SBC combination critique

[Sumtingwong]

https://www.hotrodders.com/forum/2014-h ... 30721.html

https://www.hotrod.com/articles/small-b ... enge-2014/

https://www.hotrod.com/articles/engine- ... 4-results/


This is a build I have followed that is an overperformer. I was just thinking of starting with a downsized version of this',,,,,,,the best I can anyway. Notice his valve and port sizes/along with cam,,,, maybe that's where I am confused on these.

[RevTheory]

"Chase" lol, has mentioned that if he had to do that one over again, he'd use a much smaller intake runner (head). I'm pretty sure that's the one he was talking about.

If I were you, I'd be looking for something no more than 195cc with no larger than a 2.055 intake valve. Opinions abound on whose head is best so I'll stay out of that one.

[Newold1]

4000 Pounds sterling = $5100 approx. so I am assuming you are in the UK. I know its not easy to find lots of good SBC parts there , but you've got a decent budget at least.

The reason I say 383 is "there ain't no replacement for displacement" ( not the kings english HA) If you are going to buy some nice new parts which I think you should. If you can run down or find a nice later year 350 4 bolt block they are already set up to accept hydraulic roller spiders and lifters.

Really nice 383 complete balanced rotating assemblies from companies like Scat through Summit and Jegs are set up with good cast crankshafts , 6 inch steel beam rods and good hyper-eutectic pistons and ring sets complete with bearings and oil pumps are very reasonable in cost (less than $2K)

Use a nice off the shelf close 240/248 duration @.050 -.550 lift hydraulic roller camshaft kit again from Summit -Jegs with lifters, springs retainers, locks.

Just use 2.02 " intakes and 1.60" exhaust valve and find a good shop there that can do a nice 3-5 angle 45 degree valve job on your heads with some good guide clearance fitment and bring seats and valve concentric.

just use an Edelbrock performer air gap intake and a good 850cfm Holley for your intake and carb.

This type of setup 383 properly machined and assembled will make 500HP at 5800-6000 rpms, 500lb/ft. of torque at 4500rpms and last a long time.

Not sure of your import duties or such but I think you should be able to get this done for about $4000K plus machining.

Hope this helps
Cheers

[Sumtingwong]

For some reason the initial link does not work.

But it has Chaz saying that it needed more cam. Its probably not transferrable to my build,,,,

but I thought it was a mean build regardless///////especially for a untouched head...he states it was off the shelf

[ClassAct]

I wouldn't use a 30 degree seat on a lawnmower. Ever. You could have used a smaller valve, a better valve job and made more power all day long. The steep/shallow seat has been thrashed out here to the point it's become boring. Do a search and read those threads.

Im stunned to hear this. But thank you for your measure of sharing. My build is in the theoretical stages currently. Can you place some input that would help meet my goal in your opinion. Maybe my mental connection between low lift flow and torque is a partial fallacy.?

I'm horrible with the search function. And I'm not sure the forum is back to 100% but I assume it is.

Search for the threads where the discussion on valve seat angles happened. There is more than one and they aren't that old. I'd rather use a 2.02 valve and a good, sorted out 50 degree seat that a 2.08 and a 30 or even 45 degree seat.

I'm not a big fan of big low lift numbers. There is more going on than my limited vocabulary and experience can explain, but it's been tested and proven.

I'd never ever consider a 30 degree seat unless it was a Pontiac that had a 30 degree seat as OE and you wanted it dead stock. Can't tell you how many of the pontiacs I converted to 45's. The customer never had the option to use the 30 unless the consideration was a dead stock deal.


Edit: Long before I bought my flow bench all I ever heard was its about shape shape shape. It's true. The shape of a 50 degree seat is so superior to the 30 it's not even close. I suspect that flow bench testing would be better done with test pressures as high as you can generate at lifts lower than .300ish lift and lower the test pressure as lift goes up. Just my humble thoughts.

[lefty o]

just something to compare for you. ive got a 355 sitting in the garage built 20 years ago, but not too far off of where your looking to be. 9.8:1 , worked over sportsman II's, strip dominator, 750dp, ultradyne 250x262 .525 106. made 474hp 436lb ft 111%VE. its not the happiest camper under 2000rpm but it pulls hard after that. id think your 2.05 valve will be fine, and i certainly wouldnt be concerned with a 200cc head, not in the least. thats a 20yr old combo, and im sure you can beat it with an aluminum head and more compression.

[GARY C]

If you are looking to improve low and mid lift with a 2.08 in a 4.030 chamber be prepared to do a lot of chamber work (ask me how I know ) and factor that in to what is needed for compression.

