Finally got by block back from the machine shop, crank installed, pistons & cam on order! I've got the SRP part#206072 which specs say for 80cc head volume will have 11.6:1 compression ratio. I'm told with this cr, the cam, and the application as a whole should produce around 475hp. I'm told I should be able to use 93 octane with a booster and be ok. Also, I'm looking for recommendations on what rear end gears I should apply as well.

Please provide your expertise!!!!!

 

I hate to see people calculate CR based on such little information. What you really need to know is how much your block has been decked, if any, how much it was bored, and what CC the dish of the piston is. Figure out what the compressed thickness of your gasket is and then figure in the head CC as well. All of this together will be used to calculate your CR.

**The example given by SRP may not be identical to what you have built so you really need to check for yourself.

I will add that if your CR really is 11.6:1 you will have a hell of a time running 93 octane even with a booster even with aluminum heads. If you have cast iron heads you can bet you will have an even rougher time with that CR. My advice; get an actual calculation of your CR not an estimate given by the piston manufacturer. My bet is your CR is going to be much lower than what the piston manufacturer is advertising.

Lastly, given that you seem to be excited about such high compression and moderate power output why did you not balance the rotating assembly? Was the machinist charging an arm and a leg? IMO it's great insurance to have it balanced to ensure there isn't a gross imbalance somewhere.

Anyway, good luck on your build! If you have any questions I'd be more than happy to help.

 

My build for Panos, same piston as yours, 11.75:1, fair amount of cam, 238/246, could only go with 29 degrees of timing on 93.
https://classicoldsmobile.com/forums...ess-455-a.html
I wouldn't do it on 93, he gets 95 in Sweden, only reason we did it.

What are your cam specs?

 

Not to be a buster, Mark, but you did take into account the different octane numbering scales in Europe and here, right? They use Research Octane, but we use "Anti-knock Index," which is the average of the Research Octane and the (lower) Motor Octane numbers.
Their 95 is roughly equivalent to our 91.

- Eric

 

Well, it has been bored .030 over. As for the deck height, I'm going to have to look at my paperwork. My cam specs are:
Hydraulic flat tappetBasic Operating RPM Range2,300-6,500Intake Duration at 050 inch Lift240Exhaust Duration at 050 inch Lift246Duration at 050 inch Lift240 int./246 exh.Advertised Intake Duration284Advertised Exhaust Duration296Advertised Duration284 int./296 exh.Intake Valve Lift with Factory Rocker Arm Ratio0.541 in.Exhaust Valve Lift with Factory Rocker Arm Ratio0.544 in.Valve Lift with Factory Rocker Arm Ratio0.541 int./0.544 exh.
Specifications IntakeExhaustRPM Range: Valve Lash: Valve Timing: Duration: Lobe Separation: Duration @ .050" Lift: Intake Centerline: Valve Lift: Lobe Lift: Valve Timing @ 0.006 Lift:

 

My 10.5:1 CR car has the occaisional pinging problem on 93 octane. If your CR is over 11 then ah64 pilot is dead on, you will basically have no chance on 93 unless you mix race gas or something similar with it.

 

Thats a Comp XE284, not enough off the seat time, you're going to have a problem imo.

Yes, but different countries rate it differently, i.e. my buddy in England has 97 octane and it's truly 97. He builds 11.0:1 stuff all the time, no issues.
So far Panos isn't having any problems to my knowledge.

 

I think you mean 10:75? Anyway im using our 95 and have bump the timing at 34 with no issues

 

95 Octane labeled gas in Europe, the UK, Australia, NZ, Japan, and, I think, most of Asia is the equivalent of 91 Octane labeled gas in the US, so you're getting no knocking with a 10.75:1 (or 11.75:1 ) CR and 34° of mechanical advance on 91 US-octane gas, which is fantastic.

Sounds like Mark built you a great motor!

- Eric

 

Correct, had a brain fart. But we lost a couple hp on the dyno at 31 so if you're able to run 34 with no issues then your power is easily 475+ I would think, good to hear.

Your math is off, assuming zero deck;
Swept volume 945cc
Gasket 9cc
Piston 5cc
Head 80cc
total 1039cc/94= 11.05.

Still too high for that cam. Vacuum shouldn't be a problem, however cylinder pressure will be.
Jmo.

 

I run 11:98:1,with iron heads,and I get away driving it with 93 octane.The pistons also sit .045" in the hole.Before I go to the track,I put a 50/50 mix in the tank,with 93 and 116,for good insurance.

To get a better measure of compression ratio,find out what the deck height is,and the distance down to the top ring.Then the head cc and head gasket thickness.Everything counts.

 

What are your cam specs Brian?

 

UltraDyne solid roller. dur = 259/265 @ .050, lift = .668"/.668"
The only time I had this rattle with pure 93,was when my friend was riding in it.He is 6'4",and is in the upper 200lbs range.My wife & kids don't have the same effect.

 

That cam helps no doubt.

Thanks

 

Yes it does.I had the pleasure of talking with Harold Brookshire a few times.He was great to deal with.I wish UD was still around,but last time I knew,he was at Lunati.

 

I think he's gone from there too last I heard. His last project was the VooDoo stuff I'm told.
Very few people realize his grinds have been around since the 80's. Not a bad thing just a fact.

 

Yes,he has always been more of a man-behind-the-scenes,and never really got too much credit,but he's a great one in my book.

 

Thank you everyone for your input. I think I may have forgot to also add that this will be a street car only.

 

Then you have too much compression and the wrong cam for stock heads.

Jmo

 

You are right there. I just sneaked a post into the editor`s post thread on this --subject to Joe`s approval.
It could be an issue.
mike

 

I spoke to Junior at Mondello's and he stated I should be ok considering that the deck nor the heads have not been milled. I should have around 10.5:1 compression ratio, and that the cam i have will be just right.

 

My Question is how did you machine the block without the pistons? You need them to figure your deck height also.

Gene

 

I hope they are taking into consideration that those pistons are .015 taller than a comparable Speed Pro or stock ones. Just an FYI.

I still think you have the wrong cam, too fast. It would be good for better heads, but not stock ones.

Jmo.

 

Get the assembly into the block,so you know exactly where the piston is to the deck.This isn't for guessing and estimating.If you end up with less compression,that might be a good thing,for what you are doing.If you need less compression,you could do a little work to the combustion chambers on the heads. For a strictly street application,and pump gas,I would try to get it somehere in the 9:75:1 - 10:1 range.

 

how is the build going. i am looking forward to seeing a video of the engine with new life. it sit for a long time in my barn just wanting to be built

 

The build is going great!!!! I've got the bottom end done and sealed up! Just waiting for a little extra cash so I can find some c heads and get the top end complete. Should be done by the fall!!

 

With this type of application I'm expecting to get close to 500hp. I've just decoded the rear end thats in this vehicle. Its a Chevy 10 bolt 8.2 3.08ratio. I'm imagining I'll have to change my rear end. Can someone verify this and also provide any suggestions as to what rear end I should go with if I should have to change it?

 

Unless your heads are heavily ported, that cam with 10.5:1 will get you 450 max, my guess is 435ish.

Jmo.

 

will that rear end be nough? or do I need to step it up to a 12 bolt?