Another aerodynamics question
Thread Starter
Racer
Joined: May 2020
Posts: 498
Likes: 167
Another aerodynamics question
I have been very cornered about heat build up in the engine compartment. On a hot day the temperature gauge would get up to 220 (I do have a pretty heavy duty aluminum radiator with electric fan) and the front fenders would be hot to the touch. I do have non coated headers on the car. On a whim, I decided to cut out the wall on the back side of the factory cowl hood to let in low pressure cool air. And good news! The temp gauge now doesn’t go over 200 degrees, even in 95 degree heat. Bad news! The car starts to have what feels like a bucking motion above 75mph.
So what did I screw up??
I was thinking about installing hood vent to remove more heat and reduce under hood pressure.
So what did I screw up??
I was thinking about installing hood vent to remove more heat and reduce under hood pressure.
Old Pro Solo Guy
Joined: Dec 2017
Posts: 8,135
Likes: 4,500
From: Marlton NJ
Guys do get these to run cool without hood mods.
- Make sure all your rad seals are there and tight.
- Make sure lower lip spoiler is there.
- Make sure your elec fans have a shroud that covers 100% of the rad.
- Get your engine timing corrected per Chevy Power Book or Lars. Not factory. Engine runs much cooler. Recurve distrib and run on manifold vac advance. Final settings somewhere around 12-16 degrees initial, may vary, but way more than factory 4 or 8. Maximum centrif advance must be 36 degrees period, and it should be a all-in around 3000. Vac advance (on manifold vac) should add only another 10 degrees, may need to be restricted. You will not believe how much better and cooler it runs.
- Get headers coated inside & out. Do not use wraps that will rust them out.
Team Owner
Joined: Oct 2004
Posts: 81,241
Likes: 3,063
From: altered state
St. Jude Donor '05
Vents make sense to me, less hot air in there the better. Your bucking has nothing to do with the hole you made, wonder if youre going lean?
What rpm is it happening? Can you duplicate it in N? (detecting a slight miss)
What rpm is it happening? Can you duplicate it in N? (detecting a slight miss)
1967 Pedal Car Champion
Joined: Mar 2020
Posts: 9,251
Likes: 4,319
From: US-PNW
Would checking the thermostat be prudent? (I believe most Corvettes specify the 160-180 rating range.) If there's a 195° or 200° thermostat installed won't the engine temp not drop below that when fully warmed up?
Thread Starter
Racer
Joined: May 2020
Posts: 498
Likes: 167
I haven’t changed anything with the engine. It’s running good. Too good to where I pushed the car a little too hard. I can definitely feel a buffeting effect. The hood was shaking like it wanted to open. I also forgot to mention that I have lowered down to 26” at the front wheel wells so maybe air is getting trapped?? It wasn’t doing this before I lowered it and cut a hole in the back of the hood. So I’ve messed up the aerodynamics some how.
Thread Starter
Racer
Joined: May 2020
Posts: 498
Likes: 167
Guys do get these to run cool without hood mods.
- Make sure all your rad seals are there and tight.
- Make sure lower lip spoiler is there.
- Make sure your elec fans have a shroud that covers 100% of the rad.
- Get your engine timing corrected per Chevy Power Book or Lars. Not factory. Engine runs much cooler. Recurve distrib and run on manifold vac advance. Final settings somewhere around 12-16 degrees initial, may vary, but way more than factory 4 or 8. Maximum centrif advance must be 36 degrees period, and it should be a all-in around 3000. Vac advance (on manifold vac) should add only another 10 degrees, may need to be restricted. You will not believe how much better and cooler it runs.
- Get headers coated inside & out. Do not use wraps that will rust them out.
Coated headers is definitely on the list for future mods.
Safety Car
Joined: May 2001
Posts: 4,761
Likes: 1,648
From: Fairfax Virginia
I have a 1968 C3 with the 427 and four speed. That car has no problem going above 100 mph and exhibits no buffeting either. At above 130 the C3 under full power the C3 has a Front End "Lift" problem. Even with my 427 it still lifts the suspension at higher speeds. The Indy spoiler sure makes a huge difference when attached properly.
