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Retired Air Force
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940 Posts
Discussion Starter #1
While re-building my 454 to a 489 I bought some Dart Pro-1 heads. When I went to put the manifold on I noticed that it did not fit the new heads. Now I am thinking of replacing it with a supercharger. My concern is my compression ratio. I have 10-1. I am thinking it would work OK on pump gas if I used an intercooler with the aluminum heads if I keep the boost down? The cam has 308/314 duration with 575 lift. Will it work? Who makes the best blowers?
 

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Glendale Arizona
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2,368 Posts
My guess would be your compression will be too high. Most blower motors I've seen are running 8:1 or 8.5:1 compression. Anything higher than that and you'd have to run the boost so low that it would negate any benefits of using a blower in the first place.

I'm not a motor guy so this is all speculation. I did consider putting one on my boat a few years back and although it could be done with 9.5:1 compression, my research showed that I would've been in the same situtation as you and only be able to run 5 lbs of boost or so safely (pump gas). I figured there was no point in adding all that complexity and weight for a measley 5 lbs of boost. The added horsepower probably wouldn't even overcome the weight of all that hardware.

Since this is speculation and I don't really know what I'm talking about, I'd wait for a better response.

If nothing else...........it's a bump to the top.
 

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mo balls than $cents$
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11,734 Posts
My guess would be your compression will be too high. Most blower motors I've seen are running 8:1 or 8.5:1 compression. Anything higher than that and you'd have to run the boost so low that it would negate any benefits of using a blower in the first place.

I'm not a motor guy so this is all speculation. I did consider putting one on my a few years back and although it could be done with 9.5:1 compression, my research showed that I would've been in the same situtation as you and only be able to run 5 lbs of boost or so safely (pump gas). I figured there was no point in adding all that complexity and weight for a measley 5 lbs of boost. The added horsepower probably wouldn't even overcome the weight of all that hardware.

Since I don't really know what I'm talking about, I'd wait for a better response.

If nothing else...........it's a bump to the top.
i agree, you've already got the wrong compression for pump gas boost, but its perfect for a big ole shot of nitrous:|err:D;):)devil
 

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Banned
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If you haven't done so, start measuring to find out you exact compression ratio. A kazillion motors out there have +/- 1 pt compression than there owners think they have.

Measure the combustion chambers in heads, how far piston is in the bore at TDC, piston dome/dish volume, etc,etc,etc.

Also, do you boat in high altitude all the time ? If so, how high up ?

Then we can continue with this conversation.

If you don't or can't find out exact compression ratio, we have to assume you do have 10:1 compression when giving advice and thus my answer would be lower the compression before you go blower. But, at that point, everything should me measured again to see what exactly you have, so .......

======================

What intake didn't 'fit.' Safe to assume a dual plane intake and the bolt holes in between the intake runners where had a direct path into an intake runner ?
 

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Retired Air Force
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940 Posts
Discussion Starter #5
The new pistons and the new heads should yield 10-1 although They have not been checked manually. I live in Phoenix Az but am moving to Sacremento Ca. soon.
 

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Registered
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7,464 Posts
Chart

Master Seargent heres a reference chart you might find helpfull check the actual chart (link) as the copy and paste doesn't reproduce the "highlites" Tom

http://www.blowerdriveservice.com/techcharts.php


BDS TECHNICAL CHARTS
FINAL COMPRESSION RATIO CHART
Blower Boost
COMP RATIO 2 4 6 8 10 12 14 16 18 20 22 24
6.5 7.4 8.3 9.2 10 10.9 11.8 12.7 13.6 14.5 15.3 16.2 17.0
7 8 8.9 9.9 10.8 11.8 12.7 13.6 14.5 15.3 16.2 17.0 17.9
7.5 8.5 9.5 10.6 11.6 12.6 13.6 14.6 15.7 16.7 17.8 18.6 19.5
8 9.1 10.2 11.3 12.4 13.4 14.5 15.6 16.7 17.8 18.9 19.8 20.9
8.5 9.7 10.8 12 13.1 14.3 15.4 16.6 17.8 18.9 19.8 20.9 21.9
9 10.2 11.4 12.7 13.9 15.1 16.3 17.6 18.8 20.0 21.2 22.4 23.6
9.5 10.8 12.1 13.4 14.7 16 17.3 18.5 19.8 21.1 22.4 23.6 24.8
10 11.4 12.7 14.1 15.4 16.8 18.2 19.5 20.9 22.2 23.6 24.8 26.0
10.5 11.9 13.4 14.8 16.2 17.6 19.1 20.5 21.9 23.4 24.8 26.2 27.6
11 12.5 14.0 15.5 17.0 18.5 20.0 21.5 22.9 24.5 26.0 27.5 28.9

