WELCOME TO RIVER DAVES PLACE

Cylinder head tech for roots blowers

Blackmagic94

Well-Known Member
Joined
Apr 4, 2017
Messages
3,176
Reaction score
3,993
Ok so here is the debate


Can you install to large of an intake runner CC cylinder head design on a BBC with a 6-71 blower installed


I currently run 088 Gen V 502 style iron heads (320ish cc intake, 119cc combustion) on my 468 9:1 compression BBC with a 6-71 at -17% under driven


Im considering going with alum heads that would be 360 cc intakes-125cc combustion chambers on it instead next winter



I know I would

Loss weight
decrease cylinder temps
increase flow
drop about .5-.6 compression roughly

But will it run more sluggish from the stated above, I understand I would repulley up to get the same boost and that is fine
 

Blackmagic94

Well-Known Member
Joined
Apr 4, 2017
Messages
3,176
Reaction score
3,993
The larger intake runners arent going to lead to mid range sluggishness?
 

obnoxious001

Engine building character
Joined
Dec 28, 2007
Messages
5,625
Reaction score
2,203
Ok so here is the debate


Can you install to large of an intake runner CC cylinder head design on a BBC with a 6-71 blower installed


I currently run 088 Gen V 502 style iron heads (320ish cc intake, 119cc combustion) on my 468 9:1 compression BBC with a 6-71 at -17% under driven


Im considering going with alum heads that would be 360 cc intakes-125cc combustion chambers on it instead next winter



I know I would

Loss weight
decrease cylinder temps
increase flow
drop about .5-.6 compression roughly

But will it run more sluggish from the stated above, I understand I would repulley up to get the same boost and that is fine
Clearly you think you know more than I do, so I am wasting my time trying to help.
 
Last edited:

Blackmagic94

Well-Known Member
Joined
Apr 4, 2017
Messages
3,176
Reaction score
3,993
The other great thing about aluminum heads is that they are easier to repair if they do get damaged.

Matching the cylinder heads and camshaft to the engine are extremely important. With a forced induction engine, the temperature and density of the charge is important. Do you run an intercooler?

I would probably consider something smaller than the 360 runner for 468 cu inches, and depending on usage, maybe an 8-71 blower with intercooler.

One thing to remember, hot air increases pressure (boost), but is not good for performance. Less boost with a cooler, denser air fuel charge will make as much or more power, and it will be safer to run, less chance of burning pistons.


Not changing the blower it is what it is


I run AEM Methanol/Water injection with a progressive boost controller on it, so its chemically intercooled and high octane

I will be installing a new hydro roller custom cam with whatever heads I purchase

The smaller CC intake runner heads do not have the larger CC combustions, they will be the same 119
 

rider68

Member
Joined
Mar 22, 2019
Messages
20
Reaction score
26
Seems like a 6/71 is small. Also with turning in it so slow seems like it will be hard to take advantage of larger intake runner head. Might be better keeping iron heads and going to 8/71 as you can keep your same manifold.

Sent from my moto g power (XT2041DL) using Tapatalk
 

rider68

Member
Joined
Mar 22, 2019
Messages
20
Reaction score
26
Or I could spin the blower faster lol
Yes you can. I'm curious how much boost do see with the blower spinning that speed. I have a 461 bbc with same head and 8/71 running 1 to 1. I see 12 psi. Do you fell the water/meth is needed because of the smaller blower.

Sent from my moto g power (XT2041DL) using Tapatalk
 

Blackmagic94

Well-Known Member
Joined
Apr 4, 2017
Messages
3,176
Reaction score
3,993
-17.5 I get 4-4 psi
-5 I get 7.5-8 something


I run the Meth because I’m over 9:1 static on iron heads. Plus cold air is always better so why not. My blower has a ton of Teflon strips installed on the rotors so it’s very efficient for a 6-71
 

H8Plow

Active Member
Joined
Dec 30, 2020
Messages
32
Reaction score
29
-17.5 I get 4-4 psi
-5 I get 7.5-8 something


I run the Meth because I’m over 9:1 static on iron heads. Plus cold air is always better so why not. My blower has a ton of Teflon strips installed on the rotors so it’s very efficient for a 6-71
Static compression is not the same as dynamic compression. The latter is what you need to be concerned about.
Methanol injection is a bandaid and does fail. Also a roots blower is a “positive displacment“ compressor, meaning the air is always compressed and heated. Therefore you will always have higher intake air charge temps over ambient. Your best bet if sticking with the baby blower is to put an intercooler under it and spin it faster.
Larger cc ports change “port velocity speed”, a camshaft is the component that dramatically changes this behavior.
Side note - 305’s and 315’s have been proven countless times to outfow and make better usable power “area under the curve” then big must have cylinder heads.
 

Blackmagic94

Well-Known Member
Joined
Apr 4, 2017
Messages
3,176
Reaction score
3,993
This is a large case 6-71 not a small case. While it’s not a 14-71 it’s not a baby blower.


after watching some videos from Richard holdener, the bigger heads make more power for sure on a 6-71. Also adding cubes jumped the power as well which I was surprised to see.

small volume heads have higher velocity and work better on smaller cube NA engines. Not so much the case when you are forcing the air in to a point.
 

BoostPower

Well-Known Member
Staff member
Joined
Sep 30, 2010
Messages
1,395
Reaction score
684
Ok so here is the debate


Can you install to large of an intake runner CC cylinder head design on a BBC with a 6-71 blower installed


I currently run 088 Gen V 502 style iron heads (320ish cc intake, 119cc combustion) on my 468 9:1 compression BBC with a 6-71 at -17% under driven


Im considering going with alum heads that would be 360 cc intakes-125cc combustion chambers on it instead next winter



I know I would

Loss weight
decrease cylinder temps
increase flow
drop about .5-.6 compression roughly

But will it run more sluggish from the stated above, I understand I would repulley up to get the same boost and that is fine
Bigger runners reserve more available volume / pressure. Almost all cases run better. Of course it would be a book to explain but would be a good topic on Boostpower TV


Sent from my iPhone using Tapatalk
 

Blackmagic94

Well-Known Member
Joined
Apr 4, 2017
Messages
3,176
Reaction score
3,993
Bigger runners reserve more available volume / pressure. Almost all cases run better. Of course it would be a book to explain but would be a good topic on Boostpower TV


Sent from my iPhone using Tapatalk
Been watching a lot of Richard’s dyno builds on his YouTube channel this week and he would agree. I was really shocked at how much power a 468 to 498 increase with a 6-71 picked up.
 

BoostPower

Well-Known Member
Staff member
Joined
Sep 30, 2010
Messages
1,395
Reaction score
684
Been watching a lot of Richard’s dyno builds on his YouTube channel this week and he would agree. I was really shocked at how much power a 468 to 498 increase with a 6-71 picked up.
Yep. Reserve volume is a science many DONT know about. We use big turbo plenum as to hold a huge volume of pressurised air to burst accelerate however the head runners must accept the rush


Sent from my iPhone using Tapatalk
 
Top