750 or 850 cfm Thermoquad

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dustoff440

dustoff440

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I've got one of each. My question is, in pursuit of the best throttle response as possible, is there a noticeable difference between the 750 cfm 360 tq with the small 1 3/8 primaries and the 850 cfm tq off of a 400 with the 1 1/2 primaries. I'm thinking that the 750 will be plenty enough carb for my mild 360 Magnum and hope that it will have noticeably more and crisper throttle response. What do you think???
 
Ditto on the 800cfm and 850cfm, unless it has 4847s stamped on the base, that would make it a 1,000cfm carb.
The throttle response can be just as good on a two barrel carb.
Throttle response is more so related to timing.
My .02.
 
340butterduster said:
Ditto on the 800cfm and 850cfm, unless it has 4847s stamped on the base, that would make it a 1,000cfm carb.
The throttle response can be just as good on a two barrel carb.
Throttle response is more so related to timing.
My .02.
Click to expand...

I find it hard to believe that there is only 50 cfm difference with 1/8 inch difference in the primaries. I will acknowledge that it is "referred to" as an 800 but I am actually talking about actual flow.
 
dustoff440 said:
I find it hard to believe that there is only 50 cfm difference with 1/8 inch difference in the primaries. I will acknowledge that it is "referred to" as an 800 but I am actually talking about actual flow.
Click to expand...

I suppose you are best to argue your points with the experts , as that's what I use for reference http://www.thermoquads.com/, and he has a reaally, reaally good reputation. Ask him, he is a member here, and I'm sure he will gladly give you a straight up answer. Who knows the carb. probably only flows 775cfm. Fact of the matter is, it is rated @ 800cfm.

My 340 is starving for fuel with a 750cfm rated Eddy card.

Nonetheless, your throttle response has little to do with cfm, aside from working in sink with your timing/vacuum advance.

Your spark timing and advance curve is the key to your throttle "response".
 
http://www.thermoquads.com/
according to demonsizzler site its as i said 800/850 reread it. as far as actual flow who's flow bench are you going to test it on? no two will show the same cfm. on your mild 360 i would use the 800 or the small primary carb, the big primary one is for the big dogs LOL
 
340butterduster said:
I suppose you are best to argue your points with the experts , as that's what I use for reference http://www.thermoquads.com/, and he has a reaally, reaally good reputation. Ask him, he is a member here, and I'm sure he will gladly give you a straight up answer. Who knows the carb. probably only flows 775cfm. Fact of the matter is, it is rated @ 800cfm.

My 340 is starving for fuel with a 750cfm rated Eddy card.

Nonetheless, your throttle response has little to do with cfm, aside from working in sink with your timing/vacuum advance.

Your spark timing and advance curve is the key to your throttle "response".
Click to expand...


I agree that throttle response has little to do with OVERALL cfm, but I do know that with the smaller primaries I should get a crisper and quicker INITIAL response, especially if I tune the squirter size, accel pump stroke, jets, rods etc.
Years ago I was an avid Qjet fan and got great results in trying to get that crisp quick response by using the smaller primary carbs and I was pretty sure that it would also work on a TQ. I even went so far as to cut progressively small pieces of the spring under the metering rod apparatus and kept fine sandpaper to sand the tips of the metering rods.

I have the spark timing and advance all worked out for now.Ive got an MP dizzy and just acquired an accel billet and can't wait to try that. I'm also thinking about going to an msd blaster coil and a chrome box for a little extra spark. I'm also looking to experiment with some of the exotic spark plugs.


Thanks for the info, I have read some many articles and info by different authors that it is starting to run together.

I think my problem is that I can't leave well enough alone. Years ago I had a 62ss Impala that I put an L79 327/350 horse in(boy was that a great motor) and I had the hood up so many times I wore the hood hinges out. LOL
 
EL5DEMON340 said:
http://www.thermoquads.com/
according to demonsizzler site its as i said 800/850 reread it. as far as actual flow who's flow bench are you going to test it on? no two will show the same cfm. on your mild 360 i would use the 800 or the small primary carb, the big primary one is for the big dogs LOL
Click to expand...