Final Compression Ratio Chart
BDS Stage 1 & 2 Blowers Only
- download Engine Belt Size Chart
- download Drive Chart for 1/2" Pitch Pulleys
- download Drive Ratio Chart for 8mm Pulleys
- download Drive Ratio Chart for 13.9mm & 14mm Pulleys





Final Compression Ratio Chart

This chart shows the final compression ratio combining the static compression ratio of an engine and the maximum blower boost from the blower system. It is to be used as a guideline in determining the proper maximum boost level for a specific application. Final compression ratios in excess of 12.4:1 are not recommended for use with "pump gas." The higher the final compression ratio, the higher the octane rating of the fuel must be in order to help prevent detonation and serious engine damage.
The formula for calculating your exact final compression ratio is as follows:
Final Compression Ratio (FCR) = [ (Boost÷14.7) + 1 ] x CR

Boost = Maximum blower boost
14.7 = psi at sea level
CR = engine compression ratio

Altitude plays an important role in determining compression ratios. If the altitude in the area where you normally drive is significantly higher than sea level, then your compression ratios will also vary. To determine the effects of the altitude on a calculated compression ratio, use the following formula:
Corrected Compression Ratio = FCR - [ (altitude÷1000) x 0.2 ]


= Pump Gas = Good Gas
 

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415 M3
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240 Posts
Nos

That blower/intercooler deal is going to be expensive, heavy and not what you want to be putting on top of that new motor with 10:1 compression. What do you mean the intake does not fit the new heads? Are the bolt holes slightly off, do the ports not match up? That stuff can be fixed with little effort. A nice nitrous system sounds like a better option. JMO.
 

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Retired Air Force
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940 Posts
Discussion Starter #8
I was waiting for someone to question as to why the bolts don't line up. After talking to the guy's at Dart I have discovered that the manifold may have 4 holes in it that the dart heads are not drilled for, however the rest of the holes should line up and work fine. I will have to take a closer look at it when I get home today. My tunnel ram is a nice piece, polished with a under manifold nitrous kit (300hp), I would hate to get rid of it. As someone mentioned earlier the motor would be more suitable for N02, so I hope the guy at Dart was right.
 

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Premium Member
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1,533 Posts
first off the cam is probably not good for a blower. probably the most important spec you want to look is the the Lobe-Center Angle. most likely i would guess yours is going to be in the 108-110 range and that is definately not what you want for a blower. any boosted engine is looking for a 114 or higher LCA this helps keep the blower efficient by minimizing the amount of wasted boost that would be blowing right through the chamber and out the exaust when both valves are open.

your other issue is not knowing the EXACT compression ratio of the engine. I built a 383 for a guy a few years back and he had some nice trick flow heads for it that were rated at 68cc chambers. if i would have put the engine together as it was from the machine shop with the heads as they were i would have had as much as 11.3:1 in 1 hole and as low as 9.9:1 in another. i found the heads had as small as 65cc chamber on one and as high 70cc on another. i also found that one piston was .010 in the hole and another was .013. This engine was filled with all good parts, but it doesn't take much to change the compression ratio. i highly suggested cc-ing the heads and finding the exact deck clearance, gasket thinkness and piston cc. just going off of what it should be or what the manufacturer says it should be could end up costing you a lot of money. if you don't want to do all that then i don't suggest running a blower.

AP
 
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