more carburator on 18 degree 406 cui sbc

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Re: more carburator on 18 degree 406 cui sbc

Post by Tuner » Wed Jan 17, 2018 4:36 pm

hjallle123 wrote:
Mon Jan 15, 2018 8:47 pm
Hi
I have a 18 degree smallblock with a hogan sheetmetal intake with 2 demon 750 cfm with 850cfm baseplate (just find that out)

the heads are brodix 18C heads weldtech cncported 2.18 1.625 titanium valves jesel 1.6 int 1.55 exh
flow 352 intake 700 lift 245 exh ,700 lift

cam is 114 lobe sep 110 inteke centerline

@0.50 282 in 294 exh dur ( yes the cam is about 10 degees wrong )
765 lift int 735 lift exh

( yes have degree the cam )

i did dyno tested the engine and it was making 768 horsepower on 7500 rpm
messured one carb on dyno it was flowing 495 at wot
so the engine was taking about 990 cfm

i was thinking if i am ported the heads with more flow to about 375-380 cfm on intake 265 cfm exh
changing cam with the new ported heads

can dual 1050 dominator carburators suport this

thinking.. with 0.5 vacuum the 2 dominators will flow about 1212 cfm with the sheetmetal intake

it dosnt mather if it will rev about 8000-8500 rpm

Thanks
can dual 1050 Dominator carburetors support this


Yes. #1 choice. Bob Glidden used a pair of 1050s on his 340.

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Re: more carburator on 18 degree 406 cui sbc

Post by bigjoe1 » Wed Jan 17, 2018 5:17 pm

To the O P -- I( was running a 288-304 on a 108 Cl- With the 3.75 stroke, the HP peak was at 8000 RPM- I use 1.8 intake rockers, but 1.60 exhaust rockers-- 875 intake, 710 ex lift- Rev engine to 8800 every pass



JOE SHERMAN RACING

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Re: more carburator on 18 degree 406 cui sbc

Post by F-BIRD'88 » Wed Jan 17, 2018 6:49 pm

hjallle123 wrote:
Wed Jan 17, 2018 3:35 pm
f-bird this is not brodix x heads its c heads
Yup I seen that.. These were highly reworked. bigger valves etc. Lots of hand porting. Ended up similar to what your working with.
The cam is not too big. Been there.

Unless you have the dominators there on hand to try out. I'd have to question the value of that investment.

This motor really reacted to custom built step headers (and the cam)

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Re: more carburator on 18 degree 406 cui sbc

Post by Rick360 » Thu Jan 18, 2018 1:08 am

Was the intake manifold made for the engine by Hogan? Was the head flowed with intake? Do you have csa of intake?

I wouldn't use a cam with that much duration on intake. Probably not whats hurting your power the most.

What size headers? Any exhaust used on dyno?

The heads don't flow great for the type of head and valve size.

Rick

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Re: more carburator on 18 degree 406 cui sbc

Post by induction apprentice » Thu Jan 18, 2018 6:02 am

Cams to big, Lol.....

I don't actually know that for sure. But right or wrong it's an easy thing to settle. Go to the dynamometer or track and back the exhaust lash off .010"

I will bet a honey glazed donut it will go faster and or have more average power.

Then we can all have a full blown debate / discussion on what's going on. I would love to understand it all better my self?

I would be super interested in Mike Jones take on such a change and prediction of the result of such a change?

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Re: more carburator on 18 degree 406 cui sbc

Post by hjallle123 » Thu Jan 18, 2018 6:53 pm

Rick the headers are 2 inch 26 long with 3.5 collecters use them on dyno
nope the heads are flow without intake
the intake are for another engine and the manifold is about 0.118 wrong in hight ( the intakemanifold port are 0.118 higher then port in heads and the port in heads are lower 0.118 than the intakemanifold port ) going to weld the bottom of port in heads so they match the port in intake and grind upper port . thats going to make the port more straigth

this will be done by a verry god head porter here in sweden ( Erland cox ) and he will take a look if the heads needs more porting


im going to messure the plenum also and maby add som spacer under topp plate

after that im going to look for another camshaft ( if i need it )

thinkin this would be the right way to go

how mutch plenum volyme should i have for this engine . Runners are abut 5 inch long on intake manifold



