Rocker experiment.

[Walter R. Malik]

Yes thanks for the insight.

For me, dabbling a little in chip tuning- I was looking at the weakest link, cyl 7 for heat, preignition- so was just trying to help it out. There are just as many opinions for and against the swap- did Chevy really have it that wrong in 1955? Cost was a factor for me. Not that I am a Mike Jones fan, never had his cam- but his reputation on YB is good enough that I wanted his product, he didn't have a 4/7 oem roller core at the time and I deemed it important enough to me to find a company that could supply the 4/7 swap on a quality roller core, Erson at the time was trying to drum up some new business and supplied Johnson lifters for me as well.
Me.....I wouldn't know the difference except during tune up (wires), I wouldn't talk a guy out of it at the same time.

Why do you keep saying number 7 cylinder when using that manifold it is the runner to number 8 which is the most restricted cylinder...?

[Newold1]

As I noted in my last post the issue that shows in a high performance SBC running this intake TPI manifold configuration is strictly a problem of air flows to two

stock SBC TPI (2).jpg

particular cylinders, 5 & 7 due to the physical plenum configuration and limitation of this at the rear corner of this manifold. This is not due to camshaft design, rocker arm ratio or tuning or really correctable with either. The change that can be made with firing orders on the camshaft with the 4-7 swap can help with this problem and going to special tuning on a sequential EFI system (not batch fire EFI). This will not insure the ideal even port air flow to all cylinders as this would only be possible with a different ideal plenum shape which in stock hood Corvette distributor configurations is not possible. If you look at Lingenfelter's TPI intake he developed for Accel (Super Ram)

Accel SBC Ram.jpg

you can see how he realized this issue and developed a better plenum to improve problems with this stock intake and help with this issue for additional performance in the Corvette.

[MadBill]

I think you've overlooked (as did I) the fact pointed out by Walter, namely that the OP's TPI-style manifold runner whose entry at the left rear plenum corner is restricted by the cutaway for distributor clearance cross-feeds the #8 cylinder and it's neighbor supplies cylinder #6, so the 4/7 swap from the standard 1-8-4-3-6-5-7-2 to 1-8-7-3-6-5-4-2 does not affect their relationship.

The 4/7 swap moves the 90° adjacent firing interval from 5-7 to 4-2, with (for a symmetrical manifold design) no obvious effect on breathing.

[dfarr67]

Yes thanks for the insight.

For me, dabbling a little in chip tuning- I was looking at the weakest link, cyl 7 for heat, preignition- so was just trying to help it out. There are just as many opinions for and against the swap- did Chevy really have it that wrong in 1955? Cost was a factor for me. Not that I am a Mike Jones fan, never had his cam- but his reputation on YB is good enough that I wanted his product, he didn't have a 4/7 oem roller core at the time and I deemed it important enough to me to find a company that could supply the 4/7 swap on a quality roller core, Erson at the time was trying to drum up some new business and supplied Johnson lifters for me as well.
Me.....I wouldn't know the difference except during tune up (wires), I wouldn't talk a guy out of it at the same time.

Why do you keep saying number 7 cylinder when using that manifold it is the runner to number 8 which is the most restricted cylinder...?

Well, I am misunderstanding the problem then. I don't think there is much to be done about #8, and the problem as I understood it was between 5 and 7 trying to grab the same air- where the cam option came in and shuffled things around.

[MadBill]

This article shows all the potential firing orders for a two-plane V-8: http://www.enginelabs.com/engine-tech/c ... ur-engine/ They all result in at least two adjacent cylinders firing in sequence.

The only way you might get a little relief with your set up would be if the distributor cutaway was on the right side, blocking the #7 runner, in which case a swap could at least transfer its 'sloppy seconds' burden to a runner that did not suffer the blockage issue.

[pamotorman]

using different rocker ratios on different cylinders comes in handy when the engines are not allow any mods to the heads or intake and use a spec unmodified carb.

[Newold1]

Bill My Bad! Got my cylinder numbers screwed up looking at the TPI manifold and realized its the #8 cylinder which gets restricted air flow from that pinched off corner of the stock TPI.

I was thinking about log manifolds that had runners feeding each side from the same side. The TPI is a cross runner manifold and that left rear corner feeds the 6-8 cylinder combo and hence would benefit from air feed standpoint about the same as any log plenum manifold where you always have some cylinders in the firing order then drawing from opposite sides and not adjacent to each other when using the 18726543 firing order from the 4-7,2-3 swaps on the camshaft. Sorry I added to confusion on this post.

[dfarr67]

Bill My Bad! Got my cylinder numbers screwed up looking at the TPI manifold and realized its the #8 cylinder which gets restricted air flow from that pinched off corner of the stock TPI.

I was thinking about log manifolds that had runners feeding each side from the same side. The TPI is a cross runner manifold and that left rear corner feeds the 6-8 cylinder combo and hence would benefit from air feed standpoint about the same as any log plenum manifold where you always have some cylinders in the firing order then drawing from opposite sides and not adjacent to each other when using the 18726543 firing order from the 4-7,2-3 swaps on the camshaft. Sorry I added to confusion on this post.

So you would revise the previous 2/7 rocker swap to ?

