Advantages of advancing the cam on a street engine?

[gottago]

Those numbers sound more realistic. Still a nice little streeter.

Lots of things get said along the way in all these posts .. Another...

Advancing cam timing on a Chevy v-8 would be the same on just about every one ever made because there is not much difference in piston speed and compression from a 265 to a 400. Like I said in my earlier post you almost cannot get the intake advanced too far on an SBC and especially on a street engine as the compromise is in top end power above 5000rpms.

I like it that some generalizations get spoken of once in awhile but I wonder if this one really just applied to the old days when stock heads were more the norm? Lately with the better aftermarket heads we've retarded some cams in existing combos and maintained the same or better low rpm power while increasing the top end. Just noting an earlier generalization that maybe should have been responded to before it became gospel.

[E.Roy]

Those numbers sound more realistic. Still a nice little streeter.

Lots of things get said along the way in all these posts .. Another...

Advancing cam timing on a Chevy v-8 would be the same on just about every one ever made because there is not much difference in piston speed and compression from a 265 to a 400. Like I said in my earlier post you almost cannot get the intake advanced too far on an SBC and especially on a street engine as the compromise is in top end power above 5000rpms.

I like it that some generalizations get spoken of once in awhile but I wonder if this one really just applied to the old days when stock heads were more the norm? Lately with the better aftermarket heads we've retarded some cams in existing combos and maintained the same or better low rpm power while increasing the top end. Just noting an earlier generalization that maybe should have been responded to before it became gospel.

Well he is referring to the intake lobe timing only, and it sounds like your experience is retarding an installed cam, retarding intake and exhaust together.
Still glad you posted your experience though

[GARY C]

That's true, but read through hundreds of similar combos with their dyno results. This was as good as most any 350 street combo with a real midrange on almost any dyno sheet. (no exotic parts) Perhaps that dyno was reading off then this gets a bit more mundane and could possibly be improved on. As said, don't hold too much faith in magazine articles, just questioning the big numbers and how they got there. Doesn't usually happen without a plan and build sheet from beginning to end.

Yes, 420/430 tq and 420 horse is probably more common and about where DV thought it would fall based on the parts, it was meant to be a budget build not a big dollar championship engine. If I recall without rereading it, it was suppose to exceed 400 horse on the cheep!

You're correct, they were shooting for over 400hp (dont think they were concerned about torque).
Vizard spec'd the cam to accomplish 400hp on the motor spec, and they even adjusted the engine after by jumping from 1.5 to 1.6 rockers, because they worried it wouldn't top 400hp with Vizard's spec. Talk about crushing your goal with 10% more hp, if the dyno wasn't optimistic.

Yes he gave them the cam info and said to run it with a 1.6 rocker but he wasn't at the dyno session, the other cams showed up because they doubted his cam, Johnny Hunkins the author and at the time lead editor had worked with DV enough years to try what he said, I don't even know if he is with them anymore since the 08 economy crash and Peterson publishing (i think) took over most all the mag companies and down sized everything DV did not do much for them after all that because the pay per article wouldn't even cover his dyno time.

In the old days tech guys could do some really good stuff... Not any more.

I have an article from DV back in 1983, it was a 2 part with 5 or 6 pages per part and covered everything from machine work, porting, nitrous system, trans/converter, tires, shifter, car and track times. Mike Thermos of NOS was driving the car...

Back in Dave Braswell's early days when he still had a pony tail.

[GARY C]

Those numbers sound more realistic. Still a nice little streeter.

Lots of things get said along the way in all these posts .. Another...

Advancing cam timing on a Chevy v-8 would be the same on just about every one ever made because there is not much difference in piston speed and compression from a 265 to a 400. Like I said in my earlier post you almost cannot get the intake advanced too far on an SBC and especially on a street engine as the compromise is in top end power above 5000rpms.

I like it that some generalizations get spoken of once in awhile but I wonder if this one really just applied to the old days when stock heads were more the norm? Lately with the better aftermarket heads we've retarded some cams in existing combos and maintained the same or better low rpm power while increasing the top end. Just noting an earlier generalization that maybe should have been responded to before it became gospel.

In DV's test he will optimize ICL and if they go to a higher ratio rocker the ICL is retested and in some cases needs to be retarded to compensate for the earlier valve opening caused by the increased rocker ratio.

There are a lot of little things that make dyno time well worth the money if your looking for every last pony.

