How much is to much for the street?

[76 Sting]

Compression ratio

Every head I look at around 200CC is spec'd at 64cc, which puts me at 11.1 compression.

I want to know if this is too much for the street. At the strip I can run on their gas and not concerned.

Also, is there a way to use a gasket to bring down the comp to 10.3 or something close?

Thanks guys!

 

[Art Jett]

Off the subject, but did you get your brake problem fixed?

 

[76 Sting]

Off the subject, but did you get your brake problem fixed?

Hey Art...how the hell are ya? Brakes are about 85% were they were before, but at least they will lock up now

Unfortunaltely, that will not matter now as I blew my engine at the track 2 weeks agoad

Are you enjoying yous now??

I hope all is well with you.

We wil lget together as soon as I get a new engine together, the block is at the machinist as we speak.

 

[Art Jett]

That sucks!!! I think I've got to yank out the 3.70 diff I bought about 5 months ago. It is making noise under heavy accel. Oh well, gives me something to do, right? Other than that it's great. Bought some new wheels and tires about a month ago. Love them. I'll give you a call in the near future and we'll have to drink a beer or two. Art

 

[Hib Halverson]

11.1:1 is too high for an engine running on pump gas. To safely run with that, you'd either have to compromise your spark curve with retarded timing, which kills response and runs the engine hot, or run the carb way rich at WOT which also kills response and mileage.

For an engine with the specs listed in your sig line along with having good cooling, air-fuel that is tuned properly and a spark curve which is conservative and accurately controlled, 9.5:1 or 9.75:1 is about as far as you want to go with 91-92-oct gas. If you regularly can get 93-94-oct gas you could go to 10.0. If the heads you're looking at are aluminum, you can add a quarter to a third of a point and still be ok.

Now, your sig line also talks about nitrous oxide. If your ignition set-up offers the ability to retard spark when the nitrous oxide system is active, you need to set-up that option. I'd start with 4 deg retard when the nitrous running. If you don't have that option, I'd take half a point off the compression or run some racing gasoline. In addition, you want to make sure your fuel delivery system is capable of supplying enough gas when the nitrous system is working. If you see excessive fuel pressure drop when your squeezing, you need to increase fuel flow somehow. Often this requires more than just upping the pressure. You may also need to increase the diameter of the fuel feed lines.

I'll add that another issue important to having an engine with relatively high compression running detonation-free on pump gas is an intake manifold and head combination that has high velocity and good distribution. Typically, these are too factors which are sometimes absent when heads are selected on the basis of how big the intake ports are and how radical the camshaft is.

Lastly, I'll say again that: you need good cooling with a 160 or 180 'stat, a carb with tuning that is right-on at WOT and a spark curve that is modest and accurately controlled.

 

[76 Sting]

11.1:1 is too high for the street.

For an engine with the specs listed in your sig line along with having good cooling, air-fuel that is tuned properly and a spark curve which is conservative and accurately controlled, 9.5:1 or 9.75:1 is about as far as you want to go with 91-92-oct gas. If you regularly can get 93-94-oct gas you could go 10. If the heads your looking at are aluminum, you can add a quarter to a third of a point and still be ok.

Again, you need good cooling with a 160 or 180 'stat, a carb with tuning that is right-on and a spark curve that is modest and accurately controlled.

Sorry...that was the engine that blew. Here are the new spec's so far minus the heads because I can't seem to figure that one out yet, which is why i have started this thread becasue a 64cc will put me at 11.1.1

Eagle forged 4340 crank
Stroke - 3.75

Eagle forged H beam rods
Rod - 6.0”

SRP forged Flat Top pistons
10.3 Compression Ratio (goal) trying to figure this out still
(-5cc)
419 grams each
JE Pro Seal rings
Clevite 77 bearing set


Extreme Energy Hydraulic Roller Cam #XR294HR
Duration @.050 - IN. 242 EX. 248
Valve lift W/ 1.5 rockers - IN. .540 EX. .562
Lobe sep. angle 110 deg

Heads
Don't know yet

Comp Pro Magnum Rockers #1301-16
Ratio – 1.52
Rocker stud – 3/8”

 

[Rumpity rumpity rump....]

Compression ratio

Every head I look at around 200CC is spec'd at 64cc, which puts me at 11.1 compression.

I want to know if this is too much for the street. At the strip I can run on their gas and not concerned.

Also, is there a way to use a gasket to bring down the comp to 10.3 or something close?

