Need an experts opinion...looking for more HP

[MTC_75vette]

I have a 1975 L-48 with many upgrades but it is just still not enough power for me. I was planning on adding: S/R Torquer Cast Iron Cylinder Heads, flat top hypereutectic pistons bringing the compression ratio to 10 40: 1, and boring my engine .030 over. My question is how much power do you think this will give me? Before I spend all this money I wanna make sure the power I gain is going to be high enough to suit my needs. I am currently at 275 hp and want to be in mid 300's or more....Thank you!

 

[Rodney Gold]

One upgrade cannot just be looked on in isolation , for example upgrading the heads and comp ratio wont help unless you have the carb , cam and headers to take advantage and even then , one needs more than just that to really feel the effects.
I would look elsewhere to "wake" the car up , for example a 2000-2400 stall convertor (If it's auto) and a change from lets say a 3:1 to a 3.5:1 diff ratio will give you a seat of the pants thrill , whereas heads and cam might actually make the car a dog at lower RPM without doing the stall and rear gears. Even if you DO hop it up , you will still have to do the stall and rear end thing anyway...so perhaps do it first and then add power.
You can conservatively expect around 350 hp from a 350 with good heads , a dual plane intake , a 700cfm+ carb , good headers , 10+:1 comp ratio, good ignition and a 285 Hydraulic cam.....even at this level , you will have a slightly soggy car at under 2500-3000 rpm.

 

[MTC_75vette]

One upgrade cannot just be looked on in isolation , for example upgrading the heads and comp ratio wont help unless you have the carb , cam and headers to take advantage and even then , one needs more than just that to really feel the effects.
I would look elsewhere to "wake" the car up , for example a 2000-2400 stall convertor (If it's auto) and a change from lets say a 3:1 to a 3.5:1 diff ratio will give you a seat of the pants thrill , whereas heads and cam might actually make the car a dog at lower RPM without doing the stall and rear gears. Even if you DO hop it up , you will still have to do the stall and rear end thing anyway...so perhaps do it first and then add power.
You can conservatively expect around 350 hp from a 350 with good heads , a dual plane intake , a 700cfm+ carb , good headers , 10+:1 comp ratio, good ignition and a 285 Hydraulic cam.....even at this level , you will have a slightly soggy car at under 2500-3000 rpm.

Hey Im sorry i should have told you what was done already....The motor has a Pete Jackson drive gear, comp. roller rockers, heads were ported and decked, 268 duration high energy comp. camshaft, new Stainless steel valves, 3 angle comp valve job, new Edelbrock Perma Star polished billet Manifold, new Edelbrock 650 Thunderbird 4 barrel carb., Edelbrock tri-angular Elite air cleaner, new super comp. headers, new Flowmaster Delta 40 dual exhaust. Also has new Dewitt aluminum radiator, rebuilt rear, new half shafts, new U-joints, new spindles inner and outer, new seals and bearings with 370 gears, and stall converter of 2400 rpm.

 

[JimBobC4]

Hey Im sorry i should have told you what was done already....The motor has a Pete Jackson drive gear, comp. roller rockers, heads were ported and decked, 268 duration high energy comp. camshaft, new Stainless steel valves, 3 angle comp valve job, new Edelbrock Perma Star polished billet Manifold, new Edelbrock 650 Thunderbird 4 barrel carb., Edelbrock tri-angular Elite air cleaner, new super comp. headers, new Flowmaster Delta 40 dual exhaust. Also has new Dewitt aluminum radiator, rebuilt rear, new half shafts, new U-joints, new spindles inner and outer, new seals and bearings with 370 gears, and stall converter of 2400 rpm.

wow, thats a pretty tight car already ! I have ran the heads you spoke of on an earlier 350 in a 1969 RS\SS Camaro with a similar Crane cam and intake ( Edelbrock dual plane intake and carb) with 3:73 gears.

The car lost low end throttle response after the head install, but picked up power after about 3200 RPMs.

I ran both a 600 and a 700 cfm carb. Again, the power loss at the bottom was added to the top.With the 600 cfm being the most "crisp" in throttle response.