[gottago]

Those numbers sound more realistic. Still a nice little streeter.

Lots of things get said along the way in all these posts .. Another...

Advancing cam timing on a Chevy v-8 would be the same on just about every one ever made because there is not much difference in piston speed and compression from a 265 to a 400. Like I said in my earlier post you almost cannot get the intake advanced too far on an SBC and especially on a street engine as the compromise is in top end power above 5000rpms.

I like it that some generalizations get spoken of once in awhile but I wonder if this one really just applied to the old days when stock heads were more the norm? Lately with the better aftermarket heads we've retarded some cams in existing combos and maintained the same or better low rpm power while increasing the top end. Just noting an earlier generalization that maybe should have been responded to before it became gospel.

Well he is referring to the intake lobe timing only, and it sounds like your experience is retarding an installed cam, retarding intake and exhaust together.
Still glad you posted your experience though

Well that is the tittle of the thread but I've run from 104 lsa all the way up to 118 on the street with varying centerlines. Big big difference in how they all feel and go. I thought I'd gotten too far advanced with the 104 lsa in at 102 icl instead of the recommended 104. But I am getting a bit older to where the lope and rock has lost its appeal. If anything, I'd retard that one now too.

[Olds455]

For same agrresiveness I mean similar lobe profiles and lift. I find trying to make 500 lbft and 400hp a fun challenge and I don't need more than that for the car.
Also, I like keeping this project simple and attainable for me right now

If you want 500 lb ft and 400 hp, toss the 350 and build a 400. I don't personally have the time to fight with an engine to make it do something it is incapable of achieving.

Good idea, 400ci for 550 lbft haha

Why not? I just came across a 400 built on a $2500 budget with 225cc intake port, modified Vortecs that made something like 470 ft lbs @ 4k rpm. I could probably find the link again if interested. Being that your initial goal was 450 ft lbs, I figured it'd be a contender. I think Blueprint sells a 400ci combo that makes 460/470 tq with something like 10.3:1 compression.

[E.Roy]

Excerpt from this online tech tip, from the book CHEVY BIG-BLOCKS: HOW TO BUILD MAX PERFORMANCE ON A BUDGET. by David Vizard (geared towards BBC but he applies to many engines)
https://www.chevydiy.com/chevy-big-bloc ... in-events/

"The Importance of Overlap
The events that occur in the exhaust/intake overlap period are of utmost importance. They take place before the piston really gets underway down the bore on the intake stroke. From many hours studying pressure traces of a variety of engines, one thing becomes clear, and it is the very point that makes the overlap the most important valve event, rather than the often-supposed intake closing point. This is an important point you should never let slip from your mind when it comes to valve events for maximum output...
...It should now be clear that the most important factor toward both big torque numbers and top-end power is the way you deal with over-lap. The “overlap triangle” (Figure 9.2) must be positioned at about TDC so it experiences the optimal benefits of the very strong exhaust extraction pulse that a performance exhaust system can deliver. Anything short of optimal is, in effect, like compromising an otherwise free induction event. In addition, this is critical in the case of an under-valved big-block; you need to get the intake valve underway well in advance of the piston demand. This produces a higher lift earlier on in the piston phase of the induction cycle and thus partially compensates for an intake valve that is too small for the job."

Text for the cam image:
Fig. 9.3. The most important cam parameters are the intake (1) and exhaust (2) centerlines, the LCA (6) and its relation to cam advance (A) and retard (R). Remember, cam advance/retard (7) assumes the crank is held still during cam adjustment and that is why the advance and retard appears the wrong way around. The intake duration (3) and the exhaust duration (4) positions on the cam are controlled by the LCA (6), and this positioning, along with the duration, dictates what the overlap (5) is. For a Chevy big-block, the lobe lift of the intake is a very important factor. Because the cam is physically bigger (1.950-inch journal diameter) than a small-block (1.872-inch journal diameter), the lobe can, for a given duration, have a higher lift. However, be aware that many cam companies use the same profiles for a small-block. If the profile is designed especially for a big-block and fully utilizes the extra diameter, it can result in a profile with as much as 0.012-inch greater lift.

[E.Roy]

If you want 500 lb ft and 400 hp, toss the 350 and build a 400. I don't personally have the time to fight with an engine to make it do something it is incapable of achieving.