Is my vette stock?? HAHA
Joined: Oct 2015
Posts: 20,276
Likes: 9,416
From: Im not allowed to tell you
2020 C3 of the Year Finalist - Modified
2020 Corvette of the Year Finalist (performance mods)
2019 C3 of Year Winner (performance mods)
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Is it going up and down or side to side? If it’s a fast left to right bounce in your Wheel it could be a bump steer situation and I think if you lowered the front end you may be changing the caster or camber of your wheels just enough to create this issue. I was experiencing the same thing and raised my front from 26.75 to 27.25 and it went away.
If it where an air flow issue underneath the car you would feel like the front drifts or wanders down the road. I’ve had that feel on old big boat cars (68 Mercury Montclair) at high speed and week shocks that felt like a boat rolling across waves drifting during a lane change
also,what is you sidewall height of your tires and the air pressure? If it’s to low and you have taller 15inch tire the sidewalls could be collapsing and wallowing if your running below 28 psi. I have tall thin tires on my f250 and when a tire gets low you can really feel it.
If it where an air flow issue underneath the car you would feel like the front drifts or wanders down the road. I’ve had that feel on old big boat cars (68 Mercury Montclair) at high speed and week shocks that felt like a boat rolling across waves drifting during a lane change
also,what is you sidewall height of your tires and the air pressure? If it’s to low and you have taller 15inch tire the sidewalls could be collapsing and wallowing if your running below 28 psi. I have tall thin tires on my f250 and when a tire gets low you can really feel it.
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Dr. Detroit
Joined: Mar 2012
Posts: 10,097
Likes: 4,027
From: New Braunfels Texas
Ceramic coated headers lower underhood temps pretty dramatically......the temp at the pipe is reduced to more than half.
Jebby
Thread Starter
Racer
Joined: May 2020
Posts: 498
Likes: 167
Is it going up and down or side to side? If it’s a fast left to right bounce in your Wheel it could be a bump steer situation and I think if you lowered the front end you may be changing the caster or camber of your wheels just enough to create this issue. I was experiencing the same thing and raised my front from 26.75 to 27.25 and it went away.
If it where an air flow issue underneath the car you would feel like the front drifts or wanders down the road. I’ve had that feel on old big boat cars (68 Mercury Montclair) at high speed and week shocks that felt like a boat rolling across waves drifting during a lane change
also,what is you sidewall height of your tires and the air pressure? If it’s to low and you have taller 15inch tire the sidewalls could be collapsing and wallowing if your running below 28 psi. I have tall thin tires on my f250 and when a tire gets low you can really feel it.
If it where an air flow issue underneath the car you would feel like the front drifts or wanders down the road. I’ve had that feel on old big boat cars (68 Mercury Montclair) at high speed and week shocks that felt like a boat rolling across waves drifting during a lane change
also,what is you sidewall height of your tires and the air pressure? If it’s to low and you have taller 15inch tire the sidewalls could be collapsing and wallowing if your running below 28 psi. I have tall thin tires on my f250 and when a tire gets low you can really feel it.
I did check the tires and the air pressure was good. I didn’t check the balance of the tires. That could be part of the problem.
Is my vette stock?? HAHA
Joined: Oct 2015
Posts: 20,276
Likes: 9,416
From: Im not allowed to tell you
2020 C3 of the Year Finalist - Modified
2020 Corvette of the Year Finalist (performance mods)
2019 C3 of Year Winner (performance mods)
2016 C3 of Year Finalist
wind buffetting at 75mph sounds more like a suspension issue versus a aerodynamic effect. I have a 68 that had little to no cowl on the front and a L88 hood and what ever air got under there would go out the hood or the side vents. I added a bigger air dam for cooling and its smaller than the full spoiler you can get it helped with the cooling. Prior to that the only issues I felt were above 100mph. I would look towards suspension issues or have someone drive next to you and see of they can spot any issues when you feel it happening