Keep in mind that bigger valves and shallower seats became more popular in the 80's to try to get the most out of a useless cylinder head in a day when valve train technology drastically lacked lift.

I think this is why Pontiac did that back in the day, an undersized head and lift in the .400's of an inch.

I don't know that valve size plays as big of a role now days, Here is a good example of a 2.065 valve on a 50* seat.
https://www.hotrod.com/articles/get-570 ... -pump-gas/

They also have done one very similar to this with a 2.02 as well as 2.08 valve on 50* seats all making right around the same power.

[NewbVetteGuy]

The David Vizard 128 formula recommends a 108 LSA for max power on a 350. Not trying to dredge up any of the related controversies, just one more data point on that cam LSA.

That's going to be quite a bit of overlap (not knowing the seat-to-seat duration of that roller cam) and then adding an old-school 30 deg valve job is like building a reversion machine. (If you're looking for an engine that can blacken intake runners as fast as possible, that's a good start!)

-I keep hearing that one of the reasons to step up to a Dart Platinum is the good valve job; don't mess with it, just get some good flowing valves to put in those heads that work with the OOB valve job.


Get a late roller-cam 355 short block, or better yet a 383 and just install your cam and top-end components. (If you can get it shipped from Mexico to the UK you might avoid import duty via reciprocal tax agreement (hurry up before Brexit is finalized).)


Adam

[Ericnova]

For some reason the initial link does not work.

…..especially for a untouched head...he states it was off the shelf

This post?:
https://www.hotrodders.com/forum/2014-h ... 30721.html
(Hhhmmm, won't link for me either, but you can find it with a search at that forum, the 2014 Henderson EMC entry)

You need to work on your reading comprehension a bit...that "off the shelf" head may have been off CS's shelf, but it certainly wasn't off ProFiler's shelf....it's a fully CNC ported, Chaz's port rework, SRH V2.70"MSCA, 250cc intake port volume, 2.140"/1.58" valve sizes...he only sells one full bore 23°head bigger than that.

[GARY C]

The David Vizard 128 formula recommends a 108 LSA for max power on a 350. Not trying to dredge up any of the related controversies, just one more data point on that cam LSA.

That's going to be quite a bit of overlap (not knowing the seat-to-seat duration of that roller cam) and then adding an old-school 30 deg valve job is like building a reversion machine. (If you're looking for an engine that can blacken intake runners as fast as possible, that's a good start!)

-I keep hearing that one of the reasons to step up to a Dart Platinum is the good valve job; don't mess with it, just get some good flowing valves to put in those heads that work with the OOB valve job.


Get a late roller-cam 355 short block, or better yet a 383 and just install your cam and top-end components. (If you can get it shipped from Mexico to the UK you might avoid import duty via reciprocal tax agreement (hurry up before Brexit is finalized).)


Adam

Yes, a 350 inch would probably be closer to 109 and if there is any merit to the formula a 30* seat would probably put you on a 110 or 111.

[Sumtingwong]

They also have done one very similar to this with a 2.02 as well as 2.08 valve on 50* seats all making right around the same power.

Sounds like I may need to rethink my approach.

These heads are ready for 2.02..,,,,maybe I need to look into keeping with that. I have read that seating angles higher numerically than 45 are a disaster for reliability. So perhaps I will keep it simple with a three angle 45 degree 2.02 valve seat job and hope it comes close to meeting my goals....

[ClassAct]

They also have done one very similar to this with a 2.02 as well as 2.08 valve on 50* seats all making right around the same power.

Sounds like I may need to rethink my approach.

These heads are ready for 2.02..,,,,maybe I need to look into keeping with that. I have read that seating angles higher numerically than 45 are a disaster for reliability. So perhaps I will keep it simple with a three angle 45 degree 2.02 valve seat job and hope it comes close to meeting my goals....

Not true. I run a 50 degree seat on my street junk. It's been running since 2015 and I drive it 6000-7000 miles a year. I lash the valves once a year because I feel bad if I don't.

Many are doing it. Like I said, there is a bunch of good info on here if you can find it.

[Sumtingwong]

Not true. I run a 50 degree seat on my street junk. It's been running since 2015 and I drive it 6000-7000 miles a year. I lash the valves once a year because I feel bad if I don't.

Many are doing it. Like I said, there is a bunch of good info on here if you can find it.

Good data! Thnks

[RevTheory]

You can't go wrong with a tried-and-true 45* configuration if you don't feel like messing with or feel uncomfortable with the steeper stuff.

[GARY C]

I don't know what the longest running 50* seat would look like on tear down but there are probably a million 45* seats out there with well over 200,000 miles on them.