[dfarr67]

This article shows all the potential firing orders for a two-plane V-8: http://www.enginelabs.com/engine-tech/c ... ur-engine/ They all result in at least two adjacent cylinders firing in sequence.

The only way you might get a little relief with your set up would be if the distributor cutaway was on the right side, blocking the #7 runner, in which case a swap could at least transfer its 'sloppy seconds' burden to a runner that did not suffer the blockage issue.

Great article.

[Carnut1]

Bill My Bad! Got my cylinder numbers screwed up looking at the TPI manifold and realized its the #8 cylinder which gets restricted air flow from that pinched off corner of the stock TPI.

I was thinking about log manifolds that had runners feeding each side from the same side. The TPI is a cross runner manifold and that left rear corner feeds the 6-8 cylinder combo and hence would benefit from air feed standpoint about the same as any log plenum manifold where you always have some cylinders in the firing order then drawing from opposite sides and not adjacent to each other when using the 18726543 firing order from the 4-7,2-3 swaps on the camshaft. Sorry I added to confusion on this post.

Ouch, I did the same thing. #1 and #8 look like they would have the hardest time getting a good gulp of air.

[Walter R. Malik]

Bill My Bad! Got my cylinder numbers screwed up looking at the TPI manifold and realized its the #8 cylinder which gets restricted air flow from that pinched off corner of the stock TPI.

I was thinking about log manifolds that had runners feeding each side from the same side. The TPI is a cross runner manifold and that left rear corner feeds the 6-8 cylinder combo and hence would benefit from air feed standpoint about the same as any log plenum manifold where you always have some cylinders in the firing order then drawing from opposite sides and not adjacent to each other when using the 18726543 firing order from the 4-7,2-3 swaps on the camshaft. Sorry I added to confusion on this post.

So you would revise the previous 2/7 rocker swap to ?

I did a LOT of testing with that manifold on 305 and 350 engines for Firehawk and S.C.C.A road racing, way back in the mid 80's with several firing orders and rocker arm LASH differences.
The 4,7 swap cam always ran the best; Number 2 and number 8 are the most starved cylinders. Number 8 is self explanatory just by looking at that manifold plenum however, number 2 has adjacent cylinders gulping air/fuel mixture both right before, (#4), and right after it, (#1), cross side.
Those two cylinders always wanted tighter lash with a solid lifter camshaft therefore, I could make an educated GUESS that those cylinders would benefit most from a higher ratio rocker arm.

[MadBill]

..
I did a LOT of testing with that manifold on 305 and 350 engines for Firehawk and S.C.C.A road racing, way back in the mid 80's with several firing orders and rocker arm LASH differences.
The 4,7 swap cam always ran the best; Number 2 and number 8 are the most starved cylinders. Number 8 is self explanatory just by looking at that manifold plenum however, number 2 has adjacent cylinders gulping air/fuel mixture both right before, (#4), and right after it, (#1), cross side.
Those two cylinders always wanted tighter lash with a solid lifter camshaft therefore, I could make an educated GUESS that those cylinders would benefit most from a higher ratio rocker arm.

Solid, Walter? Didn't Firehawk and SCCA Showroom Stock require the factory hydraulic cam? (and an automatic behind the 350?)

[Walter R. Malik]

..
I did a LOT of testing with that manifold on 305 and 350 engines for Firehawk and S.C.C.A road racing, way back in the mid 80's with several firing orders and rocker arm LASH differences.
The 4,7 swap cam always ran the best; Number 2 and number 8 are the most starved cylinders. Number 8 is self explanatory just by looking at that manifold plenum however, number 2 has adjacent cylinders gulping air/fuel mixture both right before, (#4), and right after it, (#1), cross side.
Those two cylinders always wanted tighter lash with a solid lifter camshaft therefore, I could make an educated GUESS that those cylinders would benefit most from a higher ratio rocker arm.

Solid, Walter? Didn't Firehawk and SCCA Showroom Stock require the factory hydraulic cam? (and an automatic behind the 350?)

YES ... they were actually hydraulic flat tappet L-69 lobe profiles; cylinders 2 and 8 had a quarter turn pre-load and the others all had .004" lash. The next year we had to use LG-4 hydraulic roller profiles so, we did some creative things in the manifold base to alleviate this phenomena.
We also had Sig Erson have someone make us special valve springs with the exact coil wire diameter, number of coils and spring diameter; but, they had .200" more free length. I think Sig Erson is still selling them.

I was trying to easily make a point, not confuse anyone with the weird actualities.

[dfarr67]

I'm so embarrassed- must be tired when reading this at the end of the day and thanks for the patience- yes it is No 8 (we're talking the same inlet of the runner and I forgot where the outlet folded under). And I have aggravated the pinch with a box notch taking away some volume as I decided to stay with oem fuel rails and fuel regulator.

[In-Tech]

We also had Sig Erson have someone make us special valve springs with the exact coil wire diameter, number of coils and spring diameter; but, they had .200" more free length. I think Sig Erson is still selling them.

Hi Walter, I believe that is the E915005 but I need to make sure that isn't the same part number for the newer FSP spring. What year was that if you remember? The original E915005 is one of the best 1.250" single springs ever produced.