Good idea, 400ci for 550 lbft haha

Why not? I just came across a 400 built on a $2500 budget with 225cc intake port, modified Vortecs that made something like 470 ft lbs @ 4k rpm. I could probably find the link again if interested. Being that your initial goal was 450 ft lbs, I figured it'd be a contender. I think Blueprint sells a 400ci combo that makes 460/470 tq with something like 10.3:1 compression.

You're right, that's the tried and easy method. Here's my reasons. I'm building to a magazine competition budget, an entire vehicle for $2018 outlay, to run 1/4, autocross and appearance score.
So I've selected the vortec 350 as my engine because of its oem roller cam block, I got a 98 bolt for for $200, and comes with roller bits I can reuse.

[randy331]

I'm building to a magazine competition budget, an entire vehicle for $2018 outlay, to run 1/4, autocross and appearance score.
So I've selected the vortec 350 as my engine because of its oem roller cam block, I got a 98 bolt for for $200, and comes with roller bits I can reuse.

Your building a 500 LB 350 and completing the car, all for $2018 ??

Randy

[ptuomov]

Over generalizing, is it correct to take as s starting point that “too small” cams run best retarded and ”too large” cams run best advanced?

As a very loose over generalization yes.

By similar generalized logic, I think that for most engines one should probably run the cams a little advanced with turbos compared to how to run the same cams in a NA engine.

[E.Roy]

I'm building to a magazine competition budget, an entire vehicle for $2018 outlay, to run 1/4, autocross and appearance score.
So I've selected the vortec 350 as my engine because of its oem roller cam block, I got a 98 bolt for for $200, and comes with roller bits I can reuse.

Your building a 500 LB 350 and completing the car, all for $2018 ??

Randy

I'm trying to yes. This is the event: http://www.grmchallenge.com
Your allowed to sell off parts of the car or parts deals and recoup up to 1/2 the budget, $1009 this year, so you can spend $2018 +$1009 if you can sell $1009 in parts. They allow 1 set of tires that don't hit the budget. I bought an e36 BMW for $450, I'll be able to recoup up to $450 on this car.
Parts I bought:
98 4bolt short block $200
Vortec heads $40 (bought long block, sold short block)
Edelbrock EPS intake $123
Working Holley 750DP $50
I need a 5speed NV3500 and bits ~$300

Making 450lbft flywheel is attainable, not sure on 500lbft but that's what I will try for.

[randy331]

I'm trying to yes. This is the event: http://www.grmchallenge.com
Your allowed to sell off parts of the car or parts deals and recoup up to 1/2 the budget, $1009 this year, so you can spend $2018 +$1009 if you can sell $1009 in parts. They allow 1 set of tires that don't hit the budget. I bought an e36 BMW for $450, I'll be able to recoup up to $450 on this car.
Parts I bought:
98 4bolt short block $200
Vortec heads $40 (bought long block, sold short block)
Edelbrock EPS intake $123
Working Holley 750DP $50
I need a 5speed NV3500 and bits ~$300

Making 450lbft flywheel is attainable, not sure on 500lbft but that's what I will try for.

Sounds interesting, and I wish you luck,... but I think your being optomistic on your tq numbers.

450 is a little optomistic for that combo, but I don't know your porting skills, so ?

Randy

[E.Roy]

I'm trying to yes. This is the event: http://www.grmchallenge.com
Your allowed to sell off parts of the car or parts deals and recoup up to 1/2 the budget, $1009 this year, so you can spend $2018 +$1009 if you can sell $1009 in parts. They allow 1 set of tires that don't hit the budget. I bought an e36 BMW for $450, I'll be able to recoup up to $450 on this car.
Parts I bought:
98 4bolt short block $200
Vortec heads $40 (bought long block, sold short block)
Edelbrock EPS intake $123
Working Holley 750DP $50
I need a 5speed NV3500 and bits ~$300

Making 450lbft flywheel is attainable, not sure on 500lbft but that's what I will try for.

Sounds interesting, and I wish you luck,... but I think your being optomistic on your tq numbers.

450 is a little optomistic for that combo, but I don't know your porting skills, so ?

Randy

I really like porting and I feel like I'm being scientific on these vortecs, I made an intake port mold which helped. My plan is porting for laminar flow, increasing roof flow, and helping the exhaust get the intake flowing on overlap.
On the intake I'm focusing on 3 areas, blending the seat to bowl, narrowing the guide boss to a vane, and taking .100" out at the pushrod pinch because I think stock it gets flow separation. And I might get the intake port flow tested to see if I'm doing it right.

