So this came up today in a conversation

[425/409ER]

I was asked about my peanut port headed 461 BBC that runs low 11's with 8:1 compression and was asked, what do you think the car would run with 12:1 compression with no other changes. I replied "I don't know?" as I do not dyno engines much because I just choose to go out to the track to test. So some of you guys may have done this in the past with increasing compression, what track times did you see and was it worth the cost to raise the compression?

 

[Don Jacks]

All else remaining the same,10.40's-10,50's would be about it.

 

[Tim]

10-3 compression runs stationary burnout really good!

 

[425/409ER]

All else remaining the same,10.40's-10,50's would be about it.

That's interesting, you think it would be that quick? I have a set of Venolia's for this engine I sure would be happy with those times with them tiny ports.

 

[Ishiftem]

What’s the weight of the car sitting on the starting line?

 

[425/409ER]

What’s the weight of the car sitting on the starting line?

3460 with me in the car with the BBC engine.

 

[blkblk63ss]

3460 with me in the car with the BBC engine.

Geez, how much do you weigh???

 

[Ishiftem]

I would say if you run 11.20s now, 10.90s MAYBE 10.80s. If your Venolias use a thinner ring, then it’s probably worth it.

 

[Mr. Chev]

you would want higher quality fuel and advance the timing to take advantage of the higher compression.
with no other changes I will hazard 40 to 50 hp more.

 

[425/409ER]

Geez, how much do you weigh???

180lbs.

 

[425/409ER]

This engine is going to the track next month with a small bump in compression that come from a new set of ported heads. Compression will go form 8:1 to 9:1 not a lot but with the style of head I am hoping to put this combo in the high 10's.

 

[427John]

Is this a Mark IV or gen5 BBC?

 

[425/409ER]

Is this a Mark IV or gen5 BBC?

Mark IV with gen V heads on it. I used the conversion gaskets to make this work, had to drill some holes in the block for better cooling with those heads.

 

[427John]

If it was a Gen V motor I was going to tip you off on Gen V closed chamber large oval port heads used on Gen V 366 and 427T truck motors that had the ~97 cc closed chamber and large oval ports used on early non HP Mark IV BBC's.They do have the smaller 1.94/1.66 valves and need to be upgraded to the 2.06/1.72, but will increase the the CR on a flattop piston 454 up to the 9-9.5 range and have the larger standard oval ports instead of the peanut ports.They have the Gen V coolant passage pattern and bolt straight on with standard Gen V head gaskets,they have a 1140 casting number instead of the 1156 number of your heads.I have a Gen V 454 with the 1156 heads that I swapped in to my truck with corvette exhaust manifolds and a 66 360 horse 396 holley intake that while it ran fine stock was pretty tame power wise, I swapped on these heads and put in a ZZ502 cam and it turned the motor into a beast compared to what it was before.Since your engine is a Mark IV you could achieve the same thing by using the 69 and earlier non HP BBC heads, but since you have already converted for use with the Gen V heads you should be able to use the 1140 heads.

 

[wristpin]

If it was a Gen V motor I was going to tip you off on Gen V closed chamber large oval port heads used on Gen V 366 and 427T truck motors that had the ~97 cc closed chamber and large oval ports used on early non HP Mark IV BBC's.They do have the smaller 1.94/1.66 valves and need to be upgraded to the 2.06/1.72, but will increase the the CR on a flattop piston 454 up to the 9-9.5 range and have the larger standard oval ports instead of the peanut ports.They have the Gen V coolant passage pattern and bolt straight on with standard Gen V head gaskets,they have a 1140 casting number instead of the 1156 number of your heads.I have a Gen V 454 with the 1156 heads that I swapped in to my truck with corvette exhaust manifolds and a 66 360 horse 396 holley intake that while it ran fine stock was pretty tame power wise, I swapped on these heads and put in a ZZ502 cam and it turned the motor into a beast compared to what it was before.Since your engine is a Mark IV you could achieve the same thing by using the 69 and earlier non HP BBC heads, but since you have already converted for use with the Gen V heads you should be able to use the 1140 heads.

 

[425/409ER]

If it was a Gen V motor I was going to tip you off on Gen V closed chamber large oval port heads used on Gen V 366 and 427T truck motors that had the ~97 cc closed chamber and large oval ports used on early non HP Mark IV BBC's.They do have the smaller 1.94/1.66 valves and need to be upgraded to the 2.06/1.72, but will increase the the CR on a flattop piston 454 up to the 9-9.5 range and have the larger standard oval ports instead of the peanut ports.They have the Gen V coolant passage pattern and bolt straight on with standard Gen V head gaskets,they have a 1140 casting number instead of the 1156 number of your heads.I have a Gen V 454 with the 1156 heads that I swapped in to my truck with corvette exhaust manifolds and a 66 360 horse 396 holley intake that while it ran fine stock was pretty tame power wise, I swapped on these heads and put in a ZZ502 cam and it turned the motor into a beast compared to what it was before.Since your engine is a Mark IV you could achieve the same thing by using the 69 and earlier non HP BBC heads, but since you have already converted for use with the Gen V heads you should be able to use the 1140 heads.

Been there done that with closed chamber heads, my peanut ported heads that I ported absolutely blew the closed chambered heads away. 11.16 open vs. 11.78 closed chamber 215 oval heads. The closed chamber heads make less power. The heads on this Mark IV engine now are L-29 Vortec Gen V with 100 cc chambers that are ported, they will be a good test for sure in a few weeks. Hope everything on this swap works.

 

[427John]

Been there done that with closed chamber heads, my peanut ported heads that I ported absolutely blew the closed chambered heads away. 11.16 open vs. 11.78 closed chamber 215 oval heads. The closed chamber heads make less power. The heads on this Mark IV engine now are L-29 Vortec Gen V with 100 cc chambers that are ported, they will be a good test for sure in a few weeks. Hope everything on this swap works.

View attachment 110653

Looks like the L29 chamber is a variation of the late closed chamber with a divider ,did you port the 215's as extensively as the peanut ports and unshroud the intake valve like you did the L29's?

 

[425/409ER]

Looks like the L29 chamber is a variation of the late closed chamber with a divider ,did you port the 215's as extensively as the peanut ports and unshroud the intake valve like you did the L29's?

Yes, the 215's got ported after they performed so poorly at the track in 2019. I have them on another 468 with a roller cam now. As for the L-29 heads you cannot unshroud them as much as the peanut port heads. Find our how they work soon, the 461 is in the car now.

 

[Skip FIx]

Theories I have read about 4% per increase in 1 ratio of compression.

 

[425/409ER]

With the heads that are pictured in post #16. I went out to the track yesterday and was rewarded with a 11.10@118mph through the mufflers. Pretty good for some old junk Vortec BBC Truck heads, these must be a 409 related head