CSA 2,751 in heads and 2.75 on intake manifold

thanks

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Re: more carburator on 18 degree 406 cui sbc

Post by Rick360 » Fri Jan 19, 2018 9:10 am

hjallle123 wrote:
Thu Jan 18, 2018 6:53 pm
CSA 2,751 in heads and 2.75 on intake manifold
Is that intake manifold csa measurement an average or at head mating surface?

What Is the intake manifold csa at plenum and avg csa of intake manifold runner?

Rick

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Re: more carburator on 18 degree 406 cui sbc

Post by Ron E » Fri Jan 19, 2018 11:28 am

I'd put all of your questions to Erland. Like you said he's good and knowledgeable as well.

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Re: more carburator on 18 degree 406 cui sbc

Post by fdicrasto » Fri Jan 19, 2018 12:48 pm

When you mentioned the intake port heights in relation to cyl. port heights, did you have the proper thickness intake gasket in place? the thicker the gasket the higher the intake port will be in relation to the cyl. head port. Not a huge difference but could make enough difference to save having to weld up intake ports if I understood you correctly.

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Re: more carburator on 18 degree 406 cui sbc

Post by hjallle123 » Fri Jan 19, 2018 3:07 pm

only silicone on intake and heads to high with gasket cant get lower

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Re: more carburator on 18 degree 406 cui sbc

Post by hjallle123 » Fri Jan 19, 2018 3:10 pm

yes i will talk to erland

csa in heads are from weldtech ,they have cnc ported the heads hut 1.1a program

csa intake are in smallest port near heads , havent messure port in plenum :(

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Re: more carburator on 18 degree 406 cui sbc

Post by Warp Speed » Sat Jan 20, 2018 4:43 am

What's the compression ratio?
A single 850 will support 850+hp easy!

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Re: more carburator on 18 degree 406 cui sbc

Post by MadBill » Sat Jan 20, 2018 9:16 am

It comes down to the definition of 'support'. The OP's reported 990 CFM air consumption would result in 2" Hg. or more manifold vacuum at peak revs, whereas most similar unconstrained race engines would be carburetted for perhaps 0.6" resulting in as much as 3% more power.
Felix, qui potuit rerum cognscere causas.

Happy is he who can discover the cause of things.

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Re: more carburator on 18 degree 406 cui sbc

Post by Warp Speed » Sat Jan 20, 2018 10:59 am

MadBill wrote:
Sat Jan 20, 2018 9:16 am
It comes down to the definition of 'support'. The OP's reported 990 CFM air consumption would result in 2" Hg. or more manifold vacuum at peak revs, whereas most similar unconstrained race engines would be carburetted for perhaps 0.6" resulting in as much as 3% more power.
While I agree more carb could be used, the dual 750s are capable of making way more than the op is.
An open 358 cup engine would make around 875hp, drawing around 1050cfm through a cup legal 830 @ 1.5" in the manifold.
Don't know the manifold depression numbers, but we did a 400+ci R07 that we ran with one of our legal manifold and carbs before installing the tunnel ram. It made 930hp @ 9000 rpms.

Indeed more carb may help, but that isn't what is holding the combo back. IMO
We used that same Hut1.1 port in the mid 90s. The good ones made about 740hp with a 358 and a flat tappet........20 years ago!

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Re: more carburator on 18 degree 406 cui sbc

Post by hjallle123 » Sat Jan 20, 2018 2:12 pm

the compression is 14.9

one carb on dyno flowed 495 at wot so 2 carbs must flowed 990 or am i wrong here , first time i was in a dyno room
should haved ask how it was messured but had a lot of other questions and forgott to ask that question
this is my first real race engine ( built by myself) so want to learn so much i can :D



what do you have for suggestion for this engine

warp speed

thanks

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