sc1 aero mods

[aerohead]

Originally Posted by arcosine

I sold my 91 CRX HF because it was a California model, 3.25 final drive, and also when I went to bleed the brakes, the fitting broke due to rust. The Saturn is a bigger car, more frontal area. I'll take a peek at the photos.

I cut 6.5 inches off the rear wing, riveted it back together and need to make some brackets to mount it behind the deck.


Looks good... 1991 was a long time ago, I worked for l Douglas Aircraft Company (Mc Donnell Douglas). I had a 1977 honda accord with a 1981 1355cc civic cvcc engine milled to 10.25:1 compression ratio, advanced ignition timing, jetted lean and a taller fifth gear. I got 50 mpg consistently without hypermilling. It would have done better with some aeromods! It finally burnt a piston.

Lets see... If I assume that your CRX top speed was 100 mph and had a 7 mph increase with the tail, then the reduction in drag would be 1-(100/107)^3 =22%, pretty good.

*The 1st-gen CRX 1.3-liter was rated by Honda @ Cd 0.32 and 18.5 ft-sq frontal area.Hucho ran it in VW's tunnel and reported Cd 0.35,for a drag factor of 6.475 ft-sq.It's top speed was 93 mph and returned 52 mpg at 55-mph (naked).
*By 1990,with the 'kit',and cardboard and duct tape mods made at 4,420' Bonneville
she ran 97.6 mph,up from 89 and change 'stripped.' When I left the Salt Flats,her mileage was up into the low 60s.
*I never could get her out of 3rd gear,so Hucho's CdA/top speed relationship doesn't help much.
*From the increase in mpg,I could use GM's mpg/CdA relationship to reverse-engineer the Cd,at 0.235 and CdA= 4.347 ft-sq which was confirmed over the phone in conversation with GM's Aero Lab personnel.
*At Chrysler Proving Grounds,one of Car and Driver's road warriors saw 98 mph @ 52-degrees F.
* Coastdown tests showed Road Horsepower to be 8.55 hp@ 50 mph,and 19.5 hp @ 70 mph.
*At nearer standard temp and pressure,she's run an even 100 mph.
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I have data for the 1991 Saturn SC and they report a Length/Height= 3.474,Cd 0.32,and Af= 20.1 ft-sq,for a CdA= 6.432 ft-sq,(a little better than the stock CRX).
*The front of the SC is great even by today's standards.Your airdam mods will correct the flow going under,so she'll be 'fully upgraded.'
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*1st-gen Insight is Cd 0.25 @ L/H= 2.854 (more like a K-form roof and nice body plan taper)
*Your CRX was Cd 0.29 @ L/H= 2.956 (roof is great but doesn't get the extra kick of plan taper).
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I think that the SC will respond really well to the tail mods.If you run a little longer tail than I did,even with the larger frontal area her CdA should come in below 5-ft-sq,easy!
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I would have liked your Accord.My mom had an automatic trans version and I could never coax more than 36 mpg out of it in straight hwy driving.

[arcosine]

I calculated 16 hp at 55 mph for the 77 accord.

I got 40 mpg with the 1600 cc CVCC engine and 35 mpg with the 78 Accord, the only difference was the heat on the intake manifold, 77 had exhaust heated and the 78 had coolant heated intake manifolds, both had 8:1 compression ratio.

[aerohead]

Originally Posted by arcosine

I calculated 16 hp at 55 mph for the 77 accord.

I got 40 mpg with the 1600 cc CVCC engine and 35 mpg with the 78 Accord, the only difference was the heat on the intake manifold, 77 had exhaust heated and the 78 had coolant heated intake manifolds, both had 8:1 compression ratio.

16 hp,ouch! 'guess we pay for those steep hatch angles.(still paying with the 2012 VW Beetle!)

Was the 1978 Accord a 'new' model body series or did they just do the engine mods? I've only owned the one Honda,and it seemed like they would introduce a new model on even years and let it run for 4-years.
That's pretty amazing about the significance of the intake tract!I wonder if California NOX standards forced them into the coolant-based system.

