heads and intake for 427 sbc

[cjperformance]

[b]MPEFI on IR t-bodies[/b] would probably be your single biggest helping hand if he will go for it..
Bigger heads and wider lsa are going to help but even with a great carb and some vac advance etc running at 2Krpm and expecting a smooth ride is in reality asking a lot from a 650+ hp 427ci NA carb engine.

I think it’s the combination of large camshaft overlap, low rpms, and part throttle that is problematic for a plenum intake manifold, whether it’s carbureted or fuel injected. Individual throttle bodies, or even independent runner carbs, that have a very small volume between the intake valve and the throttle blade seem to drive very well at cruise rpm and at part throttle even with significant camshaft overlap. That’s what I believe, who knows if it’s true.

Exactly why i say mpefi on ir.
With enough cam and head to make 650hp that is not going to be a gem at 2000 in OD with any shared plenum intake, single OR dual plane, with an unlocked auto in OD yes but manual no.

[ptuomov]

[b]MPEFI on IR t-bodies[/b] would probably be your single biggest helping hand if he will go for it..
Bigger heads and wider lsa are going to help but even with a great carb and some vac advance etc running at 2Krpm and expecting a smooth ride is in reality asking a lot from a 650+ hp 427ci NA carb engine.

I think it’s the combination of large camshaft overlap, low rpms, and part throttle that is problematic for a plenum intake manifold, whether it’s carbureted or fuel injected. Individual throttle bodies, or even independent runner carbs, that have a very small volume between the intake valve and the throttle blade seem to drive very well at cruise rpm and at part throttle even with significant camshaft overlap. That’s what I believe, who knows if it’s true.

Exactly why i say mpefi on ir.
With enough cam and head to make 650hp that is not going to be a gem at 2000 in OD with any shared plenum intake, single OR dual plane, with an unlocked auto in OD yes but manual no.

The way I've rationalized this is that with high overlap cams, the cycle is unstable.

If the cylinder doesn't fill much, then there's small exhaust pulse and small suction, which leads to worse intake filling, which leads to even smaller exhaust pulse and even smaller suction, which in turn leads to even worse intake filling, etc. On the other hand, if the cylinder fills a lot, then there's a big blowdown pulse and big suction wave, which fills the cylinder better, which creates an even bigger blowdown pulse and suction wave, etc.

With a plenum manifold that has a large volume of air between the intake valve and the throttle, there's nothing keeping this unstable process in check. At part throttle and low rpms, the engine randomly surges or bogs down.

However, if we have an individual throttle (carb or EFI) very close to the intake valve, there's very small volume of air for the overlap period to draw from. This keeps the process stable and in check. The engine doesn't randomly surge and then bog down at part throttle and low rpms.

[cjperformance]

I think it’s the combination of large camshaft overlap, low rpms, and part throttle that is problematic for a plenum intake manifold, whether it’s carbureted or fuel injected. Individual throttle bodies, or even independent runner carbs, that have a very small volume between the intake valve and the throttle blade seem to drive very well at cruise rpm and at part throttle even with significant camshaft overlap. That’s what I believe, who knows if it’s true.

Exactly why i say mpefi on ir.
With enough cam and head to make 650hp that is not going to be a gem at 2000 in OD with any shared plenum intake, single OR dual plane, with an unlocked auto in OD yes but manual no.

The way I've rationalized this is that with high overlap cams, the cycle is unstable.

If the cylinder doesn't fill much, then there's small exhaust pulse and small suction, which leads to worse intake filling, which leads to even smaller exhaust pulse and even smaller suction, which in turn leads to even worse intake filling, etc. On the other hand, if the cylinder fills a lot, then there's a big blowdown pulse and big suction wave, which fills the cylinder better, which creates an even bigger blowdown pulse and suction wave, etc.

With a plenum manifold that has a large volume of air between the intake valve and the throttle, there's nothing keeping this unstable process in check. At part throttle and low rpms, the engine randomly surges or bogs down.