The car ran on pump gas and had about 315 rwhp's.

What size of valves are you using ?

 

[Vette79]

x2 Yep, I was just going to say that you already have a very good setup. I'm still working towards that...LOL. Uhm, "Crate Motor"?

 

[MTC_75vette]

x2 Yep, I was just going to say that you already have a very good setup. I'm still working towards that...LOL. Uhm, "Crate Motor"?

I really would like to have both low end and high end power does someone recomend I select a different set of heads?

 

[Rodney Gold]

I dont think whatever you do will give you both top and bottom end , the only real way of doing this is to bore and stroke the motor to give you more cubic inches , or perhaps bolt on an underhood supercharger.
My vette is more or less the same as yours mod wise (770 carb/edelbrock heads , 10.5:1, 280h cam, roller rockers , performer , 2000 stall , 3.55 rear end , ceramic headers , SS exhaust , MSD and so on) and is on the edge of being streetable , the only way I would make it better than it is right now is to increase displacement, a 383 stroker kit or using a 400 cui block would be the way I might go .....but it's doubtful I will.
I'm on the limits of traction, car goes fast enough on public streets and have already blown up 2 TCI lower stall TQ convertors (Sat night specials)

On 265/60/15 BF goodriches at stock pressure and leaving the car in drive (5000 1-2 , 4500 2-3) the car runs a 13.4 , which imho is pretty damn good

The only mod I'm doing now is a 2600 rpm TQ that can handle the punch and Im doing some surgery on the centre consol to fit a Hurst promatic 2 shifter.

 

[mrvette]

Dunno I"d be doing a loose converter today what with gas at 4 bux....I would be going overdrive tranny the 200 4r is the simplest bolt in by far, and built right it's solid.....

I went the whole engine route years ago, essentially today it is a ZZ4 with a LT1 manifold all modified up fitted on it.....with a 200 4r, 336 gears and it get 22.222222 mpg at 90 mph cruise....not so awful evil...

I remember years ago when going from what appeared to be a proper running Qjet to a L98 setup on the original L48 engine the car came with....the MPG went from 12-14 region to 18-24 with 24 mpg being the highway average on a highway trip....this with muncie 4 speed and same 336 rear....

I would consider the FI /overdrive just for the driving pleasure.....

OH, with the L98 heads there my 355 is supposed to be pushing 400 hp....
but the torque curve is nice and flat....

 

[JimBobC4]

I really would like to have both low end and high end power does someone recomend I select a different set of heads?

what valve sizes are in your heads now ? Are they stock sized or ?

 

[MTC_75vette]

what valve sizes are in your heads now ? Are they stock sized or ?

My valves I believe are stock.

 

[MTC_75vette]

I dont think whatever you do will give you both top and bottom end , the only real way of doing this is to bore and stroke the motor to give you more cubic inches , or perhaps bolt on an underhood supercharger.
My vette is more or less the same as yours mod wise (770 carb/edelbrock heads , 10.5:1, 280h cam, roller rockers , performer , 2000 stall , 3.55 rear end , ceramic headers , SS exhaust , MSD and so on) and is on the edge of being streetable , the only way I would make it better than it is right now is to increase displacement, a 383 stroker kit or using a 400 cui block would be the way I might go .....but it's doubtful I will.
I'm on the limits of traction, car goes fast enough on public streets and have already blown up 2 TCI lower stall TQ convertors (Sat night specials)

On 265/60/15 BF goodriches at stock pressure and leaving the car in drive (5000 1-2 , 4500 2-3) the car runs a 13.4 , which imho is pretty damn good

The only mod I'm doing now is a 2600 rpm TQ that can handle the punch and Im doing some surgery on the centre consol to fit a Hurst promatic 2 shifter.

If I ran a 13.4 I would def be happy with that, are your heads cast iron or aluminum? What is your horsepower after all your mods? I would love to stroke my motor but it is just not in the budget for me at this time...but im glad to hear your response. I see your compression is 10.5 :1 I assume your using flat top pistons. I was told domed pistons give higher compression is that a good route for me to go for more power or is too much compression a bad thing?

