Compression Question

[andyman]

What kinda compression you blower guys running?

[andyman]

What kinda compression you blower guys running?

Well let me put it other way, will I be safe with 12.5 with a 1471 on a 572 chevy

[Mike Canter]

What OD are you going to use on the blower?

[andyman]

What OD are you going to use on the blower?

I really have no idea were to start but what is there is 26 on top 39 on bottom 13.9mm any recommendation of were to start at . Let me say I am not trying to rotate the earth or break any records I think this should have plenty of power and then if I do want to step it up some there is room to do so, thanks

[Mike Canter]

That is 50% OD and that sounds like you are trying to turn the world. That is a lot to start out with. Most times that racers run OD of 30+ percent the compression ratios are in the 11.5 to 11.7 area. The higher 12.5 CRs are normally used when the ODs are down in the 20% area.

[andyman]

That is 50% OD and that sounds like you are trying to turn the world. That is a lot to start out with. Most times that racers run OD of 30+ percent the compression ratios are in the 11.5 to 11.7 area. The higher 12.5 CRs are normally used when the ODs are down in the 20% area.


so do i need to change both or 1 what do u recommend I start with, thanks for the help

[andyman]

I found me a chart and i am thinking a 31 19.2 or 32 23.1 tooth bottom pulley what you thank?

[Mike Canter]

I think it would be best to explain what type of car and what you want to do with this car because you have just gone from one extreme to another. A good start out point is around a 30% to 33%OD which will give you around 32-35 lbs of boost depending on the condition of the blower. A 572 cu innch motor is also a pretty large motor to start out on with a blower. What block and heads do you have?

[andyman]

I think it would be best to explain what type of car and what you want to do with this car because you have just gone from one extreme to another. A good start out point is around a 30% to 33%OD which will give you around 32-35 lbs of boost depending on the condition of the blower. A 572 cu innch motor is also a pretty large motor to start out on with a blower. What block and heads do you have?

I have an x funny car (altered) 48 fiat, I want some thing with at least 1000+ hp I am a crowd pleaser I like to bring them to the fence, as well as burn outs. I thought you said 20% so that is were I came up with that. My blower is a new 1471 from the blower shop. I did not buy it new I got it from some1 who did and that ws the pulleys that were on it. I got a dart big m NEW dart 360 heads fresh back from dart with all new parts ss valves, je pistons, 6.700 alu ohio rods, I asked Stan at Ohio Cranks and he is the one that recommended 12.5 I need to recheck might be 12.1 but they do and sell that stuff every day so I went with his recomendation, thanks Mike

[Mike Canter]

A cr in the 12.1-12.5 area is good for OD's down around 20-25%. The problem would be that you can't up the OD with that CR without having problems with detonation. Since you are not going to be all out then maybe some though should be given to a CR of around 11.5 so you can increase the OD if you wanted to and not be locked into a low OD. I am sure that if you started out with a 20% OD and get the hang of it then you will probably increase the OD slowly up to the low to middle 30%'s. Is this a standard or High Helix blower you bought?

[andyman]

A cr in the 12.1-12.5 area is good for OD's down around 20-25%. The problem would be that you can't up the OD with that CR without having problems with detonation. Since you are not going to be all out then maybe some though should be given to a CR of around 11.5 so you can increase the OD if you wanted to and not be locked into a low OD. I am sure that if you started out with a 20% OD and get the hang of it then you will probably increase the OD slowly up to the low to middle 30%'s. Is this a standard or High Helix blower you bought?


How can I tell the difference? So is there a way to lower the comp say with a head gasket or mill the top of the piston?

[Mike Canter]

You need to contact the Blower Shop and see what you bought. You can tell by looking at the bottom of the blower. If the exit area is a large square hole then it is most likely a standard blower. If it is a pie shaped opening in the forward section only then it is most likely a High Helix. A standard blower has a 60 degree twist to the rotors and a high helix has 120 degree twist. For the application you are talking about I would say you need a high helix. Yes, you can use different thickness copper head gaskets to tailor compression but not by much. The thiness I would go is maybe a .045 and the thickess would be a .080. You really need to talk to a local engine builder who knows blower motors because of all that is required. This is not something that can be done on the internet because there are so many factors.

[andyman]

none I trust around, I have built a many aspirated motor have had my ow shop for 33 years but I will ask before I do now days it is cheaper. I thank you for your help and info I learned a few things. Another step forward this is something I take slowly. Again thanks Tell Joey Andyman from Breakaway said hi

[andyman]

none I trust around, I have built a many aspirated motor have had my ow shop for 33 years but I will ask before I do now days it is cheaper. I thank you for your help and info I learned a few things. Another step forward this is something I take slowly. Again thanks Tell Joey Andyman from Breakaway said hi

Well it is a hi hilex and I have the compression down to the mid to upper 11's now and have talked to johnny philcer he will do all the machine work and putting together. I feel at least I am on the right track now. thanks andy

[Mike Canter]

That sound good. Johnny knows what he is doing.

[RacerHog]

Andyman,
Any updates
How are things going???

:cool::confused:

[andyman]

on the race or the motor ? how thing hanging dude?

the motor I got up for sale I am going to throw a few races and see what happens. If it does not sell I will get back on it and finish it I want give these parts away glad they do not eat. I want to see some good heads up racing so I guess I got to speed my own money, see the post 5000 dollars who wants it, hell give it them but let them fight for it and I think 5000 is worth the trip, racing is a gamble anyway, later man