Heads only
Thread Starter
Melting Slicks
Joined: Apr 2001
Posts: 2,117
Likes: 213
From: Pittsburgh PA
Heads only
I have a seasoned speed shop guy suggesting a heads-only modification to my 1981 vette. Says the compression boost and 1.6 rockers will give me a noticeable power increase. No cam break-in to worry about. Has anyone done just heads and been impressed with the upgrade?
Team Owner
Joined: Oct 2004
Posts: 81,241
Likes: 3,062
From: altered state
St. Jude Donor '05
Not impressed. Noticeable...well yes but not what I ever hoped for
It will help but you need more flow...and a cam to hang the valves open earlier/longer.
What is he trying to sell you?
It will help but you need more flow...and a cam to hang the valves open earlier/longer.
What is he trying to sell you?
Last edited by cv67; Jan 24, 2020 at 09:08 PM.
Le Mans Master
Joined: Oct 2010
Posts: 6,900
Likes: 833
From: melbourne florida
2023 C3 of the Year Finalist - Modified
I'd say if you have the L-82 some small chamber heads to boost compression and some 1.6 rockers headers and intake I agree with your shop owner. You will notice a worthwhile improvement.
Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
OE 81 has deep dish pistons and needs compression ... chambers smaller than 64cc best
these iron 58cc
https://www.summitracing.com/parts/w...50-1/overview/
or these iron 59cc
https://www.summitracing.com/parts/s...make/chevrolet
or these aluminum 60cc
https://www.summitracing.com/parts/t...make/chevrolet
these iron 58cc
https://www.summitracing.com/parts/w...50-1/overview/
or these iron 59cc
https://www.summitracing.com/parts/s...make/chevrolet
or these aluminum 60cc
https://www.summitracing.com/parts/t...make/chevrolet
Last edited by jackson; Jan 25, 2020 at 12:58 AM.
Le Mans Master
Joined: Feb 1999
Posts: 8,351
Likes: 75
From: Tampa Bay FL
I have a seasoned speed shop guy suggesting a heads-only modification to my 1981 vette. Says the compression boost and 1.6 rockers will give me a noticeable power increase. No cam break-in to worry about. Has anyone done just heads and been impressed with the upgrade?
When I bought my '80, it had 96k miles and the engine was tired and leaking/burning oil. More compression would have just exposed the leaking rings and led to a shortblock refresh. I rebuilt.
Thread Starter
Melting Slicks
Joined: Apr 2001
Posts: 2,117
Likes: 213
From: Pittsburgh PA
Thanks for all of these replies. It's the stock 81 motor and cam. I've done nice long tube headers and chambered pipes, but they really didn't do a whole lot to help the breathing. I've been debating dropping a fresh 383 crate motor in it, but I'm not too excited about going that far with this car. It's a very clean, honest car, but I've already done a Tremec 5 speed, Borgeson steering, differential rebuild, a/c, carpet and just don't feel like throwing another $7k at it.
Would heads alone get it to rev more freely and higher? The torque is good, but there is not much to gain taking it past 3,500 RPM.
This shop owner wants to drive the car before solidifying his recommendations. Miles are about 75k.
Would heads alone get it to rev more freely and higher? The torque is good, but there is not much to gain taking it past 3,500 RPM.
This shop owner wants to drive the car before solidifying his recommendations. Miles are about 75k.
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Le Mans Master
Joined: Feb 1999
Posts: 8,351
Likes: 75
From: Tampa Bay FL
Thanks for all of these replies. It's the stock 81 motor and cam. I've done nice long tube headers and chambered pipes, but they really didn't do a whole lot to help the breathing. I've been debating dropping a fresh 383 crate motor in it, but I'm not too excited about going that far with this car. It's a very clean, honest car, but I've already done a Tremec 5 speed, Borgeson steering, differential rebuild, a/c, carpet and just don't feel like throwing another $7k at it.
Would heads alone get it to rev more freely and higher? The torque is good, but there is not much to gain taking it past 3,500 RPM.
This shop owner wants to drive the car before solidifying his recommendations. Miles are about 75k.