You are absolutely correct, I have been reading so much on this lately its all running together LOL see below also
 
dustoff440 said:
I've got one of each. My question is, in pursuit of the best throttle response as possible, is there a noticeable difference between the 750 cfm 360 tq with the small 1 3/8 primaries and the 850 cfm tq off of a 400 with the 1 1/2 primaries. I'm thinking that the 750 will be plenty enough carb for my mild 360 Magnum and hope that it will have noticeably more and crisper throttle response. What do you think???
Click to expand...


Use the 850 cfm T.Q. The biggest difference is that the 850 will give you an extra 20+ hp over the 800. Enough for you to notice in hp gain, David.
 
demon sizzler said:
Use the 850 cfm T.Q. The biggest difference is that the 850 will give you an extra 20+ hp over the 800. Enough for you to notice in hp gain, David.
Click to expand...

Wow 20 horsepower, I will definitely be all over that. Is it because of larger bleed and metering passages? I have a 9077s, is that a desirable model???????????
 
The 9077 is a good perf with a few simple mods. Factory jetting, metering rods and bleed size is adequate on a mostly stock engine.

No the diff in hp is because the cfm 's are 50 more on the 850. All oem 800 and 850 T.Q. 's
flow the same on the 2ndary side. For every approx 20 cfm's gained on the primary side and with corrected jetting, you can see an easy 8 hp gain. For another example:
removing the choke plate/attaching rod, you will gain 60 cfm's and about 20-25hp with corrected primary jetting.

This can easily translate to as much as 40+ hp on a higher perf level engine and that is 'cheap' hp, David.
 
I can fab the jets but it has been a while; last kit I made was for Dudek for his FAST stroker 340 build-up in Musclecar Review. The article was by Brad O'**** and I think
it was 4 part.

It takes me a full work day to fab a kit on my lathe and the vertical mill, David.
 
demon sizzler said:
I can fab the jets but it has been a while; last kit I made was for Dudek for his FAST stroker 340 build-up in Musclecar Review. The article was by Brad O'**** and I think
it was 4 part.

It takes me a full work day to fab a kit on my lathe and the vertical mill, David.
Click to expand...

You sir have earned yourself another customer. I'm going to get the car completely assembled dialed and broken in, do some spark plug readings and install an air fuel ratio gauge and then sendthe carb to you to do your masterful work of art....turning a diamond in the rough into a spectacular piece. I saw that article that car runs like a raped ape and I'm sure in part that your skills were partially responsible for the cars prowess. I have also heard good things about your work from other people. Unfortunately it will have to wait till income tax return check. Do you offer FABO members any sort of discount??
 
I can build the carb and add a 'timed' vacuum port for distributor advance. It is a mod that I do quite often and have special tooling to do it. I have been so busy this past year that I don't have much time to do the T.Q. builds since buying a '68 Coronet R/T to restore.

But I am still doing a few builds here n there. Plus it is so cold this winter that I do not
have my cleaning machines working efficiently.
 
demon sizzler said:
I can build the carb and add a 'timed' vacuum port for distributor advance. It is a mod that I do quite often and have special tooling to do it. I have been so busy this past year that I don't have much time to do the T.Q. builds since buying a '68 Coronet R/T to restore.

But I am still doing a few builds here n there. Plus it is so cold this winter that I do not
have my cleaning machines working efficiently.
Click to expand...

Understand, it will be Mar/Apr at the earliest. I will also want you to do whatever you do to make the top and bottom look new again. I plan on doing whatever it takes to keep it looking and operating like new and will definitely keep it for a long time. The best overall carbs I have used have been tq'S and I would recommend them to anyone for almost any application.
 
Hey can anybody tell me if a thermo quad 90575s would be good for a pretty much stock 1970 340? how would this perform? Thanks, Craig.
 
It has decent metering rods, jetting as-is. The two #2 pencil lead holes in the lower inside front choke tower wall needs to be covered with a dab of epoxy though, David.
 
Thanks so much for the response! I'm considering getting this off a buddy of mine. I'm not experienced in carbs,so covering the holes with epoxy will change it from a smogger? Thanks, Craig.
 
The mod will essentially re-calibrate 3 circuits to pre smogger(before 1975)specs. Primary, 2nddary and wot, David.
 
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