 

[Rodney Gold]

Stock Edelbrock straight plug 64cc Ally heads , out the box. Pistons are flat tops AFAIK , comp ratio is estimated and not actually measured. Too much compression IS a bad thing , especially if you want to run on pump gas , you gonna have to retard big time to reduce detonation and running retard will lose power and make the car run hotter.
I set my timing this way : Disconnect vacuum (I NEVER use ported vacumm for vacuum advance , always full manifold) and then rev the motor to 3500 rpm (when all centrifugal should be in) and set it to between 36-38 degrees total. Reconnect vacuum and thats it. I then fine tune it by advancing till I get pininging and then back off 2 degrees - always falls between 36-38.
The Cam I run is a 280H , Comp cam. Prolly a little more aggressive than your 268. Mine is between an Edelbrock Performer and an Edelbrock performer RPM.
I HATE edelbrock carbs , they arent as tuneable as a Holley and they have a flaw that can't be cured , and that is that the accel pump mechanism has slop built in , in that it requires a little movement for the squirter to operate and sometimes that makes for a small stumble when planting your foot.
I did try an edelbrock 800 as well as a holley 600 on the car and found the Holley 770 street demon by far the best.
Dunno the Edelbrock Permastar intake , but I do know that the air gap manifolds , all the rage now are also "shite" for anything on the street.
I have a mild shift kit in my 350 box ands have fiddled with governor weights to give me a higher WOT change point (still got a little more fiddling to do)

 

[MTC_75vette]

Stock Edelbrock straight plug 64cc Ally heads , out the box. Pistons are flat tops AFAIK , comp ratio is estimated and not actually measured. Too much compression IS a bad thing , especially if you want to run on pump gas , you gonna have to retard big time to reduce detonation and running retard will lose power and make the car run hotter.
I set my timing this way : Disconnect vacuum (I NEVER use ported vacumm for vacuum advance , always full manifold) and then rev the motor to 3500 rpm (when all centrifugal should be in) and set it to between 36-38 degrees total. Reconnect vacuum and thats it. I then fine tune it by advancing till I get pininging and then back off 2 degrees - always falls between 36-38.
The Cam I run is a 280H , Comp cam. Prolly a little more aggressive than your 268. Mine is between an Edelbrock Performer and an Edelbrock performer RPM.
I HATE edelbrock carbs , they arent as tuneable as a Holley and they have a flaw that can't be cured , and that is that the accel pump mechanism has slop built in , in that it requires a little movement for the squirter to operate and sometimes that makes for a small stumble when planting your foot.
I did try an edelbrock 800 as well as a holley 600 on the car and found the Holley 770 street demon by far the best.
Dunno the Edelbrock Permastar intake , but I do know that the air gap manifolds , all the rage now are also "shite" for anything on the street.
I have a mild shift kit in my 350 box ands have fiddled with governor weights to give me a higher WOT change point (still got a little more fiddling to do)

Rodney thanks for your help I will let you know how it all tunrs out when I am finished!

 

[JimBobC4]

I HATE edelbrock carbs , they arent as tuneable as a Holley and they have a flaw that can't be cured , and that is that the accel pump mechanism has slop built in , in that it requires a little movement for the squirter to operate and sometimes that makes for a small stumble when planting your foot.

I tune Edelbrock carbs all the time. With the proper jets and rods, its a smooth carb and can be tuned really well. I'm not sure where the "not as tuneable as a Holley" came into play. I suppose that depends on which Holley carb it is. Some only have metering blocks on the back two venturi tubes and are totally NON adjustable. I have one in the garage right now like that. You can tune all 4 venturies individually on an Edlebrock. What else do you need ?

As for the pump mechanism, its that way by design on the economy carb to save fuel. Move the adjuster to the middle or last hole for the squirter pump. If your still not getting enough gas, change the pump to a higher output unit. last but not least, put in bigger jets.Also a slight tweak with a pair of needle nose pliers helps a bit.