However, if we have an individual throttle (carb or EFI) very close to the intake valve, there's very small volume of air for the overlap period to draw from. This keeps the process stable and in check. The engine doesn't randomly surge and then bog down at part throttle and low rpms.

Correct, and i think the OPs vehicle example is a prime one for IR. It would be a different engine alltogether.
Sure, a smaller cam and/or dual plane to smooth out the lower rpms will help there but then the extra HP asked for becomes harder to achieve, yeah bigger heads then will help a bit but its all getting expensive and counter productive.
Id bet that simply fitting mpefi on ir would make it so nice everywhere that the owner may not even bother chasing more top end hp, BUT if he then wanted more hp he is on an easy platform to make hp AND driveability.

[Rick360]

How much lift does it have?

When you don't have enough lift to pull on the port good, you can make the port too big real easy. If you have a street cam with low .5xx lift a 230cc port is too big IMO. If you have .700+ lift then 230 port will be fine.

Rick

[gnicholson]

give me an example of a long independent runner mpfi manifold that will fit this thing. i would look into running a dual plane with a large carb if it wouldnt kill it on top. to bad they dont make one with big enough runners for this engine. a long runner small plenum tunnel ram would work well on this this if it would fit

[cjperformance]

give me an example of a long independent runner mpfi manifold that will fit this thing. i would look into running a dual plane with a large carb if it wouldnt kill it on top. to bad they dont make one with big enough runners for this engine.

Im talking short ITB ,,, t bodies /injectors right at the intake flange area.

Just grabbed this pic simply as a quik eg,
Hood clearance may be your issue though?

IMG_20171116_28268.jpg

[gnicholson]

theres no doubt a properly tuned ir intake with webers or fi would absolutely fix this thing .a dual plane would help also but i dont know of one thats not extensively modified that wont cost 30 hp at 6k. does anyone have an open plenum intake suggestion with moderate sized long runners that would limit low rpm intake dilution and still make good too end power. im open to modifying one by extending the runners etc if thats my best bet

[MadBill]

For top end power, I think this engine would need something like 60 mm Weber clones and a (presumably) custom manifold.

[ptuomov]

For top end power, I think this engine would need something like 60 mm Weber clones and a (presumably) custom manifold.

Don’t know about carbs, but 700hp of a 7 liter NA engine goes thru 54mm individual throttle bodies, based on past experience.

TWM I think makes SBC throttle bodies up to 62mm size.

[ptuomov]

http://www.borlainduction.com/3002-series.html

[RevTheory]

I don't think I'd be inclined to try ITBs on a lumpy-cammed engine in a Corvette where you're quite limited to what you can do to the collector length.

I'm thinking of potential fuel stand-off issues here.

[FC-Pilot]

This is where I would go direction wise. It would fit under the hood and help with low rpm drivability. You would just need to figure out a filter setup that would work.

[randy331]

Funny how on a performance forum, someone asks about improving their power level to just 1.47 HP/cube and improving the drivability along with it and it ends up,... " you can't do it without a blower " you'll need individual runners " " tunnel ram is only way "..... etc. etc, when what he's asking to achieve is already being done without the magic of tunnel rams, blowers etc.

How many really think 600+ HP out of a street able 427 cube is out of reach ?


Randy

[lefty o]

Funny how on a performance forum, someone asks about improving their power level to just 1.47 HP/cube and improving the drivability along with it and it ends up,... " you can't do it without a blower " you'll need individual runners " " tunnel ram is only way "..... etc. etc, when what he's asking to achieve is already being done without the magic of tunnel rams, blowers etc.

How many really think 600+ HP out of a street able 427 cube is out of reach ?


Randy

you forgot the multi qjet arrangement!

[gnicholson]

yes i appreciate all the replys but he still wants to use his l88 air cleaner base and hood which was modified to fit the smallblock. looking for a single 4 barrel open plenum cam head combination that can be tuned to run clean in od at 2 grand and add some power at the same time