration spoke of plenty of rpm & no penalty at all with noticeable low & mid range torque. 5500-6000 rpm capable and all.
But, maybe those fellas were just blowing smoke or had different priorities.
I wouldn’t mind a more snappy or punchy low end, as it’s just a cruiser 3:08 posi T5 anyway.

skinny z

I've been trying to educate myself on camshaft specs and all the intricacies involved. It's truly a subject unto itself.
One thing the pros will argue is that the LSA isn't relevant and is a result of properly timed valve events. Others, like Vizard make a point to the contrary.
The correlation between Vizard's formula and what a cam designer specified for my particular application I found to be very interesting. I also found it noteworthy how the spec changed, with regards to the LSA and duration (and hence the overlap) when I changed from street duty primarily to more dragstrip orientated,.
Remember too that this is also tied to the compression ratio. One benefit I see with the 58cc chamber is that you'll be able to manage a reasonable result. It would be nice to be able to tighten up the piston to head clearance. With an uncut OEM block, the pistons are likely .025-.030" down the bore at TDC. It may not be practical (or possible) to run an .015" shim head gasket with two unsurfaced decks (head and block). That's to bring the PTH clearance to around .040". Some have had success though. I prefer the composite gasket such as Mahle's 5746 but that requires the piston to be around .015" down.. Presently, I've built to a .008" piston below deck and a composition .032" gasket.

Whatever direction you intend to go, try and determine the intake valve closing point. That'll be hard to do with that GM cam as they don't list the seat to seat timing. Which I find to be major PITA when doing my calculations or running sims.
That IVC will have an impact on that low speed punch you're after. If the dynamic or running compression (DCR) is in the sweet spot, it makes for a torquey engine all other things being equal. Many engine builders put little faith in the DCR value but when we're discussing SBC's with iron heads. I've good a reasonable data base to work with and have found satisfactory results within a given range.

Mortorq

Skinny
Thanks for the info. I don’t know how one would be able to find the IVC of Chevy’s #7151 cam, don’t have the cam, let alone a Cam Doctor!
If Chevy equips their SP350/357 crate engine with that cam, would it be correct to a$$ume that a stock L31 shortblock with #059 58cc heads will be ok & just a little more “punchier”? (providing it’s kept out of detonation etc)

skinny z

I'm going to ask a few folks that may have access to all of the details on that cam. Once armed with that, I'll be able to offer more than a WAG.

skinny z

I asked around about this cam and got nothing like you've posted.
222 222 duration at .050 lift306 306 advertised duration.447” .447” lift110/118, 114 LSA
The above sounds like something GM would use. Very gentle ramps from the look of it.
With that extreme advertised duration even with a 114 LSA, overlap is a lot at 78°.
If it were me, and perhaps more investigation is required to confirm what I found, I'd stay clear of that cam.
EDIT: New accurate information came to light so all that I've posted above can be disregarded.
Still looking for seat timing though.

Fast355

iTrader: (2)

That is a 350 hp 327 151' cam, completely different cam. The SPO 7151' cam is a roller cam. 215/223 @ 0.050, 0.473 lift, 108 LSA and 109 ICL. It is essentially a LT4 Hotcam designed to fit in an otherwise stock L31 Vortec and build more torque with its lower than a LT4 compression ratio.

No idea why GM decided to re-use the last 3 digits since it only confuses people especially given they are both SBC cams.

skinny z

NOW it's starting to make sense!
Thanks Fast.
Never did check the full PN.

My comments posted above regarding its suitability can be tossed in that case.

skinny z

Back to square one though.
I'm still looking for seat timing.

skinny z

I haven't found the seat timing for the 7151 cam although, in my searches, Mike Jones of Jones Cams chimed in with this:

IF he wants a GM cam, look at # 10185071.That's what's in the 604 Crate engines.It checks: 268/274 @.006"209/222 @.050".316"/.340" Lobe Lift.474"/.510" Valve Lift, w/1.5 rockers112 LSA

Personally, and I went down this road as I mentioned, I'd go for a recommendation from the aforementioned Jones Cams. At the very least, you'll have a well calculated spec and could use it for comparisons.

Mortorq

“IF he wants a GM cam, look at # 10185071.That's what's in the 604 Crate engines.It checks: 268/274 @.006"209/222 @.050".316"/.340" Lobe Lift.474"/.510" Valve Lift, w/1.5 rockers112 LSA”

Interesting Mike Jones recommendation. Would rather keep the compression with less exh duration, have only a 3:08 cruiser rear end, no need to rpm the the thing.

#12677151 has less of a I/E duration spread with the “more torquey” 108LSA as Chevy saw fit to equip the #SP350/357 crate engine.

skinny z

There's always the option of getting a spec from Jones. His cam recommendation forms are online.
I'll say there's no obligation on your part although if the price is right (and he's competitive with Summit's price for a Comp cam) then why not. Better materials too.
I've had 3 or 4 done that way. A couple for a 383 that was never built and the latest for the engine I have now. Had a little back and forth on the last as well.
Anyway, I'll be interested in where you end up.
Be sure to post.