Would heads alone get it to rev more freely and higher? The torque is good, but there is not much to gain taking it past 3,500 RPM.
This shop owner wants to drive the car before solidifying his recommendations. Miles are about 75k.
NOTE: There are other items to replace when you replace the engine including such items as: distributor (complete), ignition wires, motor mounts, water pump, v-belts, and other misc items.
Including link to the BP 355 at Jegs for a reference on the long block price.
https://www.jegs.com/i/Blueprint+Eng...BoC0N8QAvD_BwE
Last edited by TedH; Jan 25, 2020 at 08:33 AM.
Le Mans Master
Joined: Mar 2004
Posts: 7,424
Likes: 1,458
From: Little Rock AR
I would ditch the carb, distributor, heads and cam. Those special computerized pieces are a substantial bottle neck. You could really wake it up. Need more compression, and a cam to use it.
Those "chambered mufflers" should be suitcase style, not a straight thru chambered pipe style. Those chambered pipe style mufflers are very restrictive and actually hurt breathing.
Those "chambered mufflers" should be suitcase style, not a straight thru chambered pipe style. Those chambered pipe style mufflers are very restrictive and actually hurt breathing.
Thread Starter
Melting Slicks
Joined: Apr 2001
Posts: 2,117
Likes: 213
From: Pittsburgh PA
A limiting factor to consider is the Electronic carburetor. If your L81 is stock, it has electronic carb control and a box. You need to be able to tune your carb and I've not seen a lot of good press on the L81 carb. It would be a limiter to any gains with just cylinder heads. If it were me, I would go for a Blueprint Engines roller-cammed 355 or 383 longblock and add a carb/intake. They use the 1986-newer block configuration (1-piece rear main seal) so you would have to replace your flywheel and may have to go with a different starter (you would need to verify). You would spend around $4,500 (long block plus carb/intake and flywheel) and that is a lot less than $7,000. That is parts-only and assumes you and friends pull and install the engine.
NOTE: There are other items to replace when you replace the engine including such items as: distributor (complete), ignition wires, motor mounts, water pump, v-belts, and other misc items.
Including link to the BP 355 at Jegs for a reference on the long block price.
https://www.jegs.com/i/Blueprint+Eng...BoC0N8QAvD_BwE
NOTE: There are other items to replace when you replace the engine including such items as: distributor (complete), ignition wires, motor mounts, water pump, v-belts, and other misc items.
Including link to the BP 355 at Jegs for a reference on the long block price.
https://www.jegs.com/i/Blueprint+Eng...BoC0N8QAvD_BwE
Where is the box that talks to the stock carb?
Le Mans Master
Joined: Apr 2011
Posts: 6,284
Likes: 1,170
From: Hermosa
IMO your not going to get you bang for your buck with a heads only swap. If the new heads flow better you’ll see some improvement. If they have smaller chambers you’ll see some improvement, assuming you stay out of detonation.
however their in lies some of the problem. You use a small cam with heads that flow better and have smaller chambers now you’ve increased the dynamic compression perhaps enough to make detonation your new problem. Particularly with the stock dish pistons that have no quench pad on them.
there is no half *** soulutuion without ending up with half *** results.
so to get what you want it is my opinion those pistons need changed as well as heads and cam. Then get you a non-computer controlled q-jet and a non computer controlled HEI. Then you might have something you can have fun with. However it’s gonna cost ya, no way around it to get good results.
otherwise be prepared to be underwhelmed with anything less than a full effort.
however their in lies some of the problem. You use a small cam with heads that flow better and have smaller chambers now you’ve increased the dynamic compression perhaps enough to make detonation your new problem. Particularly with the stock dish pistons that have no quench pad on them.
there is no half *** soulutuion without ending up with half *** results.
so to get what you want it is my opinion those pistons need changed as well as heads and cam. Then get you a non-computer controlled q-jet and a non computer controlled HEI. Then you might have something you can have fun with. However it’s gonna cost ya, no way around it to get good results.
otherwise be prepared to be underwhelmed with anything less than a full effort.
Last edited by REELAV8R; Jan 26, 2020 at 10:30 AM.