Technical > Matt Shaff's Engine Shop

sbc HP per cubic inch

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digster:
Thanks for the reply Matt
The current cam is smallish  I.630 E.630  268 270 @ 50 and ground on a spikey 106 Separation. Pulls very hard to 6000 rpm then its all done.
I've got a new spec. I think I'll try with the new heads. I.663 E.688  278 284 @ 50 on what should be a little broader power band 110 separation.
Matt new Heads are Brodix 12 with heavy port work 2.20 Intake valve 1.60 exhaust valves.
Stack injected, down nozzles and 16 to 1 comp.

wideopen231:
I have cpl guys who dyno tell me that most of the time with all other things being right the motor will make between 2.2 and 2.4 times the airflow of the engine.I play with desktop dyno program a lot and most of the time its real close given correct info. It also comes up pretty close to that 2.2 to 2.4 x cfm deal. Not sure that verify's anything just food for thought. I think you said 390cfm,Bill said should be 800 plus and 2.2x390 would put you closer to 850.Again that with everything be a optimal.

digster:
Thanks 231
 I assume smaller pump (engine) displacement could be made up by for by higher pump speed and still approximate the 2.2 HP per cfm rule. Using my assumption the pump would have no regard for bore vs stroke Just CFM. The pump configuration is what intrigues me.

dusterdave173:
I dyno lots of engines--I have seen all kinds of stuff but you just can't ever go wrong with bigger bore--I see some very large bore with much shorter stroke than they could have for same effort or money do amazing things as long as they have enough head.
I think on smalller CI combos you have to get it just right with runner volume , cam etc based on what RPM you will really be turning--too often I see way too much runner on pretty small CI engines.
The combos you guys are discussing 434 with those awesome heads make it hard to go wrong--just add RPM until you get what you want out of it :)
An interesting benchmark of what will do what is Scott Shaffiroffs website--You see the engine combos he builds with what parts and then see HP numbers that are usually right--Scott is more than anything a perfect business man but talk to anyone that has an engine from there and they are usually very happy--of course we need to think of the alky and induction we use but it is just a decent yardstick of popular combos.
The thing is you can go 8.90 with Craigslist, stock block used small  junk--Going 8.50's is a decent little engine --going 8.0's is a serious and way more expensive deal as far as parts needed--I am thinking 8.50 as my long term goal is somthing I can do myself and afford- I have enjoyed making things as light as possible--it always rewards in a drag engine--if not all that much faster it makes for a great engine "personality" -after that, I read about you big dogs like you were astronauts :)

masracingtd1167:
I agree with Dave A bigger bore will always make more HP . Most of the Comp Eliminator stuff is big bore like 4.125 up to 4.185 with a very short stroke like 2.800 and some are making close to 3.0 Hp per cube . 16 to 1 compression sounds kind of high to me . Maybe Matt or Dave could give some advice about that . From what I understand too much dynamic compression can cause severe detonation if the intake closes too early . I will look and see if I have some old cam cards from a couple of cams that worked for me .   

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