[arcosine]

76,77 and 78 were the same body 79 had a face lift and a 1800 cc engine.
http://jalopnik.com/1977-honda-accord/

[aerohead]

Originally Posted by arcosine

76,77 and 78 were the same body 79 had a face lift and a 1800 cc engine.
1977 honda accord News, Videos, Reviews and Gossip - Jalopnik

Yep that's what we had in the family.So it looks like the intake manifold is the culprit for the mpg difference.Pretty amazing! Appreciate the info.

[aerohead]

I found a CAR and DRIVER road test of the '91 SC.
They gave the car Cd 0.32,@ 20.1 sq ft frontal area,for CdA=6.432 sq ft.
Road horsepower from coast-down testing at Chrysler's Proving Ground indicated:
*4 hp @ 30 mph
*11 hp @ 50 mph
*24 hp @ 70 mph
The SC and Subaru SVX were two of the lowest drag cars tested by C and D,only bested by a 1966 Lotus Elan,which absorbs 21 hp @ 70 mph.

[arcosine]

I closed the mouth on my Saturn, I moved it up with a nice contour on the belly pan. The yellow coroplast belly pan was brittle and cracked, so I replaced it with white. It should get better flow under the car. I'll test it on the foxhunt tonight. The vacuum line to the hot air intake valve got brittle and broke also, but with 90F temps I don't need it too much.


... Not enough air flow, engine temp kept creeping up on interstate. Opened it up some, now temp right around half way. Seems to be less wind noise and over speeds on down hill slopes.

I wonder if it would be better to have the air inlets open on the ends and closed in the middle. This would divert some air from around the front wheels.

I think the front looks much more aero.

I wonder if a metal plate as the bottom belly pan with cooling tubes soldered to it could replace the radiator.

Maybe taking off the insulation on the hood would reduce under hood temperatures.

was Before:



now, After:



Notice the aero licence plate holder:

[arcosine]

This is an interesting link:

Automobile drag coefficient - Wikipedia, the free encyclopedia

[arcosine]

I am modding the back end. I have raised the tow hitch to inside the bumper, cut and trimmed and re welded the spare tire well 3 inches to allow the belly pan to taper upward at 15 degrees from the suspension. Pictures soon....

BEFORE:



DURING:



Big muffler sticks out:




AFTER:

[aerohead]

Originally Posted by arcosine

I closed the mouth on my Saturn, I moved it up with a nice contour on the belly pan. The yellow coroplast belly pan was brittle and cracked, so I replaced it with white. It should get better flow under the car. I'll test it on the foxhunt tonight. The vacuum line to the hot air intake valve got brittle and broke also, but with 90F temps I don't need it too much.


... Not enough air flow, engine temp kept creeping up on interstate. Opened it up some, now temp right around half way. Seems to be less wind noise and over speeds on down hill slopes.

I wonder if it would be better to have the air inlets open on the ends and closed in the middle. This would divert some air from around the front wheels.

I think the front looks much more aero.

I wonder if a metal plate as the bottom belly pan with cooling tubes soldered to it could replace the radiator.

Maybe taking off the insulation on the hood would reduce under hood temperatures.

was Before:



now, After:



Notice the aero licence plate holder:

*with the inlet at the center,you're at the forward stagnation point where the ram pressure is highest.If you were to move the opening over to the side you'd be within the corner radius,where air is accelerating and losing static pressure.It possible that air would actually flow out of the hole,not in.This happens on the oval opening of the 1st-gen Ford Taurus.
*There is a modern truck tractor which has no radiator,but rather cooling 'pods' which may be using this non-aspirated heat-exchanger.
Ford's Probe-IV had a bit of 'heat-sink' tubing type exchanger between the forward engine,and rear radiator.Research has progressed for ceramic engines which would have no cooling system whatsoever.
*the insulation under the hood may have been a result of the 'Noise/Vibration/and Harshness' work done on the car.Once your up to speed,there's probably so much volume of air moving through the engine compartment,that the acoustic blanket under the hood wouldn't make any difference in regards to engine heat.