Thanks guys!

REPLY: In my 2006 LS2 vette, im running at 10.9 CR with no trouble using 89 octane gas. I try for 93 octane when i can.

 

[76 Sting]

REPLY: In my 2006 LS2 vette, im running at 10.9 CR with no trouble using 89 octane gas. I try for 93 octane when i can.

the LS2 is a completely different breed of engine compared to this one so they are able to run at a higher CR....computers are great things

 

[Hib Halverson]

You're getting by with 89 octane because your 06 has EST (electronic spark control) and part of that is the knock retard function.

It's difficult to believe that anyone who spent the money to buy and 06 Vette is so cheap they put 89 octane gas in the car but, admittedly it will run on it, but it will run with knock retard and/or the ECM going to the low octane fuel spark tables. The result of that is reduced performance and higher coolant temp.

Penny-wise but pound-stupid, for sure.

As for the 76 Corvette, which was the subject of this thread, that engine does not have EST so it cannot run 89 octane gas unless the CR is down about 8.5 or 9:1 and/or the spark is retarded.

 

[Rumpity rumpity rump....]

You're getting buy with 89 octane because your 06 has EST.

It's hard to belive that anyone who spent the money to buy and 06 Vette is so cheap they put 89 octane gas in the car but, admittedly it will run on it but it will run with knock retard and/or the ECM going to the low octane fuel spark tables. The result of that is reduced performance and higher coolant temp.

Penny-wise and pound stupid, for sure.

As for the 76 Corvette, which was the subject of this thread, that engine does not have EST so it cannot run 89 octane gas unless the CR is down about 8.5 or 9:1 and/or the spark is retarded.

REPLY: I didnt think your reply was very nice or tactful ; I cant always find 93 octane but when i can i use it. Sometimes (especially on trips) the highest i can find is 89 .

 

[Hib Halverson]

Sorry...that was the engine that blew. Here are the new spec's so far minus the heads because I can't seem to figure that one out yet, which is why i have started this thread becasue a 64cc will put me at 11.1.1

Eagle forged 4340 crank
Stroke - 3.75

Eagle forged H beam rods
Rod - 6.0”

SRP forged Flat Top pistons
10.3 Compression Ratio (goal) trying to figure this out still
(-5cc)

(snip)


Ok.
I didn't see this post until a little later.

That's a damn big camshaft.

What's going to be the final displacement? What intake manifold is going on this motor?

 

[Vette79]

Yep, that cam seems way to big...

 

[76 Sting]

(snip)
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Ok.
I didn't see this post until a little later.

That's a damn big camshaft.

What's going to be the final displacement? What intake manifold is going on this motor?

I am back.. it will be a 383 and the manifold will likely be an Edelbrock RPM Air gap or Victor Jr

I wanted a fairly big cam because I plan to be at the strip more than on the street. I am lucky if I put 1000 miles a yr on her.

I went to SRP's web site and can't find a piston to give me mid 10's compression...do you think they have more if i call them? The only combo I see is a 9.8.1 with a 72cc chamber to low CR or 11.1 with a 64cc to high CR

 

[76 Sting]

Yep, that cam seems way to big...

to big for??

 

[Crimson Thunder]

How thick is the head gasket you are using?You could try a thicker gasket to lower the ratio a little.Its kind of a band aid approach because you will lose some quench area but it might be worth a try.
Then again you said it will spend most of its time at the track,keep at 11:1 and run race gas.

 

[76 Sting]

How thick is the head gasket you are using?You could try a thicker gasket to lower the ratio a little.Its kind of a band aid approach because you will lose some quench area but it might be worth a try.
Then again you said it will spend most of its time at the track,keep at 11:1 and run race gas.

I was thinking of that too, but I do drive it on the streets and would rather be safe then sorry as this is my 3rd engine in 1.5 years and the wife is getting on my back about the constant flow of money into her.

I think she is getting jealous..

 

[Hib Halverson]

I am back.. it will be a 383 and the manifold will likely be an Edelbrock RPM Air gap or Victor Jr

I wanted a fairly big cam because I plan to be at the strip more than on the street. I am lucky if I put 1000 miles a yr on her.

I went to SRP's web site and can't find a piston to give me mid 10's compression...do you think they have more if i call them? The only combo I see is a 9.8.1 with a 72cc chamber to low CR or 11.1 with a 64cc to high CR

Ok. I get it. The goal is drag racing.