I know 4 or 5 cars right now that run nearly as well as a fuel injected car.

All have tuned Edelbrock carbs.

The carb is a modified Carter design, it has been used on musclecars for many years, 426 hemi's, 440 Chargers, 'Cudas etc. along with several off road vehicles. Also it has no gaskets below the fuel level.

If you tune a carb by air\fuel ratio and or by looking at the spark plugs,
an Edelbrock is a decent carb to work on.

 

[Rodney Gold]

The Problem with the edelbrock carbs , well over here in South Africa that is , is that most imported units are designed for lean running , so you have to buy one of the calibration kits for it , and once you have used whatever spring , needle and jets you want , and you need to tune another - you need to buy another calibration kit (we cant get loose components here) . I have tried to adjust off idle stumbles in many edelbrocks using the pump lever hole method , changing rod springs , jets and needles and eventually just changed to a Holley and fixed it. Float level adjustment on an Edelbrock is also not that great , Far easier on a holley to do that and to change jets.
At any rate , the holley is much more adjustable on the acceleration circuit , you can change shooters , pump volumes and pump cams and power valve so can fine tune the off idle characteristics far better then the Edelbrock. I would NEVER buy one of those non adjustable Holleys anyway.
I suppose its horses for courses , but most performace v8's running here run Holleys , I have had some success with Edelbrocks , my mildly modified el Camino (actually a holden) with a 350 runs a 600 Edelbrock that worked perfectly out the box.
One of the problems I have had with holleys , especially those "remaufactured" ones is porosity or warpage of the metering blocks.

 

[JimBobC4]

The Problem with the edelbrock carbs , well over here in South Africa that is , is that most imported units are designed for lean running , so you have to buy one of the calibration kits for it , and once you have used whatever spring , needle and jets you want , and you need to tune another - you need to buy another calibration kit (we cant get loose components here) . I have tried to adjust off idle stumbles in many edelbrocks using the pump lever hole method , changing rod springs , jets and needles and eventually just changed to a Holley and fixed it. Float level adjustment on an Edelbrock is also not that great , Far easier on a holley to do that and to change jets.
At any rate , the holley is much more adjustable on the acceleration circuit , you can change shooters , pump volumes and pump cams and power valve so can fine tune the off idle characteristics far better then the Edelbrock. I would NEVER buy one of those non adjustable Holleys anyway.
I suppose its horses for courses , but most performace v8's running here run Holleys , I have had some success with Edelbrocks , my mildly modified el Camino (actually a holden) with a 350 runs a 600 Edelbrock that worked perfectly out the box.
One of the problems I have had with holleys , especially those "remaufactured" ones is porosity or warpage of the metering blocks.

Valid points. Especially the float adjustment :bash

Who thought of that ? Its a guess at best.

Also, if you buy an Edlebrock, may as well buy the whole adjustment kit as you mentioned. To get it right does require a LOT of rod changes sometimes, especially with a big cam and intake.

I'm partial to Webers myself, but they aren't very popular anymore

 

[KANE]

...I know 4 or 5 cars right now that run nearly as well as a fuel injected car...

Just another reason to go with EFI.

Seriously, once the parts are obtained, installed, and the chip is tuned to the engine... it is smooth sailing. No retuning required unless a new cam or heads are installed.

The cost is a bit steep to get going- but well worth it.

I decided to get rid of carbs all together form any Vette I'd own. 1995 was the last time I drove a Vette I owned with a carb- and haven't looked back. I'm on my second C3 with TPI and I love it.

 

[Ed's 1970]

If u want more power, a bigger motor will help a lot. And u can run a mild camshaft to make it more streetable. Look at a 400 small block or bigger. I am putting in a 540 big block soon, looks exactly like a 396, 427, or 454 the bore is just bigger and the crank is a longer stroke. I was kind of disappointed with the 350 small block in this car, it had no low end, upper end was okay but u had to rev the hell out of it. The big block is a lot stronger than a small block all around, the only downside is it uses more gas otfl
Ed