[groberts101]

I'm trying to yes. This is the event: http://www.grmchallenge.com
Your allowed to sell off parts of the car or parts deals and recoup up to 1/2 the budget, $1009 this year, so you can spend $2018 +$1009 if you can sell $1009 in parts. They allow 1 set of tires that don't hit the budget. I bought an e36 BMW for $450, I'll be able to recoup up to $450 on this car.
Parts I bought:
98 4bolt short block $200
Vortec heads $40 (bought long block, sold short block)
Edelbrock EPS intake $123
Working Holley 750DP $50
I need a 5speed NV3500 and bits ~$300

Making 450lbft flywheel is attainable, not sure on 500lbft but that's what I will try for.

Sounds interesting, and I wish you luck,... but I think your being optomistic on your tq numbers.

450 is a little optomistic for that combo, but I don't know your porting skills, so ?

Randy

I really like porting and I feel like I'm being scientific on these vortecs, I made an intake port mold which helped. My plan is porting for laminar flow, increasing roof flow, and helping the exhaust get the intake flowing on overlap. And I might get the intake port flow tested to see if I'm doing it right.

IMO, it's good to have people like Randy around as the voice of reason. He's not crapping on your dreams.. just interjecting some reality is all. Anything's possible.. at least till it's proven not to be.

I will add this. I spent tons of hours.. maybe well over 200.. on several sets of vortecs(96+).. and i can tell you for fact that gm tried like hell to create tons of swirl. Simply looking at the twisted entry's should give a clue. Doesn't matter who's bench you put them on.. the swirl meter goes nuts at higher lift ranges!

That's great for emissions and creating extra homogeneity related torque production at lower piston speeds.. but downright horrible for big lift cams and higher piston speeds. I spent almost 20 hours puttying up my last set of v6 heads trying to get high lift swirl under control. Paid off with higher peak flow numbers but iirc.. swirl was still somewhere in the 1400 rpm range at .700" lift. Finally gave up and called it good enough. Hard to make something designed to be good at one thing do something entirely different than it was intended to do.

PS. Those heads respond really well to razor thin port dividers. Pushing the pinch as wide as possible will help settle down the floor speeds and reduce the ssr workload and necessary apex height reduction and degree of layback. Good luck with it.

[E.Roy]

Sounds interesting, and I wish you luck,... but I think your being optomistic on your tq numbers.

450 is a little optomistic for that combo, but I don't know your porting skills, so ?

Randy

I really like porting and I feel like I'm being scientific on these vortecs, I made an intake port mold which helped. My plan is porting for laminar flow, increasing roof flow, and helping the exhaust get the intake flowing on overlap. And I might get the intake port flow tested to see if I'm doing it right.

IMO, it's good to have people like Randy around as the voice of reason. He's not crapping on your dreams.. just interjecting some reality is all. Anything's possible.. at least till it's proven not to be.

I will add this. I spent tons of hours.. maybe well over 200.. on several sets of vortecs(96+).. and i can tell you for fact that gm tried like hell to create tons of swirl. Simply looking at the twisted entry's should give a clue. Doesn't matter who's bench you put them on.. the swirl meter goes nuts at higher lift ranges!

That's great for emissions and creating extra homogeneity related torque production at lower piston speeds.. but downright horrible for big lift cams and higher piston speeds. I spent almost 20 hours puttying up my last set of v6 heads trying to get high lift swirl under control. Paid off with higher peak flow numbers but iirc.. swirl was still somewhere in the 1400 rpm range at .700" lift. Finally gave up and called it good enough. Hard to make something designed to be good at one thing do something entirely different than it was intended to do.

PS. Those heads respond really well to razor thin port dividers. Pushing the pinch as wide as possible will help settle down the floor speeds and reduce the ssr workload and necessary apex height reduction and degree of layback. Good luck with it.

Thanks for the input, sounds like I'm on the right course then. I edited my post on you to add this
"On the intake I'm focusing on 3 areas, blending the seat to bowl, narrowing the guide boss to a vane, and taking .100" out at the pushrod pinch because I think stock it gets flow separation."
I could tell there was a lot of swirl action, even the beak in the chamber that shrouds the intake, which I'm grinding to match 45deg seat.
It makes sense to a degree, they were making a truck head with mpg in mind.
Maybe I'll post pics

Eric