That cam will work well with the Performer RPM Air Gap. I assume the engine will rpm to 6200. Also, I think the Comp "Pro Magnum" is simply a stampped steel rocker with a roller tip. I'd use a full roller rocker arm rather than that cheap approach. Do that and you'll be able to use more of the engine rpm capability. I believe your car has a 3.55 axle but I read you also have 3.70s. With the high-stall converter you already have, your axle ratio choice is going to be driven by what tire you put on the back. My guess is to get the car to hook with 3.70s may require slicks.

If racing is the goal, I'd keep the compression and start running racing gasoline. I'd start by mixing 1:2 100 unleaded to pump gas.

You're also going to want to set-up your ignition for some kind of automatic retard feature when you squeeze the nitrous.

 

[76 Sting]

Ok. I get it. The goal is drag racing.

That cam will work well with the Performer RPM Air Gap. I assume the engine will rpm to 6200. Also, I think the Comp "Pro Magnum" is simply a stampped steel rocker with a roller tip. I'd use a full roller rocker arm rather than that cheap approach. Do that and you'll be able to use more of the engine rpm capability. I believe your car has a 3.55 axle but I read you also have 3.70s. With the high-stall converter you already have, your axle ratio choice is going to be driven by what tire you put on the back. My guess is to get the car to hook with 3.70s may require slicks.

If racing is the goal, I'd keep the compression and start running racing gasoline. I'd start by mixing 1:2 100 unleaded to pump gas.

You're also going to want to set-up your ignition for some kind of automatic retard feature when you squeeze the nitrous.

Thanks for the reply. A few additions (Heads)

Eagle forged 4340 crank
Stroke - 3.75

Eagle forged H beam rods
Rod - 6.0”

SRP forged Flat Top pistons
10.2 Compression Ratio (w/72cc heads)
(-5cc)
419 grams each
JE Pro Seal rings
Clevite 77 bearing set


Comp Cams Extreme energy Hydraulic Roller Cam
Duration @.050 - IN. 242 EX. 248
Valve lift W/ 1.5 rockers - IN. .540 EX. .562
Lobe sep. angle 110 deg

PRO1 Platinum Heads
Angle plug,
Chamber size - 72cc
IntakePort Size -200cc
Valve Sizes (in/ex) - 2.02"/1.60"
Spring 1.437D
.620” max lift

Comp Pro Magnum Rockers #1301-16
Ratio – 1.52
Rocker stud – 3/8”

The Comp Pro Magnum's are made of chromemoly steel with a full roller. You might be thinking of the regular magnum rockers. They are about $300 for the set. I have the 3.50 gear, but slicks will happen mid summer maybe some MT Street ET's.

I was actually going to buy the MSD retard module selector that way when I do turn on the NOS I can retard it form inside the car to appropreate level.


Manifold I am still stumped on looking at either the RPM Airgap or the Victor Jr that has been port matched to the 1205 gasket. I think the Victor will make more power but I don't want it to be a dog on the street....

What do you think the manifold choise should be?

 

[Ed's 1970]

All looks good in that combo! Should be 475-500 horse, in that range.
Just make sure u zero deck that block, it will make it less detonation sensitive. Also, keep an eye on the timing. Another thing u can do is polish the chambers.
Victor Jr. will make more top end than an air-gap, and I think it is more appropriate with your intended usage, camshaft selection, and compression ratio. It will not be a dog on the street either, your building a 383, this motor has more low end torque than a 350. The downside is it will not rev like a 350 would due to the longer stroke. I guess the same argument can be made of a 327 vs a 350. The bottom line is u can not beat a bigger engine. That's why I am currently building a 540 for my car.

 

[76 Sting]

All looks good in that combo! Should be 475-500 horse, in that range.
Just make sure u zero deck that block, it will make it less detonation sensitive. Also, keep an eye on the timing. Another thing u can do is polish the chambers.
Victor Jr. will make more top end than an air-gap, and I think it is more appropriate with your intended usage, camshaft selection, and compression ratio. It will not be a dog on the street either, your building a 383, this motor has more low end torque than a 350. The downside is it will not rev like a 350 would due to the longer stroke. I guess the same argument can be made of a 327 vs a 350. The bottom line is u can not beat a bigger engine. That's why I am currently building a 540 for my car.

Thanks for the tips...540, dam. Is it a prety tight fit in the engine compartment?